Aptevo announces clinical data from ongoing Phase 1b/2 RAINIER trial

Aptevo Therapeutics (APVO) announced new clinical data from its ongoing Phase 1b/2 RAINIER trial evaluating mipletamig, its CD123 x CD3 bispecific antibody, in combination with standard-of-care venetoclax and azacitidine for newly diagnosed patients with acute myeloid leukemia who are unfit for intensive chemotherapy. Across two trials, the mipletamig triplet therapy delivered remissions in 85% of evaluable frontline AML patients-which significantly exceeds results from competitor studies, including those achieved in the Viale A trial that evaluatedvenetoclax and azacitidine as doublet therapy. These updated results from the RAINIER dose expansion trial continue to demonstrate a compelling efficacy advantage alongside a strong safety profile. No cytokine release syndrome was observed in either cohorts 1 or 2. Cohort 3 Nears Full Enrollment at highest dose level evaluated to date in combination therapy. Results from the RAINIER trial to date demonstrate mipletamig’s increasingly impressive clinical profile, and highlight its potential as a differentiated, highly targeted immunotherapy with a compelling safety profile. As evidence grows, the Company believes that mipletamig is emerging as a strong candidate to reshape frontline AML treatment for unfit patients and potentially advance the standard of care. To date, 85% frontline patients across two trials have achieved remission. Of these remissions, three patients were considered to have poor prognosis at screening based on the genetic biomarkers of their disease and achieved CR. This includes: One patient who was taken off study and successfully received a transplant. This is the most favorable outcome because transplant offers the best chance for a cure, although it is a rare occurrence in the unfit AML patient population One CR patient who had no minimal residual disease (MRD-negative status) but did have the genetic biomarker TP53, which is associated with resistance to chemotherapy and some targeted therapeutics. No CRS has been reported in either cohorts 1 or 2.