Natural killer cells(NK)are important innate immune cells that do not require prior antigen exposure and can directly recognize and attack virus-infected cells and tumor cells.The activation and effector functions of NK cells are regulated by a balance of signals delivered through their surface activating receptors and inhibitory re-ceptors,which bind to ligands on target cells to achieve cytotoxicity via"induced self"and"missing self"recogni-tion models.The killing mechanisms of NK cells primarily include release of cytotoxic granules such as perforin and granzymes to induce target cell lysis,death receptor-mediated apoptosis,secretion of various cytokines,chemokines and growth factors to coordinate with other immune cells in killing tumor cells,thereby generating secondary im-mune responses and antibody-dependent cellular cytotoxicity(ADCC).