Recognition of EBV antigen expressing fibroblast or LCL targets in cytotoxicity assays by EBV-specific CD8⁺T cells derived from healthy controls or XLP patients. (A) HLA-B*2705 fibroblasts (left panels) or LCLs (right panels) were infected with either vaccinia virus expressing EBNA3A or a control vaccinia Tk- construct, or were sensitized with cognate KRP-peptide or DMSO and assayed for recognition by healthy donor–derived KRP-specific clones (top panels) or XLP1 KRP-specific clones (bottom panels). (B) HLA-A*0201 fibroblasts (left panels) or LCLs (right panels) were infected with vaccinia virus expressing either BRLF1 or the control vaccinia Tk- construct, or were sensitized with cognate YVL-peptide or DMSO and assayed for recognition by healthy donor–derived YVL-specific clones (top panels) or XLP8-derived YVL-specific clones (bottom panels). Clones were incubated at the indicated effector:target ratios in 5-hour assays. The standard deviation for the replicates were all within 10% of the value measured.