E-twenty-six-specific sequence variant 5 (ETV5) facilitates hepatocellular carcinoma progression and metastasis through enhancing polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC)-mediated immunosuppression.

Background: Despite the success of immune checkpoint blockade, a lack of understanding of the hepatocellular carcinoma (HCC) immune microenvironment impedes its development.

Objective: We aim to elucidate the essential function of E-twenty-six-specific sequence variant 5 (ETV5) in regulating the immune microenvironment in HCC.

Design: Humanised mouse models, murine orthotopic models and diethylnitrosamine/carbon tetrachloride (DEN/CCl)-induced HCC models were used to examine the function of ETV5. The downstream targets of ETV5 were screened using chromatin immunoprecipitation sequencing, CUT&Tag and RNA sequencing. Immune cells were examined using flow cytometry and immunofluorescence. S100 calcium-binding protein A9 (S100A9) was targeted by neutralising antibodies.

Results: Overexpression of ETV5 in HCC cells facilitated HCC metastasis and immune escape by recruiting and enhancing the immunosuppressive capabilities of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). Mechanistically, ETV5 transactivated programmed death ligand 1 (PD-L1) and S100A9 expression. Inhibition of S100A9 or myeloid-specific knockout of toll-like receptor 4 (TLR4)/receptor for advanced glycation endproducts (RAGE), the receptors of S100A9, impeded ETV5-induced PMN-MDSC recruitment. Meanwhile, S100A9 within the tumour microenvironment elevated ETV5 expression via the extracellular signal-regulated kinase (ERK)/nuclear factor-kappa B pathway. Additionally, ETV5 transcriptionally upregulated PD-L1 in MDSCs as well, thereby augmenting their immunosuppressive functions. Myeloid-specific knockout attenuated HCC progression. We developed monoclonal neutralising-S100A9 antibodies that effectively inhibited ETV5-mediated PMN-MDSC infiltration. Synergistic application of anti-S100A9 or TLR4/RAGE inhibitors with anti-PD-L1 therapy significantly suppressed ETV5-mediated HCC progression.

Conclusion: ETV5 facilitates HCC progression and metastasis by promoting the recruitment, infiltration and activation of PMN-MDSCs. Synergistic application of anti-S100A9 or TLR4/RAGE inhibitors with anti-PD-L1 therapy holds great promise as an effective combinational treatment strategy for ETV5-positive HCC.