Recombinant, octavalent group A streptococcal M protein vaccine

The Thousand Faces of Invasive Group A Streptococcal Infections: Update on Epidemiology, Symptoms, and Therapy

Invasive infections caused by Streptococcus pyogfenes (iGAS), commonly known as Group A Streptococcus, represent a significant public health concern due to their potential for rapid progression and life-threatening complications. Epidemiologically, invasive GAS infections exhibit a diverse global distribution, affecting individuals of all ages with varying predisposing factors. The pathogenesis of invasive GAS involves an array of virulence factors that contribute to tissue invasion, immune evasion, and systemic dissemination. In pediatrics, in the last few years, an increase in iGAS infections has been reported worldwide becoming a challenging disease to diagnose and treat promptly. This review highlights the current knowledge on pathogenesis, clinical presentations, and therapeutic approaches for iGAS in children.

Update on group A streptococcal vaccine development

PURPOSE OF REVIEW

There is a global need for well tolerated, effective, and affordable vaccines to prevent group A streptococcal infections and their most serious complications. The aim of this review is to highlight the recent progress in the identification of promising vaccine antigens and new approaches to vaccine design that address the complexities of group A streptococcal pathogenesis and epidemiology.

RECENT FINDINGS

Combination vaccines containing multiple shared, cross-protective antigens have proven efficacious in mouse and nonhuman primate models of infection. The development of complex multivalent M protein-based vaccines is continuing and several have progressed through early-stage human clinical trials. Formulations of vaccines containing universal T-cell epitopes, toll-like receptor agonists, and other adjuvants more potent than alum have been shown to enhance protective immunogenicity. Although the group A streptococcal vaccine antigen landscape is populated with a number of potential candidates, the clinical development of vaccines has been impeded by a number of factors. There are now concerted global efforts to raise awareness about the need for group A streptococcal vaccines and to support progress toward eventual commercialization and licensure.

SUMMARY

Preclinical antigen discovery, vaccine formulation, and efficacy studies in animal models have progressed significantly in recent years. There is now a need to move promising candidates through the clinical development pathway to establish their efficacy in preventing group A streptococcal infections and their complications.

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.

Safety and immunogenicity of a 30-valent M protein-based group a streptococcal vaccine in healthy adult volunteers: A randomized, controlled phase I study

BACKGROUND

Streptococcus pyogenes (group A Streptococcus, Strep A) is a widespread pathogen that continues to pose a significant threat to human health. The development of a Strep A vaccine remains an unmet global health need. One of the major vaccine strategies is the use of M protein, which is a primary virulence determinant and protective antigen. Multivalent recombinant M protein vaccines are being developed with N-terminal M peptides that contain opsonic epitopes but do not contain human tissue cross-reactive epitopes.

METHODS

We completed a Phase I trial of a recombinant 30-valent M protein-based Strep A vaccine (Strep A vaccine, StreptAnova™) comprised of four recombinant proteins containing N-terminal peptides from 30 M proteins of common pharyngitis and invasive and/or rheumatogenic serotypes, adjuvanted with aluminum hydroxide. The trial was observer-blinded and randomized in a 2:1 ratio for intramuscular administration of Strep A vaccine or an alum-based comparator in healthy adult volunteers, at 0, 30 and 180 days. Primary outcome measures were assessments of safety, including assays for antibodies that cross-reacted with host tissues, and immunogenicity assessed by ELISA with the individual vaccine peptides and by opsonophagocytic killing (OPK) assays in human blood.

RESULTS

Twenty-three Strep A-vaccinated participants and 13 controls completed the study. The Strep A vaccine was well-tolerated and there was no clinical evidence of autoimmunity and no laboratory evidence of tissue cross-reactive antibodies. The vaccine was immunogenic and elicited significant increases in geometric mean antibody levels to 24 of the 30 component M antigens by ELISA. Vaccine-induced OPK activity was observed against selected M types of Strep A in vaccinated participants that seroconverted to specific M peptides.

CONCLUSION

The Strep A vaccine was well tolerated and immunogenic in healthy adults, providing strong support for further clinical development. [ClinicalTrials.gov NCT02564237].

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.

Immunization with Streptococcal Heme Binding Protein (Shp) Protects Mice Against Group A Streptococcus Infection

Streptococcal heme binding protein (Shp) is a surface protein of the heme acquisition system that is an essential iron nutrient in Group A Streptococcus (GAS). Here, we tested whether Shp immunization protects mice from subcutaneous infection. Mice were immunized subcutaneously with recombinant Shp and then challenged with GAS. The protective effects against GAS challenge were evaluated two weeks after the last immunization. Immunization with Shp elicited a robust IgG response, resulting in high anti-Shp IgG titers in the serum. Immunized mice had a higher survival rate and smaller skin lesions than adjuvant control mice. Furthermore, immunized mice had lower GAS numbers at the skin lesions and in the liver, spleen and lung. Histological analysis with Gram staining showed that GAS invaded the surrounding area of the inoculation sites in the skin in control mice, but not in immunized mice. Thus, Shp immunization enhances GAS clearance and reduces GAS skin invasion and systemic dissemination. These findings indicate that Shp is a protective antigen.

Bromine, bear-claw scratch fasciotomies, and the Eagle effect: management of group A streptococcal necrotising fasciitis and its association with trauma

Necrotising fasciitis is a rare, but potentially fatal, soft-tissue infection. Historical depictions of the disease have been described since classical times and were mainly recorded in wartime reports of battle injuries. Although several different species of bacteria can cause necrotising fasciitis, perhaps the most widely known is group A streptococcus (GAS). Infection control, early surgical debridement, and antibiotic therapy are now the central tenets of the clinical management of necrotising fasciitis; these treatment approaches all originate from those used in wars in the past 150 years. We review reports from the 19th century, early 20th century, and mid-20th century onwards to show how the management of necrotising fasciitis has progressed in parallel with prevailing scientific thought and medical practice. Historically, necrotising fasciitis has often, but not exclusively, been associated with penetrating trauma. However, along with a worldwide increase in invasive GAS disease, recent reports have cited cases of necrotising fasciitis following non-combat-related injuries or in the absence of antecedent events. We also investigate the specific association between GAS necrotising fasciitis and trauma. In the 21st century, molecular biology has improved our understanding of GAS pathogenesis, but has not yet affected attributable mortality.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Seven-year surveillance of emm types of pediatric Group A streptococcal pharyngitis isolates in Western Greece

Background

An experimental 26-valent M protein Group A streptococcal (GAS) vaccine has entered clinical studies. Pharyngeal GAS emm type surveillances in different areas and time-periods enhance the understanding of the epidemiology of GAS pharyngitis. Moreover, these surveillances, combined with the data on GAS invasive disease, can play a significant role in the formulation of multivalent type-specific vaccines.

Methods

During a 7-year period (1999–2005), 2408 GAS isolates were recovered from consecutive children with pharyngitis in Western Greece. The overall macrolide resistance rate was 22.8%. Along the study period we noted a tendency towards significantly decreased rates of resistance, with the lowest rates occurring in 2002 (15.3%), 2003 (15%) and 2004 (16.7%). A random sample of isolates from each year, 338 (61.7%) of the 548 macrolide-resistant and 205 (11%) of the macrolide-susceptible, underwent molecular analysis, including emm typing.

Results

The 543 typed isolates had 28 different emm types. A statistically significant association was found between macrolide resistance and emm4, emm22 and emm77, whereas emm1, emm3, emm6, emm12, emm87 and emm89 were associated with macrolide susceptibility. A significant yearly fluctuation was observed in emm4, emm28 and emm77. The most common macrolide-resistant GAS were emm77 isolates harboring erm(A), either alone or in combination with mef(A), emm4 carrying mef(A), emm28 possessing erm(B), emm75 carrying mef(A), emm12 harboring mef(A) and emm22 carrying erm(A). We estimated that 82.8% of the isolates belonged to emm types included in the novel 26-valent M protein vaccine. The vaccine coverage rate was determined mainly by the increased frequency of nonvaccine emm4 isolates.

Conclusions

A limited number of emm types dominated among macrolide-susceptible and macrolide-resistant GAS isolates. We observed seasonal fluctuations, which were significant for emm4, emm28 and emm77. This type of data can serve as baseline information if the novel 26-valent M protein GAS vaccine is introduced into practice.

Human pathogenic streptococcal proteomics and vaccine development

Gram-positive streptococci are non-motile, chain-forming bacteria commonly found in the normal oral and bowel flora of warm-blooded animals. Over the past decade, a proteomic approach combining 2-DE and MS has been used to systematically map the cellular, surface-associated and secreted proteins of human pathogenic streptococcal species. The public availability of complete streptococcal genomic sequences and the amalgamation of proteomic, genomic and bioinformatic technologies have recently facilitated the identification of novel streptococcal vaccine candidate antigens and therapeutic agents. The objective of this review is to examine the constituents of the streptococcal cell wall and secreted proteome, the mechanisms of transport of surface and secreted proteins, and describe the current methodologies employed for the identification of novel surface-displayed proteins and potential vaccine antigens.

Immunogenicity of a divalent group A streptococcal vaccine

We designed and recombined the polypeptide based on the M protein of group A streptococci (GAS)--the causative pathogen of rheumatic fever and rheumatic heart disease, which would be a divalent vaccine to prevent and defend the diseases in relation to the different GAS strains. A divalent vaccine comprising three different peptide epitopes of the antiphagocytic M protein of GAS--an aminoterminal specific sequences, respectively, from the M1 and M12 proteins and J14 peptide (ASREAKKQVEKALE) within the highly conserved C-terminal repeat region of the M1 and M12 proteins--was subcutaneously delivered to mice with the adjuvant. Furthermore, the antisera titers of mice inoculated with the divalent vaccine were assayed by ELISA, and then opsonization and percentage killing against two different GAS serotypes were completed. Our data demonstrated that antisera raised against the divalent vaccine containing amino acids and M-protein-conserved C repeat region are able to kill several GAS strains isolated from the Guangzhou population. Therefore, the divalent vaccine can be used to prevent those diseases caused by GAS in an endemic area. We successfully construct the M-protein-based divalent vaccine that can bring out a high-level antisera titer of mice vaccinated with it. So, the vaccine has the potential to be used to prevent diseases caused by GAS in our country.

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.

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.

Construction and analysis of variants of a polyvalent Lyme disease vaccine: approaches for improving the immune response to chimeric vaccinogens

There is currently no Lyme disease vaccine commercially available for use in humans. Outer surface protein C (OspC) of the Borrelia has been widely investigated as a potential vaccinogen. At least 38 OspC types have been defined. While the antibody response to OspC is protective, the range of protection is narrow due to the localization of protective epitopes within OspC type-specific domains. To develop a broadly protective vaccine, we previously constructed a tetravalent chimeric vaccinogen containing epitopes from OspC types A, B, K, and D. While this construct elicited bactericidal antibody against strains bearing each of the four OspC types, its solubility was low, and decreasing IgG titer to epitopes near the C-terminus of the construct was observed. In this report, construct solubility and immunogenicity were increased by dialysis against an Arg/Glu buffer. We also demonstrate the immunogenicity of the construct in alum. To further optimize epitope-specific immune responses, several constructs were generated with differing epitope organization or with putative C-terminal protective motifs. Analyses of murine antibody titers and isotype profiles induced by these constructs revealed that while the C-terminal tags did not enhance antibody titer, specific epitope reorganization and reiteration did. These analyses provide important information that can be exploited in the development of chimeric vaccinogens in general.

Development of an OspC-based tetravalent, recombinant, chimeric vaccinogen that elicits bactericidal antibody against diverse Lyme disease spirochete strains

Lyme disease is the most common arthropod-borne disease in North America and Europe. At present, there is no commercially available vaccine for use in humans. Outer surface protein C (OspC) has antigenic and expression characteristics that make it an attractive vaccine candidate; however, sequence heterogeneity has impeded its use as a vaccinogen. Sequence analyses have identified 21 well defined OspC phyletic groups or "types" (designated A-U). In this report we have mapped the linear epitopes presented by OspC types B, K, and D during human and murine infection and exploited these epitopes (along with the previously identified type A OspC linear epitopes) in the development of a recombinant, tetravalent, chimeric vaccinogen. The construct was found to be highly immunogenic in mice and the induced antibodies surface labeled in vitro cultivated spirochetes. Importantly, vaccination induced complement-dependent bactericidal antibodies against strains expressing each of the OspC types that were incorporated into the construct. These results suggest that an effective and broadly protective polyvalent OspC-based Lyme disease vaccine can be produced as a recombinant, chimeric protein.

Multivalent group A streptococcal vaccine elicits bactericidal antibodies against variant M subtypes

Group A streptococci cause a wide spectrum of clinical illness. One of several strategies for vaccine prevention of these infections is based on the type-specific M protein epitopes. A multivalent M protein-based vaccine containing type-specific determinants from 26 different M serotypes is now in clinical trials. Recent epidemiologic studies have shown that, within some serotypes, the amino-terminal M protein sequence may show natural variation, giving rise to subtypes. This raises the possibility that vaccine-induced antibodies against the parent type may not be as effective in promoting bactericidal killing of variant subtypes. In the present study we used rabbit antisera against the 26-valent M protein-based vaccine in bactericidal tests against M1, M3, and M5 streptococci, which were represented by multiple subtypes. We show that the vaccine antibodies effectively promoted in vitro bactericidal activity despite the fact that the M proteins contained naturally occurring variant sequences in the regions corresponding to the vaccine sequence. Our results show that the variant M proteins generally do not result in significant differences in opsonization promoted by rabbit antisera raised against the 26-valent vaccine, suggesting that a multivalent M protein vaccine may not permit variant subtypes of group A streptococci to escape in a highly immunized population.

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.

Dynamics of anti-M antibody response in a mouse model following intranasal infection with group A Streptococcus M-18

Dynamics of anti-M antibody response following intranasal infection with group A Streptococcus (GAS) M-18 were investigated in a Swiss albino mouse model. Mice arranged in three groups were inoculated intranasally with 2.0x10(7) c.f.u. ml-1 of GAS M-18 on 1, 2 alternate and 3 alternate days. Plasma collected from the retro-orbital plexus was tested for antibodies by an in-house indirect ELISA. The antibody titres of the plasma samples varied from 1 : 8 to 1 : 1024 in the 1 day dose, from 1 : 4 to 1 : 256 in the 2 day dose and from 1 : 4 to 1 : 128 in the 3 day dose. Peak titres were seen on day 42 or 56 and in all cases the titres had declined by day 84. Swiss albino mouse can thus serve as a useful animal model to study different aspects of type-specific anti-M immune responses against GAS disease when designing candidate streptococcal vaccines.

Intranasal immunization with multivalent group A streptococcal vaccines protects mice against intranasal challenge infections

We have previously shown that a hexavalent group A streptococcal M protein-based vaccine evoked bactericidal antibodies after intramuscular injection. In the present study, we show that the hexavalent vaccine formulated with several different mucosal adjuvants and delivered intranasally induced serum and salivary antibodies that protected mice from intranasal challenge infections with virulent group A streptococci. The hexavalent vaccine was formulated with liposomes with or without monophosphorylated lipid A (MPL), cholera toxin B subunit with or without holotoxin, or proteosomes from Neisseria meningitidis outer membrane proteins complexed with lipopolysaccharide from Shigella flexneri. Intranasal immunization with the hexavalent vaccine mixed with these adjuvants resulted in significant levels of antibodies in serum 2 weeks after the final dose. Mean serum antibody titers were equivalent in all groups of mice except those that were immunized with hexavalent protein plus liposomes without MPL, which were significantly lower. Salivary antibodies were also detected in mice that received the vaccine formulated with the four strongest adjuvants. T-cell proliferative assays and cytokine assays using lymphocytes from cervical lymph nodes and spleens from mice immunized with the hexavalent vaccine formulated with proteosomes indicated the presence of hexavalent protein-specific T cells and a Th1-weighted mixed Th1-Th2 cytokine profile. Intranasal immunization with adjuvanted formulations of the hexavalent vaccine resulted in significant levels of protection (80 to 100%) following intranasal challenge infections with type 24 group A streptococci. Our results indicate that intranasal delivery of adjuvanted multivalent M protein vaccines induces protective antibody responses and may provide an alternative to parenteral vaccine formulations.

Serum opacity factor (SOF) of Streptococcus pyogenes evokes antibodies that opsonize homologous and heterologous SOF-positive serotypes of group A streptococci

Serum opacity factor (SOF) is a protein expressed by Streptococcus pyogenes that opacifies mammalian serum. SOF is also a virulence factor of S. pyogenes, but it has not been previously shown to elicit a protective immune response. Herein, we report that SOF evokes bactericidal antibodies against S. pyogenes in humans, rabbits, and mice. Rabbit antiserum against purified recombinant SOF2 opsonized SOF-positive M type 2, 4, and 28 S. pyogenes in human blood but had no effect on SOF-negative M type 5 S. pyogenes. Furthermore, affinity-purified human antibodies against SOF2 also opsonized SOF-positive streptococci. A combination of antisera against M2 and SOF2 proteins was dramatically more effective in killing streptococci than either antiserum alone, indicating that antibodies against SOF2 enhance the opsonic efficiency of M protein antibodies. Mice tolerated an intravenous injection of 100 microg of SOF without overt signs of toxicity, and immunization with SOF protected mice against challenge infections with M type 2 S. pyogenes. These data indicate that SOF evokes opsonic antibodies that may protect against infections by SOF-positive serotypes of group A streptococci and suggest that different serotypes of SOF have common epitopes that may be useful vaccine candidates to protect against group A streptococcal infections.

Group a streptococcal serotypes isolated from healthy schoolchildren in iran

Serotypes of group A streptococci are still a major cause of pharyngitis and some post-infectious sequelae such as rheumatic fever. As part of the worldwide effort to clarify the epidemiological pattern of group A streptococci in different countries, the present study was conducted to assess the prevalence of Streptococcus pyogenes serotypes in Iran. A total of 1588 throat swabs were taken from healthy school children in the city of Gorgan during February and March 1999. Of those isolates, 175 resulted positive for group A streptococci. The distribution pattern was similar for girls and boys, with 10.8% and 11.2%, respectively. Urban school children showed a higher rate of colonization compared to those in rural areas. Serotyping was performed on 65 of the positive isolates using standard techniques, and only 21 (32%) were M-type isolates. Their profiles fell into four types with M1 predominating, which could reflect the presence of rheumatic fever in the region. However, when isolates were challenged for T-antigen types, nearly all were positive (94%). The pattern of T types was diverse (18 types), with the most common T types being T1 (26%), TB3264 (15%), TB\1-19 & B\25\1-19 (9.2%) and T2 & 2\28 (7.7%). When isolates were tested for opacity factor, only 23 (35%) were positive while 34 (52%) responded to the serum opacity reaction test. Although the number of isolates in this study was not sufficient to make any epidemiological conclusions, the scarcity of serotyping studies in Iran could render these data useful for future attempts to develop a streptococcal vaccine.

Evaluation of synthetic, M type-specific peptides as antigens in a multivalent group A streptococcal vaccine

The recent development of emm gene sequence-based typing methodology has allowed group A streptococci (GAS) M serotype prevalence data to be determined. This information has been used to identify the components of a multivalent M protein peptide vaccine that could theoretically prevent most of the GAS-mediated diseases in the USA. In this study, we have evaluated in mice the immunogenicity and protective ability of multiple synthetic, M type-specific peptides, derived from the N-termini of three prevalent GAS serotypes (three peptides per serotype, total of nine peptides). At least one peptide, representing each of the three M types tested, was immunogenic. Five of the nine synthetic peptides tested, elicited an immune response in mice, and sera raised against four of the peptides, all possessed functional activity as demonstrated in a bactericidal assay. In vivo nasopharyngeal challenge experiments were carried out with peptides from the M1 (peptide M1-3) and M3 (peptide M3-2) proteins induced in vivo immune protection by reducing intranasal carriage. Reduction in colonization for M1-3 and M3-2 was 90% (P=0.02) and 66% (P<0.17), respectively. A reduction in colonization of 67% (P=0.03) was observed for M3-2 immunized mice when M43, a heterologous serotype, was used as the challenge strain. These results show the utility of synthetic, M type-specific peptides as antigens in a multivalent GAS vaccine.

Potential of lipid core peptide technology as a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens

This study demonstrates the effectiveness of a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens by use of lipid core peptide (LCP) technology. An LCP formulation incorporating two different protective epitopes of the surface antiphagocytic M protein of group A streptococci (GAS)--the causative agents of rheumatic fever and subsequent rheumatic heart disease--was tested in a murine parenteral immunization and GAS challenge model. Mice were immunized with the LCP-GAS formulation, which contains an M protein amino-terminal type-specific peptide sequence (8830) in combination with a conserved non-host-cross-reactive carboxy-terminal C-region peptide sequence (J8) of the M protein. Our data demonstrated immunogenicity of the LCP-8830-J8 formulation in B10.BR mice when coadministered in complete Freund's adjuvant and in the absence of a conventional adjuvant. In both cases, immunization led to induction of high-titer GAS peptide-specific serum immunoglobulin G antibody responses and induction of highly opsonic antibodies that did not cross-react with human heart tissue proteins. Moreover, mice were completely protected from GAS infection when immunized with LCP-8830-J8 in the presence or absence of a conventional adjuvant. Mice were not protected, however, following immunization with an LCP formulation containing a control peptide from a Schistosoma sp. These data support the potential of LCP technology in the development of novel self-adjuvanting multi-antigen component vaccines and point to the potential application of this system in the development of human vaccines against infectious diseases.

Protection of mice from group A streptococcal infection by intranasal immunisation with a peptide vaccine that contains a conserved M protein B cell epitope and lacks a T cell autoepitope

Infection with group A streptococci (GAS) can lead to rheumatic fever (RF) and rheumatic heart disease (RHD) which are a major health concern particularly in indigenous populations worldwide, and especially in Australian Aboriginals. A primary route of GAS infection is via the upper respiratory tract, and therefore, a major goal of research is the development of a mucosal-based GAS vaccine. The majority of the research to date has focused on the GAS M protein since immunity to GAS is mediated by M protein type-specific opsonic antibodies. There are two major impediments to the development of a vaccine-the variability in M proteins and the potential for the induction of an autoimmune response. To develop a safe and broad-based vaccine, we have therefore focused on the GAS M protein conserved C-region, and have identified peptides, J8 and the closely related J8 peptide (J14), which may be important in protective immunity to GAS infection. Using a mucosal animal model system, our data have shown a high degree of throat GAS colonisation in B10.BR mice 24h following intranasal immunisation with the mucosal adjuvant, cholera toxin B subunit (CTB), and/or diptheria toxoid (dT) carrier, or PBS alone, and challenge with the M1 GAS strain. However, GAS colonisation of the throat was significantly reduced following intranasal immunisation of mice with the vaccine candidate J8 conjugated to dT or J14-dT when administered with CTB. Moreover, J8-dT/CTB and J14-dT/CTB-immunised mice had a significantly higher survival when compared to CTB and PBS-immunised control mice. These data indicate that immunity to GAS infection can be evoked by intranasal immunisation with a GAS M protein C-region peptide vaccine that contains a protective B cell epitope and lacks a T cell autoepitope.

Parenteral and mucosal delivery of a novel multi-epitope M protein-based group A streptococcal vaccine construct: investigation of immunogenicity in mice

Primary vaccine strategies against group A streptococci (GAS) have focused on the M protein--the target of opsonic antibodies important for protective immunity. We have previously reported protection of mice against GAS infection following parenteral delivery of a multi-epitope vaccine construct, referred to as a heteropolymer. This current report has assessed mucosal (intranasal (i.n.) and oral) delivery of the heteropolymer in mice with regard to the induction and specificity of mucosal and systemic antibody responses, and compared this to parenteral delivery. GAS-specific IgA responses were detected in saliva and gut upon i.n. and oral delivery of the heteropolymer co-administered with cholera toxin B subunit, respectively. High titre serum IgG responses were elicited to the heteropolymer following all routes of delivery when administered with adjuvant. Moreover, as with parenteral delivery, serum IgG antibodies were detected to the individual heteropolymer peptides following i.n. but not oral delivery. These data support the potential of the i.n. route in the mucosal delivery of a GAS vaccine.

A lipid core peptide construct containing a conserved region determinant of the group A streptococcal M protein elicits heterologous opsonic antibodies

The study reported here investigated the immunogenicity and protective potential of a lipid core peptide (LCP) construct containing a conserved region determinant of M protein, defined as peptide J8. Parenteral immunization of mice with LCP-J8 led to the induction of high-titer serum immunoglobulin G J8-specific antibodies when the construct was coadministered with complete Freund's adjuvant (CFA) or administered alone. LCP-J8 in CFA had significantly enhanced immunogenicity compared with the monomeric peptide J8 given in CFA. Moreover, LCP-J8/CFA and LCP-J8 antisera opsonized four different group A streptococcal (GAS) strains, and the antisera did not cross-react with human heart tissue proteins. These data indicate the potential of an LCP-based M protein conserved region GAS vaccine in the induction of broadly protective immune responses in the absence of a conventional adjuvant.

Adapting immunity with subunit vaccines: case studies with group A Streptococcus and malaria

Although vaccines have widely been regarded as the most cost-effective way to improve public health, for some organisms new technological advances in vaccine design and delivery, incurring additional developmental costs, will be essential. These organisms are typically those for which natural immunity is either slow to develop or does not develop at all. Clearly, such organisms have evolved strategies to evade immune responses and innovative approaches will be required to induce a type of immune response which is both different to that which develops naturally and is effective. This article describes some approaches to develop vaccines for two such organisms (malaria parasites and Streptococcus pyogenes (group A Streptococcus)) that are associated with widespread mortality and morbidity, mostly in the poorest countries of the world. At this stage, the challenges are primarily scientific, but if these hurdles are surmounted then the challenges will become financial ones--developing much needed vaccines for people least able to afford them.

Antibodies against a synthetic peptide of SagA neutralize the cytolytic activity of streptolysin S from group A streptococci

Virtually all group A streptococci (GAS) produce streptolysin S (SLS), a cytolytic toxin that is responsible for the beta-hemolysis surrounding colonies of the organisms grown on blood agar. SLS is an important virulence determinant of GAS, and recent studies have identified a nine-gene locus that is responsible for synthesis and transport of the toxin. SLS is not immunogenic; thus, no neutralizing antibodies are evoked during the course of natural infection. In the present study, we show that a synthetic peptide containing amino acid residues 10 to 30 of the putative SLS (SagA) propeptide [SLS(10-30)] coupled to keyhole limpet hemocyanin evoked antibodies in rabbits that completely neutralized the hemolytic activity of the toxin in vitro. Inhibition of hemolysis was reversed by preincubation of the immune serum with soluble, unconjugated peptide, indicating the specificity of the antibodies. In addition, antibodies that were affinity purified over an SLS(10-30) peptide column completely inhibited SLS-mediated hemolysis. The SLS(10-30) antisera did not opsonize group A streptococci; however, when combined with type-specific M protein antisera, the SLS antibodies significantly enhanced phagocytosis mediated by M protein antibodies. Thus, we have shown for the first time that it is possible to raise neutralizing antibodies against one of the most potent bacterial cytolytic toxins known. Our data also provide convincing evidence that the sagA gene actually encodes the SLS peptide of GAS. The synthetic peptide may prove to be an important component of vaccines designed to prevent GAS infections.

Immunogenicity of a 26-valent group A streptococcal vaccine

A multivalent vaccine containing amino-terminal M protein fragments from 26 different serotypes of group A streptococci was constructed by recombinant techniques. The vaccine consisted of four different recombinant proteins that were formulated with alum to contain 400 microg of protein per dose. Rabbits were immunized via the intramuscular route at 0, 4, and 16 weeks. Immune sera were assayed for the presence of type-specific antibodies against the individual recombinant M peptides by enzyme-linked immunosorbent assay and for opsonic antibodies by in vitro opsonization tests and indirect bactericidal tests. The 26-valent vaccine was highly immunogenic and elicited fourfold or greater increases in antibody levels against 25 of the 26 serotypes represented in the vaccine. The immune sera were broadly opsonic and were bactericidal against the majority of the 26 different serotypes. Importantly, none of the immune sera cross-reacted with human tissues. Our results indicate that type-specific, protective M protein epitopes can be incorporated into complex, multivalent vaccines designed to elicit broadly protective opsonic antibodies in the absence of tissue-cross-reactive antibodies.

Binding of human C4BP to the hypervariable region of M protein: a molecular mechanism of phagocytosis resistance in Streptococcus pyogenes

The amino-terminal hypervariable region (HVR) of streptococcal M protein is required for the ability of this virulence factor to confer phagocytosis resistance. The function of the HVR has remained unknown, but the finding that many HVRs with extremely divergent sequences bind the human complement regulator C4b-binding protein (C4BP) has suggested that this ligand may play a role in phagocytosis resistance. We used the M22 system to study the function of bound C4BP and provide several lines of evidence that C4BP indeed contributes to phagocytosis resistance. First, the ability of anti-HVR antibodies to cause opsonization correlated with their ability to inhibit binding of C4BP. Secondly, a short deletion in the HVR eliminated C4BP binding and also reduced the ability of M22 to confer phagocytosis resistance. Thirdly, the addition of an excess of pure C4BP to a phagocytosis system almost completely blocked the effect of opsonizing anti-HVR antibodies. Together, our data indicate that binding of C4BP to the HVR of M22 plays an important role in phagocytosis resistance, but other properties of M22 also contribute. This study provides the first molecular insight into the mechanisms by which the HVR of an M protein confers phagocytosis resistance.

Outbreak of scarlet fever caused by an erythromycin-resistant Streptococcus pyogenes emm22 genotype strain in a day-care center

We report an outbreak of scarlet fever and pharyngeal colonization with Streptococcus pyogenes in a day-care center in Mexico City. The outbreak strain was resistant to erythromycin but susceptible to clindamycin. T-type 11,12 serotype was found in eight isolates, from two patients and six carriers, which had the emm22 gene. The recognition of streptococci resistant to macrolides causing outbreaks has implications for infection control and for improving antibiotic prescribing patterns in the day-care setting.

Group A streptococcal genotypes from pediatric throat isolates in Rome, Italy

In a study assessing genetic diversity, 114 group A streptococcus (GAS) isolates were recovered from pediatric pharyngitis patients in Rome, Italy. These isolates comprised 22 different M protein gene (emm) sequence types, 14 of which were associated with a distinct serum opacity factor/fibronectin binding protein gene (sof) sequence type. Isolates with the same emm gene sequence type generally shared a highly conserved chromosomal macrorestriction profile. In three instances, isolates with dissimilar macrorestriction profiles had identical emm types; in each of these cases multilocus sequence typing revealed that isolates with the same emm type were clones having the same allelic profiles. Ninety-eight percent of the pharyngeal isolates had emm types previously found to be highly associated with mga locus gene patterns commonly found in pharyngeal GAS isolates.

Multilocus sequence typing of Streptococcus pyogenes and the relationships between emm type and clone

Multilocus sequence typing (MLST) is a tool that can be used to study the molecular epidemiology and population genetic structure of microorganisms. A MLST scheme was developed for Streptococcus pyogenes and the nucleotide sequences of internal fragments of seven selected housekeeping loci were obtained for 212 isolates. A total of 100 unique combinations of housekeeping alleles (allelic profiles) were identified. The MLST scheme was highly concordant with several other typing methods. The emm type, corresponding to a locus that is subject to host immune selection, was determined for each isolate; of the >150 distinct emm types identified to date, 78 are represented in this report. For a given emm type, the majority of isolates shared five or more of the seven housekeeping alleles. Stable associations between emm type and MLST were documented by comparing isolates obtained decades apart and/or from different continents. For the 33 emm types for which more than one isolate was examined, only five emm types were present on widely divergent backgrounds, differing at four or more of the housekeeping loci. The findings indicate that the majority of emm types examined define clones or clonal complexes. In addition, an MLST database is made accessible to investigators who seek to characterize other isolates of this species via the internet (http://www.mlst.net).

Protective and nonprotective epitopes from amino termini of M proteins from Australian aboriginal isolates and reference strains of group A streptococci

The M protein is the primary vaccine candidate to prevent group A streptococcal (GAS) infection and the subsequent development of rheumatic fever (RF). However, the large number of serotypes have made it difficult to design a vaccine against all strains. We have taken an approach of identifying amino-terminal M protein epitopes from GAS isolates that are highly prevalent in GAS-endemic populations within the Northern Territory (NT) of Australia. Australian Aboriginals in the NT experience the highest incidence of RF worldwide. To develop a vaccine for this population, 39 peptides were synthesized, representing the amino-terminal region of the M protein from endemic GAS. Mice immunized with these peptides covalently linked to tetanus toxoid and emulsified in complete Freund's adjuvant raised high-titer antibodies. Over half of these sera reduced bacterial colony counts by >80% against the homologous isolate of GAS. Seven of the peptide antisera also cross-reacted with at least three other heterologous peptides by enzyme-linked immunosorbent assay. Antiserum to one peptide, BSA10(1-28), could recognize six other peptides, and five of these peptides could inhibit opsonization mediated by BSA10(1-28) antiserum. Cross-opsonization studies showed that six of these sera could opsonize at least one heterologous isolate of GAS. These data reveal vaccine candidates specific to a GAS-endemic area and show the potential of some to cross-opsonize multiple isolates of GAS. This information will be critical when considering which epitopes may be useful in a multiepitope vaccine to prevent GAS infection.

Multi-epitope schistosome vaccine candidates tested for protective immunogenicity in mice

The major challenge in the development of anti-schistosome vaccines is to use defined antigens to stimulate an appropriate immune response that leads to resistance. Several promising candidate vaccine antigens including the glycolytic enzyme triose-phosphate isomerase (SmTPI), a 28 kDa glutathione-S-transferase (Sm28), the myofibrilar protein paramyosin (Sm97), an integral membrane protein (Sm23) and calpain (Smcalpain) have been characterised and their primary sequences derived for Schistosoma mansoni. Furthermore, sequences are available for synthetic peptides mimicking epitopes on these molecules capable of inducing schistosome-specific T- and B-cell responses. These schistosome vaccine candidates have generally been tested with varying degrees of success as single components, with only one report of the use of a multivalent antigen or multi-epitope approach. We describe the assembly of multiple defined and different epitopes of S. mansoni into a variety of single covalent structures; these included a DNA vaccine encoding different epitopes in tandem, the polyprotein itself that is encoded by this DNA and branched synthetic peptide epitope-based polymers in which the individual epitopes are pendant from an inert backbone. Each of the vaccine constructs examined, with the exception of the DNA vaccine, generated antibodies that were capable of binding to a tandem sequence of the epitopes. Although these results were encouraging, none of the constructs protected animals from subsequent challenge infection, indicating that the immune responses elicited were inadequate or inappropriate for parasite killing in vivo.

Pathogenesis of group A streptococcal infections

Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks. emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features. At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesins have been reported, and surface plasmin-binding proteins have been defined. The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation.

emm and sof gene sequence variation in relation to serological typing of opacity-factor-positive group A streptococci

Approximately 40-60% of group A streptococcal (GAS) isolates are capable of opacifying sera, due to the expression of the sof (serum opacity factor) gene. The emm (M protein gene) and sof 5' sequences were obtained from a diverse set of GAS reference strains and clinical isolates, and correlated with M serotyping and anti-opacity-factor testing results. Attempts to amplify sof from strains with M serotypes or emm types historically associated with the opacity-factor-negative phenotype were negative, except for emm12 strains, which were found to contain a highly conserved sof sequence. There was a strong correlation of certain M serotypes with specific emm sequences regardless of strain background, and likewise a strong association of specific anti-opacity-factor (AOF) types to sof gene sequence types. In several examples, M type identity, or partial identity shared between strains with differing emm types, was correlated with short, highly conserved 5' emm sequences likely to encode M-type-specific epitopes. Additionally, each of three pairs of historically distinct M type reference strains found to share the same 5' emm sequence, were also found to share M serotype specificity. Based upon sof sequence comparisons between strains of the same and of differing AOF types, an approximately 450 residue domain was determined likely to contain key epitopes required for AOF type specificity. Analysis of two Sof sequences that were not highly homologous, yet shared a common AOF type, further implicated a 107 aa portion of this 450-residue domain in putatively containing AOF-specific epitopes. Taken together, the serological data suggest that AOF-specific epitopes for all Sof proteins may reside within a region corresponding to this 107-residue sequence. The presence of specific, hypervariable emm/sof pairs within multiple isolates appears likely to be a reliable indicator of their overall genetic relatedness, and to be very useful for accurate subtyping of GAS isolates by an approach that has relevance to decades of past M-type-based epidemiological data.

New multi-determinant strategy for a group A streptococcal vaccine designed for the Australian Aboriginal population

Infection with group A streptococci can result in acute and post-infectious pathology, including rheumatic fever and rheumatic heart disease. These diseases are associated with poverty and are increasing in incidence, particularly in developing countries and amongst indigenous populations, such as Australia's Aboriginal population, who suffer the highest incidence worldwide. Immunity to group A streptococci is mediated by antibodies against the M protein, a coiled-coil alpha helical surface protein of the bacterium. Vaccine development faces two substantial obstacles. Although opsonic antibodies directed against the N terminus of the protein are mostly responsible for serotypic immunity, more than 100 serotypes exist. Furthermore, whereas the pathogenesis of rheumatic fever is not well understood, increasing evidence indicates an autoimmune process. To develop a suitable vaccine candidate, we first identified a minimum, helical, non-host-cross-reactive peptide from the conserved C-terminal half of the protein and displayed this within a non-M-protein peptide sequence designed to maintain helical folding and antigenicity, J14 (refs. 8,9). As this region of the M protein is identical in only 70% of group A streptococci isolates, the optimal candidate might consist of the conserved determinant with common N-terminal sequences found in communities with endemic group A streptococci. We linked seven serotypic peptides with J14 using a new chemistry technique that enables the immunogen to display all the individual peptides pendant from an alkane backbone. This construct demonstrated excellent immunogenicity and protection in mice.

New protective antigen of group A streptococci

It is widely believed that the surface M protein of group A streptococci is the predominant surface protein of these organisms containing opsonic epitopes. In the present study, we identified a new surface protein, distinct from M protein, that evokes protective antibodies. A type 18 M-negative mutant was found to be both resistant to phagocytosis in human blood and virulent in mice. The wild-type strain, but not the M-negative mutant, was opsonized by antisera against purified recombinant M18 protein or a synthetic peptide copying the NH2-terminus of M18. However, antisera raised against a crude pepsin extract of the M-negative mutant opsonized both strains, indicating the presence of a protective antigen in addition to type 18 M protein. This antiserum was used to identify and purify a 24-kDa protein fragment (Spa, streptococcal protective antigen) that evoked antibodies that opsonized the M18 parent and the M-negative mutant. The results of passive mouse protection tests confirmed the presence of protective epitopes within Spa. The deduced amino acid sequence of a 636-bp 5' fragment of the spa18 gene showed no homology with sequences in GenBank. These studies reveal the presence of a new protective antigen of certain strains of group A streptococci that may prove to be an important component of vaccines to prevent streptococcal infections.

Vaccines to prevent respiratory infection: opportunities on the near and far horizon

Illnesses caused by respiratory pathogens result in great loss of life, suffering and commitment of resources for treatment. That the suffering and loss of life can be prevented through immunization has already been clearly shown with existing vaccines, such as those for Haemophilus influenzae type b, Streptococcus pneumoniae, and influenza. The emergence of drug-resistant pathogens is making reliance on therapy more expensive and perhaps less successful, accentuating the need to focus on prevention. Although several effective vaccines to prevent respiratory infections currently exist, they are underutilized globally. Improvements in immunogenicity, efficacy, and ease of administration, and lowering the costs of some of the existing vaccines would augment the potential for prevention worldwide. The greatest opportunities for the prevention of respiratory infections will rest with vaccines that will become available in the future.

Group A streptococcal vaccines

The pathogenesis of group A streptococcal infections, and antigens that contribute to protective immune responses are reviewed. Several approaches to vaccine development are discussed. Data are provided from preclinical studies of multivalent M protein-based vaccines that evoke protective antibodies in laboratory animals. Also discussed are future strategies for the development of broadly protective vaccines, and their potential impact on the incidence of streptococcal infections, and acute rheumatic fever.

Vaccine strategies to prevent rheumatic fever

Group A streptococci (GAS) are responsible for numerous human illnesses, ranging from pharyngitis to severe invasive infections, such as necrotizing fascitis and toxic shock syndrome to the postinfectious sequelae, acute rheumatic fever (ARF), and glomerulonephritis. To date, to develop a vaccine, studies have focused on the M protein. However, designing a vaccine to prevent GAS infection based on this molecule has been hampered by the vast number of M protein serotypes and the possibility that it may induce potentially harmful autoimmune reactions. In this article, the authors discuss recent approaches to overcoming the problems of an M protein-based vaccine. In addition, recent studies identifying the protective properties of other streptococcal antigens and their potential as vaccine candidates are discussed.

Multivalent group A streptococcal vaccine designed to optimize the immunogenicity of six tandem M protein fragments

One of the major challenges in the development of group A streptococcal M protein-based vaccines is the multiplicity of M types expressed by these organisms. Previous studies have shown that multivalent vaccines containing as many as eight M protein fragments in tandem were immunogenic and evoked opsonic antibodies. It was also noted that the C-terminal fragments of these hybrid proteins were often not immunogenic or evoked only low levels of opsonic antibodies, suggesting that the C-terminus of the molecule may have been preferentially degraded or altered in vivo. In the present studies, we designed a hexavalent vaccine containing protective M protein peptides from types 24, 5, 6, 19, 1, and 3 group A streptococci. In order to "protect" the carboxy-terminal components, the amino-terminal M24 fragment was reiterated on the carboxy-terminal end of the construct. The hexavalent vaccine was immunogenic in laboratory animals and evoked high titers of antibodies against each of the native M proteins represented in the vaccine and bactericidal antibodies against all six sterotypes of group A streptococci. The vaccine was equally immunogenic when delivered in alum or in complete Freund's adjuvant. None of the immune sera contained antibodies that crossreacted with human heart tissue. Our results show that complex multivalent group A streptococcal vaccines can be designed in such a way that each M protein fragment is immunogenic and evokes protective antibodies.

Molecular analysis of the role of the group A streptococcal cysteine protease, hyaluronic acid capsule, and M protein in a murine model of human invasive soft-tissue infection

Human invasive soft-tissue infections caused by group A Streptococcus are associated with significant morbidity and mortality. To investigate the pathogenesis of these serious infections, we characterized the host response to bacterial challenge with an M-type 3 isolate recovered from a patient with necrotizing fasciitis, or with isogenic gene replacement mutants deficient in cysteine protease, hyaluronic acid capsule, or M protein in a murine model of human invasive soft-tissue infection. Animals challenged with the wild-type or cysteine protease-deficient strain developed spreading tissue necrosis at the site of inoculation, became bacteremic, and subsequently died. Histopathologic examination of the necrotic lesion revealed bacteria throughout inflamed subcutaneous tissue. Arterioles and venules in the subcutaneous layer were thrombosed and the overlying tissue was infarcted. In contrast, animals challenged with either an acapsular or M protein-deficient mutant developed a focal area of tissue swelling at the site of inoculation without necrosis or subsequent systemic disease. Histopathologic examination of the soft-tissue lesion demonstrated bacteria confined within a well-formed subcutaneous abscess. We conclude that the group A streptococcal hyaluronic acid capsule and M protein, but not the cysteine protease, are critical for the development of tissue necrosis, secondary bacteremia, and lethal infection in a murine model of human necrotizing fasciitis.