Characterization of an Enhancer RNA Signature Reveals Treatment Strategies for Improving Immunotherapy Efficacy in Cancer

Abstract Non-coding RNA transcribed from active enhancers, known as enhancer RNA (eRNA), is a critical element in gene regulation with a highly specific expression pattern in the regulatory networks of tumor-infiltrating cells. Therefore, eRNA signatures could potentially be applied to represent anti-tumor immune cells and to improve cancer immunotherapy. Herein, we identified thousands of eRNAs that were significantly correlated with infiltrating immune cell abundance in more than 10,000 patient samples across a variety of cancer types. The expression of these eRNAs was mediated by transcription factors with high expression in anti-tumor immune cells, as identified through single-cell assays. An eRNA immunotherapy signature (eRIS) developed using the anti-tumor eRNAs was highly associated with the objective response rate (ORR) of immunotherapy and was elevated in patients who benefited from immune checkpoint blockade (ICB) treatment. In comparison with a signature based on protein-coding genes, the eRIS was more effective in predicting the response to immunotherapy. Integration of the eRIS with pharmacogenomic data revealed hundreds of anti-cancer drugs that have the potential to enhance immunotherapy efficacy. Finally, treatment of a mouse model of IDH mutant glioma with the histone deacetylase inhibitor vorinostat improved the effects of anti-PD-1 immunotherapy through increased abundance of infiltrating immune cells. Taken together, this study developed an eRIS with demonstrated efficacy in predicting immunotherapy response and used the eRIS to identify a series of effective combination drugs, thus highlighting the clinical utility of the eRIS in immunotherapy enhancement.