The present disclosure relates to methods for expanding and increasing the cytotoxic activity of natural killer cells comprising co-culturing, as feeder cells, a population of myeloid leukemia cells engineered to express one or more of membrane-bound IL-21 (mb IL-21) or membrane-bound IL-15 (mbIL-15) in the presence of cytokine support. The present disclosure also relates to a population of acute myeloid leukemia cells engineered to express one or more of membrane-bound IL-21 (mbIL-21) or membrane-bound IL-15 (mbIL-15). The present disclosure also relates to methods of treating cancer employing the step of expanding natural killer cells using feeder cells engineered to express one or more of membrane-bound IL-21 (mbIL-21) or membrane-bound IL-15 (mbIL-15).
