CD4 and neoplasm: Immune cells, such as NK cells and cytotoxic T cells, are capable of directly killing tumor cells using different mechanisms, whereas other immune cell subtypes, such as regulatory T cells (Tregs), a subtypes of CD4+ T helper cells, M2-type macrophages, tolerogenic DC, and MDSCs, inhibit adaptive immune responses to tumors, thereby promoting tumor progression and metastasis (11).