Integrative analysis of scRNAs-seq and scATAC-seq revealed transit-amplifying thymic epithelial cells expressing autoimmune regulator

Medullary thymic epithelial cells (mTECs) are critical for self-tolerance induction in T cells via promiscuous expression of tissue-specific antigens (TSAs), which are controlled by transcriptional regulator AIRE. Whereas AIRE-expressing (Aire ⁺ ) mTECs undergo constant turnover in the adult thymus, mechanisms underlying differentiation of postnatal mTECs remain to be discovered. Integrative analysis of single-cell assays for transposase accessible chromatin (scATAC-seq) and single-cell RNA sequencing (scRNA-seq) suggested the presence of proliferating mTECs with a specific chromatin structure, which express high levels of Aire and co-stimulatory molecules CD80 (Aire ⁺ CD80 ^hi ). Proliferating Aire ⁺ CD80 ^hi mTECs detected by using Fucci technology express a minimal level of Aire-dependent TSAs and are converted into quiescent Aire ⁺ CD80 ^hi mTECs expressing high levels of TSAs after a transit amplification. These data provide evidence for the existence of transit amplifying Aire ⁺ mTEC precursors during Aire ⁺ mTEC differentiation process of the postnatal thymus.