High-affinity CMV-specific T cells isolated from memory response. (A) Cytolytic activity of CMV-specific T cells. T cells expressing different TCRs were isolated from the peripheral blood of CMV-seropositive persons and were tested at the effector-to-target (E/T) ratio of 10:1 against CMV-peptide–pulsed HLA-A2⁺ EBV-LCLs or pp65-transduced HLA-A2⁺ EBV-LCLs (pp65-LCL) in a 4-hour cytotoxicity assay. (B) Tetramer staining was performed with PE-conjugated CMV^A2 tetramers (black line) and control PE-conjugated HA-2^A2 tetramers (gray line) for 2 hours at 4°C on representative T-cell clones expressing 1 of the 4 different CMV-specific TCRs.