G9a epigenetically suppresses <scp>CXCL10</scp> expression and inhibits anti‐tumor immunity in hepatocellular carcinoma

The immunosuppressive tumor microenvironment, characterized by limited immune cell infiltration, represents a major challenge for effective immunotherapy in hepatocellular carcinoma (HCC). Epigenetic dysregulation has emerged as a critical mechanism underlying tumorigenesis and progression; however, the specific epigenetic mechanisms governing immune infiltration remain poorly understood. Here, we investigated the role of G9a, a histone methyltransferase catalyzing H3K9 methylation, in modulating anti-tumor immunity in HCC. Bioinformatic analysis of human HCC datasets revealed a significant inverse correlation between G9a expression and T cell infiltration. Genetic ablation of G9a in hepatoma cells markedly enhanced CD8⁺ T cell recruitment and activation in immunocompetent mouse models. Through RNA sequencing and functional validation, we identified CXCL10 as the key chemokine directly repressed by G9a. Mechanistically, G9a mediates H3K9 dimethylation at the CXCL10 promoter, and G9a deletion or inhibition significantly reduced this repressive mark, resulting in increased CXCL10 expression and secretion. Importantly, neutralization of CXCL10 abolished G9a inhibition-induced enhancement of CD8⁺ T cell migration. In preclinical models, pharmacological inhibition of G9a with UNC0642 not only suppressed tumor growth by promoting T cell infiltration but also synergized with anti-PD1 therapy to achieve superior therapeutic efficacy. These findings establish G9a as an epigenetic regulator of anti-tumor immunity in HCC and provide evidence for combining G9a inhibitors with immune checkpoint blockade to improve outcomes for HCC patients who are receiving immunotherapy.