The reduced capacity of IDO-competent DCs to stimulate allogeneic T cells can be overcome by a slight modification of cell culture conditions. (A) DCs were activated with LPS/IFN-γ for 4 hours (♦) or 48 hours (■) and cocultured in graded amounts with allogeneic T cells (MLR), and their capacity to stimulate an allogeneic T-cell response was determined by [³H]thymidine incorporation. Results of 1 experiment, representative of 2 experiments, are shown. Error bars indicate the SEM. (B) DCs were activated with LPS/IFN-γ for 48 hours and were added in graded amounts to allogeneic T cells as in panel A. MLRs were set up in the presence (▩) or absence (■) of the IDO inhibitor MTHT. The allogeneic T-cell responses were determined as the percentage of CFSE-negative T cells. Results of 1 experiment, representative of 2 experiments, are shown. (C) Differently activated DCs were cocultured with the same amount of allogeneic T cells, and fresh cell culture medium was added to the cell cultures at day 4. The allogeneic T-cell responses were determined as in panel B.