Adoptive transfer of natural Tregs attenuates cGVHD. (A) Lethally irradiated C57BL/6 recipients were transplanted with 10 × 10⁶ TCD BM cells with 3 × 10⁶ CD3⁺ T cells from BALB/c.FoxP3-DTR-GFP donor mice. (B) After transplantation, the mice were injected intraperitoneally twice a week with DT from day 7. At day 14 after BMT, freshly sorted nTregs (CD4⁺CD25⁺) from BALB/c.CD45.1⁺ mice were adoptively transferred or not in the recipients. (C) Clinical scores and survival of the recipients (n = 16-34, 6 experiments). (D) Representative images of H&E and Masson’s trichrome staining of skin samples collected at day 35 after BMT. GVHD histopathology was quantified in the skin (n = 5, 1 experiment).