title: Synthetic peptides representing T-cell epitopes act as carriers in pneumococcal polysaccharide conjugate vaccines.
abstract: Improvement of antibody responses to polysaccharides through their linkage to proteins is thought to be mediated by protein-specific T helper (Th) cells. To investigate whether the carrier protein of a conjugate could be substituted by a Th epitope, Streptococcus pneumoniae type 17F polysaccharide (PS) was bromoacetylated and coupled to different peptides via their carboxy-terminal cysteines. Two peptides, one from the mycobacterial 65-kDa heat shock protein (hsp65) and the other from influenza virus hemagglutinin, are well-known Th epitopes. Two other peptides were selected from the pneumolysin sequence by Th epitope prediction methods; one of them was synthesized with cysteine either at the carboxy or the amino terminus. Three conjugates consistently elicited in mice anti-PS immunoglobulin M (IgM) and IgG responses that were not observed upon immunization with derivatized PS without peptide. The same conjugates induced no anti-PS antibody responses in athymic (nu/nu) mice, whereas clear responses were elicited in euthymic (nu/+) controls, demonstrating the thymus-dependent character of these conjugates. Only the three conjugates inducing anti-PS responses were capable of eliciting antipeptide antibodies. One of the immunogenic conjugates was studied in more detail. It induced significant protection and an anti-PS IgG response comprising all subclasses. On the basis of these results and proliferation studies with peptide and conjugate-primed cells, it is concluded that linkage of Th epitopes to PS in the right orientation enhances its immunogenicity in a thymus-dependent manner. Future possibilities for using peptides as carriers for inducing antibody responses to poorly immunogenic saccharide antigens are discussed.
authors.affiliation: Eijkman-Winkler Institute for Medical and Clinical Microbiology, Utrecht University, The Netherlands.
authors.forename: E A
authors.initials: EA
authors.lastname: de Velasco
authors.forename: D
authors.initials: D
authors.lastname: Merkus
authors.forename: S
authors.initials: S
authors.lastname: Anderton
authors.forename: A F
authors.initials: AF
authors.lastname: Verheul
authors.forename: E F
authors.initials: EF
authors.lastname: Lizzio
authors.forename: R
authors.initials: R
authors.lastname: Van der Zee
authors.forename: W
authors.initials: W
authors.lastname: Van Eden
authors.forename: T
authors.initials: T
authors.lastname: Hoffman
authors.forename: J
authors.initials: J
authors.lastname: Verhoef
authors.forename: H
authors.initials: H
authors.lastname: Snippe
mesh_terms: D000276:Adjuvants, Immunologic; D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis; D001428:Bacterial Vaccines / Q000276:immunology*; D000939:Epitopes / Q000276:immunology; D005260:Female; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000145:classification; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology*; D011008:Pneumococcal Infections / Q000276:immunology / Q000517:prevention & control*; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D013154:Spleen / Q000166:cytology / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D014614:Vaccines, Synthetic / Q000276:immunology*
chemical_list: D000276:Adjuvants, Immunologic; D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines; D000939:Epitopes; D007074:Immunoglobulin G; D010455:Peptides; D011135:Polysaccharides, Bacterial; D014614:Vaccines, Synthetic