Aptevo Therapeutics Inc. (APVO) reported new data from its RAINIER frontline AML study showing that Mipletamig, given the Venetoclax and Azacitidine, achieved an 87% clinical benefit rate and an 81% remission rate in 31 evaluable patients- results that substantially outperform historical benchmarks.
Acute myeloid leukemia (AML) is an aggressive blood cancer that primarily affects older adults, many of whom are not eligible for intensive chemotherapy. Standard frontline regimens can be difficult to tolerate, and remission rates remain modest, especially in patients with high-risk genetic features. Aptevo's latest results suggest that Mipletamig may offer a more effective option for this population.
The RAINIER trial is a Phase 1b/2, multi-center, dose-optimization study evaluating Mipletamig in combination with Venetoclax and Azacitidine in newly diagnosed AML patients who are unfit for intensive induction therapy. The Phase 1b portion uses sequential 28-day treatment cycles across multiple cohorts to determine the recommended Phase 2 dose (RP2D).
Aptevo has now completed Cohort 5, marking evaluation across all previously studied dose levels and moving the program into its final stage of dose optimization. The company is enrolling two final high dose cohorts- Cohorts 6 and 7- along with two additional six-patient groups at select dose levels to complete the dataset needed for RP2D selection. The Phase 2 dose selection and regulatory interaction remain on track for completion this year.
In the 31 evaluable frontline patients treated to date, Mipletamig in combination with Venetoclax and Azacitidine demonstrated an 87% clinical benefit rate and an 81% composite remission rate (CR/CRi), including a 65% complete remission rate. These results compare favourably to the Phase 3 VIALE-A benchmark, where Venetoclax plus Azacitidine achieved a 66.4% CR/Cri rate and a 37% CR rate.
Notably, 55% of patients who achieved CR/CRi reached measurable residual disease (MRD)- negative status- a marker often associated with more durable responses. The dataset also included patients with the high-risk TP53 mutation, a group that typically responds poorly to treatment; 36% of patients achieving remission carried this mutation.
Six patients have proceeded to allogeneic stem cell transplant, considered the best possible outcome in AML and rarely achieved in older or unfit patients. No cases of cytokine release syndrome (CRS) have been reported to date, supporting the therapy's favorable safety profile.
Mipletamig is Aptevo's lead proprietary drug candidate, designed to redirect the patient's immune system to destroy leukemic cells expressing CD123. The molecule is engineered to engage both leukemic cells and T cells while reducing the likelihood and severity of CRS through its CRIS-7 derived CD3 binding pathway. It has received orphan drug designation for AML and has been evaluated in more than 120 patients across three trials.
Aptevo's CEO Jeff Lamothe said the expanding dataset continues to show strong clinical activity and a clear path toward Phase 2 advancement, noting that the consistency of results gives the company confidence moving forward. CMO Dr. Dirk Huebner added that the focus now is on selecting a Phase 2 dose supported by a complete and well-characterized dataset.
The company implemented a 1-for-18 reverse stock split on December 29, 2025.
APVO is currently trading at $4.35, down 18.69%.
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