CD4 and cytomegalovirus infection: In addition, striking examples of the increased specificity of the CD8+ repertoire can be observed in responses to latent cytomegalovirus infection, where specific CD8+ cells often represent 10-20% of all CD8+ cells by peptide-MHC tetramer analysis, whereas CD4+ responses are more diverse and rarely comprise more than 1% of CD4+ cells [19–22].