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  <xs:element id="plrx_DebtDrawPeriodAxis" abstract="true" name="DebtDrawPeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasesInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRepurchasesInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="plrx_NovartisAgreementRDForIntegrinResearchTargetsMember" abstract="true" name="NovartisAgreementRDForIntegrinResearchTargetsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_RestrictedStockAwardsGrantedAndNotPurchasedMember" abstract="true" name="RestrictedStockAwardsGrantedAndNotPurchasedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_CollaborationAndLicenseAgreementIntegrinResearchTargetsAmount" abstract="false" name="CollaborationAndLicenseAgreementIntegrinResearchTargetsAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_AccruedExpensesAndOtherLiabilitiesMember" abstract="true" name="AccruedExpensesAndOtherLiabilitiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_ValuationAllowanceAsPercentageOnDeferredTaxAssets" abstract="false" name="ValuationAllowanceAsPercentageOnDeferredTaxAssets" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="plrx_PrepaidExpensesAndOtherCurrentAssetsTextBlock" abstract="false" name="PrepaidExpensesAndOtherCurrentAssetsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="plrx_NovartisMember" abstract="true" name="NovartisMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_NonemployeeDirectorMember" abstract="true" name="NonemployeeDirectorMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_RedeemableConvertiblePreferredStockTextBlock" abstract="false" name="RedeemableConvertiblePreferredStockTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
</xs:schema>
