CD56^dim CD62L⁺ (KIR⁻) NK cells partially lose CD62L expression in vivo, have intermediate telomere length and decrease with aging. (A) FACS analysis of cells recovered from the spleen of immunodeficient mice (NOD/SCID/γc^−/− mice, left and NOD/SCID, right), 7 days after transfer of human CD56^bright CD62L⁺, CD56^dim CD62L⁺ or CD56^dim CD62L⁻ cells, which have been sorted with high purity. NOD/SCIDγc^−/− mice were treated with IL-15+IL-15RαFc. Human NK cells were identified as hCD45⁺ CD3⁻ CD56⁺. Percentage of expression of CD56, CD62L, 2 + 3D KIR (indicated as KIR) and CD16 on recovered NK cells is shown in each quadrant. One representative experiment performed with both mouse strains of 3 independent experiments is shown. (B) Telomere length analysis of CD56^bright, CD56^dim CD62L⁺ KIR⁻ and CD56^dim CD62L⁻ KIR⁺ NK-cell subsets; box plots with median percentage of relative telomere length (RTL, see supplemental Methods) plus interquartile range of 9 different donors is shown in the left graph; median percentage of telomere shortening (telom short) of CD56^dim CD62L⁺ KIR⁻ or of CD56^dim CD62L⁻ KIR⁺ cells relative to CD56^bright ones is shown on the right. *P < .05; ** P < .01 as calculated by the paired Student t test. (C) Analysis of percentage of CD56^bright (r = −0.56, P = .003), CD56^dim CD62L⁺ (r = −0.44, P = .02), and CD56^dim CD62L⁻ (r = 0.56, P = .003) in correlation to age; Pearson correlation coefficient of 26 donors has been calculated.