Abstract: Cellular immunotherapies, new complementary therapies for tumor patients, are aimed at malignant tumors with low ability of autoimmune cells, including T cell-based chimeric antigen receptor T cell (CAR-T) therapy, tumor infiltrating lymphocytes (TILs) therapy, NK cell-based chimeric antigen receptor NK cell (CAR-NK) therapy, and autologous cell immunotherapy (CIK), as well as infusion therapies based on other immune cells such as mononuclear phagocytes like dendritic cells and macrophages. Among them, nature killer cells (NK cells), important to the body's natural immunity, matter greatly in anti-tumor, antiviral infection and immune regulation. Like T cells, it can be engineered to target tumor treatment, and can also be transfused with allogeneic NK cells, making up for the shortcomings of limited T cell source and allogeneic immune rejection. No evidence shows that patients tansfused with allogeneic NK cells may develop severe Graft Versus Host Disease (GVHD). NK cells not only expand the types of cells used in cellular immunotherapy, but also provide a broad application prospect for the formation of low-cost cellular immunotherapy products. However, there are still problems such as unstable quality of NK cells and lack of unified quality standards in the preparation process. Although some NK cell immunotherapy products have been approved by the Food and Drug Administration (FDA) or the National Medical Products Administration (NMPA), there is still no clear and publicly available standardized production system for NK cell immunotherapy products. Starting from the unique immunomodulatory mechanism of NK cells, this paper summarizes the therapeutic strategies applied by researchers in the treatment of malignant tumors in recent years and the latest progress of preclinical studies and clinical trials, and finally focuses on the research progress of in vitro expansion methods and maintenance of active function of NK cells, indicating that NK cells promise to be a unified quality of cellular immunotherapy products.

Key words: NK cells, Cell immunotherapy, Allogeneic adoptive input, In vitro amplification, CAR-NK