CD4 and neoplasm: Within the TME, the major histocompatibility complex class II (MHC-II) pathway is a crucial regulator for immune surveillance: MHC-II genes activate CD4+ helper T cells by presenting antigens that facilitate effective immune responses (3), and the CD4+ helper T cells activate CD8+ cytotoxic T cells eliminating tumor cells through a sustained and effective memory response (4–8).