Send Orders of Reprints at reprints@benthamscience.net Current Drug Delivery, 2013, 10, 39-45 39 M-Protein-derived Conformational Peptide Epitope Vaccine Candidate against Group A Streptococcus Mariusz Skwarczynski 1 , Khairul A. Kamaruzaman 1 , Saranya Srinivasan 1 , Mehfuz Zaman 1 , I-Chun Lin 1 , Michael R. Batzloff 2 , Michael F. Good 2 and Istvan Toth 1,3* 1 The University of Queensland, School of Chemistry and Molecular Biosciences, St. Lucia, Qld 4072, Australia; 2 Institute for Glycomics, Griffith University, Southport Qld 4215, Australia; 3 The University of Queensland, School of Pharmacy, Woolloongabba, Qld 4102, Australia Abstract: Identification of the most relevant epitopes is the initial challenge of peptide-based vaccine design. Chimeric conserved epitopes of the Group A Streptococcus (GAS) M-protein were used in the development of an anti-GAS vaccine candidate. Previously, these epitopes have incorporated a GCN4 peptide from yeast to maintain their native helical structure. Here, we designed a new peptide epitope based on the minimal B-cell epitope from GAS M-protein. This new epitope was able to adopt the desired helical conformation without the need for the foreign GCN4 flanking sequence. The selected epitope induced significant immune responses upon administration with external adjuvant, and when incorporated into the Lipid Core Peptide (LCP) system. Moreover, the antibodies produced against this epitope were able to recognize the native p145 sequence from M-protein. Keywords: lipid core peptide, adjuvant, Group A streptococcus, B-cell epitope, self-assembly, conformational epitope, peptide vaccine. INTRODUCTION Streptococcus pyogenes (Group A streptococcus, GAS) is a gram-positive bacterium that causes the widest range of disease in humans of all bacterial pathogens [1]. GAS-derived diseases range from pharyngitis and pharyngotonsillitis, scarlet fever, sepsis and streptococcal toxic shock syndrome to life- threatening post-infectious sequelae such as rheumatic fever and rheumatic heart disease [2]. GAS causes over 600 million human infections annually and rheumatic fever is known as the leading cause of childhood heart disease with more than 80 cases per 10 000 children in some developing countries [3]. In 2010, it was estimated that around 70 million individuals worldwide had RHD, which would result in 1.4 million deaths per year from RHD and its associated complications [4]. The high disease burden, need for a pre- emptive treatment against GAS infections and subsequent prevention of post-infection diseases, in addition to the economic cost of treatment, emphasize a serious need for the development of a vaccine against GAS. However, the whole organism or even the coil-coiled cell surface M-protein alone (which is the major virulent factor in GAS infection) cannot be used in vaccine formulation due to autoimmune responses elicited against this protein [5]. Although the antisera against M-protein is opsonic, thus protective, the presence of more than 200 different M-protein (emm) genes creates an additional obstacle to the development of a vaccine with broad *Address correspondence to this author at the School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, Australia, 4072; Tel: + 61 7 33469892; Fax: +61 7 33654273; E-mail: i.toth@uq.edu.au strain coverage [6]. Unfortunately, most of the opsonic antibodies are produced against the hyper variable N-terminal region of the M-protein. To overcome these problems, epitopes derived from conserved C-terminal region of the M-protein were investigated for the development of a vaccine [7-9]. In our previous work, a 20-mer epitope, p145 (LRRDLDASREAKKQVEKALE), was identified in the - helical C-terminal region of M-protein. When administered with an adjuvant or incorporated in a lipid core peptide system (LCP) [10-12], p145 elicited a protective antibody response in a murine model [13]. However, human T-cells specific to p145 were cross-reactive with human heart tissue [14]. The minimal B-cell epitopes derived from p145 were investigated but showed poor immunogenicity [15]. It was suggested that this loss of potency is associated with the loss of the helical conformation of the native epitope. To overcome this obstacle, the minimal epitope was embedded into helix-promoting sequences from the yeast GCN4 protein [15] that returned the native conformational structure [16]. The minimal epitope J14i (ASREAKKQVEKALE), derived from the p145 peptide and flanked with  -helix promoting sequences from yeast protein GCN4 (J14, KQAEDKVK-ASREAKKQVEKALE-QLEDKVK) resulted in J14, which was unlikely to induce cross-reactive immune responses and was protective against GAS infection in a mouse model challenge [17-19]. However, the introduction of non-epitope-derived peptide sequences may have an unfavourable effect on antigen specificity because part of the immune response is expected to be directed against the foreign GCN4 epitopes. To overcome the possibility of GCN4-directed immune responses, two copies of the J14i 1875-5704/13 $58.00+.00 © 2013 Bentham Science Publishers