An IL-15-modified NKp30×HER2 trispecific NK cell engager enhances NK cell activation and tumor cell killing

Natural killer (NK) cells represent a promising effector population for tumor immunotherapy. Conventional NK cell engagers (NKCEs), primarily targeting CD16a, show efficacy but face limitations due to receptor polymorphisms and off-target toxicity. Here, we report the development and characterization of a novel trispecific NK cell engager (TriKE) simultaneously targeting the activating receptor NKp30 and the tumor-associated antigen HER2, integrated with a modified interleukin-15 (IL-15 N72D) fused to the IL-15Rα sushi domain (IL-15RαSu) to enhance NK cell proliferation and persistence. Protein expression and affinity analyses confirmed the proper formation of the fusion protein with high-affinity binding to NKp30, HER2, and IL-15 receptor components. Flow cytometry demonstrated dose-dependent binding of the TriKE to primary human NK cells and HER2+ tumor cells. Functionally, the TriKE induced significantly greater NK cell activation, as measured by CD69 expression, compared with a bispecific engager lacking IL-15. Importantly, cytotoxicity assays revealed superior NK-mediated killing of HER2+ tumor cells upon prolonged exposure, highlighting the immunostimulatory effect of the IL-15 moiety. These results establish the αNKp30 TriKE as a potent platform to redirect NK cytotoxicity against HER2+ tumors, combining targeted receptor engagement with cytokine-driven activation to enhance NK cell-based cancer immunotherapy.