Natural killer (NK) cells are immune cells that can eliminate pathogenic microorganisms, aging cells, and tumor cells. State-of-the-art renewal has indicated the feasibility of large-scale preparation of autogenous and allogeneic NK cells from a variety of sources including peripheral blood, umbilical cord blood, placental blood, NK cell lines, and even stem cells such as pluripotent stem cells and hematopoietic stem cells. In the meantime, a range...