Aptevo points to fewer infusion problems as it steers mipletamig toward 2027 Phase 2

Aptevo Therapeutics says it has made progress on the main tolerability hurdle facing mipletamig, its drug for newly diagnosed acute myeloid leukaemia (AML). In an update on 5 November 2026, the company said a series of adjustments to the initial doses given to patients had markedly reduced reactions during infusion in its ongoing RAINIER trial.

The commercial relevance is pipeline timing. Aptevo expects to finish RAINIER by the end of 2026 and to start a Phase 2 study in 2027, so the dosing work determines what regimen it carries forward. The company links the refinements to its discussions with the US Food and Drug Administration (FDA). The update does not say what the regulator has agreed.

RAINIER tests mipletamig alongside venetoclax and azacitidine in patients who cannot tolerate intensive chemotherapy. As general context, that combination is already a common backbone for this group, so any add-on drug has to show it can be layered on without making treatment harder to tolerate.

The size of the improvement is unknown. The announcement gives no reaction rates, patient numbers or details of the dose changes. Aptevo has said RAINIER data will be presented at the American Society of Hematology (ASH) meeting in December, which should be the first chance to check the claim against figures.