Congenic BMT for arthritis renews the Treg compartment with donor-derived Tregs. Host T cells (black bar, CD90.2⁺) were distinguished from donor T cells (white bar, CD90.1⁺) using a different congenic marker. After transplantation, thymus, spleen, and LNs were analyzed at weeks 1, 3, and 7 for the presence of host and donor Tregs (TCRβ⁺CD4⁺CD25⁺Foxp3⁺). Results shown are from 2 combined experiments. (A) Percentage of host and donor Tregs. Thymus: 1 week, N = 3; 3 weeks, N = 6; and 7 weeks, N = 8. Spleen: 1 week, N = 2; 3 weeks, N = 6; and 7 weeks, N = 8. LN: 3 weeks, N = 6; and 7 weeks, N = 8. (B) Host and donor Treg distribution in synovial fluid 7 weeks post-BMT (N = 2). All results shown are in percentages (±SEM values). N.D., not determined due to lack of cells.