Opsonic human antibodies from an endemic population specific for a conserved epitope on the M protein of group A streptococci

Disruption of IL-17-mediated immunosurveillance in the respiratory mucosa results in invasive Streptococcus pyogenes infection

Introduction

Streptococcus pyogenes is a Gram-positive pathogen that causes a significant global burden of skin pyoderma and pharyngitis. In some cases, infection can lead to severe invasive streptococcal diseases. Previous studies have shown that IL-17 deficiency in mice (IL-17-/-) can reduce S. pyogenes clearance from the mucosal surfaces. However, the effect of IL-17 on the development of severe invasive streptococcal disease has not yet been assessed.

Methods

Here, we modeled single or repeated non-lethal intranasal (IN) S. pyogenes M1 strain infections in immunocompetent and IL-17-/- mice to assess bacterial colonization following a final IN or skin challenge.

Results

Immunocompetent mice that received a single S. pyogenes infection showed long-lasting immunity to subsequent IN infection, and no bacteria were detected in the lymph nodes or spleens. However, in the absence of IL-17, a single IN infection resulted in dissemination of S. pyogenes to the lymphoid organs, which was accentuated by repeated IN infections. In contrast to what was observed in the respiratory mucosa, skin immunity did not correlate with the systemic levels of IL-17. Instead, it was found to be associated with the activation of germinal center responses and accumulation of neutrophils in the spleen.

Discussion

Our results demonstrated that IL-17 plays a critical role in preventing invasive disease following S. pyogenes infection of the respiratory tract.

Hiding in plain sight: an epitope-based strategy for a subunit malaria vaccine

Recent data suggest that approaches to developing a subunit blood-stage malaria vaccine may be misdirected. While antigenic polymorphism is recognized as a challenge, efforts to counter this have primarily involved enhancing the quantity and quality of antibody with potent adjuvants, identifying conserved target proteins, or combining multiple antigens to broaden the immune response. However, paradoxically, evidence has emerged that narrowing, rather than broadening, the immune response may be required to obtain an immune response protective against multiple Plasmodium strains. Non-immunodominant, conserved epitopes are crucial. The evidence comes from studying the immune response to red cell surface-expressed antigens but should also be applicable to merozoite surface antigens. Strategies to define the targets of these highly focused immune responses are provided.

Streptococcus pyogenes vaccine candidates do not induce autoimmune responses in a rheumatic heart disease model

We have developed a candidate vaccine to protect against multiple strains of Streptococcus pyogenes infections. The candidate vaccine contains two synthetic peptides derived from S. pyogenes proteins: the M-protein epitope, p*17 and the IL-8 degrading S. pyogenes Cell-Envelope Proteinase (SpyCEP) epitope, K4S2. In this study we utilise a rat autoimmune valvulitis model that displays both the cardiac and neurobehavioural pathology associated with post-streptococcal sequelae, to assess if the vaccine candidate antigens induce autoimmune complications and inflammatory pathology. Each antigen was conjugated to carrier protein diphtheria toxoid (DT) and independently assessed for potential to induce autoimmune pathology in female Lewis rats. Rats were administered three subcutaneous doses, and one intranasal dose over a four-week study with a two-week recovery period. A positive control group received recombinant S. pyogenes M5 (rM5) protein, and the negative control group received PBS. Rats that received rM5 developed significant cardiac and neurological pathologies. There was no evidence of these pathologies in the PBS control group, or the rats administered either P*17-DT or K4S2-DT. This study provides further preclinical evidence of the safety of the vaccine candidates p*17 and K4S2 and their appropriateness as candidates in human clinical trials.

Preclinical safety and immunogenicity of Streptococcus pyogenes (Strep A) peptide vaccines

We have developed two candidate vaccines to protect against multiple strains of Strep A infections. The candidates are combinatorial synthetic peptide vaccines composed of a M protein epitope (J8 or p*17) and a non-M protein epitope (K4S2). To enhance immunogenicity, each peptide is conjugated to the carrier protein CRM₁₉₇ (CRM) and formulated with aluminium hydroxide adjuvant Alhydrogel (Alum) to make the final vaccines, J8-CRM + K4S2-CRM/Alum and p*17-CRM + K4S2-CRM/Alum. The safety and toxicity of each vaccine was assessed. Sprague Dawley rats were administered three intramuscular doses, over a six-week study with a 4-week recovery period. A control group received CRM only formulated with Alum (CRM/Alum). There was no evidence of systemic toxicity in the rats administered either vaccine. There was an associated increase in white blood cell, lymphocyte and monocyte counts, increased adrenal gland weights, adrenocortical hypertrophy, and increased severity of granulomatous inflammation at the sites of injection and the associated inguinal lymph nodes. These changes were considered non-adverse. All rats administered vaccine developed a robust and sustained immunological response. The absence of clinical toxicity and the development of an immunological response in the rats suggests that the vaccines are safe for use in a phase 1 clinical trial in healthy humans.

The Path to Group A Streptococcus Vaccines: World Health Organization Research and Development Technology Roadmap and Preferred Product Characteristics

Group A Streptococcus (GAS) infections result in a considerable underappreciated burden of acute and chronic disease globally. A 2018 World Health Assembly resolution calls for better control and prevention. Providing guidance on global health research needs is an important World Health Organization (WHO) activity, influencing prioritization of investments. Here, the role, status, and directions in GAS vaccines research are discussed. WHO preferred product characteristics and a research and development technology roadmap, briefly presented, offer an actionable framework for vaccine development to regulatory and policy decision making, availability, and use. GAS vaccines should be considered for global prevention of the range of clinical manifestations and associated antibiotic use. Impediments related to antigen diversity, safety concerns, and the difficulty to establish vaccine efficacy against rheumatic heart disease are discussed. Demonstration of vaccine efficacy against pharyngitis and skin infections constitutes a key near-term strategic goal. Investments and collaborative partnerships to diversify and advance vaccine candidates are needed.

Epidemiological consequences of enduring strain-specific immunity requiring repeated episodes of infection

Group A Streptococcus (GAS) skin infections are caused by a diverse array of strain types and are highly prevalent in disadvantaged populations. The role of strain-specific immunity in preventing GAS infections is poorly understood, representing a critical knowledge gap in vaccine development. A recent GAS murine challenge study showed evidence that sterilising strain-specific and enduring immunity required two skin infections by the same GAS strain within three weeks. This mechanism of developing enduring immunity may be a significant impediment to the accumulation of immunity in populations. We used an agent-based mathematical model of GAS transmission to investigate the epidemiological consequences of enduring strain-specific immunity developing only after two infections with the same strain within a specified interval. Accounting for uncertainty when correlating murine timeframes to humans, we varied this maximum inter-infection interval from 3 to 420 weeks to assess its impact on prevalence and strain diversity, and considered additional scenarios where no maximum inter-infection interval was specified. Model outputs were compared with longitudinal GAS surveillance observations from northern Australia, a region with endemic infection. We also assessed the likely impact of a targeted strain-specific multivalent vaccine in this context. Our model produced patterns of transmission consistent with observations when the maximum inter-infection interval for developing enduring immunity was 19 weeks. Our vaccine analysis suggests that the leading multivalent GAS vaccine may have limited impact on the prevalence of GAS in populations in northern Australia if strain-specific immunity requires repeated episodes of infection. Our results suggest that observed GAS epidemiology from disease endemic settings is consistent with enduring strain-specific immunity being dependent on repeated infections with the same strain, and provide additional motivation for relevant human studies to confirm the human immune response to GAS skin infection.

Group A Streptococcus (GAS) is a ubiquitous bacterial pathogen that exists in many distinct strains, and is a major cause of death and disability globally. Vaccines against GAS are under development, but their effective use will require better understanding of how immunity develops following infection. Evidence from an animal model of skin infection suggests that the generation of enduring strain-specific immunity requires two infections by the same strain within a short time frame. It is not clear if this mechanism of immune development operates in humans, nor how it would contribute to the persistence of GAS in populations and affect vaccine impact. We used a mathematical model of GAS transmission, calibrated to data collected in an Indigenous Australian community, to assess whether this mechanism of immune development is consistent with epidemiological observations, and to explore its implications for the impact of a vaccine. We found that it is plausible that repeat infections are required for the development of immunity in humans, and illustrate the difficulties associated with achieving sustained reductions in disease prevalence with a vaccine.

Host Pathways of Hemostasis that Regulate Group A Streptococcus pyogenes Pathogenicity

A hallmark feature of severe Group A Streptococcus pyogenes (GAS) infection is dysregulated hemostasis. Hemostasis is the primary pathway for regulating blood flow through events that contribute towards clot formation and its dissolution. However, a number of studies have identified components of hemostasis in regulating survival and dissemination of GAS. Several proteins have been identified on the surface of GAS and they serve to either facilitate invasion to host distal sites or regulate inflammatory responses to the pathogen. GAS M-protein, a surface-exposed virulence factor, appears to be a major target for interactions with host hemostasis proteins. These interactions mediate biochemical events both on the surface of GAS and in the solution when M-protein is released into the surrounding environment through shedding or regulated proteolytic processes that dictate the fate of this pathogen. A thorough understanding of the mechanisms associated with these interactions could lead to novel approaches for altering the course of GAS pathogenicity.

A quantitative Streptococcus pyogenes-human protein-protein interaction map reveals localization of opsonizing antibodies

A fundamental challenge in medical microbiology is to characterize the dynamic protein–protein interaction networks formed at the host–pathogen interface. Here, we generate a quantitative interaction map between the significant human pathogen, Streptococcus pyogenes, and proteins from human saliva and plasma obtained via complementary affinity-purification and bacterial-surface centered enrichment strategies and quantitative mass spectrometry. Perturbation of the network using immunoglobulin protease cleavage, mixtures of different concentrations of saliva and plasma, and different S. pyogenes serotypes and their isogenic mutants, reveals how changing microenvironments alter the interconnectivity of the interaction map. The importance of host immunoglobulins for the interaction with human complement proteins is demonstrated and potential protective epitopes of importance for phagocytosis of S. pyogenes cells are localized. The interaction map confirms several previously described protein–protein interactions; however, it also reveals a multitude of additional interactions, with possible implications for host–pathogen interactions involving other bacterial species.

Characterizing host-pathogen protein interactions can help elucidate the molecular basis of bacterial infections. Here, the authors use an integrative proteomics approach to generate a quantitative map of protein interactions between Streptococcus pyogenes and human saliva and plasma.

Vaccine Approaches To Protect against Group A Streptococcal Pharyngitis

Streptococcal pharyngitis (or strep throat) is a common childhood disease affecting millions of children each year, but it is one of the only childhood diseases for which a vaccine does not exist. While for decades the development of a vaccine has been the center of attention in many laboratories worldwide, with some successes, no corporate development has yet to be initiated. The reason for this probably lies in our inability to conclusively identify the streptococcal molecule or molecules responsible for the heart cross-reactive antibodies observed in the serum of rheumatic fever patients. Without this specific knowledge, any streptococcal vaccine antigen is suspect and thus not the target for a billion-dollar investment, despite the fact that the exact role of cross-reactive antibodies in rheumatic fever is still questionable. This article will describe the development of several approaches to protect against Streptococcus pyogenes infections over the past several decades.

Development of an opsonophagocytic killing assay for group a streptococcus

Group A Streptococcus (GAS) or Streptococcus pyogenes is responsible for an estimated 500,000 deaths worldwide each year. Protection against GAS infection is thought to be mediated by phagocytosis, enhanced by bacteria-specific antibody. There are no licenced GAS vaccines, despite many promising candidates in preclinical and early stage clinical development, the most advanced of which are based on the GAS M-protein. Vaccine progress has been hindered, in part, by the lack of a standardised functional assay suitable for vaccine evaluation. Current assays, developed over 50 years ago, rely on non-immune human whole blood as a source of neutrophils and complement. Variations in complement and neutrophil activity between donors result in variable data that is difficult to interpret. We have developed an opsonophagocytic killing assay (OPKA) for GAS that utilises dimethylformamide (DMF)-differentiated human promyelocytic leukemia cells (HL-60) as a source of neutrophils and baby rabbit complement, thus removing the major sources of variation in current assays. We have standardised the OPKA for several clinically relevant GAS strain types (emm1, emm6 and emm12) and have shown antibody-specific killing for each emm-type using M-protein specific rabbit antisera. Specificity was demonstrated by pre-incubation of the antisera with homologous M-protein antigens that blocked antibody-specific killing. Additional qualifications of the GAS OPKA, including the assessment of the accuracy, precision, linearity and the lower limit of quantification, were also performed. This GAS OPKA assay has the potential to provide a robust and reproducible platform to accelerate GAS vaccine development.

Contribution of cryptic epitopes in designing a group A streptococcal vaccine

A successful vaccine needs to target multiple strains of an organism. Streptococcus pyogenes is an organism that utilizes antigenic strain variation as a successful defence mechanism to circumvent the host immune response. Despite numerous efforts, there is currently no vaccine available for this organism. Here we review and discuss the significant obstacles to vaccine development, with a focus on how cryptic epitopes may provide a strategy to circumvent the obstacles of antigenic variation.

Skin infection boosts memory B-cells specific for a cryptic vaccine epitope of group A streptococcus and broadens the immune response to enhance vaccine efficacy

Antigenic diversity of the M protein is a major constraint to the development of immunity to group A streptococcus (GAS). We demonstrate that a conserved cryptic epitope that is unrecognized by the host immune system following infection can protect mice following vaccination, and that immunity is strengthened and broadened following successive infections. The observation that infection can boost and broaden, but cannot prime immunity to a cryptic epitope, may be exploited for vaccines for other pathogens.

Physicochemical characterisation, immunogenicity and protective efficacy of a lead streptococcal vaccine: progress towards Phase I trial

Globally, group A streptococcal infections are responsible for over 500,000 deaths per year. A safe vaccine that does not induce autoimmune pathology and that affords coverage for most GAS serotypes is highly desired. We have previously demonstrated that a vaccine based on the conserved M-protein epitope, J8 was safe and immunogenic in a pilot Phase I study. We subsequently improved vaccine efficacy by incorporation of a B-cell epitope from the IL-8 protease, SpyCEP, which protected IL-8 and enhanced neutrophil ingress to the site of infection. We have now substituted the carrier protein, diphtheria toxoid with its superior analogue, CRM197 which provides better immunogenicity and is widely used in licenced human vaccines. The new vaccine was compared with the DT conjugate vaccine to confirm that these modifications have not altered the physicochemical properties of the vaccine. This vaccine, when tested in an animal model of GAS infection, demonstrated significant reduction in systemic and local GAS burden, with comparable efficacy to the DT conjugate vaccine. The vaccine was shown to be equally effective in the presence of human plasma and in the presence of pre-existing DT-specific antibodies, thus minimising concerns regarding its potential efficacy in humans.

Streptococcal Immunity Is Constrained by Lack of Immunological Memory following a Single Episode of Pyoderma

The immunobiology underlying the slow acquisition of skin immunity to group A streptococci (GAS), is not understood, but attributed to specific virulence factors impeding innate immunity and significant antigenic diversity of the type-specific M-protein, hindering acquired immunity. We used a number of epidemiologically distinct GAS strains to model the development of acquired immunity. We show that infection leads to antibody responses to the serotype-specific determinants on the M-protein and profound protective immunity; however, memory B cells do not develop and immunity is rapidly lost. Furthermore, antibodies do not develop to a conserved M-protein epitope that is able to induce immunity following vaccination. However, if re-infected with the same strain within three weeks, enduring immunity and memory B-cells (MBCs) to type-specific epitopes do develop. Such MBCs can adoptively transfer protection to naïve recipients. Thus, highly protective M-protein-specific MBCs may never develop following a single episode of pyoderma, contributing to the slow acquisition of immunity and to streptococcal endemicity in at-risk populations.

GAS skin infections pose a significant health problem in the tropics. They are highly prevalent in developing countries as well as amongst the Indigenous populations of developed countries. In at-risk impoverished communities the epidemiology of GAS infections is very dynamic, leading to very high rates of streptococcal-associated serious pathology including rheumatic heart disease, glomerulonephritis and invasive GAS disease. Immunity to GAS takes over 20 years to develop and this has been attributed to sequence diversity of the type-specific surface M-protein. There are more than 250 different strains of GAS and it known that antibodies to the amino-terminal segment of the M-protein can kill organisms in a strain-specific manner in vitro. In the present study, using four different strains of GAS isolated from the skin lesions of Aboriginal patients in the Northern Territory of Australia, we make the discovery that skin infection does not induce long-lived type-specific immunity. However, following reinfection with the same strain memory B cells are generated and long-term strain-protective immunity then develops. The dependence on reinfection for the development of strain-specific immunity compounds with antigenic diversity of the M-protein and provides a rational explanation for the very slow acquisition of streptococcal immunity.

Preclinical immunogenicity and safety of a Group A streptococcal M protein-based vaccine candidate

Streptococcus pyogenes (group A streptococcus, GAS) causes a wide range of clinical manifestations ranging from mild self-limiting pyoderma to invasive diseases such as sepsis. Also of concern are the post-infectious immune-mediated diseases including rheumatic heart disease. The development of a vaccine against GAS would have a large health impact on populations at risk of these diseases. However, there is a lack of suitable models for the safety evaluation of vaccines with respect to post-infectious complications. We have utilized the Lewis Rat model for cardiac valvulitis to evaluate the safety of the J8-DT vaccine formulation in parallel with a rabbit toxicology study. These studies demonstrated that the vaccine did not induce abnormal pathology. We also show that in mice the vaccine is highly immunogenic but that 3 doses are required to induce protection from a GAS skin challenge even though 2 doses are sufficient to induce a high antibody titer.

Correlates of Protection for M Protein-Based Vaccines against Group A Streptococcus

Group A streptococcus (GAS) is known to cause a broad spectrum of illness, from pharyngitis and impetigo, to autoimmune sequelae such as rheumatic heart disease, and invasive diseases. It is a significant cause of infectious disease morbidity and mortality worldwide, but no efficacious vaccine is currently available. Progress in GAS vaccine development has been hindered by a number of obstacles, including a lack of standardization in immunoassays and the need to define human correlates of protection. In this review, we have examined the current immunoassays used in both GAS and other organisms, and explored the various challenges in their implementation in order to propose potential future directions to identify a correlate of protection and facilitate the development of M protein-based vaccines, which are currently the main GAS vaccine candidates.

Group A Streptococcal vaccine candidate: contribution of epitope to size, antigen presenting cell interaction and immunogenicity

Aim: Utilize lipopeptide vaccine delivery system to develop a vaccine candidate against Group A Streptococcus. Materials & methods: Lipopeptides synthesized by solid-phase peptide synthesis-bearing carboxyl (C)-terminal and amino (N)-terminal Group A Streptococcus peptide epitopes. Nanoparticles formed were evaluated in vivo. Results: Immune responses were induced in mice without additional adjuvant. We demonstrated for the first time that incorporation of the C-terminal epitope significantly enhanced the N-terminal epitope-specific antibody response and correlated with forming smaller nanoparticles. Antigen-presenting cells had increased uptake and maturation by smaller, more immunogenic nanoparticles. Antibodies raised by vaccination recognized isolates. Conclusion: Demonstrated the lipopeptidic nanoparticles to induce an immune response which can be influenced by the combined effect of epitope choice and size.

Immune response against M protein-conserved region peptides from prevalent group A Streptococcus in a North Indian population

BACKGROUND

Group A streptococci (GAS) cause infections with a high prevalence in most developing countries. A GAS vaccine under trial that is based on the amino-terminus of the M protein provides type-specific immunity, and hence seems ineffective in India because of heterogeneous emm types. However, the conserved C-terminal region of the M protein protects against multiple serotypes. In this paper, the immune response generated against the conserved C-repeat region of the M protein was checked in an Indian population to establish their vaccine candidature.

METHODS

When screened for GAS, patients with pharyngitis, rheumatic fever/rheumatic heart disease (RF/RHD), and invasive disease showed heterogeneous emm types, out of which five prevalent types (1-2, 11, 49, 75 and 112) were selected for the study. The C-terminal region of their M proteins showed conserved C1-, C2-, and C3-repeats. The C1-repeat was more diverse and had two different J14-like sequences. Peptides to these C-terminal regions (J14.1 and J14-R6) were designed. Antibodies against these peptides were analyzed using the sera of 130 GAS-infected volunteers.

RESULTS

Serum antibodies were significantly higher in patients with acute rheumatic fever, RHD, and invasive disease than in patients with pharyngitis or the healthy controls. The serum antibodies to these peptides was higher in teenagers and adults than in children.

CONCLUSION

Results showed an association between streptococcal disease progression and the age-related development of immunity to the conserved regions. Hence, these peptides could be considered protective in impeding streptococcal infections worldwide.

Strategies in the development of vaccines to prevent infections with group A streptococcus

There has long been interest and demand for the development of a vaccine to prevent infections caused by the Gram-positive organism group A streptococcus. Despite numerous efforts utilizing advanced approaches such as genomics, proteomics and bio-informatics, there is currently no vaccine. Here we review various strategies employed to achieve this goal. We also discuss the approach that we have pursued, a non-host reactive, conformationally constrained minimal B cell epitope from within the C-repeat region of M-protein, and the potential limitations in moving forward.

Self-adjuvanting modular virus-like particles for mucosal vaccination against group A streptococcus (GAS)

Group A streptococcus (GAS) causes a wide range of diseases, some of them related to autoimmune diseases triggered by repeated GAS infections. Despite the fact that GAS primarily colonizes the mucosal epithelium of the pharynx, the main mechanism of action of most vaccine candidates is based on development of systemic antibodies that do not cross-react with host tissues, neglecting the induction of mucosal immunity that could potentially block disease transmission. Peptide antigens from GAS M-surface protein can confer protection against infection; however, translation of such peptides into immunogenic mucosal vaccines that can be easily manufactured remains a challenge. In this work, a modular murine polyomavirus (MuPyV) virus-like particle (VLP) was engineered to display a GAS antigenic peptide, J8i. Heterologous modules containing one or two J8i antigen elements were integrated with the MuPyV VLP, and produced using microbial protein expression, standard purification techniques and in vitro VLP assembly. Both modular VLPs, when delivered intranasally to outbred mice without adjuvant, induced significant titers of J8i-specific IgG and IgA antibodies, indicating significant systemic and mucosal responses, respectively. GAS colonization in the throats of mice challenged intranasally was reduced in these immunized mice, and protection against lethal challenge was observed. This study shows that modular MuPyV VLPs prepared using microbial synthesis have potential to facilitate cost-effective vaccine delivery to remote communities through the use of mucosal immunization.

In Vivo Efficacy of a Chimeric Peptide Derived from the Conserved Region of the M Protein against Group C and G Streptococci

The J8 peptide from the conserved region of the M protein protects against group A streptococcus infections. In this study, we demonstrate that vaccination with a J8-containing formulation induces IgG that recognizes and binds group C and G streptococci. Moreover, this formulation has the potential to provide protection against infections caused by these organisms.

Evaluation of 238 antigens of Leptospira borgpetersenii serovar Hardjo for protection against kidney colonisation

Leptospirosis is a zoonotic disease affecting animals and humans worldwide. Leptospiral infection in cattle can cause reproductive failure and reduced weight gain, and importantly, infection represents a significant disease risk for farmers. Current bacterin vaccines offer protection that is short-lived and restricted at best to related serovars. The development of protective vaccines that stimulate immunity across multiple leptospiral serovars would therefore be advantageous. This study used a reverse vaccinology approach to evaluate a set of Leptospira borgpetersenii proteins in the hamster infection model. The L. borgpetersenii serovar Hardjo strain L550 genome sequence was analysed and genes encoding 262 predicted outer membrane or secreted proteins were selected. From this list, 238 proteins or protein fragments were successfully expressed and purified; 28 proteins (12%) were soluble, while the remaining 210 proteins (88%) were insoluble and purified under denaturing conditions. Proteins were mixed into 48 pools of up to five each and tested for protection against infection as assessed by renal colonisation in the hamster model of infection. None of the pools of antigens protected the hamsters against infection, despite a detectable antibody response being mounted against the majority of proteins (71%). This study is the first large scale evaluation of individual leptospiral proteins for ability to induce a protective immune response in the hamster infection model. It thus constitutes an important reference of protein immunogenicity and non-protective antigens that should be consulted before embarking on any future subunit vaccine experiments.

Cutting edge issues in rheumatic fever

Although the incidence of acute rheumatic fever and rheumatic heart disease has decreased significantly in regions of the world where antibiotics are easily accessible, there remains a high incidence in developing nations as well as in certain regions where there is a high incidence of genetic susceptibility. These diseases are a function of poverty, low socioeconomic status, and barriers to healthcare access, and it is in the developing world that a comprehensive prevention program is most critically needed. Development of group A streptococcal vaccines has been under investigation since the 1960s and 50 years later, we still have no vaccine. Factors that contribute to this lack of success include a potential risk for developing vaccine-induced rheumatic heart disease, as well as difficulties in covering the many serological subtypes of M protein, a virulence factor found on the surface of the bacterium. Yet, development of a successful vaccine program for prevention of group A streptococcal infection still offers the best chance for eradication of rheumatic fever in the twenty-first century. Other useful approaches include continuation of primary and secondary prevention with antibiotics and implementation of health care policies that provide patients with easy access to antibiotics. Improved living conditions and better hygiene are also critical to the prevention of the spread of group A streptococcus, especially in impoverished regions of the world. The purpose of this article is to discuss current and recent developments in the diagnosis, pathogenesis, and management of rheumatic fever and rheumatic heart disease.

Scabies: important clinical consequences explained by new molecular studies

In 2004, we reviewed the status of disease caused by the scabies mite Sarcoptes scabiei at the time and pointed out that very little basic research had ever been done. The reason for this was largely the lack of availability of mites for experimental purposes and, to a degree, a consequent lack of understanding of its importance, resulting in the trivial name 'itch mite'. Scabies is responsible for major morbidity in disadvantaged communities and immunocompromised patients worldwide. In addition to the physical discomfort caused by the disease, scabies infestations facilitate infection by bacterial pathogens such as Streptococcus pyogenes and Staphylococcus aureus via skin lesions, resulting in severe downstream disease such as in a high prevalence of rheumatic fever/heart disease in affected communities. We now have further evidence that in disadvantaged populations living in tropical climates, scabies rather than 'Strep throat' is an important source of S. pyogenes causing rheumatic fever and eventually rheumatic heart disease. In addition, our work has resulted in two fundamental research tools that facilitate much of the current biomedical research efforts on scabies, namely a public database containing ~45,000 scabies mite expressed sequence tags and a porcine in vivo model. Here we will discuss novel and unexpected proteins encountered in the database that appear crucial to mite survival with regard to digestion and evasion of host defence. The mode(s) of action of some of these have been at least partially revealed. Further, newly discovered molecules that may well have a similar role, such as a family of inactivated cysteine proteases, are yet to be investigated. Hence, there are now whole families of potential targets for chemical inhibitors of S. scabiei. These efforts put today's scabies research in a unique position to design and test small molecules that may specifically interfere with mite-derived molecules, such as digestive proteases and mite complement inhibitors. The porcine scabies model will be available to trial in vivo treatment with potential inhibitors. New therapies for scabies may be developed from these studies and may contribute to reduce the spread of scabies and the subsequent prevalence of bacterial skin infections and their devastating sequelae in the community.

Group a streptococcal vaccine candidates: potential for the development of a human vaccine

Currently there is no commercial Group A Streptococcus (GAS; S. pyogenes) vaccine available. The development of safe GAS vaccines is challenging, researchers are confronted with obstacles such as the occurrence of many unique serotypes (there are greater than 150 M types), antigenic variation within the same serotype, large variations in the geographical distribution of serotypes, and the production of antibodies cross-reactive with human tissue which can lead to host auto-immune disease. Cell wall anchored, cell membrane associated, secreted and anchorless proteins have all been targeted as GAS vaccine candidates. As GAS is an exclusively human pathogen, the quest for an efficacious vaccine is further complicated by the lack of an animal model which mimics human disease and can be consistently and reproducibly colonized by multiple GAS strains.

A microbial platform for rapid and low-cost virus-like particle and capsomere vaccines

Studies on a platform technology able to deliver low-cost viral capsomeres and virus-like particles are described. The technology involves expression of the VP1 structural protein from murine polyomavirus (MuPyV) in Escherichia coli, followed by purification using scaleable units and optional cell-free VLP assembly. Two insertion sites on the surface of MuPyV VP1 are exploited for the presentation of the M2e antigen from influenza and the J8 peptide from Group A Streptococcus (GAS). Results from testing on mice following subcutaneous administration demonstrate that VLPs are self adjuvating, that adding adjuvant to VLPs provides no significant benefit in terms of antibody titre, and that adjuvanted capsomeres induce an antibody titre comparable to VLPs but superior to unadjuvanted capsomere formulations. Antibodies raised against GAS J8 peptide following immunization with chimeric J8-VP1 VLPs are bactericidal against a GAS reference strain. E. coli is easily and widely cultivated, and well understood, and delivers unparalleled volumetric productivity in industrial bioreactors. Indeed, recent results demonstrate that MuPyV VP1 can be produced in bioreactors at multi-gram-per-litre levels. The platform technology described here therefore has the potential to deliver safe and efficacious vaccine, quickly and cost effectively, at distributed manufacturing sites including those in less developed countries. Additionally, the unique advantages of VLPs including their stability on freeze drying, and the potential for intradermal and intranasal administration, suggest this technology may be suited to numerous diseases where adequate response requires large-scale and low-cost vaccine manufacture, in a way that is rapidly adaptable to temporal or geographical variation in pathogen molecular composition.

Recurrent sepsis caused by Streptococcus pyogenes

I report that a 75-year-old man with severe atherosclerosis experienced two episodes of bacteremia with Streptococcus pyogenes of type emm87. Recurrent sepsis with S. pyogenes is extremely rare, and a foot ulcer was the suspected point of entry. The patient did not develop opsonizing antibodies to the isolate.

Protective efficacy of group A streptococcal vaccines containing type-specific and conserved M protein epitopes

The amino terminal region of group A streptococcal M proteins evokes type-specific immunity while the conserved C-repeat epitopes evoke cross-protective immunity against multiple serotypes. The present studies were undertaken to compare the protective efficacy of vaccines containing either type-specific (hexavalent vaccine) or conserved C-repeat (J14 vaccine) M protein epitopes and to determine if combination vaccines resulted in enhanced levels of protection. Our results indicated that the protective efficacy of the type-specific vaccine was significantly greater than that of J14 and that the addition of J14 to vaccine formulations did not enhance the level of protection achieved with type-specific formulations.

Differences among group A streptococcus epidemiological landscapes: consequences for M protein-based vaccines?

Group A streptococcus (GAS) is a bacterial pathogen responsible for a wide array of disease pathologies in humans. GAS surface M protein plays multiple key roles in pathogenesis, and serves as a target for typing and vaccine development. In this review, we have compiled GAS epidemiological studies from several countries around the world to highlight the consequences on the theoretical efficacy of two different M protein-based vaccine strategies.

Group A streptococcal vaccines: facts versus fantasy

PURPOSE OF REVIEW

This review provides an overview of progress of the development of group A streptococcal (GAS) vaccines with a focus on recent advances.

RECENT FINDINGS

Historically, GAS vaccine development has focused on the N-terminus of the M protein, which ultimately led to successful phase I/II clinical trials of a 26-valent recombinant M protein vaccine in 2004-2005. More recently, interest in antigens conserved among most, if not all, group A streptococci has increased. However, no vaccines containing these antigens have reached clinical trials. Three strategies have been used to develop conserved antigen vaccine candidates: use of the conserved region of the M protein; use of well described virulence factors as antigens, including streptococcal C5a peptidase, streptococcal carbohydrate, fibronectin-binding proteins, cysteine protease and streptococcal pili; and use of reverse vaccinology to identify novel antigens.

SUMMARY

Several vaccine candidates against GAS infection are in varying stages of preclinical and clinical development. Although there is great hope that one of these vaccine candidates will reach licensure in the next decade, only one, the multivalent N-terminal vaccine, has entered clinical trials in the last 30 years. Although strong advocacy for GAS vaccine development is important, there remains an urgent need to institute available public health control measures against GAS diseases globally, particularly in developing countries.

Correlation between bioluminescence and bacterial burden in passively protected mice challenged with a recombinant bioluminescent M49 group A streptococcus Strain

Streptococcus pyogenes, also known as group A streptococcus (GAS), is a human pathogen which infects people of all age groups. Previous work has reported that conformationally constrained chimeric peptide J8 protects against GAS challenge. In the current study, we demonstrate the utility of bioluminescent imaging as a rapid technique for monitoring bacterial dissemination following the passive transfer of rabbit anti-J8 antibodies to naïve mice and subsequent challenge with recombinant GAS strain M49, an emm type shown to be associated with poststreptococcal glomerular nephritis.

Vaccines under study: non-HIV vaccines

The development of effective vaccines has been an amazing public health achievement and has resulted in countless lives being saved. Dermatologic therapy has recently been greatly advanced by the licensure of an effective human papillomavirus vaccine and herpes zoster vaccine. Despite these successes, many infectious diseases do not currently have a preventive vaccine. We review potential vaccines against selected infectious agents, including viruses, bacteria, fungi, and protozoa that have cutaneous and mucocutaneous manifestations. The road to licensure of a new vaccine begins with exhaustive preclinical and clinical studies, and many of these will fail before a successful vaccine candidate is approved. This article focuses on vaccines that have yet to be approved for licensure.

Comprehensive analysis of antibody responses to streptococcal and tissue antigens in patients with acute rheumatic fever

Acute rheumatic fever (ARF) is an autoimmune disease occurring in individuals following untreated group A streptococcal infection believed to be triggered by antibodies to bacterial components that cross-react with human tissues. We developed a multiplexed immunoassay for the simultaneous quantitation of antibodies to nine streptococcal-related antigens including streptolysin O (SLO), DNase B, collagen I and IV, fibronectin, myosin, group A carbohydrate, M6 protein and streptococcal C5a peptidase. Utilizing this method, we examined serum from 49 ARF, 58 pharyngitis patients and age- and sex-matched controls in samples collected at initial disease onset, and at 4 weeks, 6 months and 1 year after diagnosis. Antibody responses were significantly higher for SLO, DNase B, M6 protein, group A carbohydrate and the cross-reactive antigens collagen I and myosin in ARF compared with pharyngitis patients (P <or= 0.05). Moreover, we found significantly elevated antibody responses in the ARF patients with rheumatic heart disease to fibronectin and collagen I compared with ARF patients without heart disease. The major differences between the ARF patients with and without carditis appear to be in the immune response to the putative heart valve components, collagen I and fibronectin.

Comparative in silico analysis of two vaccine candidates for group A streptococcus predicts that they both may have similar safety profiles

BACKGROUND

Concerns of immune cross-reactivity, between epitopes of the group A streptococcal (GAS) M-proteins and host proteins have hindered the progress of an effective GAS vaccine. An ideal M-protein based subunit vaccine should not elicit heart tissue cross-reactive antibody responses and should not activate M-protein specific CD4+ T-cells. In the current study we used a bioinformatic and immunoinformatic approach to assess the safety of J8 and J14, chimeric vaccine constructs containing a GAS derived M-protein epitope embedded in flanking GCN4 region. We demonstrate that at the primary amino acid level J8 and J14 show very little homology to human proteins. ProPred, RANKPEP and HLABIND algorithms failed to predict significant binding between the M-protein specific regions of J8 and J14 and class II binding alleles. A single peptide was predicted to bind to HLA class I allele B_2705. This data was supported by cellular proliferation assays demonstrating few peripheral blood mononuclear cells (PBMCs) from donors respond to J8 and J14. Reassuringly, there was no correlation between proliferation to these peptides, and proliferation to host proteins. This data suggests that J8 and J14 are unlikely to induce cross-reactive immune responses, and will be safe for use in humans.

Advances in potential M-protein peptide-based vaccines for preventing rheumatic fever and rheumatic heart disease

Rheumatic fever (RF) and rheumatic heart disease (RHD) are postinfectious complications of an infection (or repeated infection) with the Gram-positive bacterium, Streptococcus pyogenes (also known as group A streptococcus, GAS). RF and RHD are global problems and affect many indigenous populations of developed countries and many developing countries. However, RF and RHD are only part of a larger spectrum of diseases caused by this organism. The development of a vaccine against GAS has primarily targeted the abundant cell-surface protein called the M-protein. This review focuses on different M-protein-based-subunit vaccine approaches and the different delivery technologies used to administer these vaccine candidates in preclinical studies.

Bactericidal activity of M protein conserved region antibodies against group A streptococcal isolates from the Northern Thai population

Background

Most group A streptococcal (GAS) vaccine strategies have focused on the surface M protein, a major virulence factor of GAS. The amino-terminus of the M protein elicits antibodies, that are both opsonic and protective, but which are type specific. J14, a chimeric peptide that contains 14 amino acids from the M protein conserved C-region at the carboxy-terminus, offers the possibility of a vaccine which will elicit protective opsonic antibodies against multiple different GAS strains. In this study, we searched for J14 and J14-like sequences and the number of their repeats in the C-region of the M protein from GAS strains isolated from the Northern Thai population. Then, we examined the bactericidal activity of J14, J14.1, J14-R1 and J14-R2 antisera against multiple Thai GAS strains.

Results

The emm genes of GAS isolates were sequenced and grouped as 14 different J14-types. The most diversity of J14-types was found in the C1-repeat. The J14.1 type was the major sequence in the C2 and C3-repeats. We have shown that antisera raised against the M protein conserved C-repeat region peptides, J14, J14.1, J14-R1 and J14-R2, commonly found in GAS isolates from the Northern Thai population, are able to kill GAS of multiple different emm types derived from an endemic area. The mean percent of bactericidal activities for all J14 and J14-like peptide antisera against GAS isolates were more than 70%. The mean percent of bactericidal activity was highest for J14 antisera followed by J14-R2, J14.1 and J14-R1 antisera.

Conclusion

Our study demonstrated that antisera raised against the M protein conserved C-repeat region are able to kill multiple different strains of GAS isolated from the Northern Thai population. Therefore, the four conserved "J14" peptides have the potential to be used as GAS vaccine candidates to prevent streptococcal infections in an endemic area.

Divergence in the plasminogen-binding group a streptococcal M protein family: functional conservation of binding site and potential role for immune selection of variants

Group A streptococci (GAS) display receptors for the human zymogen plasminogen on the cell surface, one of which is the plasminogen-binding group A streptococcal M protein (PAM). Characterization of PAM genes from 12 GAS isolates showed significant variation within the plasminogen-binding repeat motifs (a1/a2) of this protein. To determine the impact of sequence variation on protein function, recombinant proteins representing five naturally occurring variants of PAM, together with a recombinant M1 protein, were expressed and purified. Equilibrium dissociation constants for the interaction of PAM variants with biotinylated Glu-plasminogen ranged from 1.58 to 4.99 nm. Effective concentrations of prototype PAM required for 50% inhibition of plasminogen binding to immobilized PAM variants ranged from 0.68 to 22.06 nm. These results suggest that although variation in the a1/a2 region of the PAM protein does affect the comparative affinity of PAM variants, the functional capacity to bind plasminogen is conserved. Additionally, a potential role for the a1 region of PAM in eliciting a protective immune response was investigated by using a mouse model for GAS infection. The a1 region of PAM was found to protect immunized mice challenged with a PAM-positive GAS strain. These data suggest a link between selective immune pressure against the plasminogen-binding repeats and the functional conservation of the binding domain in PAM variants.

M protein conserved region antibodies opsonise multiple strains of Streptococcus pyogenes with sequence variations in C-repeats

The development of a group A streptococcal (GAS) vaccine has focused on the M protein, a major virulence factor. Antibodies against the amino terminal domain of the M protein are generally protective but only provide type-specific immunity. J14, a 29-mer peptide sequence which contains a conserved epitope from the C-repeat region of the M protein, offers the possibility of a vaccine which will elicit protective opsonic antibodies against multiple GAS strains. In this study we have shown that antibodies raised against J14 are capable of opsonising 37 GAS isolates representing different emm types derived from a region in which GAS infection is endemic. We also demonstrate that J14 antisera is capable of opsonising GAS isolates containing J14 homologues but not J14-specific sequences, further increasing the strain coverage of this vaccine candidate. Isolates with three C-repeats were opsonised more efficiently than isolates with two repeats. Opsonisation of a strain with only a single C-repeat was dramatically lower than other strains tested. The number of C-repeats present in the M protein of individual isolates therefore appears to be the critical factor in determining bactericidal capacity of J14 antisera. The reduced opsonic capacity of sera against this strain was shown to correlate with a reduced capacity to bind J14 antisera, as demonstrated by immunofluorescence microscopy and FACS analysis. In vivo challenge experiments also confirmed the protective efficacy of immunisation with J14 peptide.