IL-15 administration expands multiple subsets of NK and memory T cells. (A) Gating strategy used for the identification of NK-cell subsets. A first gate on time versus fluorescence was drawn to exclude artifacts and singlets were selected on the basis of FSC-A and FSC-H. Monocytes and dead cells were excluded by gating on CD14^–/ViViD^– cells. Within the lymphocyte gate, NK cells were defined as those negative for CD3 and CD20 and positive for either CD56 or CD16. Two major NK-cell subsets could be identified in the RM: CD56⁺CD16⁻ and CD56⁻CD16⁺ NK cells. (B) Left, dynamics of NK-cell subsets after treatment with IL-15. Data from the different dose groups were indicated as in Figure 1. Right, 1 representative example of the dynamics of NKG2D, NKG2A, NKp80, and NKp46 expression in a RM receiving the 50-μg/kg/d dose. Data relative to baseline, day 8 and day 48 after treatment are shown from the 2 identified subsets of NK cells. (C) Gating strategy used for the identification of naive and memory T-cell subsets. Monocytes and dead cells were excluded as in panel A, and T cells were further selected for CD3⁺ positivity. Within the lymphocyte gate, CD4⁺ and CD8⁺ cells were identified (CD8⁺ T cells only are shown for more clarity). For both lineages, total memory cells are defined as those expressing CD95, while CD95- (almost exclusively CD45RA bright) naive (T_N) cells are further restricted as CD28⁺ and CCR7⁺. Within the memory cell gate, central memory (T_CM) are CCR7⁺CD28⁺, transitional memory (T_TM) are CCR7^–CD28⁺, and total effectors (T_Eff) are CCR7^–CD28^– and could be then subdivided into effector memory (T_EM; not expressing CD45RA) or terminal effectors (T_TE, expressing CD45RA). (B) Dynamics of T_N and memory T-cell subset counts in the peripheral blood after treatment with IL-15. Data from the different dose groups are shown as in Figure 1. *P < .05 for Wilcoxon rank test in IL-15–treated versus sham.