CD8A and neoplasm: In addition, during aging, the involuted thymus generates relatively increased polyclonal tTreg cells (20), which, coupled with accumulated peripheral Treg (pTreg) cells (25, 26), may infiltrate to tumor mass and establish a microenvironment that suppresses both CD8+ and CD4+ T cell-mediated antitumor immunity, facilitating tumor cell survival (16, 27, 28).