Epigenome accessibility changes before and after activation reveal distinct and progressive differentiation for human memory T cell subsets

Abstract

Abstract Memory T cells (MTC), an indispensable part of adaptive immune memory, have historically been categorized by the cell surface proteins CCR7 and CD45RA into specialized subtypes (TCM, TEM, and TEMRA), each with unique functions. However, the epigenetic characteristics that distinguish the MTC subsets as well as the gene regulatory networks governing each MTC subsets’ response to activation remain poorly understood. Here we define and categorize the transcriptional and epigenetic differences of MTC and their respective primary subsets found in human blood, both in a resting state and after ex-vivo stimulation. Resting TCM were found to be relatively more similar to naïve cells in both CD4 and CD8 lineages, while TEM exhibited greater numbers of differentially expressed genes (DEG) and alterations to chromatin accessibility. Differentially accessible regions (DAR) discerning memory subsets contained binding motifs for factors thought to regulate memory formation from the bZIP, T-box and HMG families, as well as sites for novel bHLH factors MSC and AHR that may function in MTC development. Examining the effect of stimulation on MTC gene expression and chromatin identified unique DAR and DEG modules, some of which may have initially been primed by previous activation events in naive progenitors. Primed DAR were correlated with augmented expression of important genes in MTC after stimulation, suggesting an epigenetic mechanism of regulation. Ultimately these results describe the accumulation of epigenetic alterations during primary activation and during memory development that distinguish MTC from naïve T cells, enable differentiation into distinct subsets, and influence how MTC respond to secondary activation. Supported by grants from NIH (RO1 AI113021,T32 GM0008490)