Streptococcus pyogenes, also known as group A streptococcus (GAS), is an aerotolerant gram-positive bacterium responsible for numerous human diseases and pathogenesis [1]. It infects over 750 million people and kills 500 thousand people every year [2]. Thus, there is an urgent need for development of an efficient vaccine against GAS infection. Several peptide-based vaccines against GAS reached clinical trials but they fail to deliver broadly effective protection. In general, such vaccines lack of the danger signals (such as pathogen associated molecular pattern) required to trigger immune response and therefore need the help of an adjuvant [3]. Poly hydrophobic amino acids (polyHAAs) made from natural amino acids are fully defined and biodegrade polymers. PolyHAAs were conjugated to hydrophilic peptide antigen derived from GAS M protein and self-assembled into nanoparticles. These nanoparticles induced strong immune responses after subcutaneous delivery.
This project aims to develop an intranasal delivery system for peptide-based vaccine against GAS. Peptides with different spatial arrangements of B cell epitope (J8), T cell epitope (P25) and 15 copies of leucine were synthesized by Boc and Fmoc based solid phase peptide synthesis. All the compounds were purified by HPLC and characterized by mass spectrometry. The conjugates were self-assembled into nanoparticles and/or anchor into liposomes and then examined by dynamic light scattering (DLS), circular dichroism spectrometry (CD) and transmission electron microscopy (TEM). Liner and branch compounds showed promising α helical structures and desired small size (~ 160 nm) once formulated into liposomes. The mice were immunized with self-assembled compounds or liposomes through intranasal route. The conjugate bearing polyleucine sequence on N terminus and epitope J8 on C terminus induced the highest antibody titers when formulated into liposomes.