Prospective enumeration of CD4⁺25^high T cells in patients after transplantation. (A) Nine patients were evaluated prospectively from time of transplantation (shown in weeks). Onset of cGVHD is denoted by the arrowhead and acute GVHD onset by the asterisk. CD4⁺CD25^high T cells were enumerated and expressed as percent of CD4⁺ lymphocytes (□) or as absolute peripheral blood counts × 10⁶/L (▪). Four patients (UPN011, UPN013, UPN017, UPN027) developed cGVHD during the course of the study. Three patients (UPN021, UPN036, UPN040) did not develop cGVHD, and one patient (UPN038) did not fulfill criteria for cGVHD but developed immune thrombocytopenia at week 44. (B) Dot plots showing CD4⁺CD25^high T-cell frequencies in patient UPN011 prior to the development of cGVHD (left, week 25), at its onset (middle, week 47) and following a subsequent response to treatment with cyclosporine and prednisolone (right, week 58). Percentages indicate CD4⁺ cells gated as CD25^high. Add-back experiments at week 47 confirmed that sorted CD4⁺CD25^high T cells retained their suppressive activity in vitro (not shown).