CD8⁺Bim^−/−Tregs are more potent than wild-type CD8⁺Tregs for the suppression of lethal GVHD. Irradiated Balb/c mice were transplanted with 8 × 10⁶ B6.PL (Thy1.1⁺) BM together with spleen cells (adjusted to yield a dose of 0.6 × 10⁶ αβ T cells). Animals also received either 0.6 × 10⁶ in vitro-differentiated alloantigen-induced CD8⁺ Thy1.2⁺ Tregs from Foxp^EGFP (red circles, n = 10) or Bim^−/− Foxp3^EGFP (blue boxes, n = 10) mice. (A) Representative contour plots depicting the percentage of H-2K^b+ Thy1.2⁺ Tregs 10 days posttransplantation. (B) The percentage of CD8⁺ Tregs that maintained Foxp3 expression and the absolute number of CD8⁺ Foxp3⁺ T cells in the spleen, liver, lung, and colon of mice reconstituted with adoptively transferred CD8⁺ Foxp^EGFP or CD8⁺ Bim^−/− Foxp3^EGFP Tregs cells. Data are from 2 experiments. (C) Lethally irradiated Balb/c mice were transplanted with B6 BM alone (red circle, n = 12) or together with B6 spleen cells. Cohorts of animals reconstituted with B6 BM and spleen cells then received either no additional cells (blue squares, n = 20) or in vitro-differentiated alloantigen-induced CD8⁺ Tregs from B6 Foxp^EGFP (purple triangles, n = 19) or Bim^−/− Foxp3^EGFP (green triangles, n = 19) mice at a 1:1 ratio. Overall survival is depicted. Data are the cumulative results from 4 experiments. *P < .05; **P < .01; ***P < .001.