Aptevo says mipletamig deliver 100% remission rate in RAINIER cohort 3

Aptevo Therapeutics (APVO) announced a 100% remission rate in Cohort 3 of its Phase 1b/2 RAINIER trial evaluating mipletamig, the Company’s CD123 x CD3 bispecific antibody, in combination with venetoclax + azacitidine for newly diagnosed patients with acute myeloid leukemia unfit for intensive chemotherapy. Aptevo also reported that no dose-limiting toxicities or cytokine release syndrome have been observed in the RAINIER trial, or among any frontline patients treated with mipletamig to date. The 100% remission rate achieved at the highest dose level of the RAINIER trial to date demonstrates mipletamig’s potential to redefine the frontline treatment landscape for newly diagnosed AML patients who are unfit for intensive chemotherapy. Additionally, 40% of patients treated to date have achieved minimal residual disease-negative status, a critical marker of remission that is strongly associated with improved overall outcomes in AML. Frontline AML represents a multibillion-dollar global market where current standard regimens achieve lower remission rates than those observed in RAINIER, leaving a substantial need for more effective options. By consistently delivering remissions across three increasing dose cohorts, and among frontline patients in prior trials, mipletamig positions Aptevo to compete for-and potentially expand-a high-value segment of the AML market, offering a therapy that could raise the bar for clinical outcomes and capture meaningful share of an underserved population. Equally compelling is mipletamig’s clean safety profile. Across Cohort 3 and the two prior RAINIER cohorts, no dose-limiting toxicities have been observed, and tolerability remains strong even at the highest dose tested. This differentiated safety record, reinforced by two earlier trials, supports the drug’s use alongside venetoclax and azacitidine and sets it apart from many emerging AML combinations that struggle with cytokine release syndrome and other immune-related toxicities. The combination of efficacy and consistently favorable safety underscores mipletamig’s potential to integrate smoothly into the standard of care for frontline AML. Cohort 3 enrollment is complete and Cohort 4 is actively enrolling patients at the next dose level. The Company anticipates that current findings will be presented at a major medical conference in Q4.