LSel^hi Tregs optimally protect against GVHD mortality and associated weight loss. Lethally irradiated bm12 mice were infused with MHC class II–disparate B6 BM. Cohorts of mice received 1 × 10⁶ B6 CD25-depleted CD4⁺ effector T cells alone or with ex vivo activated and expanded B6 LSel^hi or LSel^lo Tregs in a ratio of 1 T to 3 Tregs. (A) Survival is indicated. A pool of 3 experiments is shown (n = 18-26 per group; ^*P < .005 compared to CD4⁺ T cells). (B) Average weight in grams of mice from one representative experiment from panel A is indicated. ^*Only one mouse survived after this time point.