IDO-expressing, mature moDCs expand Foxp3⁺CD127^neg Tregs and induce Tregs from CD4⁺CD25^neg precursors in autologous culture. (A) Baseline expression of Foxp3 and CD127 by unprimed bulk CD4⁺ T cells was assessed by flow cytometry. T cells were cultured with or without the IDO inhibitor, l-1MT, and stimulated by autologous, mature moDCs for 6 days. The percentage of CD4⁺CD25⁺Foxp3⁺CD127^neg Tregs among all CD4⁺ T cells was assessed by flow cytometry at day 6. (B) Pooled data from 5 independent experiments show the percentage of CD4⁺CD25⁺Foxp3⁺CD127^neg Tregs at baseline before priming (d0) and after 6 days' stimulation by autologous, mature moDCs either without (□) or with (▩) [l-1MT (mean ± SEM, number of independent experiments, and P value indicated on graph). (C) Unprimed bulk T cells were sorted cytofluorographically to collect CD4⁺CD25^neg T cells. CD4⁺CD25⁺ T cells were assessed for their content of Foxp3⁺CD127^neg T cells at baseline (day 0) and after 6 days' stimulation by autologous moDCs either with (▤) or without (▩) l-1MT. Controls were unmanipulated bulk T cells at day 0 (■) and after 6 days' stimulation by autologous moDCs (□; mean ± SEM; number of independent experiments and P value indicated on graph). (D) Representative histograms show percentages of Ki67-positive T cells in CD4⁺CD25^low/intFoxp^neg (Non-Tregs) and CD4⁺CD25^brightFoxp⁺ (Tregs) cells from cultures without l-1MT, and in Tregs from l-1MT–treated cultures (mean ± SD; n = 2 independent experiments).