Setdb1 represses antitumor immunity and tertiary lymphoid structures in hepatocellular carcinoma.

BACKGROUND & AIMS: Tertiary lymphoid structures (TLSs) are ectopic lymphoid structures that develop in peripheral tissues in response to chronic inflammation or tumors. TLS maturation is associated with improved responses to tumor immunotherapy. However, the underlying mechanisms of TLS formation remain elusive. Here, we investigated the role of SETDB1 in TLS formation in hepatocellular carcinoma (HCC).

METHODS

Setdb1 was knocked out in multiple HCC models, including Akt/NRAS and Myc/CTNNB1 hydrodynamic models and Hepa1-6 orthotopic and subcutaneous tumor models. Spatial transcriptomics and multiplex staining were used to verify TLS formation. Real-time reverse-transcription PCR and western blotting were used for mechanistic investigations.

RESULTS

Low SETDB1 expression was associated with higher TLS levels in clinical samples, and Setdb1 depletion induced TLS formation in multiple HCC models. Setdb1 depletion generated cytosolic DNA and activated the cGAS pathway, which increased Cxcl12 and Zbp1 expression. Cxcl12 was upregulated in hepatocytes and cancer cells and contributed to the recruitment and maturation of B cells. Zbp1 was activated in malignant cells and induced necroptosis, contributing to TLS formation. Setdb1 depletion also increased the expression of endogenous retroviruses, which may act as neoantigens and promote B-cell maturation.

CONCLUSIONS

Our study has revealed a critical role for Setdb1 in TLS formation and suggests a potential role for Setdb1 as a therapeutic target to enhance the effects of immunotherapy in HCC.

IMPACT AND IMPLICATIONS: The current study found that Setdb1 depletion induces the formation of tertiary lymphoid structures (TLSs) in hepatocellular carcinoma (HCC). TLSs are ectopic lymphoid structures that develop in peripheral tissues in response to chronic inflammation or tumors. Mature TLSs are associated with improved responses to tumor immunotherapy. This study uncovers a new cGAS/CXCL12 pathway involved in TLS formation, providing insights into the mechanisms regulating antitumor immunity. It also provides a potential strategy for combining SETDB1 inhibition with immunotherapy for HCC treatment.