CD4 and central nervous system cancer: A variety of peripheral immune components are present in this glioma microenvironment, including myeloid derived suppressor cells (MDSCs), natural killer cells (NK cells), macrophages, neutrophils, CD4+ helper T cells (Th), CD8+ cytotoxic T lymphocytes (CTLs), and regulatory T (T reg) cells (21, 22), while their infiltration ratio is remarkably low numbers in gliomas compared to other tumors.