A method for generating or expanding a population of natural killer cells (NK cells) via using modified K562 feeder cells having expression of factors capable of increasing activation and proliferation of natural killer cells, wherein the factors capable of increasing activation and proliferation of NK cells include: (A) a co-stimulatory molecule comprises CD80 molecules, and 4-1BBL molecules; and (B) a cytokine, specifically membrane-bound IL-21 (mbIL-21).
