CD8A and neoplasm: Some studies have revealed that IL-21 may enhance the cytotoxic activity of CD8+ T cells and natural killer (NK) cells, suggesting that IL-21 functions as an antitumor agent (25, 26), while other studies have reported the immunosuppressive significance of IL-21 in promoting tumor-associated macrophage polarization and the expression of IL-10 by cytotoxic cells and B cells (12, 14, 15).