αDR3-stimulated Tregs expand over time to reduce donor T-cell activation and inflammatory cytokines after BMT. T cells were isolated from mAb-treated (αDR3 vs isotype) CD45.1⁺ C57BL/6 mice and transplanted to lethally irradiated Balb/c recipients. (A-B) Spleens were harvested from recipient mice on days 3, 7, and 14. Absolute number of donor Tregs (A) and FoxP3⁺(%) of donor CD4⁺ T cells (B) are shown (*P < .05, **P < .01, ****P < .0001). These are the combined results from 3 independent experiments (n = 15 [day 3], 18 [day 7], 14 [day 14] for isotype and n = 15 [day 3], 19 [day 7], 16 [day 14] for the αDR3 group). (C) LNs and spleen were harvested on day 7 after in vivo BrdU labeling. BrdU uptake in CD45.1⁺ FoxP3^– CD4⁺ T cells (left) and CD45.1⁺ CD8⁺ T cells (right) are shown. Representative data of 3 independent experiments are shown (n = 5 for each group; *P < .05, **P < .01, ***P < .001). (D-F) Serum levels of IFNγ (D), IL-1β (E), and TNFα (F) in recipient mice were measured on days 3, 7, and 14 by multiplex assay. Data of either group were compared by multiple Student t tests with Holm-Sidak correction (****P < .0001). These are the combined results of 7 independent experiments (n = 10 [day 3], 15 [day 7], 13 [day 14] for isotype and n = 10 [day 3], 16 [day 7], 13 [day 14] for αDR3 group; ****P < .0001).