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

Abstract

Cluster of virulence responder/sensor (CovR/S) mutant group A streptococci (GAS) are serious human pathogens of multiple M protein strains that upregulate expression of virulence factors, including the IL-8 protease Streptococcus pyogenes cell envelope proteinase (SpyCEP), thus blunting neutrophil-mediated killing and enabling ingress of bacteria from a superficial wound to deep tissue. We previously showed that a combination vaccine incorporating J8-DT (conserved peptide vaccine from the M protein) and a recombinant SpyCEP fragment protects against CovR/S mutants. To enhance the vaccine’s safety profile, we identified a minimal epitope (S2) that was the target for anti-SpyCEP Abs that could protect IL-8 from SpyCEP-mediated proteolysis. Abs from healthy humans and from mice experimentally infected with GAS also recognized S2, albeit at low titers. Native SpyCEP may be poorly immunogenic (cryptic or subdominant), and it would be to the organism’s advantage if the host did not induce a strong Ab response against it. However, S2 conjugated to diphtheria toxoid is highly immunogenic and induces Abs that recognize and neutralize SpyCEP. Hence, we describe a two-component peptide vaccine that induces Abs (anti-S2) that protect IL-8 from proteolysis and other Abs (anti-J8) that cause strain-independent killing in the presence of neutrophils. We show that either component alone is ineffectual in preventing skin infection and bacteremia due to CovR/S mutants but that the combination induces complete protection. This protection correlated with a significant influx of neutrophils to the infection site. The data strongly suggest that the lack of natural immunity to hypervirulent GAS strains in humans could be rectified by this combination vaccine.

Novel platform technology for modular mucosal vaccine that protects against streptococcus

“…Given our evidence that protection against the highly virulent CovR/S mutant GAS required the induction of antibodies capable of neutralizing two complementary virulence factors12, we developed a modular vaccine that could present more than one peptide simultaneously.…”

“…Parenteral immunization with J8-DT/alum does not protect against CovR/S mutant GAS skin infection but co-immunization with J8-DT and S2-DT co-administered with alum does protect12. We asked whether liposomes expressing both J8 and S2 would induce IgA to both peptides and mediate mucosal protection.…”

“…We previously defined two conserved vaccine peptides: J8-based on a minimal B cell epitope from the C3-repeat domain of the M protein11; and S2, from the bacterial IL-8 protease, SpyCEP12. When chemically linked to the carrier protein diphtheria toxoid (J8-DT), and administered sub-cutaneously with alum, J8 induces IgG antibodies that together with neutrophils protect mice from systemic and skin challenge with multiple GAS strains613.…”

“…When chemically linked to the carrier protein diphtheria toxoid (J8-DT), and administered sub-cutaneously with alum, J8 induces IgG antibodies that together with neutrophils protect mice from systemic and skin challenge with multiple GAS strains613. S2 is a 20-amino acid peptide from SpyCEP12. Immunization with S2-DT induces antibodies that can block the proteolytic function of SpyCEP and protect the neutrophil chemo-attractant activity of IL-8.…”

“…Immunization with S2-DT induces antibodies that can block the proteolytic function of SpyCEP and protect the neutrophil chemo-attractant activity of IL-8. The combination of J8-DT with S2-DT, administered parenterally with alum, induces IgG antibodies that can protect against skin challenge with hyper-virulent GAS organisms that have mutated their Control of Virulence Regulatory Sensor (CovR/S) and thus up-regulated SpyCEP production12.…”