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Effect of emicizumab-neutralizing antibodies on activated partial thromboplastin time-based clotting time test results in patients treated with emicizumab.
Research and Practice in Thrombosis and Haemostasis 2023 November
BACKGROUND: Emicizumab is a bispecific humanized monoclonal antibody that shortens the activated partial thromboplastin time (aPTT), making aPTT-based tests unreliable.
OBJECTIVES: To evaluate the efficacy of a mixture of 2 anti-idiotype monoclonal antibodies (anti-emi) in neutralizing emicizumab in samples from persons with hemophilia A treated with emicizumab.
METHODS: Fifty samples from persons with hemophilia A treated with emicizumab were analyzed for aPTT and factor VIII procoagulant activity; FVIII inhibitor titer was measured using Nijmegen-Bethesda assay in 50 plasma samples of additional patients (positive for FVIII inhibitor) treated with emicizumab. FVIII procoagulant activity and inhibitor titer were measured using 1-stage (Actin FS, Siemens) and chromogenic assays with bovine regents (Factor VIII Chromogenic Assay, Siemens). Emicizumab concentration was measured by modified a 1-stage assay calibrated with a drug-specific calibrator (r2 Diagnostics Inc). All the tests were performed on Sysmex CS-2400 (Sysmex) before and after the addition of anti-emi (Chugai Pharmaceutical).
RESULTS: Emicizumab concentrations measured after neutralization were <1.6 μg/mL in all samples. FVIII levels were >480 IU/dL with an aPTT of <30.8 seconds in all samples before neutralization and were <1 IU/dL with an aPTT of >70 seconds after adding anti-emi. FVIII inhibitor resulted in a false negative result in 44 of 50 samples measured with the 1-stage assay before neutralization. A good correlation (r = 0.98) was found between inhibitor titer measured using the chromogenic (insensitive to emicizumab) and 1-stage assays after neutralization.
CONCLUSION: The anti-emi antibodies were shown to completely neutralize emicizumab, making samples pretreated with anti-emi analyzable with the 1-stage assay.
OBJECTIVES: To evaluate the efficacy of a mixture of 2 anti-idiotype monoclonal antibodies (anti-emi) in neutralizing emicizumab in samples from persons with hemophilia A treated with emicizumab.
METHODS: Fifty samples from persons with hemophilia A treated with emicizumab were analyzed for aPTT and factor VIII procoagulant activity; FVIII inhibitor titer was measured using Nijmegen-Bethesda assay in 50 plasma samples of additional patients (positive for FVIII inhibitor) treated with emicizumab. FVIII procoagulant activity and inhibitor titer were measured using 1-stage (Actin FS, Siemens) and chromogenic assays with bovine regents (Factor VIII Chromogenic Assay, Siemens). Emicizumab concentration was measured by modified a 1-stage assay calibrated with a drug-specific calibrator (r2 Diagnostics Inc). All the tests were performed on Sysmex CS-2400 (Sysmex) before and after the addition of anti-emi (Chugai Pharmaceutical).
RESULTS: Emicizumab concentrations measured after neutralization were <1.6 μg/mL in all samples. FVIII levels were >480 IU/dL with an aPTT of <30.8 seconds in all samples before neutralization and were <1 IU/dL with an aPTT of >70 seconds after adding anti-emi. FVIII inhibitor resulted in a false negative result in 44 of 50 samples measured with the 1-stage assay before neutralization. A good correlation (r = 0.98) was found between inhibitor titer measured using the chromogenic (insensitive to emicizumab) and 1-stage assays after neutralization.
CONCLUSION: The anti-emi antibodies were shown to completely neutralize emicizumab, making samples pretreated with anti-emi analyzable with the 1-stage assay.
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