Survival and expansion of NK cells expressing mbIL15 in vivo. (A) Absolute number of human CD45⁺ cells in peripheral blood of mice injected with mock- or mbIL15-transduced NK cells with or without IL-2 (16 mice in total) 7 and 11 days after infusion (P = .004 with no IL-2, P = .021 with IL-2 on day 7; P = .044 and 0.026 on day 11). (B) Flow cytometric dot plots illustrate the presence of human CD45⁺, GFP⁺ NK cells in mouse peripheral blood without (top) and with IL-2 treatment (bottom) on day 11. Percentages of human CD45⁺ cells with or without GFP expression are shown. (C) Percentage of human CD45⁺ cells in various tissues of mice injected with mock- or mbIL15-transduced NK cells with or without IL-2 collected 11 days after injection. Collectively, percentages of human CD45⁺ cells were significantly higher with mbIL15 (P < .001 with no IL-2, P = .002 with IL-2).