Decreased frequency of circulating CD4⁺CD25⁺ T cells in patients with cGVHD. Percent CD4⁺CD25⁺ in PBLs was measured by flow cytometry in patient and donor samples. Values represent total positive cells including CD4⁺ CD25⁺_dim and CD25⁺_high cells. Box plots define the values for median, range, 25th, and 75th percentiles. One outlier with a value of 37.5% in the group of patients with cGVHD is not shown in the figure. P values were calculated using the Wilcoxon rank-sum test; cGVHD versus no cGVHD, P = .007; cGVHD versus healthy donors, P = .29; no cGVHD versus healthy donors, P < .001.