Radiation Therapy Promotes Hepatocellular Carcinoma Immune Cloaking via PD-L1 Upregulation Induced by cGAS-STING Activation

• DOI: 10.1016/j.ijrobp.2021.12.162
• Publication Date: 2022-01-02T14:33:52Z
• Authors: Shi-Suo Du; Gen-Wen Chen; Ping Yang; Yi-Xing Chen; Yong Hu; Qian-Qian Zhao; Yang Zhang; Rong Liu; Dan-Xue Zheng; Jian Zhou; Jia Fan; Zhao-Chong Zeng
• Keywords: 0303 health sciences; Carcinoma, Hepatocellular; Liver Neoplasms; Membrane Proteins; CD8-Positive T-Lymphocytes; Nucleotidyltransferases; B7-H1 Antigen; Up-Regulation; 3. Good health; Mice; 03 medical and health sciences; Animals; Humans

Radiation therapy (RT) is one of the main treatments for patients with unresectable hepatocellular carcinoma (HCC). Emerging evidence indicates that the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) stimulator of interferon gene (STING) pathway is crucial in RT-induced antitumor immune responses. Here, we discovered that activation of the cancer cell-intrinsic cGAS-STING pathway mediated immune cloaking after RT-induced DNA damage.Key regulatory proteins in the cGAS-STING signaling pathway in human and murine HCC cell lines were knocked out or down using CRISPR and CRISPR-associated protein 9 or small interfering RNA. The underlying mechanism of immune cloaking and clinical significance of cGAS-STING-induced programmed cell death ligand 1 (PD-L1) expression were studied with both ex vivo analyses and in vitro experiments.RT upregulated PD-L1 in patients with HCC, which correlated with poor survival. RT activated cGAS-STING, increasing immune-checkpoint PD-L1 expression in human and mouse liver cancer cells. Ionizing radiation activated the STING-TANK-binding kinase 1 (TBK1)-interferon regulatory factor 3 (IRF3) innate immune pathway, leading to PD-L1 upregulation in HCC cells and inhibiting cytotoxic T-lymphocyte activity and protecting tumor cells from immune-mediated eradication. Knockdown of cGAS, STING, TBK1, and IRF3 reversed the antitumor effect of cytotoxic T-lymphocyte-mediated cytotoxicity after ionizing radiation in vitro or in vivo. RT potentiated the antitumor effect of programmed cell death protein 1 and PD-L1 axis blockade and augmented cytotoxic T-cell (CTL) infiltration in HCC tumors in immunocompetent mice. CD8 depletion compromised the synergetic antitumor effect of combined RT and anti-PD-L1 blockade, demonstrating that CD8+ CTLs are required for antitumor immunity induced by combination therapy.Our results identified an immune-cloaking mechanism for RT-activated, innate immune cGAS-STING and suggested that RT enhances HCC immunotherapy.