CD4 and central nervous system cancer: Immune responses in GBM is characterized by low peripheral lymphocyte counts, impaired mitogen-induced responses of peripheral mononuclear cells, and accumulation of CD8+ suppressor T cells and CD4+CD25+FoxP3+Treg cells, which have been reported to play a crucial role in cancer immune surveillance and defense by inducing cytotoxic cell death and inhibiting glioma cell proliferation and migration of glioma (18–20).