Recipient Treg cells are apparent in the spleens of lethally conditioned recipient mice 1 week post-transplant of Treg-deficient BM donors. (A) B6-wt or B6-CD4^−/− mice were conditioned with 9.0 Gy TBI and 1 day later transplanted with TCD–bone marrow cells (BMC) from B6-CD4^−/− donors. Lymph node cell CD4 T cells were assessed 1 week post-transplant. (B) Dot plots of spleen cells from 2 individual mice stained for CD4 and CD25. Numbers represent the percentage of CD4 T cells expressing CD25. Histograms represent FoxP3 staining of gated CD4⁺CD25⁺ T cells.