Aptevo Reports Fewer Infusion Reactions in Mipletamig AML Study
Aptevo Therapeutics said changes to mipletamig’s initial dosing schedule substantially reduced infusion-related reactions in the RAINIER study, while planned therapeutic dosing was maintained.
Aptevo Therapeutics Inc. (NASDAQ:APVO) has reported a clinical development update for mipletamig, saying adjustments to the treatment’s initial dosing schedule substantially reduced infusion-related reactions during early treatment. The company said planned therapeutic dosing was maintained as it worked to address a tolerability objective identified during discussions with the U.S. Food and Drug Administration.
Mipletamig is being studied with venetoclax and azacitidine in patients with newly diagnosed acute myeloid leukemia who are considered unfit for intensive chemotherapy. The treatment uses a priming-dose approach, in which patients receive an initial introduction to the therapy before moving to higher doses.
Aptevo said successive changes to this regimen reduced the frequency and severity of infusion-related reactions during initial treatment. Such reactions can include fever, chills, rash and nausea. Depending on their severity, they may require additional medical intervention, interrupt treatment or lead to discontinuation.
The company said the issue is particularly relevant in frontline AML, where patients may be older or have other health conditions that affect treatment tolerability. Aptevo also said the latest findings do not establish improved efficacy or treatment persistence.
Aptevo described mipletamig’s safety and tolerability profile as encouraging throughout its clinical development. The company also reported favorable findings concerning cytokine release syndrome, a potentially serious inflammatory reaction associated with some immune-based cancer treatments.
According to Aptevo, the RAINIER study has shown clinical activity alongside the safety and tolerability findings. Previous company-reported observations included remission responses among patients with TP53-mutated AML. Aptevo also said that some patients initially considered unfit for intensive chemotherapy advanced to allogeneic stem cell transplantation.
The company said the dosing changes strengthen the tolerability component of mipletamig’s development profile. However, it cautioned that the findings do not demonstrate better efficacy or prove that patients will remain on treatment longer.
Aptevo said it continues to assess clinical activity, safety and tolerability in RAINIER and expects to complete the current study by year-end 2026. The company said it expects to conduct regulatory interactions and initiate Phase 2 development in 2027.
Mipletamig data are scheduled to be presented at the American Society of Hematology 68th Annual Meeting in New Orleans, Louisiana, from December 12-15, 2026.
Aptevo describes mipletamig as a treatment designed to bring T cells into close contact with leukemic cells and leukemic stem cells expressing CD123. The company says its CRIS-7-derived CD3 binding pathway is designed to reduce the likelihood and severity of cytokine release syndrome.
Aptevo said its forward-looking statements are based on its current intentions, beliefs and expectations and cannot be guaranteed to be accurate. The company identified risks including further assessment of preliminary or interim data, different results in later clinical trials, adverse events, unexpected safety issues, developments affecting clinical development and changes in regulatory, social, macroeconomic and political conditions.
Aptevo Therapeutics announced a clinical development milestone for mipletamig, reporting a substantial reduction in infusion-related reactions after successive refinements to its priming-dose regimen. The company said the change addresses a treatment-tolerability objective identified through discussions with the U.S. Food and Drug Administration and supports preparations for Phase 2 development.
Aptevo Therapeutics is evaluating mipletamig in combination with standard-of-care venetoclax and azacitidine in patients with newly diagnosed acute myeloid leukaemia who are unfit for intensive chemotherapy. RAINIER is described as a two-part Phase 1b/2 trial.
Aptevo Therapeutics said successive refinements to mipletamig’s initial dosing regimen substantially reduced the occurrence of infusion-related reactions during initial treatment. The company said the refinements did not compromise planned therapeutic dosing.
Infusion-related reactions can include fever, chills, rash or nausea and, depending on their severity, may require additional medical intervention, treatment interruptions or discontinuation. Aptevo Therapeutics said this is particularly relevant for frontline acute myeloid leukaemia patients who may be older or have additional health conditions affecting treatment tolerability.
Aptevo Therapeutics said mipletamig has shown an encouraging safety and tolerability profile throughout its clinical development, including favourable findings related to cytokine release syndrome. The company said the latest priming-dose refinements build on those observations by reducing infusion-related reactions during initial treatment.
Aptevo Therapeutics said the dosing refinement does not establish improved efficacy or treatment persistence. The company said reducing reactions that can interrupt therapy is clinically meaningful and may lessen a potential obstacle to continued treatment.
Aptevo Therapeutics said it has previously reported encouraging clinical activity in the RAINIER study, including remission responses in patients with TP53-mutated acute myeloid leukaemia. The company also said patients initially considered unfit for intensive chemotherapy have advanced to allogeneic stem cell transplantation.
Aptevo Therapeutics says mipletamig is designed to redirect the patient’s immune system to destroy leukemic cells and leukemic stem cells expressing CD123. It is designed to engage leukemic cells and T cells and bring them closely together to trigger the destruction of leukemic cells.
Aptevo Therapeutics says mipletamig is purposefully designed to reduce the likelihood and severity of cytokine release syndrome by using the CRIS-7-derived CD3 binding pathway. The company also reported favourable CRS findings during clinical development and said substantial reductions in IRRs and CRS were observed following successive priming-dose refinements.
Aptevo Therapeutics expects to complete the current RAINIER study by year-end 2026. The company continues to evaluate clinical activity, safety and tolerability in the study.
Aptevo Therapeutics said it expects to conduct regulatory interactions and initiate Phase 2 development in 2027. The company said the refined priming-dose regimen is informing dose selection and upcoming regulatory discussions.
Aptevo Therapeutics said mipletamig data will be presented at the American Society of Hematology 68th Annual Meeting in New Orleans, Louisiana, from December 12-15, 2026.
Aptevo Therapeutics is identified in the source as trading on NASDAQ under the ticker APVO, written as “NASDAQ:APVO”, and elsewhere as “Nasdaq:APVO”.
Aptevo Therapeutics cautions that actual results may differ materially because of factors including further assessment of preliminary or interim data, different results from later clinical trials, adverse events, unexpected safety issues, adverse clinical-development developments and changes in regulatory, social, macroeconomic and political conditions. The company also says the forward-looking statements are based on current intentions, beliefs and expectations and that it cannot guarantee their accuracy.