Aptevo Therapeutics Announces 100% Remission Rate in Cohort 3 of RAINIER Trial

Aptevo Therapeutics Inc. reported a 100% remission rate in Cohort 3 of its Phase 1b/2 RAINIER trial for mipletamig, a CD123 x CD3 bispecific antibody, in combination with venetoclax and azacitidine for newly diagnosed acute myeloid leukemia (AML) patients unfit for intensive chemotherapy. The trial showed no dose-limiting toxicities or cytokine release syndrome, and 40% of patients achieved minimal residual disease (MRD)-negative status. The results highlight mipletamig's potential to redefine frontline AML treatment, offering a safer and more effective option in a multibillion-dollar market. Cohort 4 is now enrolling, and findings are expected to be presented at a major medical conference in Q4 2025.