Infrequent occurrence of natural mutations in the pp65(495-503) epitope sequence presented by the HLA A*0201 allele among human cytomegalovirus isolates

To determine if mutations of an immunodominant HLA-restricted cytomegalovir us (CMV) peptide sequence occur in nature, the sequence corresponding to th e HLA A*0201-specific peptide CMVpp65(495-503) was determined in 50 human C MV isolates. Rare mutations were detected; 6 of 50 were silent mutations at the amino terminus of the peptide, while 3 of 50 were mutations of the nat ive methionine residue to isoleucine (M499I). The observed M499I mutation i n three isolates decreased cytolytic targeting.