Mim8 Bispecific Antibody Prophylaxis in Hemophilia A with or without Inhibitors

BACKGROUND: Mim8 (denecimig), a bispecific antibody mimicking activated factor VIII, was developed for bleeding prophylaxis in patients with hemophilia A with or without factor VIII inhibitors. METHODS: In this phase 3, randomized trial, we assigned patients 12 years of age or older with hemophilia A with or without inhibitors to receive subcutaneous Mim8 once weekly or once monthly at a dose tiered according to body weight and given in a fixed injection volume (0.8 ml). Patients who had been receiving on-demand treatment before the trial were assigned in a 1:1:1 ratio to continue on-demand treatment (group 1) or receive Mim8 once weekly (group 2a) or once monthly (group 2b). Patients who had been receiving clotting factor concentrates during a run-in phase were assigned in a 1:1 ratio to receive Mim8 once weekly (group 3) or once monthly (group 4). The first primary end point was the annualized rate of treated bleeding events (those treated with a coagulation factor product) in an evaluation of Mim8 in group 2a and Mim8 in group 2b as compared with on-demand treatment in group 1. The second was the annualized rate of treated bleeding events in an intrapatient evaluation of Mim8 in group 3 and Mim8 in group 4 as compared with clotting factor concentrate prophylaxis during the run-in phase. RESULTS: Of the 58 patients in the pretrial on-demand treatment cohort, 17 were assigned to group 1, 21 to group 2a, and 20 to group 2b. The estimated mean annualized rate of treated bleeding events was 0.57 (95% confidence interval [CI], 0.25 to 1.30) in group 2a and 0.20 (95% CI, 0.06 to 0.71) in group 2b, as compared with 15.76 (95% CI, 10.70 to 23.20) in group 1 (relative decrease, 96.4% and 98.7%, respectively; P