The helper activity of CD19^L-specific clone 21. (A) The LRH-1–specific HLA-B7–restricted CD8⁺ clone cocultured with CD19^L-negative or -positive HLA-B7/DQA1*05/B1*02 EBV-LCLs (LCLs) in the presence of its own epitope. Different dilutions of irradiated clone 21 were added in the cultures and in some conditions were supplemented with the 15-mer CD19^L peptide. The proliferation of the LRH-1–specific CD8⁺ clone after 48 h is depicted. Error bars represent the SEM of triplicate cultures. The proliferation in the presence of CD19^L-positive EBV-LCLs was significantly higher than CD19^L- negative EBV-LCLs (*, P < 0.05). (B and C) Immature DCs generated from HLA-DQ2–matched monocytes loaded with 15-mer CD19^L peptide PEIWEGEPPCLPPRD or irrelevant peptide LPPRDSLNQSLSQDL (irr.pept.; B) or with apoptotic CD19^L-negative EBV-LCLs (apCD19^Lneg-LCL) transduced with CD19^L (apCD19^Lpos-LCL; C) were cultured with clone 21 (cl.21). Apoptosis was induced by incubation of EBV-LCLs with FasL. The CD4⁺ mHag-specific T cell clone 3AB11 (irr.cl.) or CD40L-expressing fibroblasts were used as negative and positive controls, respectively. DC maturation was assessed as described in Materials and methods.