Central tolerance in IL-2Rβ^−/− mice that were adoptively transferred with allogeneic Treg cells. Eight-week-old BALB/c^scid mice (H-2^d) received a 4:1 mixture of FACS-sorted SP CD4⁺ and CD8⁺ cells (0.5 × 10⁶ total) isolated from the thymus of WT BALB/c, BALB/c→BALB/c^−/−, or B6→BALB/c^−/− mice, the latter of which were further sorted to exclude any donor H-2^b+ cells. BALB/c^scid recipients were then transplanted with BALB/c, C3H, and B6 donor skin 2 days later. Mice were monitored up to 90 days, after which they were sacrificed to assess the presence of Treg cells. (A). Skin graft survival in BALB/c^scid recipients that received the indicated donor thymocytes. The number of mice in each group of recipients and the MST of allogeneic skin grafts are listed within each the panel. (B) Rejection score of B6 skin grafts. (C) Percentage of CD4⁺Foxp3⁺ Treg cells in the whole spleen of individual recipient mice. (D) Percentage of Treg cells within the splenic CD4⁺ T-cell subset. Staining for MHC class I^d and I^b confirmed that all CD4⁺ Foxp3⁺ T cells were of H-2^d origin. Data are 4 to 5 mice/group from a single experiment.