Subset-guided IL-15 expansion of NK cells amplifies antigen-specific CD4+ T cell immunity in melanoma

Abstract Background Natural killer (NK) cells comprise heterogeneous subsets with distinct developmental trajectories and effector functions; however, whether specific NK subsets can selectively coordinate adaptive antitumor immunity remains unclear. We identified a bone marrow-derived CD11c + B220 + NK subset (DPNKs) that is selectively expanded by IL-15 and exhibits potent anti-melanoma activity. Methods Murine bone marrow cells expanded with IL-15 were sorted into DPNKs and conventional NK cells (cNKs). Antitumor efficacy was assessed in B16 melanoma models following adoptive transfer. Immune cell composition, cytokine production, antigen-specific CD4 + T cell responses, and the roles of IFN-γ, IL-4, MHC-II, and CXCR3 were investigated. Human IL-15–expanded NK cells were also evaluated. Results Compared with cNKs, DPNKs showed superior antitumor efficacy. DPNKs remodeled the tumor microenvironment toward an immunostimulatory state by increasing the intratumoral effector-to-regulatory T cell ratio and enhancing tumor antigen–specific CD4 + T cell responses. Tumor control depended on host-derived IFN-γ but not IL-4. DPNKs upregulated MHC-II and CD86 after melanoma cell interaction and promoted CD4 + T cell responses independently of intrinsic MHC-II expression. The tumor-regressive effect of DPNK treatment was attenuated by depletion of either CD4 + or CD8 + T cells compared with DPNK treatment alone. Elevated CXCR3 expression was essential for DPNK-mediated tumor control. In humans, IL-15 expansion enriched CD56 + HLA-DR + NK cells with enhanced cytotoxicity, increased CD86 expression, and T cell stimulatory capacity. Conclusion DPNKs represent a therapeutically relevant NK subset that reprograms CD4 + T cell responses in melanoma and support IL-15–based generation of immunostimulatory human NK cells for translational cancer immunotherapy.