TNF and cancer: Besides, NK cells have the advantage to turn the mentioned “cold TME” into “hot” one as follows: (1) the infused NK cells reach the tumor site and directly lyse cancer cells; (2) NK cells secrete inflammatory cytokines such as interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), to recruit CD8+ T cells and promote its cytotoxicity; and (3) NK cells recruit dendritic cells (DCs) at tumor sites through the release of cytokines and chemokines [9, 10], which can present tumor antigens and prime CD8+ T cells.