Istvan Toth
The University of Queensland, St Lucia, Queensland, Australia

Abstract:

Lipid-core-peptide synthetic vaccine: The fully synthetic peptide vaccine delivery system (lipid core peptide-LCP) incorporating lipidic adjuvant, a dendritic peptide or carbohydrate based carrier and antigenic peptide epitopes into a single molecular entity, has been demonstrated to induce high immune response without the need for additional adjuvants.1,2 This system however exhibits synthetic, purification, and characterisation difficulties. The purpose of this research was to develop a method for the synthesis and immunological evaluation of high molecular weight, very pure vaccine candidates. The developed system was used to synthesise a four antigenic peptide containing prophylactic lipopeptide GAS vaccine candidate using solid phase peptide synthesis and native chemical ligation.

The peptide building blocks incorporating antigens from GAS strains common to northern Australian Aboriginal populations were synthesised using stepwise solid-phase peptide synthesis. Three copies of 2-amino-D,L-dodecanoic acid were incorporated into one of the building blocks to act as an adjuvant. Thioester peptides were synthesised using a trityl-associated mercaptopropionic acid leucine linker. Peptide building blocks were ligated in phosphate buffer pH 7.5 in the presence of 2-mercaptoethanesulfonate, and tris-2-carboxyethyl phosphine hydrochloride. Due to the highly lipophilic nature of the products, 1% (w/v) sodium dodecyl sulphate was utilised to solubilise peptide starting materials and synthesised products during ligation reactions. The tetra-epitopic lipopeptide GAS vaccine candidate was synthesised in high purity (> 99%) and good overall yield (~45%). The immunological activity of the synthesised vaccine was assessed in B10.BR mice. Systemic antigen-specific IgG antibodies were elicited in response each of the three incorporated peptide antigens without the need for additional adjuvants.

Nanotechnology in vaccine delivery: Subunit vaccines containing the minimal microbial components necessary to stimulate appropriate immune responses have potential to overcome strong allergic response or autoimmunity found in classical vaccines. However, the major obstacle in development of such vaccines is very limited choice of adjuvants (immune stimulators) accepted for human use. A team from the School of Chemistry and molecular Biosciences, University of Queensland, in collaboration with the Australian Institute for Bioengineering and Nanotechnology and the Queensland Institute of Medical Research, have developed a novel antigen delivery system utilizing self-adjuvanting polymeric dendrimer (Skwarczynski, M.; Zaman, M.; Urbani, C. N.; Lin, I-C.; Jia, Z.; Batzloff, M. R.; Good, M. F.; Monteiro, M. J.; Toth, I. Angew. Chem. Int. Ed. 2010, 49, 5742-5745). Self-assembly of the dendritic structures into nanoparticles (figure) allowed proper presentation of antigen (group A streptococci B-cell epitopes) to immune system and elucidated a strong immune response, without help of external adjuvant, in mice models. It was also found that chemical conjugation of epitopes with polymer core (but not classical physical mixture) was crucial to elicit an immune response.