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  <element id="plx_StockIssuedDuringPeriodSharesSalesAgreement" name="StockIssuedDuringPeriodSharesSalesAgreement" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="plx_StockIssuedDuringPeriodValueSalesAgreement" name="StockIssuedDuringPeriodValueSalesAgreement" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="plx_ProceedsFromSaleOfShortTermDeposits" name="ProceedsFromSaleOfShortTermDeposits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="plx_AgreementAmendmentPaymentReceivable" name="AgreementAmendmentPaymentReceivable" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <element id="plx_ChangeInAmountReceivableForAchievementOfRegulatoryAndCommercialMilestones" name="ChangeInAmountReceivableForAchievementOfRegulatoryAndCommercialMilestones" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="plx_RevenuePerformanceObligationNumber" name="RevenuePerformanceObligationNumber" nillable="true" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" />
  <element id="plx_SevenPointFivePercentageSeniorSecuredConvertibleNotesDue2024Member" name="SevenPointFivePercentageSeniorSecuredConvertibleNotesDue2024Member" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <element id="plx_StockIssuedDuringPeriodValueWarrantsExercises" name="StockIssuedDuringPeriodValueWarrantsExercises" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="plx_StockIssuedDuringPeriodSharesWarrantsExercises" name="StockIssuedDuringPeriodSharesWarrantsExercises" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="plx_PercentageOfPremiumToClosingPriceOfStock" name="PercentageOfPremiumToClosingPriceOfStock" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" />
  <element id="plx_ProceedsFromVariableConsideration" name="ProceedsFromVariableConsideration" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <element id="plx_VariableConsideration" name="VariableConsideration" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" />
  <element id="plx_ReductionToAccumulatedRevenueRecognized" name="ReductionToAccumulatedRevenueRecognized" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
</schema>
