Abstract LB132: C8orf76 promotes colorectal tumorigenesis by promoting an immunosuppressive microenvironment and is a therapeutic target for boosting anti-PD-1 efficacy

Abstract Immune checkpoint blockade (ICB) therapy demonstrated limited efficacy in colorectal cancer (CRC), and identification of intrinsic factors modulating immune suppression in CRC is an unmet need. Here, we revealed that Chromosome 8 open reading frame 76 (C8orf76) drives immunosuppression and is a molecular target to boost ICB therapy in CRC. C8orf76 is upregulated in primary CRCs compared to adjacent normal tissues in 2 independent CRC cohorts and its expression predicts poor patient survival. Intestine-specific C8orf76 knockin in mice exacerbated AOM/DSS-induced CRC, accompanied by increased intratumoral myeloid-derived suppressor cells (MDSCs) but reduced IFN-γ+ and granzyme B+ CD8+ T cells, inferring that C8orf76 promotes immunosuppression in CRC. Consistently, genetic depletion of C8orf76 augmented antitumour immunity in CT26 (MSS-CRC) and MC38 (MSI-H-CRC) allograft models. Integrated RNA-seq and ChIP-seq revealed that C8orf76 functions as a transcription factor to drive NDST1 expression, which activates the PI3K-Akt-NF-κB signaling cascade. Activated NF-κB in turn promotes the expression and secretion of CXCL1, a major chemoattractant for MDSCs. Consequently, C8orf76-induced CXCL1 mediates the recruitment of MDSCs via CXCR2 to antagonize functional CD8+ T cells in tumor immune microenvironment of CRC. Confirming this, targeting NDST1 or CXCR2 could reverse C8orf76 induced immunosuppression in vivo. Finally, we tested the translational value of C8orf76 using genetic ablation or vesicle-like nanoparticles (VNPs)-encapsulated C8orf76-siRNA. In line with our hypothesis, we demonstrated that targeting C8orf76 by genetic ablation or VNPs-encapsulated C8orf76-siRNA potentiated the anti-PD1 efficacy in both MSI-H and MSS CRC models. In summary, C8orf76 drives immunosuppression through a NDST1-CXCL1/CXCR2 axis, and targeting C8orf76 is a promising approach to boost ICB therapy efficacy in CRC. Citation Format: Hongyan Gou, Shang Guo, Xiaohong Wang, Xia Jiang, Chi Chun Wong, Huarong Chen, Chunxian Wei, Lingxue Shi, Zengren Zhao, Jun Yu. C8orf76 promotes colorectal tumorigenesis by promoting an immunosuppressive microenvironment and is a therapeutic target for boosting anti-PD-1 efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB132.