Host Treg are not required for persistence of BM tolerance. Sublethally irradiated DEREG or WT mice were grafted with DBA/2 BM under cover of 2.10⁶  DEREG Treg in vitro cultured in presence of (B6 × DBA/2)F1 antigen-presenting cells. Treg depletion, by diphtheria toxin (DTx) injection, was performed 1 (A), 2 (B), or 4 (C) weeks after transplantation. BM allograft survival was assessed by flow cytometry (illustrated in left panels) up to 10 weeks after grafting by analyzing the percentage of allogeneic cells in PBMC (quantitative assessment in right panels). Indicated are mean values ± SD (n ≥ 4, 4 independent experiments).