We tested the cytotoxic activity of NK cells against 3 leukemia target cell lines: K562 derived from a patient with chronic myelogenous leukemia and highly sensitive to NK-cell killing due to a lack of HLA and high NKG2DL expression; and the mixed-lineage leukemia (MLL)-rearranged cell lines MV-4-11 and SEM. The gene discussed is KMT2A; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.