Proof of concept for a single-dose Group B Streptococcus vaccine based on capsular polysaccharide conjugated to Qß virus-like particles.

A maternal vaccine to protect neonates against Group B Streptococcus invasive infection is an unmet medical need. Such a vaccine should ideally be offered during the third trimester of pregnancy and induce strong immune responses after a single dose to maximize the time for placental transfer of protective antibodies. A key target antigen is the capsular polysaccharide, an anti-phagocytic virulence factor that elicits protective antibodies when conjugated to carrier proteins. The most prevalent polysaccharide serotypes conjugated to tetanus or diphtheria toxoids have been tested in humans as monovalent and multivalent formulations, showing excellent safety profiles and immunogenicity. However, responses were suboptimal in unprimed individuals after a single shot, the ideal schedule for vaccination during the third trimester of pregnancy. In the present study, we obtained and optimized self-assembling virus-like particles conjugated to Group B Streptococcus capsular polysaccharides. The resulting glyco-nanoparticles elicited strong immune responses in mice already after one immunization, providing pre-clinical proof of concept for a single-dose vaccine.

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated.

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10(2) µM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10(2) µM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro.

Investigating the immunodominance of carbohydrate antigens in a bivalent unimolecular glycoconjugate vaccine against serogroup A and C meningococcal disease.

Multicomponent constructs, obtained by coupling different glycans to the carrier protein, have been proposed as a way to co-deliver multiple surface carbohydrates targeting different strains of one pathogen and reduce the number of biomolecules in the formulation of multivalent vaccines. To assess the feasibility of this approach for anti-microbial vaccines and investigate the potential immunodominance of one carbohydrate antigen over the others in these constructs, we designed a bivalent unimolecular vaccine against serogroup A (MenA) and C (MenC) meningococci, with the two different oligomers conjugated to same molecule of carrier protein (CRM197). The immune response elicited in mice by the bivalent MenAC construct was compared with the ones induced by the monovalent MenA and MenC vaccines and their combinations. After the second dose, the bivalent construct induced good levels of anti-MenA and anti-MenC antibodies with respect to the controls. However, the murine sera from the MenAC construct exhibited good anti-MenC bactericidal activity, and very low anti-MenA functionality when compared to the monovalent controls. This result was explained with the diverse relative avidities against MenA and MenC polysaccharides, which were measured in the generated sera. The immunodominant effect of the MenC antigen was fully overcome following the third immunization, when sera endowed with higher avidity and excellent bactericidal activity against both MenA and MenC expressing strains were elicited. Construction of multicomponent glycoconjugate vaccines against microbial pathogens is a feasible approach, but particular attention should be devoted to study and overcome possible occurrence of immune interference among the carbohydrates.

Immunoactivity of protein conjugates of carba analogues from Neisseria meningitidis a capsular polysaccharide.

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that is a major cause of epidemic meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of a liquid glycoconjugate vaccine against MenA are hampered by the poor hydrolytic stability of its capsular polysaccharide (CPS), consisting of (1→6)-linked 2-acetamido-2-deoxy-α-d-mannopyranosyl phosphate repeating units. The replacement of the ring oxygen with a methylene group to generate a carbocyclic analogue leads to enhancement of its chemical stability. Herein, we report conjugation of carbocyclic analogue monomer, dimer, and trimer to the protein carrier CRM197. After immunization in mice, only the conjugated trimer was able to induce specific anti-MenA polysaccharide IgG antibodies with in vitro bactericidal activity, although to a lesser extent than pentadecamer and hexamer oligomers obtained from mild acid hydrolysis of the native polysaccharide conjugated to the same protein carrier. This study represents the first proof-of-concept that hydrolytically stable structural analogues of saccharide antigens can be used for the development of efficacious antimicrobial preventative therapies. Conjugates with longer carbocyclic oligomers and/or precise acetylation patterns could further increase the induced immune response to a level comparable with those of commercially available anti-meningococcal glycoconjugate vaccines.

Synthesis of Staphylococcus aureus type 5 capsular polysaccharide repeating unit using novel L-FucNAc and D-FucNAc synthons and immunochemical evaluation.

Staphylococcus aureus is a major cause of nosocomial infections. Glycoconjugates of type 5 and 8 capsular polysaccharides have been investigated for vaccine application. The proposed structure of type 5 polysaccharide is: →4-ß-D-ManNAcA-(1→4)-α-L-FucNAc(3OAc)-(1→3)-ß-D-FucNAc-(1→. The stereocontrolled insertion of these three glycosydic bonds is a real synthetic challenge. In the present paper we report the preparation of two novel versatile L- and D-fucosamine synthons from commercially available starting materials. In addition we applied the two building blocks to the synthesis of type 5 trisaccharide repeating unit. The immunochemical properties of the synthesized trisaccharide were assessed by competitive ELISA and by immunodot blot analysis using sera of mice immunized with type 5 polysaccharide conjugated to CRM(197). The results suggest that although the type 5 S. aureus trisaccharide is recognized by specific anti polysaccharide antibodies in dot blot, structures longer than the trisaccharide may be needed in order to significantly compete with the native type 5 polymer in the binding with sera from mice immunized with S. aureus type 5 polysaccharide-CRM(197) conjugate.