Administered Treg are dispensable for persistence of tolerance to BM allografts. Sublethally irradiated B6 WT mice were grafted with CBA BM coinjected with 2.10⁶  DEREG or WT Treg in vitro cultured with (CBA × B6)F1 antigen-presenting cells. Treg depletion by diphtheria toxin (DTx) injection was performed 1 (A), 2 (B), or 4 (C) weeks after transplantation. Allograft survival was followed up to 100 days. Shown is the percentage of donor cells among PBMC, as assessed by flow cytometry, mean values ± SD (n ≥ 5, 4 independent experiments).