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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xml:lang="en-US">Financial Instrument [Axis]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xml:lang="en-US">Financial Instrument [Axis]</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DocumentAndEntityInformationAbstract" xlink:to="opxa_DocumentAndEntityInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US">Document And Entity Information [Abstract]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US">Entity Registrant Name</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US">Entity Central Index Key</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xml:lang="en-US">Is Entity a Well-known Seasoned Issuer?</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCurrentReportingStatus_lbl" xml:lang="en-US">Is Entity's Reporting Status Current?</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US">Document Fiscal Period Focus</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xml:lang="en-US">Statement of Financial Position [Abstract]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US">Assets</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US">Current assets:</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xml:lang="en-US">Other current assets</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US">Total current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US">Property &amp; equipment, net of accumulated depreciation of $2,516,189 and $2,443,600, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US">Other long-term assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US">Total assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xml:lang="en-US">Liabilities and Stockholders' Equity</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xml:lang="en-US">Accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xml:lang="en-US">Accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="us-gaap_DeferredRevenueCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueCurrent" xlink:to="us-gaap_DeferredRevenueCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredRevenueCurrent_lbl" xml:lang="en-US">Deferred revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NotesPayableCurrent" xlink:label="us-gaap_NotesPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesPayableCurrent" xlink:to="us-gaap_NotesPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesPayableCurrent_lbl" xml:lang="en-US">Notes payable - insurance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US">Total current liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xml:lang="en-US">Long term liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="us-gaap_DeferredRevenueNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueNoncurrent" xlink:to="us-gaap_DeferredRevenueNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredRevenueNoncurrent_lbl" xml:lang="en-US">Deferred revenue, net of current portion</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US">Total liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US">Commitments and contingencies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xml:lang="en-US">Stockholders' equity:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockValue_lbl" xml:lang="en-US">Preferred stock, no par value, 10,000,000 shares authorized, none issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US">Common stock, $0.01 par value, 150,000,000 shares authorized, 6,982,909 and 6,982,909 shares issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapital" xlink:to="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xml:lang="en-US">Additional paid in capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US">Accumulated deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_StockholdersEquity_lbl" xml:lang="en-US">Total stockholders' equity</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US">Total liabilities and stockholders' equity</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xml:lang="en-US">Property &amp; equipment, accumulated depreciation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockNoParValue" xlink:label="us-gaap_PreferredStockNoParValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockNoParValue" xlink:to="us-gaap_PreferredStockNoParValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockNoParValue_lbl" xml:lang="en-US">Preferred stock, no par value</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesAuthorized" xlink:to="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xml:lang="en-US">Preferred stock, shares authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xml:lang="en-US">Preferred stock, shares issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesOutstanding" xlink:to="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xml:lang="en-US">Preferred stock, shares outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US">Common stock, par value</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US">Common stock, shares authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US">Common stock, shares issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xml:lang="en-US">Common stock, shares outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_IncomeStatementAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xml:lang="en-US">Income Statement [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_RevenuesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenuesAbstract_lbl" xml:lang="en-US">Revenue:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ContractsRevenue" xlink:label="us-gaap_ContractsRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractsRevenue" xlink:to="us-gaap_ContractsRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ContractsRevenue_lbl" xml:lang="en-US">Option Revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xml:lang="en-US">Research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpense" xlink:to="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xml:lang="en-US">General and administrative</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_GainLossOnDispositionOfAssets" xlink:label="us-gaap_GainLossOnDispositionOfAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnDispositionOfAssets" xlink:to="us-gaap_GainLossOnDispositionOfAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_GainLossOnDispositionOfAssets_lbl" xml:lang="en-US">Loss on disposition of assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationAndAmortization" xlink:to="us-gaap_DepreciationAndAmortization_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xml:lang="en-US">Depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US">Operating loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestIncomeExpenseNet" xlink:to="us-gaap_InterestIncomeExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xml:lang="en-US">Interest income, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="us-gaap_OtherNonoperatingIncomeExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherNonoperatingIncomeExpense" xlink:to="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xml:lang="en-US">Other income and expense, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetIncomeLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasicAndDiluted" xlink:to="us-gaap_EarningsPerShareBasicAndDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted_lbl" xml:lang="en-US">Basic and diluted loss per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" xlink:label="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" xlink:to="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_lbl" xml:lang="en-US">Weighted average shares outstanding - Basic and diluted</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementTable_lbl" xml:lang="en-US">Statement [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementLineItems_lbl" xml:lang="en-US">Statement [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_StatementEquityComponentsAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StatementEquityComponentsAxis_2_lbl" xml:lang="en-US">Equity Components [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesOutstanding" xlink:to="us-gaap_SharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_SharesOutstanding_lbl" xml:lang="en-US">Beginning Balance, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_StockholdersEquity_2_lbl" xml:lang="en-US">Beginning Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_CancellationOfFractionalSharesShares" xlink:label="opxa_CancellationOfFractionalSharesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_CancellationOfFractionalSharesShares" xlink:to="opxa_CancellationOfFractionalSharesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_CancellationOfFractionalSharesShares_lbl" xml:lang="en-US">Cancellation of fractional shares, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_CancellationOfFractionalSharesAmount" xlink:label="opxa_CancellationOfFractionalSharesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_CancellationOfFractionalSharesAmount" xlink:to="opxa_CancellationOfFractionalSharesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_CancellationOfFractionalSharesAmount_lbl" xml:lang="en-US">Cancellation of fractional shares, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SharesIssuedUnderAtthemarketProgramShares" xlink:label="opxa_SharesIssuedUnderAtthemarketProgramShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SharesIssuedUnderAtthemarketProgramShares" xlink:to="opxa_SharesIssuedUnderAtthemarketProgramShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_SharesIssuedUnderAtthemarketProgramShares_lbl" xml:lang="en-US">Shares issued under the at-the-market program, shares</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SharesSubscribedUnderAtTheMarketProgram" xlink:label="opxa_SharesSubscribedUnderAtTheMarketProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SharesSubscribedUnderAtTheMarketProgram" xlink:to="opxa_SharesSubscribedUnderAtTheMarketProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_SharesSubscribedUnderAtTheMarketProgram_lbl" xml:lang="en-US">Shares issued under the at-the-market program, amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_lbl" xml:lang="en-US">Costs associated with rights offering</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xml:lang="en-US">Common stock sold for cash, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xml:lang="en-US">Common stock sold for cash, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockIssuedDuringPeriodSharesWarrantsExercised" xlink:label="opxa_StockIssuedDuringPeriodSharesWarrantsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockIssuedDuringPeriodSharesWarrantsExercised" xlink:to="opxa_StockIssuedDuringPeriodSharesWarrantsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockIssuedDuringPeriodSharesWarrantsExercised_lbl" xml:lang="en-US">Exercise of warrants, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockIssuedDuringPeriodValueWarrantsExercised" xlink:label="opxa_StockIssuedDuringPeriodValueWarrantsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockIssuedDuringPeriodValueWarrantsExercised" xlink:to="opxa_StockIssuedDuringPeriodValueWarrantsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockIssuedDuringPeriodValueWarrantsExercised_lbl" xml:lang="en-US">Exercise of warrants, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationAndExerciseOfStockOptions_lbl" xml:lang="en-US">Option expense</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLoss_2_lbl" xml:lang="en-US">Net loss</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesOutstanding" xlink:to="us-gaap_SharesOutstanding_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_SharesOutstanding_2_lbl" xml:lang="en-US">Ending Balance, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_StockholdersEquity_3_lbl" xml:lang="en-US">Ending Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US">Cash flows from operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Adjustments to reconcile net loss to net cash provided by (used in) operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedStockExpense" xlink:label="us-gaap_RestrictedStockExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestrictedStockExpense" xlink:to="us-gaap_RestrictedStockExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RestrictedStockExpense_lbl" xml:lang="en-US">Restricted stock expense</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:to="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xml:lang="en-US">Shares issued for services</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Depreciation" xlink:label="us-gaap_Depreciation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Depreciation" xlink:to="us-gaap_Depreciation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Depreciation_lbl" xml:lang="en-US">Depreciation</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnDispositionOfAssets" xlink:to="us-gaap_GainLossOnDispositionOfAssets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:label="us-gaap_GainLossOnDispositionOfAssets_2_lbl" xml:lang="en-US">Loss on disposition of equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockOptionPlanExpense" xlink:label="us-gaap_StockOptionPlanExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockOptionPlanExpense" xlink:to="us-gaap_StockOptionPlanExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StockOptionPlanExpense_lbl" xml:lang="en-US">Option expense</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xml:lang="en-US">Changes in:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssets" xlink:label="us-gaap_IncreaseDecreaseInOtherCurrentAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOtherCurrentAssets" xlink:to="us-gaap_IncreaseDecreaseInOtherCurrentAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_IncreaseDecreaseInOtherCurrentAssets_lbl" xml:lang="en-US">Other current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayable" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable_lbl" xml:lang="en-US">Accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilities_lbl" xml:lang="en-US">Accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xml:lang="en-US">Deferred revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets" xlink:label="us-gaap_IncreaseDecreaseInOtherNoncurrentAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOtherNoncurrentAssets" xlink:to="us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_lbl" xml:lang="en-US">Other long-term assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_lbl" xml:lang="en-US">Net cash used in operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US">Cash flows from investing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xml:lang="en-US">Purchase of property &amp; equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_lbl" xml:lang="en-US">Net cash used in investing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US">Cash flows from financing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xml:lang="en-US">Common stock and warrants sold for cash, net of offering costs</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="us-gaap_ProceedsFromWarrantExercises" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromWarrantExercises" xlink:to="us-gaap_ProceedsFromWarrantExercises_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromWarrantExercises_lbl" xml:lang="en-US">Cash generated from exercise of warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_CashPaidForFractionalShares" xlink:label="opxa_CashPaidForFractionalShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_CashPaidForFractionalShares" xlink:to="opxa_CashPaidForFractionalShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="opxa_CashPaidForFractionalShares_lbl" xml:lang="en-US">Cash paid for fractional shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfNotesPayable" xlink:to="us-gaap_RepaymentsOfNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfNotesPayable_lbl" xml:lang="en-US">Note payable - insurance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsOfStockIssuanceCosts" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xml:lang="en-US">Payment of deferred offering costs</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_lbl" xml:lang="en-US">Net cash provided by financing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US">Net change in cash and cash equivalents</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xml:lang="en-US">Cash and cash equivalents at beginning of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xml:lang="en-US">Cash and cash equivalents at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_CashPaidDuringPeriodForAbstract" xlink:label="opxa_CashPaidDuringPeriodForAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_CashPaidDuringPeriodForAbstract" xlink:to="opxa_CashPaidDuringPeriodForAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_CashPaidDuringPeriodForAbstract_lbl" xml:lang="en-US">Cash paid for:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InterestPaid" xlink:label="us-gaap_InterestPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPaid" xlink:to="us-gaap_InterestPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestPaid_lbl" xml:lang="en-US">Interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxesPaid" xlink:label="us-gaap_IncomeTaxesPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxesPaid" xlink:to="us-gaap_IncomeTaxesPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxesPaid_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xml:lang="en-US">NON-CASH TRANSACTIONS</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_UnpaidOfferingCosts" xlink:label="opxa_UnpaidOfferingCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_UnpaidOfferingCosts" xlink:to="opxa_UnpaidOfferingCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_UnpaidOfferingCosts_lbl" xml:lang="en-US">Unpaid offering costs</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_UnpaidAdditionsToPropertyAndEquipment" xlink:label="opxa_UnpaidAdditionsToPropertyAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_UnpaidAdditionsToPropertyAndEquipment" xlink:to="opxa_UnpaidAdditionsToPropertyAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_UnpaidAdditionsToPropertyAndEquipment_lbl" xml:lang="en-US">Unpaid additions to property and equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SubscriptionReceivable" xlink:label="opxa_SubscriptionReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SubscriptionReceivable" xlink:to="opxa_SubscriptionReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_SubscriptionReceivable_lbl" xml:lang="en-US">Subscription receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ConversionOfNotesPayableToCommonStock" xlink:label="opxa_ConversionOfNotesPayableToCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ConversionOfNotesPayableToCommonStock" xlink:to="opxa_ConversionOfNotesPayableToCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ConversionOfNotesPayableToCommonStock_lbl" xml:lang="en-US">Conversion of notes payable to common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_IssuanceOfCommonStockForAccruedInterest" xlink:label="opxa_IssuanceOfCommonStockForAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_IssuanceOfCommonStockForAccruedInterest" xlink:to="opxa_IssuanceOfCommonStockForAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_IssuanceOfCommonStockForAccruedInterest_lbl" xml:lang="en-US">Issuance of common stock for accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_DiscountOnConvertibleNotesRelatedToAbstract" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToAbstract" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToAbstract_lbl" xml:lang="en-US">Discount on convertible notes relating to:</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_DiscountOnConvertibleNotesRelatedToWarrants" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToWarrants" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToWarrants_lbl" xml:lang="en-US">Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature_lbl" xml:lang="en-US">Beneficial conversion feature</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:to="us-gaap_CapitalExpendituresIncurredButNotYetPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid_lbl" xml:lang="en-US">Unpaid additions to property and equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SharesIssuedAsDeferredOfferingCosts" xlink:label="opxa_SharesIssuedAsDeferredOfferingCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SharesIssuedAsDeferredOfferingCosts" xlink:to="opxa_SharesIssuedAsDeferredOfferingCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_SharesIssuedAsDeferredOfferingCosts_lbl" xml:lang="en-US">Shares issued as deferred offering costs</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_AccountingPoliciesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xml:lang="en-US">Accounting Policies [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_lbl" xml:lang="en-US">Basis of Presentation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xml:lang="en-US">Significant Accounting Polices</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract" xlink:label="us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract" xlink:to="us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredCostsCapitalizedPrepaidAndOtherAssetsDisclosureAbstract_lbl" xml:lang="en-US">Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherAssetsDisclosureTextBlock" xlink:label="us-gaap_OtherAssetsDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsDisclosureTextBlock" xlink:to="us-gaap_OtherAssetsDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsDisclosureTextBlock_lbl" xml:lang="en-US">Other Current Assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EquityAbstract" xlink:label="us-gaap_EquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityAbstract" xlink:to="us-gaap_EquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityAbstract_lbl" xml:lang="en-US">Equity [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:to="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xml:lang="en-US">Equity</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xml:lang="en-US">Disclosure of Compensation Related Costs, Share-based Payments [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xml:lang="en-US">Stock-Based Compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRecognitionPolicyTextBlock" xlink:to="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xml:lang="en-US">Revenue Recognition</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:to="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xml:lang="en-US">Cash and Cash Equivalents</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Reclassifications" xlink:label="us-gaap_Reclassifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Reclassifications" xlink:to="us-gaap_Reclassifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Reclassifications_lbl" xml:lang="en-US">Reclassifications</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock" xlink:label="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock" xlink:to="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock_lbl" xml:lang="en-US">Other Current Assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xml:lang="en-US">Stock Option Activity</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ScheduleOfWarrantActivity" xlink:label="opxa_ScheduleOfWarrantActivity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ScheduleOfWarrantActivity" xlink:to="opxa_ScheduleOfWarrantActivity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ScheduleOfWarrantActivity_lbl" xml:lang="en-US">Warrant Activity</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SignificantAccountingPolicesDetailsAbstract" xlink:label="opxa_SignificantAccountingPolicesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SignificantAccountingPolicesDetailsAbstract" xlink:to="opxa_SignificantAccountingPolicesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_SignificantAccountingPolicesDetailsAbstract_lbl" xml:lang="en-US">Significant Accounting Polices Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DepositsSavingsDeposits" xlink:label="us-gaap_DepositsSavingsDeposits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepositsSavingsDeposits" xlink:to="us-gaap_DepositsSavingsDeposits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DepositsSavingsDeposits_lbl" xml:lang="en-US">Cash in savings account</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InterestIncomeDomesticDeposits" xlink:label="us-gaap_InterestIncomeDomesticDeposits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestIncomeDomesticDeposits" xlink:to="us-gaap_InterestIncomeDomesticDeposits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestIncomeDomesticDeposits_lbl" xml:lang="en-US">Interest income</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InventoryRawMaterialsAndSupplies" xlink:label="us-gaap_InventoryRawMaterialsAndSupplies" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InventoryRawMaterialsAndSupplies" xlink:to="us-gaap_InventoryRawMaterialsAndSupplies_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InventoryRawMaterialsAndSupplies_lbl" xml:lang="en-US">Custom reagents</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredFinanceCostsCurrentNet" xlink:label="us-gaap_DeferredFinanceCostsCurrentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredFinanceCostsCurrentNet" xlink:to="us-gaap_DeferredFinanceCostsCurrentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredFinanceCostsCurrentNet_lbl" xml:lang="en-US">Deferred offering costs</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrent" xlink:to="us-gaap_PrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseCurrent_lbl" xml:lang="en-US">Prepaid expenses</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsCurrent" xlink:to="us-gaap_OtherAssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OtherAssetsCurrent_2_lbl" xml:lang="en-US">Total Other Current Assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherPrepaidExpenseCurrent" xlink:label="us-gaap_OtherPrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherPrepaidExpenseCurrent" xlink:to="us-gaap_OtherPrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherPrepaidExpenseCurrent_lbl" xml:lang="en-US">Advance payments to vendors and consultants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xml:lang="en-US">Options</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xml:lang="en-US">Number of Shares, Outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xml:lang="en-US">Options, Granted</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xml:lang="en-US">Options, Exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_lbl" xml:lang="en-US">Options, Forfeited and canceled</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xml:lang="en-US">Number of Shares, Outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_lbl" xml:lang="en-US">Number of Shares, Exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract_lbl" xml:lang="en-US">Weighted Average Exercise Price, Options</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price, Outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantInPeriodWeightedAverageExercisePrice" xlink:label="opxa_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantInPeriodWeightedAverageExercisePrice" xlink:to="opxa_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price options, Granted</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price options, Exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price options, Forfeited and canceled</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xml:lang="en-US">Weighted average exercise price, Outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price, Exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractTermAbstract" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractTermAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractTermAbstract" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractTermAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractTermAbstract_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Options</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="opxa_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm1" xlink:to="opxa_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm1_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Exercisable</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsIntrinsicValueAbstract" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsIntrinsicValueAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsIntrinsicValueAbstract" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsIntrinsicValueAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsIntrinsicValueAbstract_lbl" xml:lang="en-US">Intrinsic Value, Options</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xml:lang="en-US">Outstanding Aggregate Intrinsic Value, beginning of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_2_lbl" xml:lang="en-US">Outstanding Aggregate Intrinsic Value, end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xml:lang="en-US">Exercisable Aggregate Intrinsic Value</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="us-gaap_ClassOfWarrantOrRightTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_ClassOfWarrantOrRightTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightTable_lbl" xml:lang="en-US">Class of Warrant or Right [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems_lbl" xml:lang="en-US">Class of Warrant or Right [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_2_lbl" xml:lang="en-US">Class of Warrant or Right [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsRollforward" xlink:label="opxa_StockholdersEquityWarrantsOrRightsRollforward" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsRollforward" xlink:to="opxa_StockholdersEquityWarrantsOrRightsRollforward_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsRollforward_lbl" xml:lang="en-US">Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares" xlink:to="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares_lbl" xml:lang="en-US">Number of Shares, Outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriod" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriod" xlink:to="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriod_lbl" xml:lang="en-US">Warrants, Granted</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriod" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriod" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriod_lbl" xml:lang="en-US">Warrants, Exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriod" xlink:label="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriod" xlink:to="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriod_lbl" xml:lang="en-US">Warrants, Forfeited and canceled</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares" xlink:to="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingNumberOfUnderlyingShares_2_lbl" xml:lang="en-US">Number of Shares, Outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingNumberOfUnderlyingShares" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingNumberOfUnderlyingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingNumberOfUnderlyingShares" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingNumberOfUnderlyingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingNumberOfUnderlyingShares_lbl" xml:lang="en-US">Number of Shares, Exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsWeightedAverageExercisePriceAbstract" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageExercisePriceAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageExercisePriceAbstract" xlink:to="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageExercisePriceAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageExercisePriceAbstract_lbl" xml:lang="en-US">Weighted Average Exercise Price, Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfUnderlyingShares" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfUnderlyingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfUnderlyingShares" xlink:to="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfUnderlyingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfUnderlyingShares_lbl" xml:lang="en-US">Weighted average exercise price, Outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodWeightedAverageExercisePrice" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodWeightedAverageExercisePrice" xlink:to="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price warrants, Granted</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodWeightedAverageExercisePrice" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodWeightedAverageExercisePrice" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageExercisePriceOfExercisableUnderlyingShares_lbl" xml:lang="en-US">Weighted average exercise price, Exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsWeightedAverageRemainingContractualTermAbstract" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageRemainingContractualTermAbstract" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageRemainingContractualTermAbstract_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageRemainingContractualTermInYears" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageRemainingContractualTermInYears" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageRemainingContractualTermInYears_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Outstanding at beginning of period</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingWeightedAverageRemainingContractualTermInYearsEnd_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Outstanding at end of period</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingWeightedAverageRemainingContractualTermInYears" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingWeightedAverageRemainingContractualTermInYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisableOutstandingWeightedAverageRemainingContractualTermInYears_lbl" xml:lang="en-US">Weighted Average Remaining Contract Term, Exercisable</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsWeightedAverageIntrinsicValueAbstract" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageIntrinsicValueAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageIntrinsicValueAbstract" xlink:to="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageIntrinsicValueAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsWeightedAverageIntrinsicValueAbstract_lbl" xml:lang="en-US">Intrinsic Value, Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue_lbl" xml:lang="en-US">Outstanding Aggregate Intrinsic Value, Beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodIntrinsicValue" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsGrantedInPeriodIntrinsicValue_lbl" xml:lang="en-US">Aggregate Intrinsic Value Granted</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodIntrinsicValue" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisedInPeriodIntrinsicValue_lbl" xml:lang="en-US">Aggregate Intrinsic Value Exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriodIntrinsicValue" xlink:label="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriodIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriodIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriodIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockholdersEquityWarrantsOrRightsForfeitedInPeriodIntrinsicValue_lbl" xml:lang="en-US">Aggregate Intrinsic Value Forfeited</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsOutstandingIntrinsicValue_2_lbl" xml:lang="en-US">Outstanding Aggregate Intrinsic Value, End of period</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockholdersEquityWarrantsOrRightsExercisableIntrinsicValue" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisableIntrinsicValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockholdersEquityWarrantsOrRightsExercisableIntrinsicValue" xlink:to="opxa_StockholdersEquityWarrantsOrRightsExercisableIntrinsicValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="opxa_StockholdersEquityWarrantsOrRightsExercisableIntrinsicValue_lbl" xml:lang="en-US">Exercisable Aggregate Intrinsic Value</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_StockbasedCompensationDetailsNarrativeAbstract" xlink:label="opxa_StockbasedCompensationDetailsNarrativeAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_StockbasedCompensationDetailsNarrativeAbstract" xlink:to="opxa_StockbasedCompensationDetailsNarrativeAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_StockbasedCompensationDetailsNarrativeAbstract_lbl" xml:lang="en-US">Stock-based Compensation Details Narrative</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_UnamortizedStockBasedCompensationExpense" xlink:label="opxa_UnamortizedStockBasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_UnamortizedStockBasedCompensationExpense" xlink:to="opxa_UnamortizedStockBasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="opxa_UnamortizedStockBasedCompensationExpense_lbl" xml:lang="en-US">Unamortized stock-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AllocatedShareBasedCompensationExpense" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xml:lang="en-US">Option expense</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_CashPaidDuringPeriodForAbstract" xlink:to="opxa_CashPaidDuringPeriodForAbstract_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_CashPaidDuringPeriodForAbstract_doc" xml:lang="en-US">Cash Paid During Period For [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToAbstract" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToAbstract_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToAbstract_doc" xml:lang="en-US">Discount On Convertible Notes Related To [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToBeneficialConversionFeature_doc" xml:lang="en-US">Discount On Convertible Notes Related To Beneficial Conversion Feature</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DiscountOnConvertibleNotesRelatedToWarrants" xlink:to="opxa_DiscountOnConvertibleNotesRelatedToWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_DiscountOnConvertibleNotesRelatedToWarrants_doc" xml:lang="en-US">Discount On Convertible Notes Related To Warrants</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_DocumentAndEntityInformationAbstract" xlink:to="opxa_DocumentAndEntityInformationAbstract_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_DocumentAndEntityInformationAbstract_doc" xml:lang="en-US">Document And Entity Information [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_OtherAssetsCurrentLineItems" xlink:label="opxa_OtherAssetsCurrentLineItems" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_OtherAssetsCurrentLineItems_doc" xml:lang="en-US">Other Assets, Current [Line Items]</link:label>
      <link:loc xlink:type="locator" xlink:href="opxa-20160331.xsd#opxa_OtherAssetsCurrentTable" xlink:label="opxa_OtherAssetsCurrentTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_OtherAssetsCurrentTable" xlink:to="opxa_OtherAssetsCurrentTable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_OtherAssetsCurrentTable_doc" xml:lang="en-US">Other Assets, Current [Table]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_WarrantShareMember" xlink:to="opxa_WarrantShareMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_WarrantShareMember_doc" xml:lang="en-US">Warrant Share [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePriceAbstract_doc" xlink:type="arc" />
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice" xlink:to="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="opxa_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageExercisePrice_doc" xml:lang="en-US">Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Weighted Average Exercise Price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrent_2_lbl" xml:lang="en-US">Assets, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Assets_2_lbl" xml:lang="en-US">Assets [Default Label]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrent_2_lbl" xml:lang="en-US">Liabilities, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Liabilities_2_lbl" xml:lang="en-US">Liabilities</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquity_4_lbl" xml:lang="en-US">Stockholders' Equity Attributable to Parent</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xml:lang="en-US">Liabilities and Equity</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnDispositionOfAssets" xlink:to="us-gaap_GainLossOnDispositionOfAssets_3_lbl" xlink:type="arc" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingIncomeLoss_2_lbl" xml:lang="en-US">Operating Income (Loss)</link:label>
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