Synthetic β-(1→6)-Linked N-Acetylated and Nonacetylated Oligoglucosamines Used To Produce Conjugate Vaccines for Bacterial Pathogens

Vaccines for pathogens usually target strain-specific surface antigens or toxins, and rarely is there broad antigenic specificity extending across multiple species. Protective antibodies for bacteria are usually specific for surface or capsular antigens. beta-(1 -> 6)-Poly-N-acetyl-D-glucosamine (PNAG) is a surface polysaccharide produced by many pathogens, including Staphylococcus aureus, Escherichia coli, Yersinia pestis, Bordetella pertussis, Acinetobacter baumannii, and others. Protective antibodies to PNAG are elicited when a deacetylated glycoform (deacetylated PNAG [dPNAG]; <30% acetate) is used in conjugate vaccines, whereas highly acetylated PNAG does not induce such antibodies. Chemical derivation of dPNAG from native PNAG is imprecise, so we synthesized both beta-(1 -> 6)-D-glucosamine (GlcNH(2)) and beta-(1 -> 6)-D-N-acetylglucosamine (GlcNAc) oligosaccharides with linkers on the reducing termini that could be activated to produce sulfhydryl groups for conjugation to bromoacetyl groups introduced onto carrier proteins. Synthetic 5-mer GlcNH(2) (5GlcNH(2)) or 9GlcNH(2) conjugated to tetanus toxoid (TT) elicited mouse antibodies that mediated opsonic killing of multiple S. aureus strains, while the antibodies that were produced in response to 5GlcNAc-or 9GlcNAc-TT did not mediate opsonic killing. Rabbit antibodies to 9GlcNH(2)-TT bound to PNAG and dPNAG antigens, mediated killing of S. aureus and E. coli, and protected against S. aureus skin abscesses and lethal E. coli peritonitis. Chemical synthesis of a series of oligoglucosamine ligands with defined differences in N acetylation allowed us to identify a conjugate vaccine formulation that generated protective immune responses to two of the most challenging bacterial pathogens. This vaccine could potentially be used to engender protective immunity to the broad range of pathogens that produce surface PNAG.