Correlation of therapy and frequency of CD4⁺CD25^hi T cells in patients with CLL. (A) Patients treated with fludarabine less than 18 months prior to T-cell analysis (flud < 1.5a) were compared with healthy controls (control), untreated (no tx), otherwise treated patients with CLL (w/o flud) or patients with CLL treated with fludarabine more than 18 month prior to analysis (flud > 1.5a) for the frequency of CD4⁺CD25^hi T cells as assessed by multicolor flow cytometry. Shown here are median, 75 percentile (box), SD (whiskers), and outliers (dots); ^*P < .01 for flud < 1.5a versus flud > 1.5a by Student t test. (B) Serial analysis of CD4⁺CD25^hi T cells for the 3 CLL treatment subgroups at 2 different time points separated by at least 6 months.