Treg T cells in the spleens of mice after reduced-intensity and high- intensity TBI. B6-wt (CD45.2) recipient mice were conditioned with various doses of irradiation ranging from 3.0 to 14.0 Gy. With the exception of the 3.0 Gy (single dose), conditioning was delivered using 2 equivalent split doses beginning on day −1 with an overnight rest between doses. On day 0, conditioned mice were transplanted with 5 × 10⁶ TCD-BM from B6-CD45.1 donors. Spleen cells from transplanted animals were analyzed 16 (A) and 35 (B) days post-HCT to determine the numbers of donor versus host CD4⁺CD25⁺Foxp3⁺ present. Results represent staining from pools of 4 mice per group.