Immunogenicity Assessment of Cell Wall Carbohydrates of Group A Streptococcus via Self-Adjuvanted Glyco-lipopeptides.

Identifying the immunogenic moieties and their precise structure of carbohydrates plays an important role for developing effective carbohydrate-based subunit vaccines. This study assessed the structure-immunogenicity relationship of carbohydrate moieties of a single repeating unit of group A carbohydrate (GAC) present on the cell wall of group A Streptococcus (GAS) using a rationally designed self-adjuvanted lipid-core peptide, instead of a carrier protein. Immunological evaluation of fully synthetic glyco-lipopeptides (particle size: 300-500 nm) revealed that construct consisting of higher rhamnose moieties (trirhamnosyl-lipopeptide) was able to induce enhanced immunogenic activity in mice, and GlcNAc moiety was not found to be an essential component of immunogenic GAC mimicked epitope. Trirhamnosyl-lipopeptide also showed 75-97% opsonic activity against four different clinical isolates of GAS and was comparable to a subunit peptide vaccine (J8-lipopeptide) which illustrated 65-96% opsonic activity.

Development of conformational mimetics of conserved Streptococcus pyogenes minimal epitope as vaccine candidates.

One of the factors responsible for the poor immunogenicity of synthetic peptide antigens is the lack of conformational integrity. Embedding the minimal epitopes in helix-promoting peptide sequences has successfully enhanced the immunogenicity of the epitopes derived from the alpha-helical regions of the M protein of group A streptococci (Streptococcus pyogenes, GAS). However, the introduction of "foreign" peptide sequences is believed to have an unfavourable impact on the antigen specificity. In the current study, we employed a non-peptide approach, using topological carbohydrate templates, to induce helical conformation of the peptide antigens. Utilized together with the advances of the lipid core peptide system and chemoselective ligation, five GAS vaccine candidates incorporating the minimal epitope J14i (ASREAKKQVEKALE) were synthesized with high purity. Circular dichroism studies indicated that the template-assembled peptides formed alpha-helix bundles. This atom-economic strategy also reduces the complexity and cost of vaccine production by simply reducing the peptide epitope size.