Ex vivo evaluation of the effect of plasma-derived factor VIII/von Willebrand factor in patients with severe hemophilia A on emicizumab prophylaxis.

Hemophilia A (HA) patients under emicizumab prophylaxis may require the concomitant use of procoagulant factors for breakthrough bleedings or immune tolerance induction (ITI). The aim of this study is to evaluate the ex vivo procoagulant effect of plasma-derived FVIII concentrates containing von Willebrand factor (pdFVIII/VWF) in samples from patients with severe HA without inhibitors on emicizumab prophylaxis. Samples from healthy controls (HC) and HA patients were drawn in sodium citrate plus corn trypsin inhibitor tubes and spiked with increasing concentrations of pdFVIII/VWF concentrates (10-400 IU/dL) (Fanhdi/Alphanate, Grifols), activated prothrombin complex concentrate (aPCC, 0.5 U/mL) or recombinant activated factor VII (rFVIIa, 0.9 µg/mL). Global coagulation was measured by rotational thromboelastometry (ROTEM) (clotting time [CT] and time to maximum clot formation velocity [MAXV-t]) and thrombin generation (TG) assay (thrombin peak [TP] and endogenous thrombin potential [ETP]). Samples from HA patients under emicizumab prophylaxis showed CT and MAXV-t values above HC levels, while TP and ETP were below HC levels. Ex vivo pdFVIII/VWF supplementation increased TP and ETP and shortened CT and MAXV-t dose-dependently. At 50 IU/dL (≈25 IU/kg), pdFVIII/VWF normalized clot formation and restored TG within HC normal range. The highest pdFVIII/VWF concentration (400 IU/dL) and rFVIIa did not result in an excessive procoagulant profile. However, aPCC induced ex vivo an excessive TG and markedly decreased ROTEM parameters (CT and MAXV-t). Coagulation parameters of both methods significantly correlated at baseline and with increasing concentrations of pdFVIII/VWF. High doses of pdFVIII/VWF concentrates, similar to those used for ITI, did not trigger a multiplying procoagulant effect to samples from HA patients on emicizumab prophylaxis, evidencing their low thrombotic risk in these patients.