A Synthetic M Protein Peptide Synergizes with a CXC Chemokine Protease To Induce Vaccine-Mediated Protection against Virulent Streptococcal Pyoderma and Bacteremia

Abstract

Infections caused by Streptococcus pyogenes (group A Streptococcus [GAS]) are highly prevalent in the tropics, in developing countries, and in the Indigenous populations of developed countries. These infections and their sequelae are responsible for almost 500,000 lives lost prematurely each year. A synthetic peptide vaccine (J8-DT) from the conserved region of the M protein has shown efficacy against disease that follows i.p. inoculation of bacteria. By developing a murine model for infection that closely mimics human skin infection, we show that the vaccine can protect against pyoderma and subsequent bacteremia caused by multiple GAS strains, including strains endemic in Aboriginal communities in the Northern Territory of Australia. However, the vaccine was ineffective against a hypervirulent cluster of virulence responder/sensor mutant GAS strain; this correlated with the strain’s ability to degrade CXC chemokines, thereby preventing neutrophil chemotaxis. By combining J8-DT with an inactive form of the streptococcal CXC protease, S. pyogenes cell envelope proteinase, we developed a combination vaccine that is highly effective in blocking CXC chemokine degradation and permits opsonic Abs to kill the bacteria. Mice receiving the combination vaccine were strongly protected against pyoderma and bacteremia, as evidenced by a 100–1000-fold reduction in bacterial burden following challenge. To our knowledge, a vaccine requiring Abs to target two independent virulence factors of an organism is unique.

Combinatorial Synthetic Peptide Vaccine Strategy Protects against Hypervirulent CovR/S Mutant Streptococci

“…J8-specific Abs are opsonic in the presence of neutrophils. However, J8-DT was recently shown to be ineffective against highly virulent GAS strains that have upregulated SpyCEP as a result of mutations within CovR/S (36). This lack of vaccine efficacy could be reversed by combining an inactive 553-aa recombinant fragment of SpyCEP with J8-DT.…”

“…Because J8-speciifc Abs require neutrophils for effect (36) and because CovR/S mutants upregulate SpyCEP and impede neutrophil migration to the site of sepsis (43), we tested whether the combination vaccine comprising S2-DT and J8-DT would protect against CovR/S mutant organisms. J8-DT and either S2-DT or rSpyCEP were mixed in a ratio of 1:1 or 3:1, respectively, by weight and tested in a skin challenge model (36).…”

“…34,35). J8-DT is a minimal epitope vaccine candidate based on a highly conserved sequence within the C3 repeat of the M protein that can protect mice from skin and deep tissue infections caused by multiple emm strains (36). J8-specific Abs are opsonic in the presence of neutrophils.…”

“…Inbred female BALB/c mice (4-6 wk old) were infected via the skin route of infection as previously described (36). The mice were anesthetized with an i.p.…”

“…For the J8-DT plus S2-DT combination vaccine, the immunogens were mixed in a ratio of 1:1 by weight and formulated in Alum as described previously (36). The J8-DT plus rSpyCEP combination vaccine consisted of 30 mg of the former and 10 mg of the latter immunogen, formulated in Alum.…”