CD4 and neoplasm: PD-L1 expressed by glioma, in addition to increasing the number of T-reg cells, inhibits the functions of T lymphocytes and induces apoptosis of tumor-specific CD4+ and CD8+ T lymphocytes by decreasing the production of cytokines such as Inter-leukin-2 (IL-2) and interleukin-10 (IL-10) [78,79].