Aptevo Therapeutics (NASDAQ:APVO) saw its shares jump sharply Tuesday after the company reported encouraging clinical data from its Phase 1b/2 RAINIER trial evaluating mipletamig, a first-in-class CD123 x CD3 bispecific antibody, in patients with newly diagnosed acute myeloid leukemia (AML) who are unfit for intensive chemotherapy.
Aptevo said that Cohort 3 of the trial achieved a 100% remission rate, with 40% of patients reaching minimal residual disease (MRD)-negative status, a key indicator linked to improved long-term outcomes.
The trial also reported no dose-limiting toxicities or cytokine release syndrome, highlighting a favorable safety profile for the therapy in combination with venetoclax and azacitidine.
The RAINIER trial, which is exploring mipletamig across multiple dose levels, is designed to assess both efficacy and tolerability in frontline AML patients.
The results from Cohort 3 mark the highest dose tested to date and demonstrate consistent responses across previous cohorts. Cohort 4 is now actively enrolling patients at the next dose level.
"Cohort 3 demonstrates the kind of progress that changes expectations for frontline AML therapy," Aptevo CEO Marvin White said in a statement.
“Delivering a 100% remission rate reinforces our conviction that mipletamig is more than an active agent—it’s a differentiated medicine designed to integrate with the venetoclax and azacitidine backbone and elevate outcomes for patients who have had too few options for too long."
Dr Dirk Huebner, Aptevo chief medial officer, added, "Across the RAINIER trial to date, mipletamig has achieved near-universal remissions while maintaining a safety profile that is very well managed in the clinic. This balance of potency and tolerability is exactly what physicians need to confidently adopt a new frontline regimen."
Shares of Aptevo added 16% at $1.67 in the early afternoon on Tuesday.