Anti-group A streptococcal vaccine epitope: structure, stability, and its ability to interact with HLA class II molecules

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.

Rapid determination of quaternary protein structures in complex biological samples

The understanding of complex biological systems is still hampered by limited knowledge of biologically relevant quaternary protein structures. Here, we demonstrate quaternary structure determination in biological samples using a combination of chemical cross-linking, high-resolution mass spectrometry and high-accuracy protein structure modeling. This approach, termed targeted cross-linking mass spectrometry (TX-MS), relies on computational structural models to score sets of targeted cross-linked peptide signals acquired using a combination of mass spectrometry acquisition techniques. We demonstrate the utility of TX-MS by creating a high-resolution quaternary model of a 1.8 MDa protein complex composed of a pathogen surface protein and ten human plasma proteins. The model is based on a dense network of cross-link distance constraints obtained directly in a mixture of human plasma and live bacteria. These results demonstrate that TX-MS can increase the applicability of flexible backbone docking algorithms to large protein complexes by providing rich cross-link distance information from complex biological samples.

Protein structure determination in complex biological samples is still challenging. Here, the authors develop a computational modeling-guided cross-linking mass spectrometry method, obtaining a high-resolution model of a 1.8 MDa protein assembly from cross-links detected in a mixture of human plasma and bacteria.

Next-Generation Sequencing Reveals That HLA-DRB3, -DRB4, and -DRB5 May Be Associated With Islet Autoantibodies and Risk for Childhood Type 1 Diabetes

The possible contribution of HLA-DRB3, -DRB4, and -DRB5 alleles to type 1 diabetes risk and to insulin autoantibody (IAA), GAD65 (GAD autoantibody [GADA]), IA-2 antigen (IA-2A), or ZnT8 against either of the three amino acid variants R, W, or Q at position 325 (ZnT8RA, ZnT8WA, and ZnT8QA, respectively) at clinical diagnosis is unclear. Next-generation sequencing (NGS) was used to determine all DRB alleles in consecutively diagnosed patients ages 1-18 years with islet autoantibody-positive type 1 diabetes (n = 970) and control subjects (n = 448). DRB3, DRB4, or DRB5 alleles were tested for an association with the risk of DRB1 for autoantibodies, type 1 diabetes, or both. The association between type 1 diabetes and DRB1*03:01:01 was affected by DRB3*01:01:02 and DRB3*02:02:01. These DRB3 alleles were associated positively with GADA but negatively with ZnT8WA, IA-2A, and IAA. The negative association between type 1 diabetes and DRB1*13:01:01 was affected by DRB3*01:01:02 to increase the risk and by DRB3*02:02:01 to maintain a negative association. DRB4*01:03:01 was strongly associated with type 1 diabetes (P = 10(-36)), yet its association was extensively affected by DRB1 alleles from protective (DRB1*04:03:01) to high (DRB1*04:01:01) risk, but its association with DRB1*04:05:01 decreased the risk. HLA-DRB3, -DRB4, and -DRB5 affect type 1 diabetes risk and islet autoantibodies. HLA typing with NGS should prove useful to select participants for prevention or intervention trials.

Streptococcus pyogenes strains in Sao Paulo, Brazil: molecular characterization as a basis for StreptInCor coverage capacity analysis

BACKGROUND

Several human diseases are caused by Streptococcus pyogenes, ranging from common infections to autoimmunity. Characterization of the most prevalent strains worldwide is a useful tool for evaluating the coverage capacity of vaccines under development. In this study, a collection of S. pyogenes strains from Sao Paulo, Brazil, was analyzed to describe the diversity of strains and assess the vaccine coverage capacity of StreptInCor.

METHODS

Molecular epidemiology of S. pyogenes strains was performed by emm-genotyping the 229 isolates from different clinical sites, and PCR was used for superantigen profile analysis. The emm-pattern and tissue tropism for these M types were also predicted and compared based on the emm-cluster classification.

RESULTS

The strains were fit into 12 different emm-clusters, revealing a diverse phylogenetic origin and, consequently, different mechanisms of infection and escape of the host immune system. Forty-eight emm-types were distinguished in 229 samples, and the 10 most frequently observed types accounted for 69 % of all isolates, indicating a diverse profile of circulating strains comparable to other countries under development. A similar proportion of E and A-C emm-patterns were observed, whereas pattern D was less frequent, indicating that the strains of this collection primarily had a tissue tropism for the throat. In silico analysis of the coverage capacity of StreptInCor, an M protein-conserved regionally based vaccine candidate developed by our group, had a range of 94.5 % to 59.7 %, with a mean of 71.0 % identity between the vaccine antigen and the predicted amino acid sequence of the emm-types included here.

CONCLUSIONS

This is the first report of S. pyogenes strain characterization in Sao Paulo, one of the largest cities in the world; thus, the strain panel described here is a representative sample for vaccine coverage capacity analysis. Our results enabled evaluation of StreptInCor candidate vaccine coverage capacity against diverse M-types, indicating that the vaccine candidate likely would induce protection against the diverse strains worldwide.

StreptInCor: a model of anti-Streptococcus pyogenes vaccine reviewed

Streptococcus pyogenes infections remain a health problem in multiple countries because of poststreptococcal sequelae, such as rheumatic fever and rheumatic heart disease. The epidemiological growth of streptococcal diseases in undeveloped and developing countries has encouraged many groups to study vaccine candidates for preventing group A streptococcus infections. We developed a vaccine epitope (StreptInCor) composed of 55 amino acid residues of the C-terminal portion of the M protein that encompasses both T and B cell protective epitopes. Using human blood samples, we showed that the StreptInCor epitope is recognized by individuals bearing different HLA class II molecules and could be considered a universal vaccine epitope. In addition, the StreptInCor molecular structure was solved by nuclear magnetic resonance spectroscopy, and a series of structural stability experiments was performed to elucidate its folding/unfolding mechanism. Using BALB-c and HLA class II transgenic mice, we evaluated the immune response over an extended period and found that StreptInCor was able to induce a robust immune response in both models. No cross-reaction was observed against cardiac proteins. The safety of the vaccine epitope was evaluated by analyzing histopathology, and no autoimmune or pathological reactions were observed in the heart or other organs. Vaccinated BALB/c mice challenged with a virulent strain of S. pyogenes had 100 % survival over 30 days. Taking all results into account, StreptInCor could be a safe and effective vaccine against streptococcus-induced disease.

Rheumatic Heart Disease: Molecules Involved in Valve Tissue Inflammation Leading to the Autoimmune Process and Anti-S. pyogenes Vaccine

The major events leading to both rheumatic fever (RF) and rheumatic heart disease (RHD) are reviewed. Several genes are involved in the development of RF and RHD. The inflammatory process that results from S. pyogenes infection involves the activation of several molecules such as VCAM and ICAM, which play a role in the migration of leukocytes to the heart, particularly to the valves. Specific chemokines, such as CXCL3/MIP1α as well as CCL1/I-309 and CXCL9/Mig, attract T cells to the myocardium and valves, respectively. The autoimmune reactions are mediated by both the B- and T-cell responses that begin at the periphery, followed by the migration of T cell clones to the heart and the infiltration of heart lesions in RHD patients. These cells recognize streptococcal antigens and human-tissue proteins. Molecular mimicry between streptococcal M protein and human proteins has been proposed as the triggering factor leading to autoimmunity in RF and RHD. The production of cytokines from peripheral and heart-infiltrating mononuclear cells suggests that T helper 1 and Th17 cytokines are the mediators of RHD heart lesions. The low numbers of IL-4 producing cells in the valvular tissue might contribute to the maintenance and progression of the valve lesions. The identification of a vaccine epitope opens a perspective of development of an effective and safe vaccine to prevent S. pyogenes infections, consequently RF and RHD.

Analysis of the coverage capacity of the StreptInCor candidate vaccine against Streptococcus pyogenes

Streptococcus pyogenes is responsible for infections as pharyngitis, sepsis, necrotizing fasciitis and streptococcal toxic shock syndrome. The M protein is the major bacterial antigen and consists of both polymorphic N-terminal portion and a conserved region. In the present study, we analyzed the in vitro ability of StreptInCor a C-terminal candidate vaccine against S. pyogenes to induce antibodies to neutralize/opsonize the most common S. pyogenes strains in Sao Paulo by examining the recognition by sera from StreptInCor immunized mice. We also evaluated the presence of cross-reactive antibodies against human heart valve tissue. Anti-StreptInCor antibodies were able to neutralize/opsonize at least 5 strains, showing that immunization with StreptInCor is effective against several S. pyogenes strains and can prevent infection and subsequent sequelae without causing autoimmune reactions.

StreptInCor: a candidate vaccine epitope against S. pyogenes infections induces protection in outbred mice

Infection with Streptococcus pyogenes (S. pyogenes) can result in several diseases, particularly in children. S. pyogenes M protein is the major virulence factor, and certain regions of its N-terminus can trigger autoimmune sequelae such as rheumatic fever in susceptible individuals with untreated group A streptococcal pharyngitis. In a previous study, we utilized a large panel of human peripheral blood cells to define the C-terminal protective epitope StreptInCor (medical identity), which does not induce autoimmune reactions. We recently confirmed the results in HLA-transgenic mice. In the present study, we extended the experimental assays to outbred animals (Swiss mice). Herein, we demonstrate high titers of StreptInCor-specific antibodies, as well as appropriate T-cell immune responses. No cross-reaction to cardiac myosin was detected. Additionally, immunized Swiss mice exhibited 87% survival one month after challenge with S. pyogenes. In conclusion, the data presented herein reinforce previous results in humans and animals and further emphasize that StreptInCor could be an effective and safe vaccine for the prevention of S. pyogenes infections.

Updated model of group A Streptococcus M proteins based on a comprehensive worldwide study

Group A Streptococcus (GAS) M protein is an important virulence factor and potential vaccine antigen, and constitutes the basis for strain typing (emm-typing). Although >200 emm-types are characterized, structural data were obtained from only a limited number of emm-types. We aim to evaluate the sequence diversity of near-full-length M proteins from worldwide sources and analyse their structure, sequence conservation and classification. GAS isolates recovered from throughout the world during the last two decades underwent emm-typing and complete emm gene sequencing. Predicted amino acid sequence analyses, secondary structure predictions and vaccine epitope mapping were performed using MUSCLE and Geneious software. A total of 1086 isolates from 31 countries were analysed, representing 175 emm-types. emm-type is predictive of the whole protein structure, independent of geographical origin or clinical association. Findings of an emm-type paired with multiple, highly divergent central regions were not observed. M protein sequence length, the presence or absence of sequence repeats and predicted secondary structure were assessed in the context of the latest vaccine developments. Based on these global data, the M6 protein model is updated to a three representative M protein (M5, M80 and M77) model, to aid in epidemiological analysis, vaccine development and M protein-related pathogenesis studies.

A vaccine against Streptococcus pyogenes: the potential to prevent rheumatic fever and rheumatic heart disease

Streptococcus pyogenes causes severe, invasive infections such as the sequelae associated with acute rheumatic fever, rheumatic heart disease, acute glomerulonephritis, uncomplicated pharyngitis, and pyoderma. Efforts to produce a vaccine against S. pyogenes began several decades ago, and different models have been proposed. We have developed a vaccine candidate peptide, StreptInCor, comprising 55 amino acid residues of the C-terminal portion of the M protein and encompassing both the T- and B-cell protective epitopes. The present article summarizes data from the previous 5 years during which we tested the immunogenicity and safety of StreptInCor in different animal models. We showed that StreptInCor overlapping peptides induced cellular and humoral immune responses of individuals bearing different HLA class II molecules. These results are consistent with peptides that have a universal vaccine epitope. The tridimensional molecular structure of StreptInCor was elucidated by nuclear magnetic resonance spectroscopy, which showed that its structure is composed of two microdomains linked by an 18-residue α-helix. Additionally, we comprehensively evaluated the structural stability of the StreptInCor peptide in different physicochemical conditions using circular dichroism. Additional experiments were performed with inbred, outbred, and HLA class II transgenic mice. Analysis of several organs of these mice showed neither deleterious nor autoimmune reactions even after a long period of vaccination, indicating that the StreptInCor candidate peptide could be considered as an immunogenic and safe vaccine.

HLA class II transgenic mice develop a safe and long lasting immune response against StreptInCor, an anti-group A streptococcus vaccine candidate

Streptococcus pyogenes infections remain a health problem in several countries because of post-streptococcal sequelae, such as rheumatic fever and rheumatic heart disease. We developed a vaccine epitope (StreptInCor) composed of 55 amino acid residues of the C-terminal portion of the M protein that encompasses both T and B cell protective epitopes. Recently, by using human blood samples, we showed that the StreptInCor epitope is able to bind to different HLA class II molecules and that it could be considered a universal vaccine epitope. In the present work, we evaluated the immune response of HLA class II transgenic mice against aluminum hydroxide-absorbed StreptInCor. After a period of one year, several organs were analyzed histologically to verify the safety of the candidate vaccine epitope. Our results showed that StreptInCor is able to induce robust and safe and long lasting immune response without deleterious reactions in several organs. In conclusion, the results presented here indicate that StreptInCor could be considered a safe vaccine against severe streptococcus-induced diseases.

Genes, autoimmunity and pathogenesis of rheumatic heart disease

Pathogenesis of rheumatic heart disease (RHD) remains incompletely understood. Several genes associated with RHD have been described; most of these are involved with immune responses. Single nucleotide polymorphisms in a number of genes affect patients with RHD compared to controls. Molecular mimicry between streptococcal antigens and human proteins, including cardiac myosin epitopes, vimentin and other intracellular proteins is central to the pathogenesis of RHD. Autoreactive T cells migrate from the peripheral blood to the heart and proliferate in the valves in response to stimulation with specific cytokines. The types of cells involved in the inflammation as well as different cytokine profiles in these patients are being investigated. High TNF alpha, interferon gamma, and low IL4 are found in the rheumatic valve suggesting an imbalance between Th1 and Th2 cytokines and probably contributing to the progressive and permanent valve damage. Animal model of ARF in the Lewis rat may further contribute towards understanding the ARF.