Frequency of CD4⁺CD25^hi T cells. (A) Flow cytometric analysis of CD4 and CD25 on peripheral blood-derived T cells of a healthy individual and a patient with CLL. Cells were either stained with the appropriate isotype controls (left panel) or CD4 and CD25 mAbs (right panel). CD4⁺CD25⁺ T cells were divided into CD25^lo and CD25^hi cells according to previously published data.²⁵  Numbers represent percentage of events within the respective rectangle. Settings shown here were used for the analysis of all samples under study. (B) Frequency of CD4⁺CD25^hi T cells in 26 control and all 73 CLL samples. Shown here are median, 75 percentile (box), SD (whiskers), and outliers (dots) (^*P < .001, Student t test). (C) Frequency of CD8⁺CD25^hi T cells.