Modified clot waveform analysis to measure plasma coagulation potential in the presence of the anti‐factor IXa/factor X bispecific antibody emicizumab

Abstract

Background Emicizumab is an anti-activated factor IX/FX bispecific antibody that mimics activated FVIII cofactor function. Emicizumab does not require activation by thrombin, and its effect on shortening the activated partial thromboplastin time (APTT) is much greater than that of FVIII. Therefore, the APTT has limited utility in hemophilia A (HA) patients treated with emicizumab. Aim To evaluate the global coagulation potential of emicizumab. Methods Clot waveform analysis (CWA) with prothrombin time (PT)/APTT mixed reagents was used to define hemostatic monitoring protocols in HA patients. A modified parameter, adjusted-|min1| (Ad|min1|), was developed. Maximum and minimum percentage transmittance were defined as 100% and 0% in the precoagulation and postcoagulation phases, respectively. Ad|min1| was calculated as an index of the maximum velocity of the coagulation process. Results Ad|min1| obtained with mixed-trigger reagent (PT/APTT/buffer, 1 : 15 : 135) in the presence of emicizumab optimally corresponded to the conversion rate estimated in animals; 0.2-0.4 IU dL equivalent FVIII per 1 μg mL emicizumab). Ex vivo addition of emicizumab to HA plasma with or without inhibitors resulted in concentration-dependent increases in Ad|min1|, with some individual variations. The addition of various concentrations of FVIII to HA plasma mixed with emicizumab resulted in dose-dependent increases in Ad|min1|. Similarly, mixtures of activated prothrombin complex concentrate and emicizumab added to HA plasma resulted in dose-dependent increases in Ad|min1|. In contrast, enhanced coagulation potential appeared to be better defined by the clot time than by Ad|min1| in experiments using recombinant activated FVII. Conclusion The PT/APTT reagent-triggered adjusted CWA could provide a useful means of assessing global coagulation potential in emicizumab-treated HA patients, with enhanced activity neither masking nor being masked by FVIII or bypassing agents.

Modified clot waveform analysis to measure plasma coagulation potential in the presence of the anti‐factor IXa/factor X bispecific antibody emicizumab: comment

“…AHA patients showed no severe bleeding on treatment with rh FVIIa, suggesting that the FVIII activity according to the modified PT waveform method exerted real hemostatic ability. Although hemophilic patients in the present study were not treated with EHL‐FVIII or emicizumab, which cannot be monitored, the FVIII activity according to the modified PT waveform method may induce real hemostasis, as described in Nogami's report . In conclusion, FVIII according to the modified PT waveform adding recombinant FIX may efficiently reflect the effect of bypass therapy such as rhFVIIa.…”

“…Therefore, we read with great interest the recent article by Nogami et al . , in which the modified clot waveform (CWA), the prothrombin time (PT)/APTT‐triggered adjusted CWA, was reported to be an effective modality for assessing the global coagulation potential in emicizumab‐treated hemophilia A cases.…”

An anti‐factor IXa/factor X bispecific antibody, emicizumab, improves ex vivo coagulant potentials in plasma from patients with acquired hemophilia A

“…One of mechanisms on type 1 inhibitors appeared to interfere with the binding of FVIIIa to phospholipid surfaces, which is essential for the formation of the tenase complex, whereas that on type 2 inhibitors appeared to decrease FXa generation by inhibiting thrombin‐catalyzed FVIII activation . In addition, we have previously demonstrated the additive effect of FVIII in the presence of emicizumab in modified CWA . Taken together, it may be that residual FVIII:C levels in the presence of type 2 inhibitor positively or additively influenced the effects of emicizumab, but the precise mechanism remains unclear.…”

“…Unlike FVIII, emicizumab does not require activation by thrombin, and the shortening effect of the antibody on the activated partial thromboplastin time is more pronounced than that of FVIII . The results obtained in activated partial thromboplastin time‐based clotting assays, therefore, do not directly reflect potential emicizumab activity.…”

“…The results obtained in activated partial thromboplastin time‐based clotting assays, therefore, do not directly reflect potential emicizumab activity. Alternatively, global coagulation assays including clot waveform analysis, thrombin generation assay, and rotational thromboelastometry have been reported as useful techniques for assessing hemostasis in these circumstances . The global coagulation effects of emicizumab in AHA patients remain unknown, however, although conventional assays in some cases with AHA treated with emicizumab have been reported .…”