It has been shown that the infusion of donor, but not recipient, CD4+CD25+ Tregs can rescue mice from lethal GVHD in an IL-10-dependent manner [47], and that donor-graft-derived, but not recipient-derived, IL-10 is critical for Treg-mediated suppression of GVHD [52]. Here, CD4 is linked to graft versus host disease.