Epigenetic regulation of T cells by Polycomb group proteins.

T cells are critical for pathogen elimination, tumor surveillance, and immunoregulation. The development, activation, and differentiation of CD8 and CD4 T lymphocytes are a set of complex and dynamically regulated events that require epigenetic control. The Polycomb group (PcG) proteins are a family of diverse and evolutionarily conserved epigenetic modulators fundamentally involved in several mechanisms of gene regulation. PcG proteins can assemble into distinct repressor complexes, the two most understood being the Polycomb Repressor Complex (PRC)1 and PRC2, which control chromatin structure mainly through posttranslational modifications of histones. In this review, we will summarize the most recent findings regarding the diverse roles performed by PcG proteins in T cell biology. We will focus on PRC1 and PRC2 contribution to the regulation of T cell development in the thymus, CD4 T cell differentiation in helper or regulatory phenotypes and CD8 T cell fate commitment in the context of infections and cancer, highlighting the known mechanisms and knowledge gaps that still need to be addressed.