The absence of DNAM-1 on donor cells promotes T_reg expansion. 5 × 10⁶ BM and 0.5 × 10⁶ CD3⁺ T cells from B6.WT or B6.DNAM-1^−/− donor mice were transplanted into lethally irradiated C3H recipients. TCD bone marrow from B6.WT donors was transplanted into irradiated C3H recipients as non-GVHD controls. (A) Serum cytokines at day 5 (n = 14 to 17 per T-cell–replete group and n = 6 in TCD control). (B) Serum cytokines at day 12 (n = 4 to 5 per T-cell–replete group and n = 3 in TCD control). (C) Total, IFN-γ⁺, and TNF⁺ donor CD4⁺ T-cell numbers (H-2D^b+CD3⁺CD4⁺) and the total donor CD8⁺ T cell numbers (H-2D^b+CD3⁺CD8⁺) at day 5 and 12 (n = 10 per group, combined from 2 replicate experiments). (D) ⁵¹Cr release assay with allogeneic (P210) and syngeneic (EL4) tumor targets at day 12. Representative data of mean with standard error of the mean (SEM) from triplicate wells are shown from 2 replicate experiments. (E) Donor FoxP3⁺ CD4⁺ T-cell numbers (Foxp3⁺H-2D^b+CD3⁺CD4⁺) at days 4, 7, and 10 after BMT (n = 3 per group at days 4 and 7; n = 9 to 10, combined from 2 replicate experiments at day 10). (F) The FoxP3⁺ cell percentage within donor CD4⁺ T cells (H-2D^b+CD3⁺CD4⁺) at day 10 after BMT (n = 13 to 14, combined from 3 replicate experiments at day 10). ***P = .0007; *P < .05 ; B6.DNAM-1^−/− vs B6.WT.