Lipid Peptide Core Nanoparticles as Multivalent Vaccine Candidates against Streptococcus pyogenes Mariusz Skwarczynski, A Bibi Hamideh Parhiz, A Fatemeh Soltani, A Saranya Srinivasan, A Khairul A. Kamaruzaman, A I-Chun Lin, A and Istvan Toth A,B A The University of Queensland, School of Chemistry and Molecular Biosciences, St. Lucia, Qld 4072, Australia. B Corresponding author. Email: i.toth@uq.edu.au Traditional vaccine approaches for Group A streptococcus (GAS) infection are inadequate owing to the host’s production of cross-reactive antibodies that recognize not only the bacteria but also human tissue. To overcome this problem a peptide subunit-based vaccine was proposed, which would incorporate only minimal non-cross reactive epitopes. However, special delivery systems/adjuvants were required because short peptides are not immunogenic. In this study we have incorporated two epitopes from two different GAS proteins into a lipid core peptide (LCP) self-adjuvanting delivery system to achieve better protection against a wide range of GAS serotypes. Multivalent and monovalent constructs were synthesized with the help of an azide alkyne cycloaddition (click) reaction and their ability to self-assemble under aqueous conditions was examined. The compounds significantly differed in their ability to form small size nanoparticles, which are believed to be most appropriate for peptide-based subunit vaccine delivery. The LCP conjugates possessing two different epitopes, in contrast to monoepitopic constructs, formed small nanoparticles (5–15 nm) presumably owing to a suitable hydrophilic-hydrophobic balance of the molecules. Manuscript received: 15 July 2011. Manuscript accepted: 9 September 2011. Published online: 3 October 2011. Streptococcus pyogenes (Group A streptococcus, GAS) can cause a variety of diseases including common tonsillitis, scarlet fever, sepsis, toxic shock syndrome and necrotizing fasciitis as well as life-threatening post-infectious diseases such as rheu- matic fever and rheumatic heart disease. [1] Rheumatic fever and rheumatic heart disease are major causes of heart disease in children and are responsible for between 25 and 50 % of cardiac conditions in developing countries. The World Health Organi- zation recently reported that worldwide 18.1 million people currently suffer from a serious GAS disease and 1.78 million new cases occur each year. GAS-induced diseases are respon- sible for over 500000 deaths annually with 350000 of these being from rheumatic heart disease. [2] Vaccines are suggested to be the optimal tool for fighting and preventing GAS associated diseases. Such a vaccine is of particular significance to Aus- tralia, as the Australian aboriginal populations of the Northern Territory and northern Queensland have the highest reported incidence of rheumatic fever in the world. [2] However, tradi- tional vaccine approaches with whole pathogens or their frag- ments for GAS infection are inadequate owing to the host’s production of cross-reactive antibodies, which recognize not only the bacteria but also human tissue. [3] Streptococcus pyogenes displays streptococcal group A antigens that are also the virulence factors presented on its cell wall. These include capsular polysaccharide, peptidoglycan and lipoteichoic acid, R and T proteins, and various surface proteins, including M protein, fimbrial proteins, fibronectin-binding proteins, and cell-bound streptokinase. [4] Among them the M protein has been identified as the major virulence factor in GAS infection [5] and is the main target for vaccine development. The development of an effective vaccine for GAS has been chal- lenged by the induced autoimmunity from epitopes derived from M protein. [6,7] The minimal B-cell epitopes from the conserved region of M protein, which are believed to be safe, showed little or no immunogenicity unless bound to a delivery platform. [8] The use of toxic adjuvants to stimulate an immune response to the desired epitopes was also required. Fibronectin-binding proteins such as SfbI also play a key role in bacterial attachment to host cells, colonization and cellular invasion. The highly conserved fibronectin-binding repeat region (FNBR) of SfbI has been suggested to be the minimal protein domain required to elicit protective immunity. [9,10] We have developed a promising vaccine delivery system, lipid core peptide (LCP), which is able to induce a strong immune response to the incorporated epitopes without the help of additional adjuvant. [11,12] The lipoamino acid-based core of the LCP functions as the lipidic self-adjuvanting moiety target- ing toll-like receptor 2 on dendritic cells, [13,14] while lysine or other polyvalent linking moieties [15,16] serve as the branching moiety for epitope incorporation into the structure. Previously, we have applied J14 epitope, derived from the helical C repeat region of M protein that lacks a human heart cross-reactive T-cell epitope, to produce vaccine candidates. [17–20] This epi- tope, shown to be non-cross reactive with human tissue, [21] was CSIRO PUBLISHING Aust. J. Chem. www.publish.csiro.au/journals/ajc Ó CSIRO 2011 10.1071/CH11292 Communication RESEARCH FRONT