Antibody Targeting Soluble NKG2D Ligand MIC Enhances Adoptive T-Cell Therapy in an NK Cell-Dependent Mechanism

Background/Objectives: Antigen-specific adoptive CD8+ T-cell therapy has demonstrated promising clinical activity in selected cancers; however, its broader efficacy against solid tumors remains limited by the immunosuppressive tumor microenvironment (TME), which compromises the persistence and function of transferred T-cells. A clinically relevant component of the human solid-tumor TME is soluble MHC class I chain-related molecules A and B (sMICA and sMICB, collectively termed sMIC), which are tumor-derived soluble NKG2D ligands that are not naturally expressed in mice. sMIC promotes tumor immune evasion through multiple mechanisms, but whether therapeutic clearance of sMIC can enhance the efficacy of adoptive T-cell therapy remains unclear. Methods: B16F10 melanoma cells engineered to express soluble MICB (B16F10-sMICB) were implanted subcutaneously into syngeneic B6/MICB mice. Once tumors became palpable, mice were randomized to four treatment groups: (1) no treatment; (2) adoptive transfer of gp100-specific Pmel CD8+T cells; (3) the sMIC-targeting monoclonal antibody B10G5; or (4) B10G5 combined with Pmel adoptive cell transfer. Pmel CD8+T cells were administered once intravenously, and B10G5 was administered intraperitoneally twice weekly at approximately 3 mg/kg. Tumor growth and body weight were monitored twice weekly. To determine the contribution of natural killer (NK) cells to the therapeutic effect of the combination treatment, NK cells were depleted using the anti-NK1.1 antibody PK136. The impact of NK cells on CD8+T cell function during B10G5/sMIC stimulation was further evaluated ex vivo. Results: Therapeutic targeting of sMIC with B10G5 significantly enhanced the antitumor efficacy of adoptively transferred Pmel CD8+T cells and was associated with increased donor T-cell persistence, tumor infiltration, and antigen-specific effector function. NK cell depletion markedly diminished the antitumor efficacy of the B10G5/Pmel combination and reduced the abundance, activation, and effector function of donor CD8+ T-cells. Consistent with these in vivo findings, ex vivo depletion of NK cells impaired IFN-γ production by NKG2D+CD8+ T-cells during B10G5/sMIC stimulation, supporting a functional role for NK cells in sustaining CD8+T cell responses. Conclusions: These findings provide evidence that therapeutic targeting of tumor-derived sMIC can enhance the efficacy of antigen-specific adoptive CD8+T cell therapy by promoting the persistence and function of transferred T-cells. Importantly, our results identify NK cells as critical contributors to the enhanced therapeutic response, revealing functional cooperation between NK cells and adoptively transferred CD8+T cells during sMIC-targeted therapy. Together, these findings provide preclinical proof-of-concept for combining sMIC-targeting antibodies with adoptive T-cell therapy to improve antitumor immunity against sMIC+ solid tumors.