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Anti-cancer activity can be improved by engineering immune cells to express chimeric antigen receptors (CARs) that recognize tumor-associated antigens. Retroviral vector gene transfer strategies allow stable and durable transgene expression. Here, we used alpharetroviral vectors to modify NK-92 cells, a natural killer cell line, with a third-generation CAR designed to target the IL-3 receptor subunit alpha (CD123), which is strongly expressed on the surface of acute myeloid leukemia (AML) cells. Alpharetroviral vectors also contained a transgene cassette to allow constitutive expression of human IL-15 for increased NK cell persistence in vivo. The anti-AML activity of CAR-NK-92 cells was tested via in vitro cytotoxicity assays with the CD123+ AML cell line KG-1a and in vivo in a patient-derived xenotransplantation CD123+ AML model. Unmodified NK-92 cells or NK-92 cells modified with a truncated version of the CAR that lacked the signaling domain served as controls. Alpharetroviral vector-modified NK-92 cells stably expressed the transgenes and secreted IL-15. Anti-CD123-CAR-NK-92 cells exhibited enhanced anti-AML activity in vitro and in vivo as compared to control NK-92 cells. Our data (1) shows the importance of IL-15 expression for in vivo persistence of NK-92 cells, (2) supports continued investigation of anti-CD123-CAR-NK cells to target AML, and (3) points towards potential strategies to further improve CAR-NK anti-AML activity.