Infusion of splenic T cells from anti-DR3–treated donors reduces cGVHD severity. (A) Representative flow cytometry plot and a summary of 6 independent experiments indicating expansion of splenic FoxP3-GFP⁺ donor cells in the CD4⁺ population after a single dose of 0.5 mg/kg anti-DR3 antibody (4C12) 3 days before the transplantation. **P < .01. (B-C) Collagen deposition in perivascular regions of liver parenchyma (B; blue staining) and the peribronchiolar area of the lung (C; Masson’s trichrome staining, bright-field microscopy using Nikon Eclipse Ti microscope, original magnification ×200). (D) Arterial oxygen saturation (SpO₂) measured using pulse oximetry in cGVHD (iso) and cGVHD (anti-DR3) animals. *P < .05 (Mann-Whitney U test); n = 12 for cGVHD (iso) and n = 14 for cGVHD (anti-DR3). Bars represent standard error of the mean.