Mipletamig in combination with venetoclax and azacitidine - (RAINIER)

September 3, 2026: Aptevo Therapeutics (NASDAQ: APVO) reported interim RAINIER Phase 1b/2 data for mipletamig plus venetoclax and azacitidine in frontline AML patients unfit for intensive chemotherapy, highlighting TP53-mutated AML. Among 14 evaluable TP53-mutated patients, 13 (93%) had clinical benefit; 11 achieved CR or CRi (79%), including 9 complete remissions. The company said this compares with a published 41% composite remission rate for venetoclax plus azacitidine in treatment-naïve patients with poor-risk cytogenetics and TP53-mutated AML.

RAINIER is an open-label, multi-center dose-optimization study that will be followed by Phase 2. Aptevo said the current dose-optimization phase is expected to complete by year-end 2026, with regulatory interaction planned in 1H27 to determine next steps.

Separately, the company said solid tumor programs APVO451 and its Niowave radiopharmaceutical collaboration are expected to enter IND-enabling studies in 2027, with the first radiopharmaceutical program targeting nectin-4.