EBNA1 sequence variation influences CD8⁺ effector T-cell responses. Peptide-specific T cells from an HLA-B8 EBV-seropositive control and an HLA-B8 PTLD patient were expanded from their PBMCs using EBNA1 peptides YNLRRGIAL and YNLRRGTAL. (A) Specificity of the expanded T cells was determined using YNLRRGIAL-HLA-B*0801 or YNLRRGTAL-HLA-B*0801 allophycocyanin-labeled pentamer, PerCP-labeled anti–human CD8 monoclonal antibody and FITC-labeled anti–human CD3 monoclonal antibody. The percentage of CD8⁺ T cells is shown. (B) The YNLRRGIAL and YNLRRGTAL expanded T cells were restimulated with YNLRRGIAL and YNLRRGTAL peptides at various concentrations and assayed for IFN-γ and CD107a/b production as previously described in Figure 2. The CD107a/b results are shown for YNLRRGIAL expanded CD8⁺ T cells at various concentrations of matched peptide and YNLRRGTAL expanded CD8⁺ T cells with the highest concentration of matched peptide. (C) The YNLRRGIAL and YNLRRGTAL expanded T cells were also used in a standard 5-hour ⁵¹Cr release assay against autologous PHA blast cells that were pretreated with various concentrations of YNLRRGIAL or YNLRRGTAL peptide. Samples were tested in duplicate with less than 3% SEM and an effector/target ratio of 20:1.