Enhancing NK Cell Activity in Colorectal Cancer with an Fc-Optimized Antibody Targeting CD276 (B7-H3).

BACKGROUND & AIMS: Colorectal cancer (CRC) represents a major global health burden due to its high incidence and mortality, particularly in the advanced stages, with limited treatment options. While therapies that block the PD-1/PD-L1 pathway have demonstrated clinical benefit, their success in CRC is largely confined to patients with high microsatellite instability (MSI-H) tumors. Innovative immunotherapeutic solutions are critically needed for the majority of CRC cases. CD276 (B7-H3), a B7 family immune checkpoint molecule, is overexpressed in many cancers including CRC. Significant CD276 upregulation in CRC cell lines compared to benign tissues has been previously demonstrated. In this study, the potential of an Fc-optimized anti-CD276 monoclonal antibody to enhance natural killer (NK) cell activity in CRC was evaluated. METHODS: An Fc-optimized monoclonal antibody, 8H8_SDIE, was developed to enhance NK cell activity by increasing CD16 binding. In vitro experiments were conducted using human CRC cell lines and peripheral blood mononuclear cells (PBMCs) from healthy adult donors to evaluate the binding specificity of 8H8_SDIE to CD276. NK cell activation was assessed by measuring the upregulation of activation markers (CD69, CD25, and CD107a) and secretion of cytotoxic mediators (IFNγ, granzyme B, and perforin). Cytotoxicity assays were performed to determine NK cell-mediated tumor cell lysis. RESULTS: 8H8_SDIE specifically bound to CD276-positive CRC cells and significantly enhanced NK cell activation. These effects included increased levels of activation and cytotoxic mediators. In cytotoxicity assays, 8H8_SDIE demonstrated potent NK cell-mediated lysis of CRC cells. CONCLUSION: The Fc-optimized anti-CD276 antibody 8H8_SDIE effectively enhanced NK cell reactivity against CD276-positive CRC cells and induced tumor cell lysis in vitro. These findings suggest that 8H8_SDIE holds potential as a novel immunotherapeutic candidate for CRC, particularly for patients with microsatellite-stable disease, and warrants further evaluation in advanced preclinical and future clinical studies.