Percent CD4⁺CD25⁺ in PBLs correlates with Treg suppressive function in cGVHD. (A) CTL reactivity against a pool of class I-restricted common viral peptides was assessed by IFNγ ELISPOT assays before and after CD25⁺ T-cell depletion using 15 samples collected from patients with cGVHD. Depletion of CD25⁺ cells was confirmed by flow cytometry for each sample. (B) Percent inhibition was measured for 15 patients with cGVHD and values are plotted together with percent CD4⁺CD25⁺. One sample generated a negative value and was interpreted as null. Correlation between the 2 variables was calculated using a rank-based Spearman test (r_s = 0.59, P = .02).