Ability of naive T cells to break skin graft tolerance of IL-2Rβ^−/− mice that were adoptively transferred with allogeneic Treg cells. Eight-week-old Rag2^−/−/γc^−/− mice (H-2^b) received 7 × 10⁶ unfractionated spleen (SP) cells isolated from BALB/c→B6^−/− mice along with the indicated numbers of unfractionated (A-B) or CD25-depleted (C) naive T cells isolated from IL-2Rβ^−/− (A) or WT CD45.1 B6 congenic (B-C) mice. The naive T cells were from autoimmune-free IL-2Rβ^−/− mice due to the transfer of syngeneic Treg cells at birth. Rag2^−/−/γc^−/− recipients were then transplanted with BALB/c, C3H, and B6 skin 2 days later. The number of mice in each group of recipients, combined from 2 independent experiments, and the MST of skin grafts are listed within each the panel.