<?xml version="1.0" encoding="us-ascii" standalone="yes"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2022-07-20T16:21:07.4535034+00:00 -->
<!-- Version            : 5.0.1.747 -->
<!-- Package ID         : b41cc3d76b2443e6a1e91b5393ff3522 -->
<!-- Copyright (c) 2022 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedPeriodStartLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedPeriodStartLabel" xlink:type="simple" />
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  <link:roleRef roleURI="http://www.xbrl.org/2009/role/netLabel" xlink:href="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd#netLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/label/axisDefault" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-roles-2022.xsd#axisDefault" xlink:type="simple" />
  <link:labelLink xlink:role="http://www.xbrl.org/2003/role/link" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCentralIndexKey" xlink:type="locator" xlink:label="dei_EntityCentralIndexKey" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CoverAbstract" xlink:type="locator" xlink:label="dei_CoverAbstract" />
    <link:label xml:lang="en-US" xlink:label="dei_CoverAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
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    <link:label xml:lang="en-US" xlink:label="dei_EntityRegistrantName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Entity Registrant Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityRegistrantName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
    <link:label xml:lang="en-US" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CurrentFiscalYearEndDate" xlink:type="locator" xlink:label="dei_CurrentFiscalYearEndDate" />
    <link:label xml:lang="en-US" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Current Fiscal Year End Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityFilerCategory" xlink:type="locator" xlink:label="dei_EntityFilerCategory" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFilerCategory_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFilerCategory_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityEmergingGrowthCompany" xlink:type="locator" xlink:label="dei_EntityEmergingGrowthCompany" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Emerging Growth Company</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityEmergingGrowthCompany" xlink:to="dei_EntityEmergingGrowthCompany_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Emerging Growth Company</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntitySmallBusiness" xlink:type="locator" xlink:label="dei_EntitySmallBusiness" />
    <link:label xml:lang="en-US" xlink:label="dei_EntitySmallBusiness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntitySmallBusiness" xlink:to="dei_EntitySmallBusiness_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntitySmallBusiness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCommonStockSharesOutstanding" xlink:type="locator" xlink:label="dei_EntityCommonStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock Shares Outstanding</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentFiscalYearFocus" xlink:type="locator" xlink:label="dei_DocumentFiscalYearFocus" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Year Focus</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Year Focus</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentFiscalPeriodFocus" xlink:type="locator" xlink:label="dei_DocumentFiscalPeriodFocus" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Period Focus</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Period Focus</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentType" xlink:type="locator" xlink:label="dei_DocumentType" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentType_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentType_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_AmendmentFlag" xlink:type="locator" xlink:label="dei_AmendmentFlag" />
    <link:label xml:lang="en-US" xlink:label="dei_AmendmentFlag_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amendment Flag</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_AmendmentFlag_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentPeriodEndDate" xlink:type="locator" xlink:label="dei_DocumentPeriodEndDate" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentQuarterlyReport" xlink:type="locator" xlink:label="dei_DocumentQuarterlyReport" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Quarterly Report</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentQuarterlyReport" xlink:to="dei_DocumentQuarterlyReport_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Quarterly Report</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentTransitionReport" xlink:type="locator" xlink:label="dei_DocumentTransitionReport" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentTransitionReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentTransitionReport" xlink:to="dei_DocumentTransitionReport_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentTransitionReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityInteractiveDataCurrent" xlink:type="locator" xlink:label="dei_EntityInteractiveDataCurrent" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityInteractiveDataCurrent" xlink:to="dei_EntityInteractiveDataCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCurrentReportingStatus" xlink:type="locator" xlink:label="dei_EntityCurrentReportingStatus" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Current Reporting Status</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCurrentReportingStatus" xlink:to="dei_EntityCurrentReportingStatus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Current Reporting Status</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityShellCompany" xlink:type="locator" xlink:label="dei_EntityShellCompany" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityShellCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityShellCompany" xlink:to="dei_EntityShellCompany_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityShellCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_TradingSymbol" xlink:type="locator" xlink:label="dei_TradingSymbol" />
    <link:label xml:lang="en-US" xlink:label="dei_TradingSymbol_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_TradingSymbol" xlink:to="dei_TradingSymbol_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_TradingSymbol_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_Security12bTitle" xlink:type="locator" xlink:label="dei_Security12bTitle" />
    <link:label xml:lang="en-US" xlink:label="dei_Security12bTitle_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_Security12bTitle" xlink:to="dei_Security12bTitle_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_Security12bTitle_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Security12b Title</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_SecurityExchangeName" xlink:type="locator" xlink:label="dei_SecurityExchangeName" />
    <link:label xml:lang="en-US" xlink:label="dei_SecurityExchangeName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_SecurityExchangeName" xlink:to="dei_SecurityExchangeName_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_SecurityExchangeName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityFileNumber" xlink:type="locator" xlink:label="dei_EntityFileNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFileNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFileNumber" xlink:to="dei_EntityFileNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFileNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity File Number</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityIncorporationStateCountryCode" xlink:type="locator" xlink:label="dei_EntityIncorporationStateCountryCode" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Incorporation, State or Country Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityIncorporationStateCountryCode" xlink:to="dei_EntityIncorporationStateCountryCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Incorporation State Country Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityTaxIdentificationNumber" xlink:type="locator" xlink:label="dei_EntityTaxIdentificationNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Tax Identification Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityTaxIdentificationNumber" xlink:to="dei_EntityTaxIdentificationNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Tax Identification Number</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine1" xlink:type="locator" xlink:label="dei_EntityAddressAddressLine1" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line One</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressAddressLine1" xlink:to="dei_EntityAddressAddressLine1_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Address Line1</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine2" xlink:type="locator" xlink:label="dei_EntityAddressAddressLine2" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line Two</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressAddressLine2" xlink:to="dei_EntityAddressAddressLine2_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Address Line2</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressCityOrTown" xlink:type="locator" xlink:label="dei_EntityAddressCityOrTown" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
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    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address City Or Town</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressStateOrProvince" xlink:type="locator" xlink:label="dei_EntityAddressStateOrProvince" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressStateOrProvince" xlink:to="dei_EntityAddressStateOrProvince_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address State Or Province</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressPostalZipCode" xlink:type="locator" xlink:label="dei_EntityAddressPostalZipCode" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressPostalZipCode" xlink:to="dei_EntityAddressPostalZipCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Postal Zip Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CityAreaCode" xlink:type="locator" xlink:label="dei_CityAreaCode" />
    <link:label xml:lang="en-US" xlink:label="dei_CityAreaCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CityAreaCode" xlink:to="dei_CityAreaCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_CityAreaCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LocalPhoneNumber" xlink:type="locator" xlink:label="dei_LocalPhoneNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_LocalPhoneNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Local Phone Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LocalPhoneNumber" xlink:to="dei_LocalPhoneNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_LocalPhoneNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Local Phone Number</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfFinancialPositionAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Financial Position [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract" xlink:type="locator" xlink:label="us-gaap_AssetsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_AssetsCurrentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current assets:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets Current [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents At Carrying Value</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsCurrent" xlink:type="locator" xlink:label="us-gaap_OtherAssetsCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsCurrent" xlink:to="us-gaap_OtherAssetsCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets Current</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent" xlink:type="locator" xlink:label="us-gaap_AssetsCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets Current</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and equipment, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Net</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right-use-of assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseRightOfUseAsset" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:type="locator" xlink:label="us-gaap_Goodwill" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Goodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Goodwill" xlink:to="us-gaap_Goodwill_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Goodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:type="locator" xlink:label="us-gaap_OtherIntangibleAssetsNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherIntangibleAssetsNet" xlink:to="us-gaap_OtherIntangibleAssetsNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Intangible Assets Net</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsNoncurrent" xlink:type="locator" xlink:label="us-gaap_OtherAssetsNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets Noncurrent</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets" xlink:type="locator" xlink:label="us-gaap_Assets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities and Stockholders&#8217; Equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities And Stockholders Equity [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current liabilities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable And Accrued Liabilities Current</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease liability</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilityCurrent" xlink:to="us-gaap_OperatingLeaseLiabilityCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability Current</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term loan obligation, current</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtCurrent" xlink:to="us-gaap_LongTermDebtCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Current</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noncurrent operating lease liability</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability Noncurrent</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtNoncurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term loan obligation</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Noncurrent</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:type="locator" xlink:label="us-gaap_WarrantsAndRightsOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantsAndRightsOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant liability</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantsAndRightsOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrants And Rights Outstanding</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_Liabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" />
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    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders&#8217; equity:</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Abstract]</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,952 shares issued and outstanding at June 30, 2022 and December 31, 2021</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, $0.001 par value; 100,000,000 shares authorized; 22,468,682 and 15,510,025 issued and outstanding at June 30, 2022 and December 31, 2021, respectively</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Value</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated deficit</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings Accumulated Deficit</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:type="locator" xlink:label="us-gaap_StockholdersEquity" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total stockholders&#8217; equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="locator" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities and stockholders&#8217; equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities And Stockholders Equity</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:type="locator" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value (in dollars per share)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockParOrStatedValuePerShare" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Par Or Stated Value Per Share</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesAuthorized" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares authorized (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesAuthorized" xlink:to="us-gaap_PreferredStockSharesAuthorized_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Authorized</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares issued (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Issued</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares outstanding (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesOutstanding" xlink:to="us-gaap_PreferredStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Outstanding</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:type="locator" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value (in dollars per share)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Par Or Stated Value Per Share</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesAuthorized" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares authorized (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Authorized</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issued (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Issued</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares outstanding (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Outstanding</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementAbstract" xlink:type="locator" xlink:label="us-gaap_IncomeStatementAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_IncomeStatementAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingExpensesAbstract" xlink:type="locator" xlink:label="us-gaap_OperatingExpensesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating expenses:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpensesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Expenses [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Expense</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">General and administrative</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">General And Administrative Expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingExpenses" xlink:type="locator" xlink:label="us-gaap_OperatingExpenses" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total operating expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Expenses</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss" xlink:type="locator" xlink:label="us-gaap_OperatingIncomeLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Operating loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Income Loss</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherIncomeAndExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other income (expense):</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherIncomeAndExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Income And Expenses [Abstract]</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Investment Income Interest</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Interest expense</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other expense</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nonoperating Income Expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Income Loss</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareBasic" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss per share, basic</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasic" xlink:to="us-gaap_EarningsPerShareBasic_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share Basic</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareDiluted" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss per share, diluted</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share Diluted</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basic weighted average shares used in calculating net loss per share attributable to common stockholders</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number Of Shares Outstanding Basic</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Diluted weighted average shares used in calculating net loss per share attributable to common stockholders</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number Of Diluted Shares Outstanding</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_StockIssuedDuringPeriodSharesWarrantsExercise" xlink:type="locator" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period shares warrants exercise.</link:label>
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    <link:loc xlink:href="pstv-20220630.xsd#pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares" xlink:type="locator" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period shares warrants exercise(shares).</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares" xlink:to="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementOfStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Stockholders Equity [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfStockholdersEquityAbstract" xlink:to="us-gaap_StatementOfStockholdersEquityAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Equity Components [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_EquityComponentDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockMember" xlink:type="locator" xlink:label="us-gaap_PreferredStockMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred Stock [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockMember" xlink:to="us-gaap_PreferredStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockMember" xlink:to="us-gaap_CommonStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapitalMember" xlink:to="us-gaap_AdditionalPaidInCapitalMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Deficit [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsMember" xlink:to="us-gaap_RetainedEarningsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:type="locator" xlink:label="us-gaap_SharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesOutstanding" xlink:to="us-gaap_SharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Outstanding</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveVerboseLabel">Sale of common stock, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value New Issues</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveVerboseLabel">Sale of common stock, net, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares New Issues</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Conversion of Series B Convertible Preferred Stock into common stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:to="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Conversion Of Convertible Securities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Conversion of Series B Convertible Preferred Stock into common stock (share)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Conversion Of Convertible Securities</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock for exercise of warrants</link:label>
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    <link:label xml:lang="en-US" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Issuance of common stock for exercise of warrants (in shares)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance (in shares)</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ChangeOfOperatingLeaseAssetsAndLiabilities" xlink:type="locator" xlink:label="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities" />
    <link:label xml:lang="en-US" xlink:label="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Change of operating lease assets and liabilities.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities" xlink:to="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_NonCashLeaseExpense" xlink:type="locator" xlink:label="pstv_NonCashLeaseExpense" />
    <link:label xml:lang="en-US" xlink:label="pstv_NonCashLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Non cash lease expense.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_NonCashLeaseExpense" xlink:to="pstv_NonCashLeaseExpense_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition" xlink:type="locator" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition" />
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for IPRD asset acquired in an asset acquisition.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition" xlink:to="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ProceedsFromWarrantExercises1" xlink:type="locator" xlink:label="pstv_ProceedsFromWarrantExercises1" />
    <link:label xml:lang="en-US" xlink:label="pstv_ProceedsFromWarrantExercises1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Proceeds from warrant exercises.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ProceedsFromWarrantExercises1" xlink:to="pstv_ProceedsFromWarrantExercises1_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_UnpaidOfferingCosts" xlink:type="locator" xlink:label="pstv_UnpaidOfferingCosts" />
    <link:label xml:lang="en-US" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Unpaid Offering Costs.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_UnpaidOfferingCosts" xlink:to="pstv_UnpaidOfferingCosts_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CashPaidDuringPeriodForAbstract" xlink:type="locator" xlink:label="pstv_CashPaidDuringPeriodForAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidDuringPeriodForAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid during period for:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CashPaidDuringPeriodForAbstract" xlink:to="pstv_CashPaidDuringPeriodForAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Cash Flows [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows used in operating activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:type="locator" xlink:label="us-gaap_DepreciationDepletionAndAmortization" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationDepletionAndAmortization" xlink:to="us-gaap_DepreciationDepletionAndAmortization_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation Depletion And Amortization</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts" xlink:type="locator" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of deferred financing costs and debt discount</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfFinancingCostsAndDiscounts" xlink:to="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Of Financing Costs And Discounts</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAdjustmentOfWarrants" xlink:type="locator" xlink:label="us-gaap_FairValueAdjustmentOfWarrants" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in fair value of liability instruments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAdjustmentOfWarrants" xlink:to="us-gaap_FairValueAdjustmentOfWarrants_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Adjustment Of Warrants</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensation" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change of operating lease assets and liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ChangeOfOperatingLeaseAssetsAndLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Change Of Operating Lease Assets And Liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_NonCashLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash lease expense</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_NonCashLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Non Cash Lease Expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increases (decreases) in cash caused by changes in operating assets and liabilities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Operating Capital [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssets" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOtherCurrentAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherCurrentAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOtherCurrentAssets" xlink:to="us-gaap_IncreaseDecreaseInOtherCurrentAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherCurrentAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Other Current Assets</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Payable And Accrued Liabilities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash used in operating activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows (used in) investing activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of property and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Property Plant And Equipment</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireIntangibleAssets" xlink:to="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Intangible Assets</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">In process research and development acquired</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For I P R D Asset Acquired In An Asset Acquisition</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash used in investing activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:type="locator" xlink:label="us-gaap_RepaymentsOfLongTermDebt" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Principal payments of long-term obligations</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermDebt" xlink:to="us-gaap_RepaymentsOfLongTermDebt_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repayments Of Long Term Debt</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeasePrincipalPayments" xlink:type="locator" xlink:label="us-gaap_FinanceLeasePrincipalPayments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinanceLeasePrincipalPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Payment of financing lease liability</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FinanceLeasePrincipalPayments" xlink:to="us-gaap_FinanceLeasePrincipalPayments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinanceLeasePrincipalPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finance Lease Principal Payments</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ProceedsFromWarrantExercises1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from exercise of warrants</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ProceedsFromWarrantExercises1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Warrant Exercises1</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of common stock, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Common Stock</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by financing activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net increase (decrease) in cash and cash equivalents</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash and cash equivalents at beginning of period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash and cash equivalents at end of period</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental disclosure of cash flows information:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidDuringPeriodForAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid during period for:</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidDuringPeriodForAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid During Period For [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestPaidNet" xlink:type="locator" xlink:label="us-gaap_InterestPaidNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPaidNet" xlink:to="us-gaap_InterestPaidNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Paid Net</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental schedule of non-cash investing and financing activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unpaid offering cost</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unpaid Offering Costs</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability" xlink:type="locator" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Right-of-use asset obtained in exchange for lease liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability" xlink:to="us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Right Of Use Asset Obtained In Exchange For Finance Lease Liability</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:type="locator" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Organization Consolidation And Presentation Of Financial Statements [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:type="locator" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and New Accounting Standards</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Basis Of Presentation And Significant Accounting Policies [Text Block]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_UseOfEstimatesTextBlock" xlink:type="locator" xlink:label="pstv_UseOfEstimatesTextBlock" />
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    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_UseOfEstimatesTextBlock" xlink:to="pstv_UseOfEstimatesTextBlock_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_UseOfEstimatesAbstract" xlink:type="locator" xlink:label="pstv_UseOfEstimatesAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_UseOfEstimatesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Use of Estimates [Abstract]</link:label>
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    <link:label xml:lang="en-US" xlink:label="pstv_UseOfEstimatesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Use Of Estimates [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_UseOfEstimatesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_UseOfEstimatesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Use Of Estimates [Text Block]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_DisclosureOfLiquidityTextBlock" xlink:type="locator" xlink:label="pstv_DisclosureOfLiquidityTextBlock" />
    <link:label xml:lang="en-US" xlink:label="pstv_DisclosureOfLiquidityTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure of liquidity.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_DisclosureOfLiquidityTextBlock" xlink:to="pstv_DisclosureOfLiquidityTextBlock_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LiquidityAbstract" xlink:type="locator" xlink:label="pstv_LiquidityAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_LiquidityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Liquidity Abstract</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LiquidityAbstract" xlink:to="pstv_LiquidityAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LiquidityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liquidity [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DisclosureOfLiquidityTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liquidity</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DisclosureOfLiquidityTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Liquidity [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosuresAbstract" xlink:type="locator" xlink:label="us-gaap_FairValueDisclosuresAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosuresAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosuresAbstract" xlink:to="us-gaap_FairValueDisclosuresAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementInputsDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementInputsDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueMeasurementInputsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurements</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueMeasurementInputsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs Disclosure [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_DebtDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureAbstract" xlink:to="us-gaap_DebtDisclosureAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_DebtDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term Loan Obligations</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureTextBlock" xlink:to="us-gaap_DebtDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Disclosure [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareAbstract" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareTextBlock" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loss per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareTextBlock" xlink:to="us-gaap_EarningsPerShareTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies Disclosure [Text Block]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LicenseAgreementDisclosureTextBlock" xlink:type="locator" xlink:label="pstv_LicenseAgreementDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure of accounting policy for license agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LicenseAgreementDisclosureTextBlock" xlink:to="pstv_LicenseAgreementDisclosureTextBlock_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LicenseAgreementAbstract" xlink:type="locator" xlink:label="pstv_LicenseAgreementAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_LicenseAgreementAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement abstract.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LicenseAgreementAbstract" xlink:to="pstv_LicenseAgreementAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LicenseAgreementAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreements</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Disclosure [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteAbstract" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityNoteAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityNoteAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity Note [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityNoteAbstract" xlink:to="us-gaap_StockholdersEquityNoteAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders&apos; Equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:to="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity Note Disclosure [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:type="locator" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:type="locator" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based Compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Compensation Related Costs Share Based Payments [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RisksAndUncertaintiesAbstract" xlink:type="locator" xlink:label="us-gaap_RisksAndUncertaintiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RisksAndUncertaintiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Risks And Uncertainties [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RisksAndUncertaintiesAbstract" xlink:to="us-gaap_RisksAndUncertaintiesAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">COVID-19 Pandemic and CARES Act</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock" xlink:to="us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnusualOrInfrequentItemsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unusual Or Infrequent Items Disclosure [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and New Accounting Standards</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Basis Of Accounting Policy Policy [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:type="locator" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recently Issued Accounting Pronouncements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:to="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">New Accounting Pronouncements And Changes In Accounting Principles [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UseOfEstimates" xlink:type="locator" xlink:label="us-gaap_UseOfEstimates" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UseOfEstimates" xlink:to="us-gaap_UseOfEstimates_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Use Of Estimates</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCostTableTextBlock" xlink:type="locator" xlink:label="us-gaap_LeaseCostTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCostTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Lease Costs</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseCostTableTextBlock" xlink:to="us-gaap_LeaseCostTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCostTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Cost Table [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Future Minimum Annual Lease Payments under Operating Leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Maturity Table [Text Block]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock Option Activity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Activity Table [Text Block]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net cash used in operating activities</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ClosingBidPriceForCommonStockHadFallenBelow" xlink:type="locator" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow" />
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing bid price for common stock had fallen.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ClosingBidPriceForCommonStockHadFallenBelow" xlink:to="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ConsecutiveBusinessDays" xlink:type="locator" xlink:label="pstv_ConsecutiveBusinessDays" />
    <link:label xml:lang="en-US" xlink:label="pstv_ConsecutiveBusinessDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Consecutive business days.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ConsecutiveBusinessDays" xlink:to="pstv_ConsecutiveBusinessDays_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Closing bid price for common stock had fallen below</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Closing Bid Price For Common Stock Had Fallen Below</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ConsecutiveBusinessDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consecutive business days</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ConsecutiveBusinessDays_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Consecutive Business Days</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ClosingBidPrice" xlink:type="locator" xlink:label="pstv_ClosingBidPrice" />
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing bid price.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ClosingBidPrice" xlink:to="pstv_ClosingBidPrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Closing bid price</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ClosingBidPrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Closing Bid Price</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PeriodForRegainCompliance" xlink:type="locator" xlink:label="pstv_PeriodForRegainCompliance" />
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodForRegainCompliance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Period for regain compliance.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PeriodForRegainCompliance" xlink:to="pstv_PeriodForRegainCompliance_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodForRegainCompliance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period for regain compliance</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodForRegainCompliance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Period For Regain Compliance</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod" xlink:type="locator" xlink:label="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod" />
    <link:label xml:lang="en-US" xlink:label="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrants issued, underwritten public offering, period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod" xlink:to="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:type="locator" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value By Balance Sheet Grouping [Table]</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Balance Sheet Grouping [Table]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SeriesUWarrantsMember" xlink:type="locator" xlink:label="pstv_SeriesUWarrantsMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesUWarrantsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series U warrants member</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SeriesUWarrantsMember" xlink:to="pstv_SeriesUWarrantsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesUWarrantsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series U Warrants [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesUWarrantsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series U Warrants [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants issued, underwritten public offering, period</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_WarrantsIssuedUnderwrittenPublicOfferingPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrants Issued Underwritten Public Offering Period</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_DebtInstrumentFloatingInterestRatePercentage" xlink:type="locator" xlink:label="pstv_DebtInstrumentFloatingInterestRatePercentage" />
    <link:label xml:lang="en-US" xlink:label="pstv_DebtInstrumentFloatingInterestRatePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Floating interest rate for funds borrowed, under the debt agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_DebtInstrumentFloatingInterestRatePercentage" xlink:to="pstv_DebtInstrumentFloatingInterestRatePercentage_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ClassOfWarrantOrRightExpirationDate" xlink:type="locator" xlink:label="pstv_ClassOfWarrantOrRightExpirationDate" />
    <link:label xml:lang="en-US" xlink:label="pstv_ClassOfWarrantOrRightExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">The date that the warrant or right expires.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ClassOfWarrantOrRightExpirationDate" xlink:to="pstv_ClassOfWarrantOrRightExpirationDate_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Table]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="us-gaap_DebtInstrumentNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Name [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_TermLoanMember" xlink:type="locator" xlink:label="pstv_TermLoanMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Second amendment to the amended and restated loan and security agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_TermLoanMember" xlink:to="pstv_TermLoanMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term Loan [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_TermLoanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Term Loan [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeAxis" xlink:to="srt_RangeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeMember" xlink:to="srt_RangeMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MinimumMember" xlink:to="srt_MinimumMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MaximumMember" xlink:to="srt_MaximumMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis" xlink:type="locator" xlink:label="us-gaap_VariableRateAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:type="locator" xlink:label="us-gaap_VariableRateDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_VariableRateDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Domain]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:type="locator" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">LIBOR [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:to="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">London Interbank Offered Rate L I B O R [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:type="locator" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instrument</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeInstrumentRiskAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instrument Risk [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:type="locator" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Contract</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_DerivativeContractTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Contract Type [Domain]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateFloorMember" xlink:type="locator" xlink:label="us-gaap_InterestRateFloorMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestRateFloorMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Floor [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestRateFloorMember" xlink:to="us-gaap_InterestRateFloorMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestRateFloorMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Floor [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instrument</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_FinancialInstrumentAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instrument [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Transfers And Servicing Of Financial Instruments Types Of Financial Instruments [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LoanAndSecurityAgreementMember" xlink:type="locator" xlink:label="pstv_LoanAndSecurityAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Loan and security agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LoanAndSecurityAgreementMember" xlink:to="pstv_LoanAndSecurityAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan and Security Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LoanAndSecurityAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Loan And Security Agreement [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupClassificationAxis" xlink:type="locator" xlink:label="us-gaap_DisposalGroupClassificationAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupClassificationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Disposal Group Classification</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupClassificationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Group Classification [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:type="locator" xlink:label="us-gaap_DisposalGroupClassificationDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupClassificationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Disposal Group Classification</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisposalGroupClassificationDomain" xlink:to="us-gaap_DisposalGroupClassificationDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisposalGroupClassificationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Group Classification [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember" xlink:type="locator" xlink:label="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sale of the japanese subsidiary and certain assets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember" xlink:to="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of the Japanese Subsidiary and Certain Assets [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Japanese Subsidiary And Certain Assets [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Line Items]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentOfferingDate1" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentOfferingDate1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentOfferingDate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Origination Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentOfferingDate1" xlink:to="us-gaap_DebtInstrumentOfferingDate1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentOfferingDate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Offering Date1</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentFaceAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Original Loan Amount</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentFaceAmount" xlink:to="us-gaap_DebtInstrumentFaceAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Face Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DebtInstrumentFloatingInterestRatePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest rate</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DebtInstrumentFloatingInterestRatePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Floating Interest Rate Percentage</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis variable rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Basis Spread On Variable Rate1</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentMaturityDate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maturity date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentMaturityDate" xlink:to="us-gaap_DebtInstrumentMaturityDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Maturity Date</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFeeAmount" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentFeeAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentFeeAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fees amount associated with loan</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentFeeAmount" xlink:to="us-gaap_DebtInstrumentFeeAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentFeeAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Fee Amount</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares callable by warrants (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Number Of Securities Called By Warrants Or Rights</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant exercise price (in dollars per share)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Exercise Price Of Warrants Or Rights1</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Date from which warrants are exercisable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable" xlink:to="us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRighstDateFromWhichWarrantsOrRightsExercisable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Righst Date From Which Warrants Or Rights Exercisable</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ClassOfWarrantOrRightExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant expiration date</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ClassOfWarrantOrRightExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Expiration Date</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_MinimumLiquidityCovenantAmount" xlink:type="locator" xlink:label="pstv_MinimumLiquidityCovenantAmount" />
    <link:label xml:lang="en-US" xlink:label="pstv_MinimumLiquidityCovenantAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Minimum liquidity covenant amount.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_MinimumLiquidityCovenantAmount" xlink:to="pstv_MinimumLiquidityCovenantAmount_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForLoans" xlink:type="locator" xlink:label="us-gaap_PaymentsForLoans" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsForLoans_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payments for principal, interest and fees</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForLoans" xlink:to="us-gaap_PaymentsForLoans_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsForLoans_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments For Loans</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MinimumLiquidityCovenantAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum liquidity covenant</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MinimumLiquidityCovenantAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minimum Liquidity Covenant Amount</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_DebtPrincipalRepaymentStartDate" xlink:type="locator" xlink:label="pstv_DebtPrincipalRepaymentStartDate" />
    <link:label xml:lang="en-US" xlink:label="pstv_DebtPrincipalRepaymentStartDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt principal repayment start date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_DebtPrincipalRepaymentStartDate" xlink:to="pstv_DebtPrincipalRepaymentStartDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_DebtPrincipalRepaymentStartDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt principal repayment start date</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DebtPrincipalRepaymentStartDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Principal Repayment Start Date</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LongTermDebtOutstandingThresholdAmount" xlink:type="locator" xlink:label="pstv_LongTermDebtOutstandingThresholdAmount" />
    <link:label xml:lang="en-US" xlink:label="pstv_LongTermDebtOutstandingThresholdAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Long term debt outstanding threshold amount.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LongTermDebtOutstandingThresholdAmount" xlink:to="pstv_LongTermDebtOutstandingThresholdAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LongTermDebtOutstandingThresholdAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Long Term Debt Outstanding Threshold Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LongTermDebtOutstandingThresholdAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Long Term Debt Outstanding Threshold Amount</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCovenantCompliance" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentCovenantCompliance" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentCovenantCompliance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Covenant Compliance</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentCovenantCompliance" xlink:to="us-gaap_DebtInstrumentCovenantCompliance_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DebtInstrumentCovenantCompliance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument Covenant Compliance</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_InterestExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfDebtDiscountPremium" xlink:type="locator" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash amortization</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfDebtDiscountPremium" xlink:to="us-gaap_AmortizationOfDebtDiscountPremium_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Of Debt Discount Premium</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_OptionsMember" xlink:type="locator" xlink:label="pstv_OptionsMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_OptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Options.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_OptionsMember" xlink:to="pstv_OptionsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_OptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Outstanding Stock Options [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_OptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Options [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantMember" xlink:type="locator" xlink:label="us-gaap_WarrantMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Outstanding Warrants [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantMember" xlink:to="us-gaap_WarrantMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrant [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dilutive common shares excluded from the calculations of diluted loss per share (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LeaseCommencementDate" xlink:type="locator" xlink:label="pstv_LeaseCommencementDate" />
    <link:label xml:lang="en-US" xlink:label="pstv_LeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lease commencement date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LeaseCommencementDate" xlink:to="pstv_LeaseCommencementDate_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_OperatingLeasesExpiryYear" xlink:type="locator" xlink:label="pstv_OperatingLeasesExpiryYear" />
    <link:label xml:lang="en-US" xlink:label="pstv_OperatingLeasesExpiryYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases, expiry year.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_OperatingLeasesExpiryYear" xlink:to="pstv_OperatingLeasesExpiryYear_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RecordedUnconditionalPurchaseObligationTable" xlink:type="locator" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Unconditional Purchase Obligation [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RecordedUnconditionalPurchaseObligationTable" xlink:to="us-gaap_RecordedUnconditionalPurchaseObligationTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation [Table]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:type="locator" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Related Party Transactions By Related Party [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:type="locator" xlink:label="us-gaap_RelatedPartyDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_RelatedPartyDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Related Party [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CharlottesvilleMember" xlink:type="locator" xlink:label="pstv_CharlottesvilleMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Charlottesville</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CharlottesvilleMember" xlink:to="pstv_CharlottesvilleMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Charlottesville [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Charlottesville [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_MedidataSolutionsIncMember" xlink:type="locator" xlink:label="pstv_MedidataSolutionsIncMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_MedidataSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Medidata solutions, inc.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_MedidataSolutionsIncMember" xlink:to="pstv_MedidataSolutionsIncMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_MedidataSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Medidata Solutions, Inc. [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MedidataSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Medidata Solutions Inc [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis" xlink:type="locator" xlink:label="us-gaap_TypeOfArrangementAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_TypeOfArrangementAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Arrangement [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="locator" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Arrangements And Nonarrangement Transactions [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_ServicesAgreementMember" xlink:type="locator" xlink:label="pstv_ServicesAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_ServicesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Services agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_ServicesAgreementMember" xlink:to="pstv_ServicesAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_ServicesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Services Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_ServicesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Services Agreement [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PiramalPharmaSolutionsIncMember" xlink:type="locator" xlink:label="pstv_PiramalPharmaSolutionsIncMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_PiramalPharmaSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Piramal pharma solutions inc.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PiramalPharmaSolutionsIncMember" xlink:to="pstv_PiramalPharmaSolutionsIncMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_PiramalPharmaSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Piramal Pharma Solutions, Inc. [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PiramalPharmaSolutionsIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Piramal Pharma Solutions Inc [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis" xlink:type="locator" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Unconditional Purchase Obligation by Category of Item Purchased</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis" xlink:to="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation By Category Of Item Purchased [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain" xlink:type="locator" xlink:label="us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unconditional Purchase Obligation, Category of Goods or Services Acquired</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain" xlink:to="us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnconditionalPurchaseObligationCategoryOfGoodsOrServicesAcquiredDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unconditional Purchase Obligation Category Of Goods Or Services Acquired [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PreClinicalResearchStudyObligationsMember" xlink:type="locator" xlink:label="pstv_PreClinicalResearchStudyObligationsMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractual obligation to provide funding of research and development costs over periods that initially exceed one year or the normal operating cycle, if longer.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PreClinicalResearchStudyObligationsMember" xlink:to="pstv_PreClinicalResearchStudyObligationsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre-clinical Research Study Obligations [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Pre Clinical Research Study Obligations [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_LitigationCaseAxis" xlink:type="locator" xlink:label="srt_LitigationCaseAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_LitigationCaseAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Litigation Case</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_LitigationCaseAxis" xlink:to="srt_LitigationCaseAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_LitigationCaseAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Case [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_LitigationCaseTypeDomain" xlink:type="locator" xlink:label="srt_LitigationCaseTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="srt_LitigationCaseTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Litigation Case</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_LitigationCaseTypeDomain" xlink:to="srt_LitigationCaseTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_LitigationCaseTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Case Type [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LoremVascularPteLtdMember" xlink:type="locator" xlink:label="pstv_LoremVascularPteLtdMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_LoremVascularPteLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lorem Vascular, Pte. Ltd.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LoremVascularPteLtdMember" xlink:to="pstv_LoremVascularPteLtdMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LoremVascularPteLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lorem Vascular Pte Ltd [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LoremVascularPteLtdMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lorem Vascular Pte Ltd [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RecordedUnconditionalPurchaseObligationLineItems" xlink:type="locator" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Unconditional Purchase Obligation [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RecordedUnconditionalPurchaseObligationLineItems" xlink:to="us-gaap_RecordedUnconditionalPurchaseObligationLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_OperatingLeasesExpiryYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases expiry year</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_OperatingLeasesExpiryYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Expiry Year</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, term of contract</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseTermOfContract" xlink:to="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Term Of Contract</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, existence of option to extend [true false]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" xlink:to="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Existence Of Option To Extend</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseOptionToExtend" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseOptionToExtend" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseOptionToExtend_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, option to extend</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseOptionToExtend" xlink:to="us-gaap_LesseeOperatingLeaseOptionToExtend_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseOptionToExtend_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Option To Extend</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, renewal term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:to="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Renewal Term</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease commencement date</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LeaseCommencementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Commencement Date</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseExpirationDate1" xlink:type="locator" xlink:label="us-gaap_LeaseExpirationDate1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseExpirationDate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, expiration date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseExpirationDate1" xlink:to="us-gaap_LeaseExpirationDate1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseExpirationDate1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Expiration Date1</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease, weighted average discount rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:to="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Weighted Average Discount Rate Percent</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease, weighted average remaining term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:to="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Weighted Average Remaining Lease Term1</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities" xlink:type="locator" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities" />
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for amounts included in the measurement of lease liabilities.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities" xlink:to="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_FinanceLeaseExpenseAbstract" xlink:type="locator" xlink:label="pstv_FinanceLeaseExpenseAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_FinanceLeaseExpenseAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Finance lease expense.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_FinanceLeaseExpenseAbstract" xlink:to="pstv_FinanceLeaseExpenseAbstract_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CashPaymentInformationAbstract" xlink:type="locator" xlink:label="pstv_CashPaymentInformationAbstract" />
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash payment information.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CashPaymentInformationAbstract" xlink:to="pstv_CashPaymentInformationAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCostAbstract" xlink:type="locator" xlink:label="us-gaap_LeaseCostAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease expense:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseCostAbstract" xlink:to="us-gaap_LeaseCostAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Cost [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseCost" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseCost" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseCost" xlink:to="us-gaap_OperatingLeaseCost_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Cost</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_FinanceLeaseExpenseAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finance lease expense:</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_FinanceLeaseExpenseAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finance Lease Expense [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetAmortization" xlink:type="locator" xlink:label="us-gaap_FinanceLeaseRightOfUseAssetAmortization" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinanceLeaseRightOfUseAssetAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation of right-of-use assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FinanceLeaseRightOfUseAssetAmortization" xlink:to="us-gaap_FinanceLeaseRightOfUseAssetAmortization_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinanceLeaseRightOfUseAssetAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finance Lease Right Of Use Asset Amortization</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCost" xlink:type="locator" xlink:label="us-gaap_LeaseCost" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total lease expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseCost" xlink:to="us-gaap_LeaseCost_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Cost</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash payment information:</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Payment Information [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeasePayments" xlink:type="locator" xlink:label="us-gaap_OperatingLeasePayments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating cash used for operating leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasePayments" xlink:to="us-gaap_OperatingLeasePayments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Payments</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinanceLeasePrincipalPayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing cash used for financing leases</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total cash paid for amounts included in the measurement of lease liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For Amounts Included In Measurement Of Lease Liabilities</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseExpense" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rent expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseExpense" xlink:to="us-gaap_OperatingLeaseExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" xlink:to="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liabilities Payments Due [Abstract]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remainder of 2022</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Remainder Of Fiscal Year</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2023</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Next Twelve Months</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Two</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2025</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Three</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total minimum lease payments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: amount representing interest</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Undiscounted Excess Amount</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiability" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiability" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Present value of obligations under leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiability" xlink:to="us-gaap_OperatingLeaseLiability_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: current portion</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SalesOrderTerm" xlink:type="locator" xlink:label="pstv_SalesOrderTerm" />
    <link:label xml:lang="en-US" xlink:label="pstv_SalesOrderTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sales order term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SalesOrderTerm" xlink:to="pstv_SalesOrderTerm_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SalesOrderTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sales order term</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SalesOrderTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sales Order Term</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_MasterServicesAgreementDate" xlink:type="locator" xlink:label="pstv_MasterServicesAgreementDate" />
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Master services agreement date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_MasterServicesAgreementDate" xlink:to="pstv_MasterServicesAgreementDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Master service agreement date</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Master Services Agreement Date</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_MasterServicesAgreementInitialTerm" xlink:type="locator" xlink:label="pstv_MasterServicesAgreementInitialTerm" />
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementInitialTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Master services agreement initial term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_MasterServicesAgreementInitialTerm" xlink:to="pstv_MasterServicesAgreementInitialTerm_lbl" />
    <link:loc xlink:href="pstv-20220630.xsd#pstv_MasterServicesAgreementTermsDescription" xlink:type="locator" xlink:label="pstv_MasterServicesAgreementTermsDescription" />
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementTermsDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Master services agreement Terms description.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_MasterServicesAgreementTermsDescription" xlink:to="pstv_MasterServicesAgreementTermsDescription_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementInitialTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Master services agreement initial term</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementInitialTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Master Services Agreement Initial Term</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementTermsDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Master services agreement terms, Description</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_MasterServicesAgreementTermsDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Master Services Agreement Terms Description</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractualObligation" xlink:type="locator" xlink:label="us-gaap_ContractualObligation" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractualObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contractual obligation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractualObligation" xlink:to="us-gaap_ContractualObligation_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractualObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contractual Obligation</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CompensatoryDamagesAndOperational" xlink:type="locator" xlink:label="pstv_CompensatoryDamagesAndOperational" />
    <link:label xml:lang="en-US" xlink:label="pstv_CompensatoryDamagesAndOperational_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Compensatory damages and operational.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CompensatoryDamagesAndOperational" xlink:to="pstv_CompensatoryDamagesAndOperational_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_CompensatoryDamagesAndOperational_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Compensatory damages and operational</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CompensatoryDamagesAndOperational_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Compensatory Damages And Operational</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LitigationSettlementExpense" xlink:type="locator" xlink:label="us-gaap_LitigationSettlementExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LitigationSettlementExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Litigation settlement, expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LitigationSettlementExpense" xlink:to="us-gaap_LitigationSettlementExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LitigationSettlementExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Settlement Expense</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others By Type [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others Type [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_UTHSALicenseAgreementMember" xlink:type="locator" xlink:label="pstv_UTHSALicenseAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_UTHSALicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">UTHSA License Agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_UTHSALicenseAgreementMember" xlink:to="pstv_UTHSALicenseAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_UTHSALicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">UTHSA License Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_UTHSALicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">U T H S A License Agreement [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRoyalties" xlink:type="locator" xlink:label="us-gaap_PaymentsForRoyalties" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsForRoyalties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License fee payment in cash</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForRoyalties" xlink:to="us-gaap_PaymentsForRoyalties_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsForRoyalties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments For Royalties</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PreferredStockDividendRatePercentageEliminatedDate" xlink:type="locator" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate" />
    <link:label xml:lang="en-US" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Preferred stock dividend rate percentage eliminated date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PreferredStockDividendRatePercentageEliminatedDate" xlink:to="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfStockByClassTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Stock By Class [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_ScheduleOfStockByClassTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Stock By Class [Table]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:type="locator" xlink:label="us-gaap_StatementClassOfStockAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_StatementClassOfStockAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Class Of Stock [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:type="locator" xlink:label="us-gaap_ClassOfStockDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_ClassOfStockDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Stock [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SeriesAConvertiblePreferredStockMember" xlink:type="locator" xlink:label="pstv_SeriesAConvertiblePreferredStockMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series A convertible preferred stock.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SeriesAConvertiblePreferredStockMember" xlink:to="pstv_SeriesAConvertiblePreferredStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series A Convertible Preferred Stock [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series A Convertible Preferred Stock [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SeriesBConvertiblePreferredStockMember" xlink:type="locator" xlink:label="pstv_SeriesBConvertiblePreferredStockMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B convertible preferred stock.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SeriesBConvertiblePreferredStockMember" xlink:to="pstv_SeriesBConvertiblePreferredStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series B Convertible Preferred Stock [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series B Convertible Preferred Stock [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SeriesCConvertiblePreferredStockMember" xlink:type="locator" xlink:label="pstv_SeriesCConvertiblePreferredStockMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Series C convertible preferred stock.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SeriesCConvertiblePreferredStockMember" xlink:to="pstv_SeriesCConvertiblePreferredStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series C Convertible Preferred Stock [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Series C Convertible Preferred Stock [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_TwoThousandEighteenRightsOfferingMember" xlink:type="locator" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand eighteen rights offering.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_TwoThousandEighteenRightsOfferingMember" xlink:to="pstv_TwoThousandEighteenRightsOfferingMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2018 Rights Offering [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Eighteen Rights Offering [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:type="locator" xlink:label="us-gaap_ClassOfStockLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ClassOfStockLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Stock [Line Items]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockDividendRatePercentage" xlink:type="locator" xlink:label="us-gaap_PreferredStockDividendRatePercentage" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible preferred stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockDividendRatePercentage" xlink:to="us-gaap_PreferredStockDividendRatePercentage_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Dividend Rate Percentage</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series A 3.6% Convertible preferred stock eliminated date</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Dividend Rate Percentage Eliminated Date</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_NumberOfPreferredStockSharesExercised" xlink:type="locator" xlink:label="pstv_NumberOfPreferredStockSharesExercised" />
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number Of Preferred Stock Shares Exercised.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_NumberOfPreferredStockSharesExercised" xlink:to="pstv_NumberOfPreferredStockSharesExercised_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of preferred stock, shares converted</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Preferred Stock Shares Exercised</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember" xlink:type="locator" xlink:label="us-gaap_CommonClassAMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonClassAMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Class A [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonClassAMember" xlink:to="us-gaap_CommonClassAMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonClassAMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Class A [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassBMember" xlink:type="locator" xlink:label="us-gaap_CommonClassBMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonClassBMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Class B [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonClassBMember" xlink:to="us-gaap_CommonClassBMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonClassBMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Class B [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_RepresentativeSeriesUWarrantMember" xlink:type="locator" xlink:label="pstv_RepresentativeSeriesUWarrantMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_RepresentativeSeriesUWarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Representative Series U Warrant.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_RepresentativeSeriesUWarrantMember" xlink:to="pstv_RepresentativeSeriesUWarrantMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_RepresentativeSeriesUWarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Representative Warrants [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_RepresentativeSeriesUWarrantMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Representative Series U Warrant [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock issued (in shares)</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of securities called by warrant or right</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockPricePerShare" xlink:type="locator" xlink:label="us-gaap_SaleOfStockPricePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock, Price Per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockPricePerShare" xlink:to="us-gaap_SaleOfStockPricePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Price Per Share</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:type="locator" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants expected term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantsAndRightsOutstandingTerm" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Warrants And Rights Outstanding Term</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_NumberOfWarrantsExercised" xlink:type="locator" xlink:label="pstv_NumberOfWarrantsExercised" />
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of warrants exercised</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_NumberOfWarrantsExercised" xlink:to="pstv_NumberOfWarrantsExercised_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:type="locator" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of warrant outstanding</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightOutstanding" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Outstanding</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of warrants exercised</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Warrants Exercised</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PeriodExercisableFromTheDateOfIssuance" xlink:type="locator" xlink:label="pstv_PeriodExercisableFromTheDateOfIssuance" />
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodExercisableFromTheDateOfIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to the period exercisable from the date of issuance.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PeriodExercisableFromTheDateOfIssuance" xlink:to="pstv_PeriodExercisableFromTheDateOfIssuance_lbl" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:type="locator" xlink:label="us-gaap_InvestmentTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Investment Type [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:type="locator" xlink:label="us-gaap_InvestmentTypeCategorizationMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="us-gaap_InvestmentTypeCategorizationMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Investment Type Categorization [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_TwentyTwentyPurchaseAgreementMember" xlink:type="locator" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Twenty twenty purchase agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_TwentyTwentyPurchaseAgreementMember" xlink:to="pstv_TwentyTwentyPurchaseAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Purchase Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Twenty Twenty Purchase Agreement [Member]</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <link:label xml:lang="en-US" xlink:label="dei_LegalEntityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal Entity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LegalEntityAxis" xlink:to="dei_LegalEntityAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_LegalEntityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Legal Entity [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityDomain" xlink:to="dei_EntityDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_LincolnParkCapitalFundLLCMember" xlink:type="locator" xlink:label="pstv_LincolnParkCapitalFundLLCMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_LincolnParkCapitalFundLLCMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lincoln park capital fund, LLC.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_LincolnParkCapitalFundLLCMember" xlink:to="pstv_LincolnParkCapitalFundLLCMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_LincolnParkCapitalFundLLCMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lincoln Park Capital Fund, LLC [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_LincolnParkCapitalFundLLCMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lincoln Park Capital Fund L L C [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CommitmentFeeMember" xlink:type="locator" xlink:label="pstv_CommitmentFeeMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitment fee.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CommitmentFeeMember" xlink:to="pstv_CommitmentFeeMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitment Fee [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitment Fee [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CanaccordGenuityLLCMember" xlink:type="locator" xlink:label="pstv_CanaccordGenuityLLCMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Canaccord Genuity LLC [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CanaccordGenuityLLCMember" xlink:to="pstv_CanaccordGenuityLLCMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Canaccord Genuity L L C [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:type="locator" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsidiary Sale Of Stock [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:type="locator" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Name Of Transaction [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_AtTheMarketOfferingProgramMember" xlink:type="locator" xlink:label="pstv_AtTheMarketOfferingProgramMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">At the market offering program.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_AtTheMarketOfferingProgramMember" xlink:to="pstv_AtTheMarketOfferingProgramMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">At The Market Offering Program [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">At The Market Offering Program [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_SalesAgreementMember" xlink:type="locator" xlink:label="pstv_SalesAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_SalesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sales agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_SalesAgreementMember" xlink:to="pstv_SalesAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_SalesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sales Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_SalesAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sales Agreement [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_TwoThousandTwentyTwoDistributionAgreementMember" xlink:type="locator" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand twenty two distribution agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_TwoThousandTwentyTwoDistributionAgreementMember" xlink:to="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2022 Distribution Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Two Distribution Agreement [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_DistributionAgreementMember" xlink:type="locator" xlink:label="pstv_DistributionAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Distribution agreement member.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_DistributionAgreementMember" xlink:to="pstv_DistributionAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Distribution Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Distribution Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of common stock, net</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodExercisableFromTheDateOfIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period exercisable from the date of issuance</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PeriodExercisableFromTheDateOfIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Period Exercisable From The Date Of Issuance</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_PercentageIssuanceOfCommonStock" xlink:type="locator" xlink:label="pstv_PercentageIssuanceOfCommonStock" />
    <link:label xml:lang="en-US" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage issuance of common stock.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_PercentageIssuanceOfCommonStock" xlink:to="pstv_PercentageIssuanceOfCommonStock_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage issuance of common stock</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Issuance Of Common Stock</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharePrice" xlink:type="locator" xlink:label="us-gaap_SharePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Closing price per share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Price</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssued" xlink:type="locator" xlink:label="us-gaap_SharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining common stock issued and sold (in shares)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_CommonStockSalesAvailableForIssuance" xlink:type="locator" xlink:label="pstv_CommonStockSalesAvailableForIssuance" />
    <link:label xml:lang="en-US" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock, sales, available for issuance.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_CommonStockSalesAvailableForIssuance" xlink:to="pstv_CommonStockSalesAvailableForIssuance_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining availability under financing facility</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Sales Available For Issuance</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:type="locator" xlink:label="us-gaap_PlanNameAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Axis]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:type="locator" xlink:label="us-gaap_PlanNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameDomain" xlink:to="us-gaap_PlanNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_StockBasedCompensation2015EquityIncentivePlan1Member" xlink:type="locator" xlink:label="pstv_StockBasedCompensation2015EquityIncentivePlan1Member" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2015EquityIncentivePlan1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock based compensation 2015 equity incentive plan 1 member.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_StockBasedCompensation2015EquityIncentivePlan1Member" xlink:to="pstv_StockBasedCompensation2015EquityIncentivePlan1Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2015EquityIncentivePlan1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2015 Plan [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2015EquityIncentivePlan1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Based Compensation2015 Equity Incentive Plan1 [Member]</link:label>
    <link:loc xlink:href="pstv-20220630.xsd#pstv_StockBasedCompensation2020EquityIncentivePlanMember" xlink:type="locator" xlink:label="pstv_StockBasedCompensation2020EquityIncentivePlanMember" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2020EquityIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock based compensation 2020 equity incentive plan.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pstv_StockBasedCompensation2020EquityIncentivePlanMember" xlink:to="pstv_StockBasedCompensation2020EquityIncentivePlanMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2020EquityIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Plan [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="pstv_StockBasedCompensation2020EquityIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Based Compensation2020 Equity Incentive Plan [Member]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities remaining and available for future issuances (in shares)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance as of June 30, 2022 (in shares)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at June 30, 2022 (in shares)</link:label>
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    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
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    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Rollforward</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance as of December 31, 2021 (in dollars per share)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance as of June 30, 2022 (in dollars per share)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested and expected to vest at June 30, 2022 (in dollars per share)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at June 30, 2022 (in dollars per share)</link:label>
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    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price</link:label>
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    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
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