NK cell cytotoxicity is most powerful against acute myeloid leukemia (AML) cells, whereas their capacity to lyse ALL cells is generally low. We have developed a novel method to expand and redirect NK cells towards CD19, a molecule highly expressed on the surface of B-lineage ALL cells but not expressed on normal cells other than B-lymphocytes. In this method, donor NK cells are first expanded by co-culture with the cell line K562-mb15-41BBL and interleukin (IL)-2. Then, the expanded NK cells are transduced with a signaling receptor that binds to CD19 (anti-CD19-BB-zeta). NK cells expressing these receptors showed powerful anti-leukemic activity against CD19+ ALL cells in vitro and in an animal model of leukemia.