IFNγ production, but not CD107a expression, is increased after CMV reactivation. PBMCs from seronegative (black bars, n = 10), seropositive (no CMV reactivation, white bars, n = 5), and seropositive (CMV reactivation, gray bars, n = 8) recipients at the indicated time points were incubated in either medium alone (not shown) or with K562 cells for 5 hours. (A) CD107a expression (left panel) and IFNγ production (right panel) was measured on NKG2C⁺ NK cells. Bars represent the means ± SEM. NKG2C⁺ cells from different groups of recipients were compared at each time point using the Student t test. *P ≤ .05. (B) NKG2C⁺ NK cells from seropositive (CMV reactivation) recipients were further gated as being KIR⁺ (black bars) or KIR⁻ (white bars) based on staining with a cocktail of Abs against CD158a/h, CD158b/j, and CD158e, and IFNγ production was measured for each subset. Bars represent the means ± SEM. KIR⁺ and KIR⁻ NK cells were compared at each time point using the paired t test. *P ≤ .05. (C) NKG2C⁺ NK cells from seropositive (CMV reactivation) recipients were further gated as being CD57⁺ (black bars) or CD57⁻ (white bars) and IFNγ production was measured for each subset. Bars represent the means ± SEM. CD57⁺ and CD57⁻ NK cells were compared at each time point using the paired t test. *P ≤ .05. (D) IFNγ, T-bet, and IL-15Rα mRNA expression were measured on resting PBMCs at 6 months and 1 year after HCT. Samples were normalized to 18S RNA. Bars represent the means ± SEM. Recipients who reactivated CMV and those who did not were compared at each time point using the t test. *P ≤ .05, **P < .01, and ***P < .001.