Increased absolute numbers of CD4⁺CD25⁺ and CD8⁺CD25⁺ T cells are present in PBSC grafts of SCT patients with GVHD. Increased absolute numbers of CD4⁺CD25⁺ and CD8⁺CD25⁺ T cells were present in donor PBSC grafts of recipients who experienced GVHD (•) compared with those who did not (○). Values were calculated using actual infused cell doses of CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells and quantitation of CD25 expression on donor graft T cells as assessed by flow cytometry. All P values were obtained using the Mann-Whitney U test.