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  <xs:element id="mgnx_MillstoneRevenueRecognized" abstract="false" name="MillstoneRevenueRecognized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_CollaborationAndLicenseAgreementsAbstract" abstract="true" name="CollaborationAndLicenseAgreementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mgnx_ZaiLabMember" abstract="true" name="ZaiLabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_IMabBiopharmaCollaborationAndLicenseAgreementClinicalSupplyMember" abstract="true" name="IMabBiopharmaCollaborationAndLicenseAgreementClinicalSupplyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_OptInFee" abstract="false" name="OptInFee" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_ProceedsfromStockOptionsExercisedAndESPPPurchases" abstract="false" name="ProceedsfromStockOptionsExercisedAndESPPPurchases" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_A2021ZaiLabAgreementsMember" abstract="true" name="A2021ZaiLabAgreementsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_TotalAnnualFixedPayments" abstract="false" name="TotalAnnualFixedPayments" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_IncyteMGA012ClinicalServicesMember" abstract="true" name="IncyteMGA012ClinicalServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_CommonStockMaximumAmountAvailableForIssuance" abstract="false" name="CommonStockMaximumAmountAvailableForIssuance" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_IncyteMGA012AgreementMember" abstract="true" name="IncyteMGA012AgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_RevenueFromGovernmentAgreementsMember" abstract="true" name="RevenueFromGovernmentAgreementsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_IncyteMGA012SupplyAgreementMember" abstract="true" name="IncyteMGA012SupplyAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_IncyteMGA012AgreementClinicalActivitiesMember" abstract="true" name="IncyteMGA012AgreementClinicalActivitiesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_JanssenBiotechIncMember" abstract="true" name="JanssenBiotechIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_ZaiLabsCollaborationAndLicenseAgreementMargetuximabMember" abstract="true" name="ZaiLabsCollaborationAndLicenseAgreementMargetuximabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mgnx_NonRefundableUpfrontFees" abstract="false" name="NonRefundableUpfrontFees" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReceivedForEachVestedAward" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReceivedForEachVestedAward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mgnx_NonrefundableUpfrontFeesNetOfTaxWithholding" abstract="false" name="NonrefundableUpfrontFeesNetOfTaxWithholding" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_RevenuesFromCMOAgreementsMemberMember" abstract="true" name="RevenuesFromCMOAgreementsMemberMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_JanssenCollaborationAndLicenseAgreementMember" abstract="true" name="JanssenCollaborationAndLicenseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_ProceedsfromRoyaltiesPercent" abstract="false" name="ProceedsfromRoyaltiesPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mgnx_RevenueMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" abstract="false" name="RevenueMultipleDeliverableArrangementsDeterminationOfSellingPriceAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_ContractManufacturingMember" abstract="true" name="ContractManufacturingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_IncyteCorporationMember" abstract="true" name="IncyteCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_OneTimeMillstoneCredit" abstract="false" name="OneTimeMillstoneCredit" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mgnx_A2018ZaiLabCollaborationAndLicenseAgreementMember" abstract="true" name="A2018ZaiLabCollaborationAndLicenseAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mgnx_NonrefundablePaymentTaxWithholding" abstract="false" name="NonrefundablePaymentTaxWithholding" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
