SYNTHETIC PEPTIDE VACCINES - PALMITOYLATION OF PEPTIDE ANTIGENS BY A THIOESTER BOND INCREASES IMMUNOGENICITY

Synthetic peptides have frequently been used to immunize animals. Howe ver, peptides less than about 20 to 30 amino acids long are poor immun ogens. In general, to increase its immunogenicity, the presentation of the peptide should be improved, and molecular weight needs to be incr eased. Many attempts have been made to couple peptide immunogens to di fferent carrier proteins [e.g. keyhole limper haemocyanin (KLH) or ova lbumin]. This leads to very complex structures, however. We used a con trolled conjugation of a peptide to a single long-chain fatty acid lik e palmitic acid by a thioester or an amide bond. It was found that the se S-palmitoylated peptides were much more immunogenic than N-palmitoy lated peptides and at least similar to KLH-conjugated peptides with re spect to appearance and magnitude of induced antibodies (canine parvov irus) or immunocastration effect (gonadotropin-releasing hormone). For chemical synthesis of thioesters, we established conditions for solut ion and solid-phase synthesis. In both phases, Cys(SBut) could only be deprotected efficiently using phosphines, and S-acylation was accompl ished using standard coupling at pH 5. We speculate that, in vivo, the presence of an appropriate fatty acid chain, chemically linked throug h a labile thioester bond, greatly enhances immunogenicity, because it represents a favourable substrate for cleavage by cellular thioestera ses in cells of the immune system. (C) Munksgaard 1997.