Tyrosinase-Related Protein2 Peptide with Replacement of N-Terminus Residue by Cysteine Binds to H-2K and Induces Antigen-Specific Cytotoxic T Lymphocytes after Conjugation with CpG-DNA.

Recent studies have shown the potent efficacy of peptide-based vaccines for cancer immunotherapy. Immunological performance is optimized through the co-delivery of adjuvant and antigenic peptide molecules to antigen-presenting cells simultaneously. In our previous study, we showed that a conjugate consisting of 40-mer CpG-DNA and an antigenic ovalbumin peptide through disulfide bonding could efficiently induce ovalbumin-specific cytotoxic T lymphocyte (CTL) responses in vivo. In this study, based on the conjugation design, we prepared a conjugate consisting of 30-mer CpG-DNA (CpG30) and a cancer antigenic peptide of Tyrosinase-related protein 2 (TRP2) using a cysteine residue attached at the N-terminus of TRP2. However, the immunization of mice with this conjugate did not induce efficient TRP2-specific immune responses. It was thought that the resultant peptide (10-mer) cleaved from the conjugate might be too long to fit into the H-2K molecule because the optimal length for binding to it is 8-9 amino acids. We newly designed a conjugate consisting of CpG30 and the C-TRP2 peptide (9-mer), in which the N-terminal serine residue of TRP2 is replaced by a cysteine. By adjusting the peptide length, we succeeded in inducing strong TRP2 peptide-specific CTL activity upon immunization with the CpG30-C-TRP2 conjugate. Furthermore, various CpG30-C-TRP2 conjugates having other CpG-DNA sequences or cysteine analogues also induced the same level of CTL activity. Therefore, CpG-C-peptide conjugates prepared by replacement of the amino acid residue at the N-terminus with a cysteine residue could be a new and effective platform for peptide vaccines for targeting specific antigens of cancers and infectious diseases.