Immunogenicity in mice and non-human primates of the Group A Streptococcal J8 peptide vaccine candidate conjugated to CRM197

Peptide-Protein Conjugation and Characterization to Develop Vaccines for Group A Streptococcus

Peptide conjugates have been widely used for developing vaccines that prevent common bacterial infections for which peptides alone are either ineffective or provide only short-term protection. Among several carrier proteins, diphtheria toxoid and CRM₁₉₇ (a genetically detoxified diphtheria toxin) are considered safe and have been used in several licensed vaccines. For developing a vaccine against group A streptococcus (GAS), antigens from conserved region of M protein and the IL-8 protease, SpyCEP, have been identified. In this chapter, we describe a method for producing peptide-conjugate subunit GAS vaccines, which involves maleimide conjugation of peptides to a carrier protein and their subsequent characterization.

Antibodies to the conserved region of the M protein and a streptococcal superantigen cooperatively resolve toxic shock-like syndrome in HLA-humanized mice

Invasive streptococcal disease (ISD) and toxic shock syndrome (STSS) result in over 160,000 deaths each year. We modelled these in HLA-transgenic mice infected with a clinically lethal isolate expressing Streptococcal pyrogenic exotoxin (Spe) C and demonstrate that both SpeC and streptococcal M protein, acting cooperatively, are required for disease. Vaccination with a conserved M protein peptide, J8, protects against STSS by causing a dramatic reduction in bacterial burden associated with the absence of SpeC and inflammatory cytokines in the blood. Furthermore, passive immunotherapy with antibodies to J8 quickly resolves established disease by clearing the infection and ablating the inflammatory activity of the M protein, which is further enhanced by addition of SpeC antibodies. Analysis of 77 recent isolates of Streptococcus pyogenes causing ISD, demonstrated that anti-J8 antibodies theoretically recognize at least 73, providing strong support for using antibodies to J8, with or without antibodies to SpeC, as a therapeutic approach.

Application of built-in adjuvants for epitope-based vaccines

Several studies have shown that epitope vaccines exhibit substantial advantages over conventional vaccines. However, epitope vaccines are associated with limited immunity, which can be overcome by conjugating antigenic epitopes with built-in adjuvants (e.g., some carrier proteins or new biomaterials) with special properties, including immunologic specificity, good biosecurity and biocompatibility, and the ability to vastly improve the immune response of epitope vaccines. When designing epitope vaccines, the following types of built-in adjuvants are typically considered: (1) pattern recognition receptor ligands (i.e., toll-like receptors); (2) virus-like particle carrier platforms; (3) bacterial toxin proteins; and (4) novel potential delivery systems (e.g., self-assembled peptide nanoparticles, lipid core peptides, and polymeric or inorganic nanoparticles). This review primarily discusses the current and prospective applications of these built-in adjuvants (i.e., biological carriers) to provide some references for the future design of epitope-based vaccines.

Investigation of group A Streptococcus immune responses in an endemic setting, with a particular focus on J8

Sustained control of group A Streptococcus (GAS) infections in settings of poverty has proven to be challenging, and an effective vaccine may be the most practical long-term strategy to reduce GAS-related disease burden. Candidate GAS vaccines based on the J8 peptide have demonstrated promising immunogenicity in mice, however, less is known about the role of J8 antibodies in the human immune response to GAS infection. We analysed the stimulation of J8 antibodies in response to infection, and the role of existing J8 antibodies in protection against subsequent infection, using data collected in the Fijian population: (1) cross sectional population serosurvey; (2) paired serum collection for assessment of M-specific and J8 antibody responses; and (3) longitudinal assessment of GAS infection and immunity. Median J8 antibody concentrations peaked in the 5-14 year age group, but there was no sustained increase with age. J8 antibody concentration was neither a significant predictor of time to next infection, nor did it show any relationship to the time since last recorded skin infection. Similarly, J8 antibody fold changes over a defined period were associated neither with the time since last skin infection, nor the number of intervening skin infections. While strong M-specific antibody responses were observed for skin infection, similarly strong J8 antibody responses were not observed. There is no indication that antibodies to the J8 antigen would be useful as either a marker of GAS infection or a measure of population immunity, with J8 antibody responses to infection fleeting, if existent at all.

Evaluation of safety and immunogenicity of a group A streptococcus vaccine candidate (MJ8VAX) in a randomized clinical trial

BACKGROUND

Group A streptococcus (GAS) is a serious human pathogen that affects people of different ages and socio-economic levels. Although vaccination is potentially one of the most effective methods to control GAS infection and its sequelae, few prototype vaccines have been investigated in humans. In this study, we report the safety and immunogenicity of a novel acetylated peptide-protein conjugate vaccine candidate MJ8VAX (J8-DT), when delivered intramuscularly to healthy adults.

METHODS

A randomized, double-blinded, controlled Phase I clinical trial was conducted in 10 healthy adult participants. Participants were randomized 4:1 to receive the vaccine candidate (N = 8) or placebo (N = 2). A single dose of the vaccine candidate (MJ8VAX), contained 50 μg of peptide conjugate (J8-DT) adsorbed onto aluminium hydroxide and re-suspended in PBS in a total volume of 0.5 mL. Safety of the vaccine candidate was assessed by monitoring local and systemic adverse reactions following intramuscular administration. The immunogenicity of the vaccine was assessed by measuring the levels of peptide (anti-J8) and toxoid carrier (anti-DT)-specific antibodies in serum samples.

RESULTS

No serious adverse events were reported over 12 months of study. A total of 13 adverse events (AEs) were recorded, two of which were assessed to be associated with the vaccine. Both were mild in severity. No local reactogenicity was recorded in any of the participants. MJ8VAX was shown to be immunogenic, with increase in vaccine-specific antibodies in the participants who received the vaccine. The maximum level of vaccine-specific antibodies was detected at 28 days post immunization. The level of these antibodies decreased with time during follow-up. Participants who received the vaccine also had a corresponding increase in anti-DT serum antibodies.

CONCLUSIONS

Intramuscular administration of MJ8VAX was demonstrated to be safe and immunogenic. The presence of DT in the vaccine formulation resulted in a boost in the level of anti-DT antibodies.

TRIAL REGISTRATION

ACTRN12613000030774.

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.

A modification-specific peptide-based immunization approach using CRM197 carrier protein: Development of a selective vaccine against pyroglutamate Aβ peptides

Strategies aimed at reducing cerebral accumulation of the amyloid-β (Aβ) peptides have therapeutic potential in Alzheimer's disease (AD). Aβ immunization has proven to be effective at promoting Aβ clearance in animal models but adverse effects have hampered its clinical evaluation. The first anti-Aβ immunization clinical trial, which assessed a full-length Aβ1-42 vaccine, increased the risk of encephalitis most likely because of autoimmune pro-inflammatory T helper 1 (Th1) response against all forms of Aβ. Immunization against less abundant but potentially more pathologically relevant Aβ products, such as N-terminally-truncated pyroglutamate-3 Aβ (AβpE3), could provide efficacy and improve tolerability in Aβ immunotherapy. Here, we describe a selective vaccine against AβpE3, which uses the diphtheria toxin mutant CRM197 as carrier protein for epitope presentation. CRM197 is currently used in licensed vaccines and has demonstrated excellent immunogenicity and safety in humans. In mice, our AβpE3:CRM197 vaccine triggered the production of specific anti-AβpE3 antibodies that did not cross-react with Aβ1-42, non-cyclized AβE3, or N-terminally-truncated pyroglutamate-11 Aβ (AβpE11). AβpE3:CRM197 antiserum strongly labeled AβpE3 in insoluble protein extracts and decorated cortical amyloid plaques in human AD brains. Anti-AβpE3 antibodies were almost exclusively of the IgG1 isotype, suggesting an anti-inflammatory Th2 response bias to the AβpE3:CRM197 vaccine. To the best of our knowledge, this study shows for the first time that CRM197 has potential as a safe and suitable vaccine carrier for active and selective immunization against specific protein sequence modifications or conformations, such as AβpE3.

Modification of the classical Lancefield assay of group A streptococcal killing to reduce inter-donor variation

The lack of a surrogate-of-immunity assay presents a major barrier to Streptococcus pyogenes research. Modification of the Lancefield assay to include an antibody digestion step reduced inter-donor variation and permitted detection of the anti-streptococcal activity of intravenous immunoglobulin and convalescent serum, thus facilitating retrospective evaluation of immunity using stored samples.

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The lack of a surrogate-of-immunity assay is a major barrier to S. pyogenes research.

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Pre-treatment of whole blood with IdeS standardised bacterial growth between donors.

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IdeS was subsequently inhibited using a non-cytotoxic iodoacetamide derivative.

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The bactericidal action of stored samples could then be measured by Lancefield assay.

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The modified assay facilitates retrospective dissection of anti-S. pyogenes immunity.

Preclinical evaluations of peptide-conjugate vaccines targeting the antigenic domain-2 of glycoprotein B of human cytomegalovirus

The Antigenic Domain 2 (AD-2) is a short region near the N-terminus of glycoprotein B of human cytomegalovirus (HCMV). AD-2 has been shown to contain linear epitopes that are targets for neutralizing monoclonal antibodies from human subjects with natural HCMV infection. However, AD-2 appears to be masked by the adjacent immunodominant AD-1 region. We assessed a serum panel from HCMV-seropositive individuals and found a wide range of antibody titers to AD-2; these did not correlate to serum neutralization. To expose potential epitopes in AD-2, we constructed a series of AD-2 peptide-conjugate vaccines. Mice were immunized 3 times and produced high and sustained antibody titers to AD-2 peptides, but neutralization was weak even after a single boost with whole HCMV virions. Rabbits were likewise immunized with AD-2 peptide vaccines, and produced a robust antibody response, but neutralization was inferior to a recombinant gB vaccine with an oil-in-water adjuvant. These results highlight the challenges of developing a peptide-based vaccine specific to the HCMV gB AD-2 region.

Identifying protective Streptococcus pyogenes vaccine antigens recognized by both B and T cells in human adults and children

No commercial vaccine exists against Group A streptococci (GAS; Streptococcus pyogenes) and only little is known about anti-GAS protective immunity. In our effort to discover new protective vaccine candidates, we selected 21 antigens based on an in silico evaluation. These were all well-conserved among different GAS strains, upregulated in host-pathogen interaction studies, and predicted to be extracellular or associated with the surface of the bacteria. The antigens were tested for both antibody recognition and T cell responses in human adults and children. The antigenicity of a selected group of antigens was further validated using a high-density peptide array technology that also identified the linear epitopes. Based on immunological recognition, four targets were selected and tested for protective capabilities in an experimental GAS infection model in mice. Shown for the first time, three of these targets (spy0469, spy1228 and spy1801) conferred significant protection whereas one (spy1643) did not.

Adaptive Immunity against Streptococcus pyogenes in Adults Involves Increased IFN-γ and IgG3 Responses Compared with Children

Each year, millions of people are infected with Streptococcus pyogenes, leading to an estimated 500,000 annual deaths worldwide. For unknown reasons, school-aged children have substantially higher infection rates than adults. The goal for this study was to provide, to our knowledge, the first detailed characterization of the human adaptive immune response against S. pyogenes in both children and adults. We report that all adults in our study, as well as most children, showed immunity against the two conserved group A streptococci (GAS) Ags, streptococcal C5a peptidase and immunogenic secreted protein. The response primarily consisted of three subsets of Th1 T cells, in which the TNF-α(+) and IL-2(+)TNF-α(+) subsets were most frequent. Humoral immunity was dominated by IgG1 and IgG3, whereas the Th2-associated IgG4 isotype was only detected at very low amounts. IgG3 levels correlated significantly with IFN-γ, but not with IL-5, IL-13, IL-17, or TNF-α. Interestingly, children showed a similar pattern of Ag-specific cytokine release, but displayed significantly lower levels of IgG3 and IFN-γ compared with adults. Thus, human immune responses against S. pyogenes consist of a robust Th1 cellular memory response in combination with IgG1/IgG3-dominated humoral immunity that increase with age. The significance of these data regarding both the increased GAS infection rate in children and the development of protective GAS vaccines is discussed.

The contribution of non-human primate models to the development of human vaccines

The non-human primates (NHPs) model in biomedical research has contributed to the study of human infectious, autoimmune, oncogenic, and neurological diseases. This review focuses on the importance of NHP models in vaccine development for tuberculosis, pertussis, Dengue, group A streptococcus (Streptococcus pyogenes) infection, HIV infection, and certain diseases in the elderly (influenza, for example). From understanding disease pathogenesis and mechanisms of protection, to assessing vaccine safety and efficacy, we discuss selected cases where the importance of the use of NHP models is highlighted.