(A) HLA A2.1 transgenic mice recognize pp65_495-503 and develop CTL that lyse EBVLCL targets which express endogenously processed HCMV pp65. Mice were immunized once with pp65_495-503 as described in the text and Materials and Methods. After five in vitro stimulations, the CTL were tested against uninfected JY cells, or infected with pp65 (pp65Vac) or wt (wtVac) vaccinia viruses. A non-HLA A2.1 EBVLCL was included as a control. The specificity of the CTL for pp65_495-503 peptide was shown in an assay using peptide-loaded T2 cells using either the pp65 or a p53 HLA A2 epitope. A standard CRA was performed using 5,000 targets at an E:T of 2 (▥) and 20 (▪). (B) HCMV-infected fibroblasts are lysed by immunized splenic effectors. MRC-5 which expresses HLA A*0201 and non-HLA A*0201 fibroblasts were infected for 16 hours with HCMV strain AD169. The infected and noninfected fibroblasts were chromated, and 2,000 were used as targets for each point in a standard CRA using peptide-stimulated murine splenic effectors as in (A). Simultaneously, the recognition of peptide-loaded and nonloaded T2 cells was evaluated using the same effector population. (▥), E:T = 2; (▪), E:T = 20.