Stability of NK cell expansions with time. (A) Example of KIR repertoire stability in an adult with a sampling interval of 2 years. Shown is the frequency of cells expressing the indicated combination of KIRs in the NKG2A^- CD56^dim NK cell compartment. (B) Summary showing the stability of NKG2C⁺ (black) and activating KIR⁺ (red) expansions in CMV-seropositive individuals at sampling intervals ranging from 6 months to 4 years. (C,D) NK cells were labeled with CFSE, stimulated in vitro with IL-15, and cocultured with 221.AEH cells. (C) Density plots show KIR expression patterns of the indicated NK cell subsets at day 0, before proliferation. (D) Density plots show the phenotype of proliferating (CFSE-negative) and nonproliferating cells (CFSE-positive) at days 7 and 14, and their KIR expression patterns at day 7 (bottom). Results are representative of 3 independent experiments. (E) Frequency of Ki67⁺ NKG2C⁺ NK cells in peripheral blood of healthy donors. Three groups of donors were analyzed: CMV-seronegative donors (n = 46), and CMV-seropositive donors with (n = 48) and without (n = 100) expansion in the NKG2C⁺ NK cell compartment. Bars in the box and a whisker plot represent the highest and the lowest interquartiles.