HDAC1 and neoplasm: Furthermore, in accordance with recent findings in tumor-associated T cells that genes regulating chromatin modification are coexpressed in proliferative subpopulations of T cells (34), we also observed that gene signatures associated with chromatin modification (i.e., Ezh2, Hdac2, Hdac3, Hat1, and Hdac1) were predominantly detected in cells of cluster 5 (Figure 4G), suggesting that chromatin modification–mediated epigenetic regulatory mechanisms might underlie the upregulation of proliferative markers and cell cycle–related genes during PR.