Abstract PR014: ARID4B induces immune escape in high-grade serous ovarian cancer by upregulating B3GNT5-mediated glycosphingolipid synthesis

Abstract Introduction: Modulating the tumor immune microenvironment in a molecularly defined manner remains a major challenge in cancer immunotherapy. For example, how epigenetic regulators remodel tumor microenvironment to evade immune surveillance remains poorly understood. ARID4B is often overexpressed in high-grade serous ovarian cancer (HGSOC). The current study aims to investigate the mechanism by which ARID4B drives immunosuppressive landscape HGSOC and develop novel therapeutic strategies to overcome the immunosuppressive microenvironment in an ARID4B-dependent manner. Methods: To investigate the effect of ARID4B in HGSOC, we generate ARID4B wild-type/knockout isogeneic cell lines and analyzed transcriptional changes by RNA sequencing and profile ARID4B genome-wide distribution by Cut&Run. To evaluate whether ARID4B-dependent tumor formation requires an intact immune system, we compared tumor formation of ARID4B wild-type/knockout isogeneic cell line in immunocompetent syngeneic orthotopic HGSOC models and immunodeficient mouse models. The effect of ARID4B on T cell activation and cytotoxicity was evaluated in vitro by co-culturing OT1 T cell with HGSOC cell lines and analyzed the activation and cytotoxic marker via flow cytometry. Glycosylation changes were assessed by lectin staining and flow cytometry. Immunocompetent syngeneic orthotopic HGSOC models, established using the isogenic cell lines, were used to study the combination effect of the FDA-approved orphan drug Eliglustat, served as a glycosphingolipid synthesis inhibitor, with immune checkpoint inhibitor anti-PD-L1. Result: High ARID4B expression predicts a shorter survival in HGSOC. While loss of ARID4B does not impair tumor cell growth in vitro or in immunodeficient mouse models in vivo, ARID4B knockout significantly reduces tumor formation in immunocompetent mice. This effect is abolished upon in vivo depletion of CD8+ T cells using a neutralizing antibody, indicating an immune-dependent mechanism. Genome-wide approaches reveal that ARID4B directly binds to the promoter of the glycosyltransferase gene B3GNT5, thereby upregulating its expression. Elevated B3GNT5 expression promotes the synthesis of lacto-series glycosphingolipid in tumor cells, which suppress CD8+ T cell infiltration and impair their cytotoxicity. Notably, inhibition of glycosphingolipid synthesis genetically or using clinically applicable small molecule inhibitor Eliglustat synergizes with immunotherapy such as immune checkpoint blockade in an ARID4B and B3GNT5-dependent manner. Conclusion: ARID4B drives an immunosuppressive microenvironment through B3GNT5 mediated lacto-series glycosphingolipid enrichment. The enriched lacto-chain glycosphingolipid causes reduced cytotoxicity and elevated exhaustion of CD8+ T cells. Our findings uncover an ARID4B–B3GNT5–glycosphingolipid axis that mediates tumor immune evasion and suggest a glycosylation-targeted strategy to enhance immunotherapy in ARID4B overexpressing ovarian cancer. Citation Format: Yiming Fang, Simona Lombardi, Hao Nie, Xiaojin Luan, Ayumu Matsuoka, He Huang, Liping Liao, Xu Zhang, Danwei Wang, Yuan Qi, Shengqing Gu, Rugang Zhang. ARID4B induces immune escape in high-grade serous ovarian cancer by upregulating B3GNT5-mediated glycosphingolipid synthesis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research; 2025 Sep 19-21; Denver, CO. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl):Abstract nr PR014.