CD57⁺CD56^dimCD16⁺ NK cells proliferate less than CD57⁻CD56^dimCD16⁺ NK cells in vitro but are not more sensitive to AICD. (A) CD57⁺ and CD57⁻ sorted NK cells were CFSE-labeled and cultured in 100 IU/mL IL-2 with K562 cells expressing membrane-tethered IL-15 and 4-1BBL. Cells were analyzed by flow cytometry at different time points. Representative histograms of CFSE dilution over time (thin line represents CD57⁺; and bold line, CD57⁻; n = 7 for A, n = 3 for B). (B) Total PBMCs were activated with plate-bound antibodies (10 μg/mL) in 200 IU/mL IL-2 for 6 hours. Flow cytometry was performed, and CD56^dimCD16⁺ NK cells were gated on CD57⁺ and CD57⁻ cells. The percentages of cells expressing annexin V were determined for each subset (black bars represent CD57⁺; and white bars, CD57⁻). *P < .05. **P < .005. P values were determined between CD57⁺ NK cells and CD57⁻ NK cells (n = 5).