Suppressive activity of Tr cells by immature DCs. Naive CD4⁺ T cells labeled with CFSE were stimulated with mature DCs in the presence of T_(imm) or T_(mat) cells at a 1:1 ratio. (A) After 5 days of culture, the amount of proliferation was determined by flow cytometric analysis. (B) Naive CD4⁺ T cells were stimulated with immature DCs and infected with lentivirus encoding ΔLNGFR 5 days after initiation of the culture. ΔLNGFR⁺ cells were purified and restimulated with immature DCs twice. Autologous CD4⁺ T cells were labeled with CFSE and were stimulated with mature DCs in the absence or presence of a 1:1 ratio of ΔLNGFR⁺ T_(imm) cells. After 5 days of coculture, the amount of proliferation of the naive CD4⁺ T cells was determined by flow cytometric analysis. Shown are histograms gated on NGFR-negative cells. Results are representative of 2 independent experiments.