The S598 Q600Y epitope elicited a CTL response in the CNS of rJ.S Q600Y infected mice, with nearly 30% of all CD8 T cells recognizing the determinant ( Figure 2D ). In addition, CTL primed by S598 Q600Y cross-reacted with the native S598 determinant. The converse was not true, however, as cells primed by the native epitope failed to produce IFN-c when stimulated with S598 Q600Y peptide ( Figure 2D ). Of note, the CTL response to the dominant D b -restricted S510 epitope in rJ.S Q600Y -infected mice was diminished relative to responses in mice infected with wildtype rJ virus ( Figure 2D , E).