RIG-I-targeted immunotherapy synergizes with immune checkpoint inhibition in a hepatocellular carcinoma model.

Retinoic acid-inducible gene-I (RIG-I) is a cytoplasmic pattern recognition receptor that senses short double-stranded RNA with uncapped 5'-triphosphate (3p-RNA). Upon activation, RIG-I induces type I interferons and proinflammatory cytokines, thereby promoting adaptive immunity. Thus, RIG-I activation is a promising approach for creating a proinflammatory tumor microenvironment. In this study, we investigated its therapeutic potential in hepatocellular carcinoma (HCC). We explored and confirmed RIG-I expression and signaling in human HCC samples and cell lines. The therapeutic potential of RIG-I activation by 3p-RNA for the treatment of HCC was investigated in vitro and in syngeneic murine orthotopic tumor models. In vivo, 3p-RNA treatment significantly reduced the tumor burden, delayed disease progression, and achieved partial complete remission of RIL-175 tumors with durable immune memory. However, no therapeutic effects were observed in the Hep-55.1C model. Tumor clearance depended on CD4⁺ and CD8⁺ T cells, but not NK cells. Additionally, 3p-RNA induced PD-L1 expression on HCC cells, enhancing their sensitivity to anti-PD-1 immune checkpoint therapy in vivo. RIG-I activation via 3p-RNA therapy shows promise as an immunotherapeutic strategy for hepatocellular carcinoma (HCC). Future investigations need to focus on tumor-intrinsic factors to understand heterogeneity between tumors and to overcome resistance mechanisms.