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  <xs:element id="plrx_IncomeTaxExaminationNumberOfExaminationsPending" abstract="false" name="IncomeTaxExaminationNumberOfExaminationsPending" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="plrx_DeferredTaxLiabilitiesFixedAssetBasis" abstract="false" name="DeferredTaxLiabilitiesFixedAssetBasis" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_AccruedResearchAndDevelopmentExpensesCurrent" abstract="false" name="AccruedResearchAndDevelopmentExpensesCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_ComputerEquipmentAndSoftwareMember" abstract="true" name="ComputerEquipmentAndSoftwareMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_PerformanceBasedRestrictedStockUnitsTSRGoalMember" abstract="true" name="PerformanceBasedRestrictedStockUnitsTSRGoalMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_PublicOfferingMember" abstract="true" name="PublicOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_NumberOfVotesPerShareOfCommonStock" abstract="false" name="NumberOfVotesPerShareOfCommonStock" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="plrx_PerformanceStockUnitsMember" abstract="true" name="PerformanceStockUnitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_EmployeeStockOptionAndPurchasePlanMember" abstract="true" name="EmployeeStockOptionAndPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_LeasedSpaceUnderNonCancellableOperatingLease" abstract="false" name="LeasedSpaceUnderNonCancellableOperatingLease" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:areaItemType"/>
  <xs:element id="plrx_TermLoanFacilityMember" abstract="true" name="TermLoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_AccretionAmortizationOfDiscountsAndPremiumsInvestmentsAndDebt" abstract="false" name="AccretionAmortizationOfDiscountsAndPremiumsInvestmentsAndDebt" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_TwoThousandAndTwentyStockOptionsAndIncentivePlanMember" abstract="true" name="TwoThousandAndTwentyStockOptionsAndIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_ContractualArrangementsCancellationPeriod" abstract="false" name="ContractualArrangementsCancellationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="plrx_StartingFromJanuary12018Member" abstract="true" name="StartingFromJanuary12018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_PercentageOfRevenueContributedByRelatedParty" abstract="false" name="PercentageOfRevenueContributedByRelatedParty" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="plrx_AccountingPoliciesTable" abstract="true" name="AccountingPoliciesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="plrx_EffectiveIncomeTaxRateReconciliationNondeductibleExecutiveCompensationSection162mLimitation" abstract="false" name="EffectiveIncomeTaxRateReconciliationNondeductibleExecutiveCompensationSection162mLimitation" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="plrx_ValuationAllowanceAsPercentageOnDeferredTaxAssets" abstract="false" name="ValuationAllowanceAsPercentageOnDeferredTaxAssets" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="plrx_EricLefebvreMember" abstract="true" name="EricLefebvreMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_BernardCoulieMember" abstract="true" name="BernardCoulieMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="plrx_MatureInOneYearOrLessMember" abstract="true" name="MatureInOneYearOrLessMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_TwoThousandFifteenAndTwoThousandTwentyEquityIncentivePlanMember" abstract="true" name="TwoThousandFifteenAndTwoThousandTwentyEquityIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_NonemployeeDirectorMember" abstract="true" name="NonemployeeDirectorMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_CashAndCashEquivalentsAtCarryingValueRounded" abstract="false" name="CashAndCashEquivalentsAtCarryingValueRounded" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_PerformanceBasedRestrictedStockUnitsMember" abstract="true" name="PerformanceBasedRestrictedStockUnitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_PaymentsOfDeferredOfferingCosts" abstract="false" name="PaymentsOfDeferredOfferingCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAveragePeerGroupCorrelationCoefficient" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAveragePeerGroupCorrelationCoefficient" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:decimalItemType"/>
  <xs:element id="plrx_DebtDrawTrancheTwoMember" abstract="true" name="DebtDrawTrancheTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_AuditorInformationAbstract" abstract="true" name="AuditorInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="plrx_ScheduleOfShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsValuationAssumptionsTableTextBlock" abstract="false" name="ScheduleOfShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsValuationAssumptionsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="plrx_PrepaidExpensesAndOtherCurrentAssetsTextBlock" abstract="false" name="PrepaidExpensesAndOtherCurrentAssetsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="plrx_UnderlyingCommonStockFairValue" abstract="false" name="UnderlyingCommonStockFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="plrx_InterestAndOtherIncomeExpenseNet" abstract="false" name="InterestAndOtherIncomeExpenseNet" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_DebtDrawPeriodDomain" abstract="true" name="DebtDrawPeriodDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="plrx_PropertyPlantAndEquipmentUsefulLivesTableTableTextBlock" abstract="false" name="PropertyPlantAndEquipmentUsefulLivesTableTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="plrx_DeferredTaxAssetsValuationAllowanceRollForward" abstract="true" name="DeferredTaxAssetsValuationAllowanceRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="plrx_ProceedsFromIssuancesOfCommonStockUnderBenefitPlans" abstract="false" name="ProceedsFromIssuancesOfCommonStockUnderBenefitPlans" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficient" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficient" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:decimalItemType"/>
  <xs:element id="plrx_LongTermDebtAccretionOfFinalPayment" abstract="false" name="LongTermDebtAccretionOfFinalPayment" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="plrx_DebtDrawPeriodAxis" abstract="true" name="DebtDrawPeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="plrx_PublicOfferingAndPrivatePlacementMember" abstract="true" name="PublicOfferingAndPrivatePlacementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
</xs:schema>
