Interim data from Aptevo Therapeutics Inc.’s ongoing RAINIER clinical trial show that the investigational therapy mipletamig, when combined with standard frontline treatment for acute myeloid leukemia (AML), delivered an 86% clinical benefit rate. The combination therapy with venetoclax and azacitidine resulted in a 79% remission rate among evaluable patients, with 55% of those achieving remission reaching MRD-negative status, where highly sensitive tests could not detect remaining leukemia cells.
The safety profile of mipletamig appears particularly notable, as no patients treated to date have experienced cytokine release syndrome (CRS), a common and potentially serious immune reaction that can force discontinuation of therapy. This safety aspect is crucial for therapies intended to be used in combination with existing treatments, where tolerability is key to keeping patients on therapy, especially older or medically unfit individuals who cannot tolerate intensive chemotherapy.
Mipletamig is a bispecific antibody designed to target CD123, a marker commonly found on AML leukemia cells, while simultaneously connecting with T-cells, the immune system’s natural cancer fighters. This approach aims to direct the immune system to attack and destroy leukemia cells while maintaining a safety profile that allows combination with existing frontline treatments. The company’s phase 1b dose optimization trial, RAINIER, is evaluating mipletamig in combination with venetoclax and azacitidine in patients newly diagnosed with AML who are older or unable to receive intensive chemotherapy.
AML affects approximately 22,000 people in the United States each year and remains one of the most aggressive adult leukemias. For many patients, especially those who cannot tolerate intensive treatment, therapeutic advances that improve outcomes without adding significant toxicity remain an important goal. The emerging data suggest mipletamig may have the potential to enhance the current frontline AML treatment approach, improving patient responses while maintaining the safety and tolerability needed for vulnerable patient populations.
Marvin White, President and Chief Executive Officer of Aptevo Therapeutics, stated that the frontline data show mipletamig has the potential to play a meaningful role in future frontline AML treatment. The combination of strong remission outcomes with the continued absence of cytokine release syndrome represents an encouraging combination of efficacy and safety for therapies intended to work alongside existing frontline AML treatments. The study is being conducted in two stages, beginning with a phase 1b portion designed to determine the optimal dose, followed by a larger phase 2 study to further evaluate the therapy’s effectiveness.
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