Introduction: Group A Streptococcus 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 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 attached to surface membrane of liposome by a lipid moiety. This work aims to examine the influence of special arrangement of cholesterol- antigen conjugates in liposomal formulation on system immunogenicity.
Methods: Synthesis of the peptide vaccine candidates containing J8 and P25 peptide epitopes was carried out by Fmoc SPPS method and cholesterol was conjugated to pure antigens at RT. Anchoring of the lipopeptides to a liposome membrane surface was performed using a film hydration method. An in vivo study was determined to evaluate the effectiveness of vaccine constructs upon intranasal immunization in mice to induce humoral immunity.
Results: Cholesterol was conjugated to four multiple antigen peptides containing B cell epitope (J8) and the T helper peptide (P25) successfully according to ESI-MS and analytical RP-HPLC. The particle sizes of synthesized liposomes were the same while the charges of particles were different. Additionally, the highest antibody titres (IgG) displayed in mice vaccinated with L4 (Ac-J8-K(CH)-P25+ liposome). Similar but slightly weaker responses were detected when mice treated with other liposome formultions.
Conclusion: There was no significant difference between the immunogenicity of lipopeptide-anchored liposomes although the positions of epitopes and lipid moieties were different.
Acknowledgements: This work was supported by the National Health and Medical Research Council of Australia (NHMRC) grant number 1132975.
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