Aptevo Therapeutics Inc. (Nasdaq: APVO) announced on September 3, 2026, that its mipletamig triplet demonstrated a 93% clinical benefit rate in a study of patients with a difficult-to-treat form of acute myeloid leukemia (AML).
The results were reported in a press release filed as Exhibit 99.1 to the company's Form 8-K. The data comes from 14 evaluable patients with TP53-mutated AML who were treated with mipletamig in combination with venetoclax and azacitidine. This patient population has historically responded poorly to treatment.
Of the 14 patients, 13 experienced clinical benefit. This category includes complete remission (CR), complete remission with incomplete hematologic recovery (CRi), partial response (PR), and morphologic leukemia-free state (MLFS). Specifically, 11 patients achieved CR or CRi, including nine complete remissions.
Aptevo noted that the 79% CR/CRi rate observed with the mipletamig triplet compares favorably to a published 41% composite remission rate for venetoclax plus azacitidine in treatment-naïve patients with poor-risk cytogenetics and TP53-mutated AML.
The company stated that the RAINIER study is evaluating mipletamig in combination with venetoclax and azacitidine in frontline AML patients who are unfit to receive standard high-intensity chemotherapy. Aptevo plans to complete the current phase of the trial by year-end and anticipates regulatory interaction in the first half of 2027.
Mipletamig is Aptevo’s lead proprietary drug candidate, designed to redirect the immune system to destroy leukemic cells expressing CD123. The candidate has received orphan drug designation for AML under the Orphan Drug Act.
