Association of donor CD4⁺ FOXP3⁺ cells with aGvHD development. Scatterplots represent T_reg fractions or absolute numbers in patients before (pre) and 30 days after transplantation (d30); SD products (SD) and donors (Don). Horizontal bars indicate the median of each group. A 2-tailed, nonparametric Mann-Whitney test was applied to examine for differences between patients with no or grade I aGvHD and patients with clinically significant (≥ grade II) aGvHD development. (A) Pretransplantation CD4⁺ FOXP3⁺ content had no impact on later aGvHD development. (B) No impact of CD4⁺ FOXP3⁺ cells in SD products. (C) No impact of CD4⁺ FOXP3⁺ cells recovered 30 days after transplantation. (D) Donor CD4⁺ FOXP3⁺ cells had significant (P = .019) impact on later aGvHD development. (E,F) The absolute number of donor CD4⁺ CD25⁺ FOXP3⁺ cells was significantly associated with later aGvHD development (P = .045) but not the absolute number of donor CD4⁺ CD25⁻ FOXP3⁺ cells.