Novel CMV antigens presented to CD8⁺ CTLs by RV798-infected fibroblasts are predominantly encoded by IE and E genes. (A) Fifty-eight CTL clones that were specific for undefined CMV antigens were tested for their ability to lyse autologous fibroblasts infected for various durations with RV798. Data are shown for 2 CTL clones, clone 1-240 (▪) and clone 1-241 (▴), that exhibited a lytic pattern representative of 47 of the 58 clones and for one CTL clone, clone 2-B23 (▵), that exhibited a lytic pattern representative of the remaining 11 clones. A CTL clone specific for IE-1, clone 1-189 (□), is included as a control. (B) Presentation of novel CMV antigens by RV798-infected fibroblasts requires de novo gene expression. Forty-seven CTL clones that recognized targets as early as 2 hours after infection with RV798 were tested for their ability to lyse autologous fibroblasts either mock-infected (□), infected with RV798 for 4 hours (▦), or infected with RV798 for 4 hours in the presence of actinomycin D (▪). Representative data are shown for 3 CTL clones (clone 1-102 is pp65-specific; clone 1-240 and 1-241 are specific for unknown CMV antigens). (C) Eleven CTL clones that only recognized targets infected for longer than 8 hours were tested for their ability to lyse autologous fibroblasts either mock-infected (□) or infected with RV798 for 48 hours (▦), or infected with RV798 for 48 hours in the presence of ganciclovir (▪) at 10 μM to abrogate L gene expression. Representative data for 3 of 11 CTL clones from 3 different donors is shown at an E/T of 10:1.