IL-2 induced decreases in proliferation of the CD4⁺/CD25⁺ subset that were strongly correlated with the expansion of this subset. (A) Representative density plot of CD4⁺ T cells at month 0 and month 12 from an IL-2 group patient, examining surface expression of CD25 and intracellular expression of Ki67. The striking increase of the CD4⁺/CD25⁺ subset at month 12 can be noted. (B) Paired data and median percent expression of Ki67 in CD4⁺/CD25⁺ T cells in the IL-2 group at month 0 and month 12. A statistically significant decrease in Ki67 expression was noted (P < .001) at month 12 compared to month 0. (C) No statistically significant changes were observed in Ki67 expression in the CD4⁺/CD25–T cells. (D) A strong association was found between the decreases in Ki67 expression of the CD4⁺/CD25⁺ T cells and the increases in the number of these cells (Spearman correlation, r = –0.9, P < .001).