CD4⁺CD25⁺Foxp3⁺ regulatory T cells prevent the propagation of GVHD mediated through the indirect alloreactive pathway. (A) Lethally irradiated Balb Rag mice (900 cGy) (n = 3) received transplants of 5-10 × 10⁶ B6 Rag BM cells. Sixty-eight days after transplantation, animals were killed, and CD11c⁺ cells were isolated from the liver and lung of recipients as described in “Cell isolation.” The percentage of donor-derived H-2K^b+ CD11c⁺ dendritic cells in each of these organs is depicted. Data are presented as the mean plus or minus 1 SD and are representative of 3 individual experiments. Actual values are 97.5 (± 0.35) for liver and 92.6 (± 1.1) for lung. (B,C) Lethally irradiated Balb/c mice received transplants of TCD B6 BM (10 × 10⁶) plus 3 × 10⁵ B6 spleen cells. At 20-22 days after transplantation, spleen cells (adjusted to yield a T-cell dose of 0.5 × 10⁶ cells) were transplanted into either B6 Rag (■) (n = 5) or B6 Rag BM→ Balb Rag chimeric mice that were 60 to 70 days after transplantation of B6 Rag BM cells (□) (n = 7). B6 Rag and B6 Rag BM→ Balb Rag mice that received spleen cells from primary GVHD animals were then killed 60 to 62 days after transplantation. Serial weight curves (B) and overall pathological score for the colon and liver (C) are depicted. Data are presented as the mean plus or minus SEM and are the cumulative results from 2 experiments. (D,E) Lethally irradiated Balb/c mice received transplants of TCD B6 BM (10 × 10⁶) plus 3 × 10⁵ B6 spleen cells. At 20 days after transplantation, spleen cells (adjusted to yield a T-cell dose of 0.5 × 10⁶ cells) were transplanted into B6 Rag BM→ Balb Rag chimeric mice alone (■) (n = 5) or together with an equivalent number of purified CD4⁺CD25⁺ B6.PL T cells (□) (n = 4). Mice were killed 85 days after transplantation. Serial weight curves (D) and overall pathological score (± SD; E) are depicted. Statistics: *P < .05.