SEATTLE, WA — May 6, 2026 — Leads & Copy — Aptevo Therapeutics Inc. (Nasdaq:APVO) announced new clinical results from its RAINIER frontline acute myeloid leukemia (AML) trial today.
The company is on track to complete the Phase 1b dose-optimization trial and select the recommended Phase 2 dose (RP2D) this year. The Phase 2 trial will administer mipletamig in combination with venetoclax and azacitidine, similar to the current study.
Data from 31 evaluable frontline AML patients treated to date, including data through RAINIER Cohort 5 and four patients from a previously completed dose expansion trial, show that mipletamig, when combined with venetoclax and azacitidine, has demonstrated an 87% clinical benefit rate (CR/CRi/PR) and an 81% remission rate (CR/CRi). These results reflect a consistent profile of clinical activity and favorable safety as the dataset expands.
Dosing has progressed through all previously evaluated mipletamig dose levels with the completion of Cohort 5. The trial has now entered its final stage, which includes:
- Two final dose-level cohorts—Cohorts 6 and 7—representing the highest dose levels of mipletamig evaluated. Enrollment in Cohort 6 is nearing completion.
- Two groups of six additional patients will be enrolled at select dose levels, with the first enrolling concurrently with Cohort 6.
These activities will complete the dataset required for RP2D selection and the planned Phase 2 regulatory interaction, with the trial on track for completion this year.
According to Jeff Lamothe, President and Chief Executive Officer of Aptevo Therapeutics, the remaining work is clearly defined and the study is on track for completion this year. Lamothe stated the strength and consistency of the data gives the company confidence in its path forward to select the Phase 2 dose and advance into Phase 2.
The data from the evaluable frontline patient population (N=31) shows mipletamig in combination with venetoclax and azacitidine has demonstrated:
- 87% clinical benefit rate, demonstrating broad anti-leukemia activity and blast reduction across response categories
- 81% achieved CR or CRi (remission), comparing favorably to the historical benchmark
- 65% achieved CR (complete remission), comparing favorably to the historical benchmark
- 55% of patients who achieved CR/CRi had blast reductions that reached the important measurable residual disease-negative level
- 36% of patients with remissions had the TP53 genetic mutation, a high-risk biomarker typically associated with poor prognosis in AML
- Six patients treated to date have proceeded to allogeneic stem cell transplant
- No cytokine release syndrome reported
According to the company, these data outperform the benchmark and demonstrate mipletamig’s potential to meaningfully enhance frontline AML treatment in older and/or unfit patients by improving efficacy outcomes without materially increasing toxicity.
Dirk Huebner, M.D., Chief Medical Officer of Aptevo Therapeutics, said dose selection is progressing with a focus on identifying a Phase 2 dose supported by a complete and well-characterized dataset.
The RAINIER trial is a Phase 1b/2 dose-optimization, multi-center, multi-cohort, open-label study. Subjects are adults aged 18 or older, newly diagnosed with AML, who are not eligible for intensive induction chemotherapy. The Phase 1b trial consists of 28-day cycles of treatment across multiple sequential cohorts.
Mipletamig is Aptevo’s wholly owned lead proprietary drug candidate being evaluated for the treatment of AML. The drug candidate is differentiated by design to redirect the immune system of the patient to destroy leukemic cells and leukemic stem cells expressing the target antigen CD123. Mipletamig has been evaluated in more than 120 patients over three trials to date.
Aptevo Therapeutics Inc. (Nasdaq: APVO) is a clinical-stage biotechnology company focused on developing novel bispecific and trispecific immunotherapies for the treatment of cancer. All pipeline candidates were created from two proprietary platforms, ADAPTIR and ADAPTIR-FLEX.
Source: Aptevo Therapeutics
