CCL5 and primary central nervous system lymphoma: Further clustering of the T cell subpopulation in PCNSL gave rise to four subpopulations with specific gene signatures, including T helper cell group (LTB, NEAT1, and IL7R), NKT cell group (DUSP1, CCL5, and JUNB), MPC cell group (UBE2C, STMN1, and BIRC5), and classical T cell group (NCL, HNRNPA3, and DUT).