Abstract 4267: Cancer cell-extrinsic effect of immune checkpoint IGSF8

Abstract Background: We recently discovered IGSF8 (Immunoglobulin superfamily member 8) as a novel innate immune checkpoint on cancer cells by interacting with KIR3DL2 on natural killer (NK) cells (Cell, 2024). Anti-IGSF8 antibody enhanced NK cell-mediated cancer cell killing and suppressed tumor growth in multiple syngeneic tumor models. In Phase 1 clinical trial, anti-IGSF8 antibody showed favorable safety profiles and promising monotherapy activities. While IGSF8 is overexpressed on cancer cells, it is also expressed on various immune cells within the tumor microenvironment. In this study, we investigated the cancer cell-extrinsic effects of IGSF8 in tumor immunity. Methods: We generated germline IGSF8 knockout (KO) C57BL/6 mice using CRISPR-Cas9 technology. To evaluate the impact of IGSF8 deficiency on tumor immunity, we inoculated these KO mice with various syngeneic tumors and analyzed immune cell populations in tumor tissue and tumor draining lymph nodes by flow cytometry. To investigate antigen (Ag)-specific anti-tumor immunity, we implanted OVA-expressing B16-F10 melanoma in the KO mice, and quantified the Ag-specific CD8+ T cells with OVA257-264 tetramer and Ag-specific dendritic cells with antibodies specific for H-2Kb/SIINFEKL complexes. We also treated tumor-bearing wild-type (WT) mice with anti-IGSF8 antibody to compare the anti-tumor and immunoregulatory effects of IGSF8 blocking to those observed in IGSF8 KO animals. Results: IGSF8 KO C57BL/6 mice were viable and fertile. Tumor growth was significantly suppressed in IGSF8 KO mice compared to WT controls across multiple syngeneic models, including B16-F10 melanoma, RM1 prostate cancer, MC38 colon cancer, and LLC non-small cell lung cancer. After tumor challenge, KO mice had a significantly higher frequency of activated CD44+, PD-1+ T cells from both tumor tissue and tumor draining lymph nodes. In the OVA-expressing tumor model, we observed elevated levels of OVA257-264 tetramer+ CD8+ T cells and H-2Kb bound SIINFEKL+ dendritic cells in KO mice. Treatment of WT mice with anti-IGSF8 antibody recapitulated these findings, demonstrating enhanced activated T cell frequencies comparable to those observed in KO animals. Conclusion: Genetic ablation of IGSF8 or its therapeutic blockade with anti-IGSF8 antibody significantly suppressed syngeneic tumor growth, associated with enhanced antigen-specific T cell and dendritic cell responses. These findings reveal a previously unknown cancer cell-extrinsic function of IGSF8 in regulating tumor immunity, further supporting IGSF8 as a promising target for cancer immunotherapy. Citation Format: Xiangyang Wu, Flavian D. Brown, Jin Wang, Yixuan Tang, Chao Liu, X. Shirley Liu, Xingfeng Bao, Tengfei Xiao. Cancer cell-extrinsic effect of immune checkpoint IGSF8 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4267.