CTL recognition of EBV-transformed LCLs by gB-specific CTL clones in the presence or absence of peptide epitope DYSNTHSTRYV. Data from 2 different clones isolated from HLA-DR7⁺, DR4^- (CTL OB12.3) and HLA-DR7⁺, DR4⁺ (CTL OB12.16) individuals are presented in panels A and B, respectively. An effector-to-target ratio of 5:1 was used for both assays. These data are representative of 5 different experiments based on 4 different CTL clones. (C) Split-well analysis of CTL microcultures generated in limiting dilution analysis. Each point on the graph indicates the level of lysis for each CTL microculture of 2 target populations: HLA-DR4⁺ LCLs (y-axis) and DAP-DR7 cells, which express HLA-DR7, preincubated with peptide DYSNTHSTRYV (x-axis). DAP DR7 cells were also used as targets without peptide presensitization (data not shown); CTL microcultures lysed less than 5% of DAP DR7 targets without peptide presensitization. CTL microcultures from 2 different donors (donor 1, HLA-DR7⁺, DR4^-; donor 2, HLA-DR7⁺, DR4⁺) were tested in these assays. Representative data from 24 replicates with 5 × 10⁴ cells/well are presented. ^*P < .0001.