Date Published: March 29, 2017
Publisher: Public Library of Science
Author(s): Chih-Feng Kuo, Nina Tsao, I-Chen Hsieh, Yee-Shin Lin, Jiunn-Jong Wu, Yu-Ting Hung, Paulo Lee Ho.
Streptococcus pyogenes (group A Streptococcus; GAS) causes clinical diseases, including pharyngitis, scarlet fever, impetigo, necrotizing fasciitis and streptococcal toxic shock syndrome. A number of group A streptococcus vaccine candidates have been developed, but only one 26-valent recombinant M protein vaccine has entered clinical trials. Differing from the design of a 26-valent recombinant M protein vaccine, we provide here a vaccination using the polyvalence epitope recombinant FSBM protein (rFSBM), which contains four different epitopes, including the fibronectin-binding repeats domain of streptococcal fibronectin binding protein Sfb1, the C-terminal immunogenic segment of streptolysin S, the C3-binding motif of streptococcal pyrogenic exotoxin B, and the C-terminal conserved segment of M protein. Vaccination with the rFSBM protein successfully prevented mortality and skin lesions caused by several emm strains of GAS infection. Anti-FSBM antibodies collected from the rFSBM-immunized mice were able to opsonize at least six emm strains and can neutralize the hemolytic activity of streptolysin S. Furthermore, the internalization of GAS into nonphagocytic cells is also reduced by anti-FSBM serum. These findings suggest that rFSBM can be applied as a vaccine candidate to prevent different emm strains of GAS infection.
Group A streptococcus (GAS) is an important human pathogen, and it causes a variety of diseases ranging from noninvasive pharyngitis to invasive diseases, such as necrotizing fasciitis, sepsis, and streptococcal toxic shock syndrome. GAS also causes nonsuppurative complications, including acute glomerulonephritis and rheumatic fever. The number of clinical invasive GAS cases has increased worldwide over the past twenty years [1–6]. The burden of GAS invasive diseases was estimated in developed countries as 17.8 million new cases per year, and at least 517,000 deaths per year caused by severe GAS infection and its severe complications have been reported . Although several vaccine candidates against GAS infection have been developed, only one 26-valent recombinant M protein vaccine has achieved success in a class II clinical trial [7–9]. M protein is encoded by the emm gene and more than 220 emm types have been reported . The most prevalent emm genotypes associated with invasive GAS infection are emm1, emm3, emm4, emm6, emm12, emm28, and emm89 in Canada, the United States, and European countries [1–3, 5]. In contrast, a higher diversity of emm types has been found in Africa and Pacific regions [4, 6]. In Taiwan, the leading emm types of GAS isolated from invasive infection are emm1, emm4, emm11, emm12, and emm102 [11, 12]. M protein consists of an N-terminal variable domain and a conserved C-terminal domain. Expression of M protein on the bacterial surface is important for GAS virulence, as this mediates the adhesion and internalization of GAS into host cells [13–16]. The N-terminal domain of M protein can bind to serum complement regulator C4b-binding protein (C4BP), which helps GAS avoid phagocytic killing by interfering with host complement activation . The 26-valent recombinant M protein vaccine is designed to induce antibodies that target the N-terminal sequences of the most common emm types of GAS in developed countries [7–9]. Furthermore, a synthetic peptide-based vaccine that targets the conserved C-terminal domain of M proteins also achieved protective immunity against different emm types of GAS infection [18, 19]. However, the repeat immunization of recombinant M5 protein, which contains the N-terminal and C-terminal domains, induces autoimmune response against cardiac tissues and causes rheumatic heart disease .
Our previous report found that a combinative vaccination of synthetic peptides derived from the C-terminal epitope of streptolysin S and the C3-binding motif of SPE B can elicit a specific immune response against GAS infection. Although a recombinant M protein vaccine against the N-terminal variable residues of 26 different serotypes of GAS has entered clinical trials, it did not target other virulence factors of GAS. In this study, we synthesized, expressed, and purified a recombinant FSBM protein that contained a C-terminal conserved segment of M protein, the FnBR domain of Sfb1, the C3-binding motif of SPE B, and an immunogenic domain of SLS. The immunization of the recombinant FSBM protein successfully induced antibodies against SPE B and SLS (Fig 3A and 3B).