Skin graft survival when the donor Treg cells and allograft differ in only a single MHC class I or II alloantigen. Eight- to 12-week-old BALB/c IL-2Rβ^−/− mice that were adoptively treated with the indicated population of Treg cells at birth (denoted as the donor Treg strain→IL-2Rβ^−/− recipient strain) received BALB/c, C3H, and B6^bm3 (B6^bm3) or B6^bm12 (B6^bm12) skin grafts. (A) Tolerance to B6^bm3 skin. (B) Tolerance to B6^bm12 skin. The number of mice/group, combined from 2 independent experiments, and the MST of the allogeneic skin grafts are listed within each panel of the figure.