1-7F9–induced clearance of AML cells by human NK cells in NOD-SCID mice. (A) Flow cytometric analysis of KIR and NKG2A expression by the polyclonal IL-2–activated NK-cell population that was used as effector cells in the in vitro cytotoxicity and the in vivo tumor rejection experiments shown in panels B and C, respectively. (B) □, Lysis of primary human AML cells by KIR ligand-matched NK cells, without (□) or with 1-7F9 antibody (). (The NK cells were isolated from a healthy donor having the same HLA class I allotype groups as the AML target cells.) E:T ratio was 15:1. Results were analyzed by Student t test (***P < .005). (C) NOD-SCID mice infused with autologous NK cells and AML target cells at 1:3 E:T ratio died of leukemia within 65 days. Treatment with 1-7F9 (250 μg/mouse) rescued mice challenged with NK and AML cells at an E:T ratio of 1:12, but not at an E:T of 1:18. N = 5 mice per group. Results have been analyzed by Kaplan Meier log rank test (***P < .005). Similar results were obtained in a repeat experiment.