Extra Foxp3^GFP+ Tregs infused at the time of BMT are retraceable during follow-up and remain functional. Arthritic mice were treated with 2 × 10⁶ congenic BM cells (BMT). In addition, 2 treatment groups received 250,000 or 500,000, GFP⁺ Tregs in the BM graft. Blood was analyzed 1, 3, 5, and 7 weeks after BMT. (A) Percentages of additional infused Foxp3^GFP+ Tregs (left), host TCRβ⁺CD4⁺ T cells (middle), donor TCRβ⁺CD4⁺ T cells (right). PGIA+BMT, N = 4; PGIA+BMT+250,000 Tregs, N = 5; PGIA+BMT+500,000 Tregs, N = 5. (B) Suppression assay of Tregs from PGIA+BMT-treated mice (white bar), non-GFP Tregs from mice treated with PGIA+BMT+250,000 (light gray), and Foxp3^GFP+ Tregs from mice treated with BMT+250,000 Tregs (dark gray). Tregs were added in 1:2 and 1:10 ratios to healthy effector T cells (Teff). Tregs were pooled per treatment group before adding to the effector T cells. PGIA+BMT, N = 2 mice; PGIA+BMT+250,000 Tregs, N = 3.