CD8A and glioblastoma: Immunosuppressive cells include tumor-associated microglia and macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), and regulatory B cells (Bregs), while the anti-tumor immune cells include T cells (CD4+ helper T cells, CD8+ cytotoxic T cells) and natural killer (NK) cells, etc. Infiltration or dysfunction of these cells is one of the causes of the highly immunosuppressive and “cold” TME phenotype of the GBM (26).