CD4 and neoplasm: Richard Kennedy et al. pointed out that CD4 + T memory cells can enhance anti-tumor response by enhancing clonal expansion of tumor site, preventing activation-induced cell death, and giving priority to the generation of immune memory cells by CTL as antigen presenting cells [40], which is consistent with the low infiltration level of CD4 memory resting T cells caused by high expression of P2RY6 in our study.