A prospective, multicenter, open-label phase III study of emicizumab prophylaxis in patients with acquired hemophilia A.

Background: Emicizumab is a bispecific antibody that mimics the cofactor function of activated factor (F) VIII. It prevents bleeds in patients with congenital hemophilia A regardless of the inhibitor status; however, no prospective clinical studies have been conducted for emicizumab in patients with acquired hemophilia A (PwAHA).

Objectives: To describe the primary analysis results from a prospective, multicenter, open-label phase III study evaluating the efficacy, safety, and pharmacokinetics of emicizumab in PwAHA (AGEHA; JapicCTI-205151).

Methods: Emicizumab was administered subcutaneously at 6 mg/kg on day 1 and 3 mg/kg on day 2, followed by 1.5 mg/kg once weekly from day 8 onward. Predefined criteria for the completion of dosing included FVIII activity of >50 IU/dL.

Results: By the cutoff date (April 23, 2021), 12 patients on immunosuppressive therapy were enrolled, and 11 of them (91.7%) completed emicizumab treatment. The mean trough plasma emicizumab concentration rapidly reached a steady state (1 week), achieving the efficacious level that was established in patients with congenital hemophilia A (>30 μg/mL). Before first emicizumab administration, 7 patients (58.3%) experienced 77 major bleeds. During emicizumab treatment, no major bleeds occurred in any patient. Neither death due to bleeding or infection nor any study treatment-related serious adverse event was reported. One asymptomatic, nonserious deep vein thrombosis was discovered with no laboratory findings indicating any trend toward hypercoagulation.

Conclusion: These results suggest that emicizumab prophylaxis with the tested dosing regimen and completion criteria may have a favorable benefit-risk profile in PwAHA.