CD4 and neoplasm: Immune cells may have opposing functions in oral oncogenesis, i.e., a class of macrophages, myeloid-derived suppressor cells, regulatory T cells and CD4+ T helper type 2 (Th2) cells may share pro-tumor functions, whereas another class of macrophages, dendritic cells, natural killer cells, CD8+ T cells and CD4+ Th1 cells may have anti-tumor actions (11).