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<0.001 for both comparisons). Of the 196 patients in the pretrial prophylaxis cohort, 98 each were assigned to group 3 or group 4. The estimated mean annualized rate of treated bleeding events was 2.25 (95% CI, 1.37 to 3.71) in group 3, as compared with 4.90 (95% CI, 3.65 to 6.56) during the run-in phase (relative decrease, 54.0%; P=0.006), and 1.78 (95% CI, 1.18 to 2.71) in group 4, as compared with 3.12 (95% CI, 2.25 to 4.32) (relative decrease, 42.8%; P=0.006). Injection-site reactions were reported in 103 of 4005 injections (2.6%). No patient was reported to have a thromboembolic event or clinical evidence of neutralizing anti-Mim8 antibodies. CONCLUSIONS Among patients with hemophilia A with or without inhibitors, Mim8 prophylaxis was superior to on-demand treatment and clotting factor concentrate prophylaxis regarding the annualized rate of treated bleeding events.