Absence of RORγt/T-bet of donor T cells leads to augmented differentiation of T regulatory cells. Fourteen days after injection of donor TCD-BM (ly5.1⁺) with WT, T-bet^−/−, RORγt^−/−, or RORγt^−/−/T-bet^−/− T cells into lethally irradiated BALB/c mice (n = 4), recipient spleen was removed and measured for expression of CD4, CD25, Foxp3, ly5.1, and H-2K^b. (A) Expression of CD25 and Foxp3 is shown on gated donor CD4⁺ T cells (H2K ^b+ly5.1⁻). (B) Absolute number of donor Tregs (CD4⁺CD25⁺Foxp⁺) in recipient spleen. Data are shown from 1 representative experiment of 3 replicates. Asterisk indicates statistical significance: **P < .01.