Adoptive transfer of NK cells fails to control the growth of tumor targets shown to be NK-sensitive in vitro. (A) Specific lysis of chromium labeled A20 tumor cells by IL-2–stimulated C57BL/6 NK after a 4-hour incubation. Median ± error is shown. (B) Primary AML cells (C57BL/6, H-2^b) did not uptake chromium and apoptosis was detected by flow cytometric caspase activation assay after a 2-hour incubation with IL-2 stimulated Balb/c NK cells. Inset shows an example of caspase activity flow cytometry plots. Median ± error is shown. (C) Tumor burden by BLI of Balb/c mice receiving 1 × 10⁶ luciferase-expressing A20 tumor cells on day −7, followed on day 0 by TBI, BM rescue and a concurrent infusion of 0.5 × 10⁶ C57BL/6 NK cells (bottom panel) or PBS (top panel). One representative mouse from each group is shown (left), and summary statistics with n = 4 per group (right). (D) Survival of mice bearing disseminated A20 lymphoma treated with TBI and BM rescue with or without NK cells; P = .62. (E) Tumor burden by flow cytometry of BM from C57BL/6 mice 26 days after injection of 1 × 10³gfp⁺Hoxa9-Meis1 leukemia with or without 1 × 10⁶ NK cells (allogeneic FVB, H-2^q; syngeneic C57BL/6, H-2^b) after TBI and BM rescue. Gated on total live cells. (F) Survival of mice receiving allogeneic (FVB H-2^q) or syngeneic (C57BL6 H-2^b) NK cells along with Hoxa9-Meis1 leukemia; P = .93. Data are representative of at least 3 experiments with at least 4 mice per group (A,C,E), or are a composite of 2 experiments with n = 13 to 14 per group (D,F).