METHODS FOR SELECTING AND PRODUCING T CELL PEPTIDE EPITOPES AND VACCINES INCORPORATING SAID SELECTED EPITOPES

摘要

We systematically investigated proteasome-mediated generation of fourteen different well-defined CTL epitopes. Synthetic peptides (26 residues) containing known CTL-epitopes flanked by their natural amino acids have been used as substrates for the 20S proteasome in vitro. After several time intervals, peptide digests were analyzed by electrospray mass spectrometry to determine the major fragments produced by the proteasome. In 12 out of 14 peptide digests, the correct C-terminal residue of the CTL-epitope was generated by proteasomal cleavage. The N-terminal residue of the epitope was generally not exactly defined by the proteasome. In most cases, fragments with the correct C-terminal residue were elongated several amino acids at the N-terminus. For two CTL-epitopes we found that their longer precursor peptides, as generated by the proteasome, correlated with efficient TAP translocation. For one CTL-epitope we found that a natural mutation directly flanking the C-terminal residue of the CTL-epitope precursor disrupted the specific C-terminal cleavage site and resulted in a non-functional cleavage product. This study indicates that proper CTL-epitope generation requires correct C-terminal cleavage by the proteasome, and allows N-terminal elongation of CTL-epitope precursor peptides.