Structure-Activity Analysis of Cyclic Multicomponent Lipopeptide Self-Adjuvanting Vaccine Candidates Presenting Group A Streptococcus Antigens.

Group A Streptococcus (GAS) infection causes a range of life-threatening diseases, including rheumatic heart disease. Cyclic peptides offer an attractive solution for presentation of short peptide antigens due to their stability and structurally constrained conformation. We investigated a cyclic carrier decapeptide incorporating a B cell GAS peptide epitope, a universal T helper epitope, and a synthetic toll-like receptor 2-targeting moiety as a possible self-adjuvanting GAS vaccine. A structure-activity relationship of the cyclic lipopeptide vaccine showed successful induction of J8-specific systemic immunoglobulin G (IgG) antibodies when administered subcutaneously without an additional adjuvant. Interestingly, the physical mixture control induced the highest titers of all vaccine compounds, with antibodies from mice immunized with this physical mixture control shown to effectively opsonize multiple strains of clinically isolated GAS bacteria. This study showed the capability for a self-adjuvanting cyclic delivery system to act as a vehicle for the delivery of GAS peptide antigens to treat GAS infections.