Augmented emicizumab-driven coagulation potential in hemophilia A state by in vitro and in vivo supplementation of combined factors IX and X.

BACKGROUND: Persons with hemophilia A (HA) and inhibitors undergoing emicizumab prophylaxis require bypassing agents when breakthrough bleeding occurs. Recent studies have demonstrated that either factor (F)IX or FX supplementation can improve coagulation potential of emicizumab-treated persons with HA and inhibitors. OBJECTIVES: This study assessed the effect of combined supplementation with FIX and FX on the coagulation potential in emicizumab-treated HA state. METHODS: FVIII-deficient plasmas were spiked with emicizumab (50 μg/mL), FX (100 IU/dL), and various FIX levels (100-1600 IU/dL). Plasmas from emicizumab-treated persons with HA and inhibitors were also added with FIX/FX (100 IU/dL each). Coagulation potential was assessed by maximum coagulation velocity (Ad|min1|) using tissue factor (TF)/ellagic acid-triggered clot waveform analysis and peak thrombin (PeakTh) using TF-triggered thrombin generation assay. For in vivo method, emicizumab (3 mg/kg) and human (h)FIX/hFX (100 IU/kg each) were intravenously administered to HA mice (emicizumab-HA mice). Coagulation potentials in these mice with or without additional hFIX/hFX (100 IU/dL each) were assessed by clotting time plus clot formation time (CT + CFT) and blood loss using rotational thromboelastometry and tail-clip assay. RESULTS: Ad|min1| and PeakTh in FVIII-deficient plasmas with emicizumab, FIX, and FX increased in FIX dose dependently. Addition of FIX and FX (100 IU/dL each) to emicizumab-supplemented FVIII-deficient plasma and plasma of emicizumab-treated persons with HA and inhibitor improved both parameters to normal levels. CT+CFT and blood loss in emicizumab-HA mice with additional hFIX/hFX (100 IU/dL each) administration were significantly shorter and decreased than those in emicizumab-HA mice. The thrombotic markers largely did not change. CONCLUSION: Combined FIX and FX supplementation could enhance coagulation potential in emicizumab-treated persons with HA and inhibitors.