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Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti‐idiotype monoclonal antibodies
Author(s) -
Nogami K.,
Soeda T.,
Matsumoto T.,
Kawabe Y.,
Kitazawa T.,
Shima M.
Publication year - 2018
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.14135
Subject(s) - monoclonal antibody , titer , idiotype , antibody , monoclonal , medicine , immunology
Essentials Emicizumab (Emi) affects the APTT‐based assays of factor (F)VIII activity and inhibitor titer. A mixture of two anti‐Emi monoclonal antibodies (mAb) effectively neutralized the Emi activity. Anti‐Emi mAbs completely eliminated the influence of Emi on FVIII activity and inhibitor titer. The inclusion of anti‐Emi mAbs in routine FVIII assays would be useful for Emi‐treated patients.Summary Background Emicizumab is an anti‐factor (F) IX a/X bispecific monoclonal antibody ( mA b), mimicking the factor (F) VIII a cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time ( APTT ) is more pronounced than that of factor (F) VIII . APTT ‐based FVIII activity ( FVIII :C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab. Aim To establish a reliable APTT ‐based assay to measure FVIII in the presence of emicizumab. Methods Plasmas from hemophilia A ( HA ) patients without or with inhibitors were studied using one‐stage FVIII :C and Bethesda inhibitor assays. Two recombinant anti‐idiotype mA bs to emicizumab (anti‐emicizumab mA bs) were prepared, rc AQ 8 to anti‐ FIX a‐Fab and rc AJ 540 to anti‐ FX ‐Fab. Results The combined anti‐idiotype mA bs (2000 n m each) eliminated the effects of emicizumab on APTT s of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX (a)/ FX (a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 μ m = ~150 μg mL −1 ) at all reference levels of FVIII . The addition of anti‐emicizumab mA bs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII :C. Anti‐ FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti‐ FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti‐idiotype mA bs, allowing accurate assessment of inhibitor titers. Conclusion The in vitro inclusion of anti‐emicizumab mA bs in the standard one‐stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII :C and inhibitor titers.