IDO-competent DCs induce the differentiation of adaptive regulatory T cells. Total CD4⁺ T cells or naive CD4⁺CD45RA⁺ T cells were cocultured with IDO-competent DCs (activated with LPS/IFN-γ for 48 hours) and, after termination of the MLR, were sorted by flow cytometry into a CD4⁺CD25⁻ and a CD4⁺CD25⁺ population. These separate T-cell populations were subsequently cocultured with fresh autologous T cells (1:1) which were stained with CFSE. The bars indicate the median percentage of CFSE-negative cells after 5 days of culture. indicates the percentage of CFSE-negative fresh T cells only without (left) or with anti-CD3 stimulation (right; controls); , percentage of CFSE-negative fresh T cells cocultured with CD4⁺CD25⁻ T cells retrieved from the MLR; , percentage of CFSE-negative fresh T cells cocultured with CD4⁺CD25⁺ T cells retrieved from the MLR. Error bars indicate the range of experimental results of 4 consecutively tested donor/responder pairs. P = n.s.