Aptevo Therapeutics says it has substantially reduced infusion-related reactions in patients receiving mipletamig, its investigational treatment for acute myeloid leukemia (AML), by refining the drug’s initial dosing regimen. The change is intended to improve tolerability as the company prepares to advance the treatment into Phase 2 development.
Mipletamig is being studied with the AML drugs venetoclax and azacitidine in newly diagnosed patients who are not fit for intensive chemotherapy. Aptevo plans to present data at the American Society of Hematology meeting in December and expects its ongoing RAINIER dose-optimization study to finish by year-end 2026.
Key details
- The adjustment is to the priming-dose regimen. Mipletamig is introduced gradually before patients move to higher doses. Aptevo says successive changes to this initial dosing approach have substantially reduced infusion-related reactions during early treatment.
- The aim is to improve tolerability without changing planned therapeutic dosing. The announcement says the reduction in reactions was achieved without compromising the intended treatment dose.
- The reactions are distinct from cytokine release syndrome. Infusion-related reactions can include fever, chills, rash or nausea. Aptevo also described mipletamig’s findings on cytokine release syndrome, a potentially serious immune-related reaction, as favorable throughout its clinical development.
- The study is testing a three-drug combination in frontline AML. RAINIER is evaluating mipletamig alongside venetoclax and azacitidine in newly diagnosed patients considered unfit for intensive chemotherapy.
- Aptevo says earlier RAINIER results showed clinical activity. The company has reported remission responses among patients with TP53-mutated AML, a high-risk group, and said some patients initially considered unfit for intensive chemotherapy went on to receive an allogeneic stem cell transplant.
- More data are expected in December. Aptevo plans to present mipletamig data at the ASH annual meeting, scheduled for Dec. 12–15, 2026. The announcement did not provide numerical results for the reduction in infusion reactions.
What changes for investors
The dose refinements address a treatment-tolerability objective identified in Aptevo’s discussions with the FDA and add a favorable tolerability point as the company prepares for the next stage of development. The announcement does not establish that mipletamig improves survival or other efficacy outcomes; the reported advance is a reduction in infusion-related reactions.