Ten of 47 evaluable frontline patients with acute myeloid leukemia treated with mipletamig in combination with venetoclax and azacitidine advanced to allogeneic stem cell transplant, a rate that raises the question of whether this regimen can unlock potentially curative options for patients initially deemed unfit for intensive chemotherapy.
Aptevo Therapeutics Inc. disclosed that nine of these patients were part of the ongoing Phase 1b RAINIER trial, while one came from a previously completed dose expansion trial. The company noted that this patient population typically faces limited treatment options due to advanced age or underlying health conditions. In contrast, historical data from the pivotal Phase 3 VIALE-A trial showed that only 0.7% of patients treated with venetoclax and azacitidine alone underwent stem cell transplantation. Aptevo acknowledged that cross-trial comparisons are limited by differences in patient populations, study design, and follow-up periods.
Dirk Huebner, M.D., Chief Medical Officer at Aptevo, stated that these observations add to the clinical evidence supporting mipletamig's potential to improve outcomes in frontline AML. He highlighted that reaching transplant requires an adequate response to initial treatment, medical eligibility, and a suitable donor, making the advancement of these ten patients a significant indicator of the drug's activity. The company emphasized that stem cell transplant can offer eligible patients the possibility of long-term remission or cure.
Aptevo expects to conclude the current dose optimization stage of the RAINIER trial by the end of 2026. The company plans to interact with regulators and initiate a Phase 2 clinical trial in the first half of 2027. Mipletamig is designed to engage leukemic cells and T cells to trigger the destruction of CD123-expressing cells. The drug has received orphan drug designation for AML. Aptevo's broader pipeline includes solid tumor candidates such as APVO451 and radiopharmaceutical programs in collaboration with Niowave, with IND-enabling studies expected in 2027.