Identification of HLA-A24-restricted CTL epitope encoded by the matrix protein pp65 of human cytomegalovirus.

The activation of a specific cellular immune response against human cytomegalovirus (CMV) is an important key factor to solving CMV infection after bone marrow transplantation (BMT). In the present study, our purpose was to identify the HLA-A24-restricted cytotoxic T cell (CTL) epitope from the CMV immunogenic matrix protein pp65. We selected five CMV pp65 peptides with HLA-A24 binding motif from the HLA peptide binding predictions web site. Peptide binding assay was performed using biotinylated HLA-A24-restricted MAGE-1 peptide as a reference peptide and transporter associated with antigen processing (TAP)-deficient T2-A24 cells expressing high level of HLA-A24 protein as target cells. After co-incubation of biotinylated MAGE-1 and titrated amounts of competitor peptides with T2-A24 cells, the binding of each peptide was analyzed on a flow cytometer. Peptide binding assay showed that three out of five peptides derived from CMV pp65 bound to T2-A24 cells with various affinity levels. CTL induction assay using peptide-pulsed DC derived from eight HLA-A24(+) donors revealed that the peptide (QYDPVAALF) with the highest affinity was able to elicit potent CTLs which killed peptide-pulsed TISI cells. These CTLs were found to show the killing activity against human fibroblast cells transduced with both HLA-A*2402 and CMV pp65 cDNAs, and CMV-infected HLA-A24(+) fibroblast cells. These results suggested that the peptide (QYDPVAALF) is one of HLA-A24-restricted CTL epitope derived from CMV pp65 protein and may be of therapeutic value in peptide-based vaccines against CMV infection in BMT patients.