Aptevo's Mipletamig Demonstrates 86% Clinical Benefit in Frontline AML Treatment with Favorable Safety Profile

Acute myeloid leukemia (AML) represents one of the most challenging blood cancers to treat, particularly for older patients or those with comorbidities who cannot withstand intensive chemotherapy. For these individuals, treatment options are limited and outcomes often remain poor. Aptevo Therapeutics Inc. (NASDAQ: APVO), a clinical-stage biotechnology company, is developing mipletamig, an investigational therapy designed to be used alongside standard-of-care treatment in newly diagnosed patients. New interim data from the ongoing RAINIER clinical trial indicate that mipletamig enhances patient results while adding limited toxicity.

Across evaluable frontline AML patients treated to date, the combination of mipletamig with venetoclax and azacitidine delivered an 86% clinical benefit rate, including a 79% remission rate. In AML, remission typically signifies that leukemia cells have been reduced to very low levels in the bone marrow, either as a complete remission or complete remission with incomplete blood count recovery. Notably, 55% of patients who achieved remission reached MRD-negative status, meaning highly sensitive tests could not detect any remaining leukemia cells. Achieving MRD negativity is considered an important marker of deeper disease control and the potential for longer-lasting responses.

Equally significant is the therapy's safety profile. No patients treated to date have experienced cytokine release syndrome (CRS), a common and potentially serious immune reaction that can force patients to discontinue therapy. Avoiding CRS is especially crucial for drugs intended to be used in combination with other treatments, where safety and tolerability are key to keeping patients on therapy. Collectively, 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, especially for older or medically unfit patients.

Mipletamig is a bispecific antibody, a molecule designed to serve two purposes simultaneously. One side locks onto leukemia cancer cells, specifically targeting a marker called CD123 that is commonly found on AML leukemia cells. The other side connects with T-cells, the immune system's natural cancer fighters. By bringing these two together, the therapy helps direct the immune system to attack and destroy leukemia cells. This targeted approach is designed to activate the immune response against AML while maintaining a safety profile that allows the drug to be combined 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. 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. 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 original release can be viewed on www.newmediawire.com.