A variety of peripheral immune cells exist in the glioma microenvironment, including myeloid-derived suppressor cells (MDSCs), natural killer (NK) cells, macrophages, neutrophils, CD4+ helper T (Th) cells, CD8+ cytotoxic T lymphocytes (CTLs), and regulatory T cells (Treg) (41, 42). This evidence concerns the gene CD8A and central nervous system cancer.