Group A Streptococcus (GAS), which is a species of Gram-positive bacterium, is one of the major causes of morbidity and mortality in developing countries. In more recent years, many researchers have made efforts to create effective vaccines against GAS. Most of the vaccine studies has focused on the subunit vaccines based on M protein. However, the application of whole protein as a vaccine antigen can lead to autoimmune reactions. As a result of this, epitopes derived from M protein have been utilized as an effective and safer alternative vaccine. In our study, we have selected J8 peptide that is derived from highly conserved C-repeat region of GAS M-protein and P25 peptide as B cell and T cell epitopes, respectively. Nonetheless, these epitopes could not induce strong immune responses on their own. To overcome this drawback, these epitopes have been incorporated into nanoparticles. Lipid-based nanoparticles, especially the liposome-based structures, have received a lot of attention as potential adjuvants and carriers for vaccines due to their ability to deliver antigens to antigen-presenting cell (APC). In this work, we made an attempt to synthesize liposomal surface-associated antigens that are capable of evoking a strong immunogenicity. Therefore, for this project the peptide is attached to liposome membrane surface with the help of a lipid moiety conjugated to the peptide antigen.
Based on ESI-MS and analytical RP-HPLC, cholesteryl hemisuccinate (CH) which is considered as a lipid moiety was conjugated to five multiple antigen peptides containing J8 and P25 successfully to prepare branched and linear nano-sized lipopeptide subunit vaccines candidates against GAS using Fmoc SPPS and click reaction. Analyses on the lipopeptide-anchored liposomes, which were synthesised using film hydration method to produce unilamellar liposomes, showed that liposomal formulations had small particles size and positive charged.