IDDF2021-ABS-0115 Enhancer dysregulation of myeloid-derived suppressor cells in hepatocellular carcinoma

Abstract

Background Though immune checkpoint blockade (ICB) therapies have shown promise to treat HCC, the insufficient T cell infiltration to the non-inflamed tumor restricts the effectiveness of ICB therapy to a minority of HCC patients. As a key player in the tumor microenvironment (TME), myeloid-derived suppressor cells (MDSC) were reported to correlate with resistance to ICB and poor prognosis. Given the fact that enhancer reprogramming of MDSC is crucial to the MDSC identity and function, this study aims to identify the enhancer targets that are significantly contributing to MDSC immunosuppressiveness and to study the potential of myeloid targeting for improving immunotherapy efficacy. Methods Single-cell RNA sequencing (sc-RNA-seq) of ICB-resistant patients was performed to understand the immune profile of patients and the heterogeneity of TME in HCC. The expression and immune profile of MDSC signature genes were determined by flow cytometry analysis in immune cells from tumor-bearing mice and HCC patients. FANTOM5 (Functional Annotation of the Mammalian Genome) database and JEME (Joint Effects of Multiple Enhancers) algorithm were used to identify enhancer RNA (eRNA) locations and expressions. Functional significance and molecular mechanisms of signature genes were conducted by gene knockdown in human blood-derived MDSCs, followed by mRNA and protein detection, q-ChIP-PCR and multi-colour flow cytometry. Results MDSCs were negatively correlated with CD8+ T cell proportion in ICB-resistant patients. A novel MDSC signature gene, EREG has been identified. Its expression is correlated with non-responsiveness in HCC patients. It is enriched in MDSCs of HCC patients and correlated with poor prognosis. Moreover, high EREG expression is correlated with increased tumor size and decreased tumor-infiltrating lymphocytes in ICB resistance mouse models. Mechanistically, it was found that eRNAs control the upregulation of EREG in MDSCs. Inhibition of eRNAs could reduce MDSC proliferation and T cell suppressive activity. Conclusions Our data demonstrated the intricate interaction of enhancer regulation of EREG in MDSC and ICB resistance, delineating a new epigenetic mechanism underlying tumor immune evasion. Identifying this novel enhancer-regulated target might uncover new immunosuppressive mechanism and MDSC-directed strategy for improving HCC immunotherapy efficacy.