STAT-5 mediates mTOR-independent signaling upon IL-15 activation. (A) Phosphorylation of STAT-3 (n = 8) or STAT-5 (n = 7) were compared between NK cells activated with IL-2 or IL-15 in the presence or absence of torin-1. Alternatively, a selective STAT-5 inhibitor (400 μM) was added in combination with torin-1 during IL-15 activation of NK cells and (B) K562 lysis was assessed after 48 hours of activation or following an additional 24 hours of cytokine withdrawal. (C) Frequencies of CD25⁺ cells and expression intensities of CD25 on IL-15–activated NK cells. (D) Expression levels of intracellular Bcl-2 and (E) oxygen consumption and glycolytic potential were measured in NK cells cultured under described conditions. Results from multiple donors (n > 5) were summarized and presented as mean ± SD. Representative histograms were chosen based on proximity to average values. *P < .05; **P < .01; Mann-Whitney nonparametric U test. MFI, mean fluorescence intensity.