Abstract 4318: Genome-wide in vivo CRISPR screen identifies the role of SRSF9 in immunotherapy response regulation in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is a leading malignant tumor globally and the second-highest cause of cancer-related mortality. The insidious nature and high recurrence rates of HCC largely necessitate systemic therapies for many patients, particularly those based on immune checkpoint inhibitors. For advanced HCC, the combination of atezolizumab and bevacizumab (Atezo+Beva) has become the preferred first-line treatment, providing superior survival benefits compared to sorafenib. However, the response rate to this therapy remains under 30%, with the underlying resistant mechanism still unclear. Therefore, identifying and characterizing predictive biomarkers associated with the response to Atezo+Beva therapy is essential for improving clinical prognosis in patients with advanced HCC. Here, we performed an in vivo genome-wide CRISPR screen model after anti-programmed death ligand 1 (anti-PD-L1) and anti-vascular endothelial growth factor a (anti-VEGFa) treatment to investigate genomic modulators of the immunotherapy response in HCC. Our screening identified serine and arginine rich splicing factor 9 (SRSF9) as a critical gene involved in the anti-immunotherapy regulation. Knockout of SRSF9 in mouse tumor cells significantly enhanced the sensitivity of primary tumors and the lung metastasis to anti-PD-L1 and anti-VEGFa treatment. This finding was further validated using SRSF9-overexpression mouse model. Functional assays indicated that without immunotherapy SRSF9 had a minimal direct effect on the proliferation of multiple HCC cell lines, aligning with the analytical results derived from the DepMap database. Clinically, SRSF9 expression was increased in multiple cancer types compared to normal counterparts and was positively correlated with poor survival in HCC patients following Atezo-Bev therapy. Furthermore, high SRSF9 expression could negate the prognostic advantage typically seen in patients with strong CD8+ T cell function. In addition, SRSF9 could decrease the secretion of interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) in tumor environment. These suggested a potential role for SRSF9 in downregulating CD8+ T cell activity. The underlying mechanism of how SRSF9 inhibits the response of HCC patients to Atezo+Beva therapy still needs further investigation. In conclusion, our study reveals the significant role of SRSF9 in modulating the response to immunotherapy in HCC, indicating its substantial potential for expanding the cohort of patients who may benefit from Atezo+Beva therapy and enhancing their prognosis. Further exploration of the underlying mechanisms will be undertaken in the future. Citation Format: Nanzhou Yu, Jie Luo, Beibei Ru, Renyue Ji, Lanqi Gong, Peng Jiang, Xinyuan Guan. Genome-wide in vivo CRISPR screen identifies the role of SRSF9 in immunotherapy response regulation in hepatocellular carcinoma [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 4318.