Modulation of antigen-specific immune responses by mDC^Zol+. (A) Detection of MP-specific CD8⁺ cells by pentamer staining after 10 days of stimulation of autologous T cells with different mDC subsets (mDC^MP−Zol−, mDC^MP+Zol−, mDC^MP−Zol+, and mDC^MP+Zol+). MP-specific CD8⁺ cells are identified by APC-CD8 and pentamer–r-phycoerythrin staining after backgating on viable T cells. The highest frequency is observed after stimulation with mDC^MP+Zol+. Representative dot plots are from 1 of 2 experiments. Values in the top right quadrants represent the frequency of MP-specific CD8⁺ cells in the T lymphocyte population. (B) Cytotoxic activity exerted by T cells against T2^MP− (■) and T2^MP+ cells (□) after 2 rounds of stimulation with autologous mDC^MP−Zol−, mDC^MP+Zol−, mDC^MP−Zol+, and mDC^MP+Zol+. Bars represent the mean (± SEM) of 3 experiments and refer to an effector:target ratio of 1, 3:1. The cytotoxic activity of T cells stimulated with mDC^MP+Zol− is higher than after stimulation with mDC^MP−Zol−, indicating the generation of MP-specific cytotoxic CD8⁺ T cells. Cytotoxicity after stimulation with mDC^MP−Zol+ is not antigen-specific, because it is similar against T2^MP− and T2^MP+ cells. Cytotoxicity against T2^MP+ cells after stimulation with mDC^MP+Zol+ is significantly higher than after stimulation with mDC^MP+Zol− (P = .01), indicating that further MP-specific cytotoxicity is generated under these conditions. Cytotoxicity against T2^MP− cells, which is similar after stimulation with mDC^MP−Zol+ and mDC^MP+Zol+, represents the nonantigen-specific background mediated by γδ T cells. (C) Cytotoxic activity detected after stimulation with mDC^MP+Zol+ is partly abrogated by anti-MHC class I antibodies. T2^MP− and T2^MP+ cells were incubated with anti-MHC class I antibodies for 30 minutes before mixing with effector cells. Results are from 1 of 2 experiments. Bars represent cytotoxic values at an effector:target ratio of 1, 3:1.