M-protein-derived conformational peptide epitope vaccine candidate against Group A Streptococcus

Identification of the most relevant epitopes is the initial challenge of peptide-based vaccine design. Chimeric conserved epitopes of the Group A Streptococcus (GAS) M-protein were used in the development of an anti-GAS vaccine candidate. Previously, these epitopes have incorporated a GCN4 peptide from yeast to maintain their native helical structure. Here, we designed a new peptide epitope based on the minimal B-cell epitope from GAS M-protein. This new epitope was able to adopt the desired helical conformation without the need for the foreign GCN4 flanking sequence. The selected epitope induced significant immune responses upon administration with external adjuvant, and when incorporated into the Lipid Core Peptide (LCP) system. Moreover, the antibodies produced against this epitope were able to recognize the native p145 sequence from M-protein.

Apoptosis and dysfunction of blood dendritic cells in patients with falciparum and vivax malaria

Acute Plasmodium infections in humans result in dendritic cell dysfunction and apoptosis caused in part by elevated levels of IL-10.

Malaria causes significant morbidity worldwide and a vaccine is urgently required. Plasmodium infection causes considerable immune dysregulation, and elicitation of vaccine immunity remains challenging. Given the central role of dendritic cells (DCs) in initiating immunity, understanding their biology during malaria will improve vaccination outcomes. Circulating DCs are particularly important, as they shape immune responses in vivo and reflect the functional status of other subpopulations. We performed cross-sectional and longitudinal assessments of the frequency, phenotype, and function of circulating DC in 67 Papuan adults during acute uncomplicated P. falciparum, P. vivax, and convalescent P. falciparum infections. We demonstrate that malaria patients display a significant reduction in circulating DC numbers and the concurrent accumulation of immature cells. Such alteration is associated with marked levels of spontaneous apoptosis and impairment in the ability of DC to mature, capture, and present antigens to T cells. Interestingly, sustained levels of plasma IL-10 were observed in patients with acute infection and were implicated in the induction of DC apoptosis. DC apoptosis was reversed upon IL-10 blockade, and DC function recovered when IL-10 levels returned to baseline by convalescence. Our data provide key information on the mechanisms behind DC suppression during malaria and will assist in developing strategies to better harness DC’s immunotherapeutic potential.

Cross-species malaria immunity induced by chemically attenuated parasites

Vaccine development for the blood stages of malaria has focused on the induction of antibodies to parasite surface antigens, most of which are highly polymorphic. An alternate strategy has evolved from observations that low-density infections can induce antibody-independent immunity to different strains. To test this strategy, we treated parasitized red blood cells from the rodent parasite Plasmodium chabaudi with seco-cyclopropyl pyrrolo indole analogs. These drugs irreversibly alkylate parasite DNA, blocking their ability to replicate. After administration in mice, DNA from the vaccine could be detected in the blood for over 110 days and a single vaccination induced profound immunity to different malaria parasite species. Immunity was mediated by CD4+ T cells and was dependent on the red blood cell membrane remaining intact. The human parasite, Plasmodium falciparum, could also be attenuated by treatment with seco-cyclopropyl pyrrolo indole analogs. These data demonstrate that vaccination with chemically attenuated parasites induces protective immunity and provide a compelling rationale for testing a blood-stage parasite-based vaccine targeting human Plasmodium species.

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

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

Polymer-peptide hybrids as a highly immunogenic single-dose nanovaccine

AIM

To explore four-arm star poly(t-butyl)acrylate (P(t)BA)-peptide and linear P(t)BA-peptide conjugates as a vaccine-delivery system against Group A Streptococcus.

MATERIALS & METHODS

P(t)BA nanoparticles bearing J14 peptide epitopes were prepared via alkyne-azide 1,3-dipolar cycloaddition 'click' reaction. The conjugated products were self-assembled into small or large nanoparticles. These nanoparticle vaccine candidates were evaluated in vivo and J14-specific antibody titers were assessed.

RESULTS & DISCUSSION

Mice vaccinated with the nanoparticles were able to produce J14-specific IgG antibodies without the use of an external adjuvant after a single immunization. We have demonstrated for the first time that the immune responses against self-assembled P(t)BA nanoparticles are stronger for the smaller sized (~20 nm) nanoparticles compared with the larger (~500 nm) P(t)BA nanoparticles.

CONCLUSION

PtBA analogs have the potential to be developed as potent carrier systems for single-dose synthetic vaccines.

An efficient, chemically-defined semisynthetic lipid-adjuvanted nanoparticulate vaccine development system

A novel vaccine development platform that enables the site-specific conjugation of synthetic lipid adjuvants to recombinant proteins was produced. This technology facilitates the simple and efficient production of homogeneous, chemically-defined, semisynthetic lipoprotein vaccines. Using a polytope 'string-of-beads' approach, a synthetic gene incorporating seven Streptococcus pyogenes M protein strain-specific antigens, and a conserved M protein antigen (J14) was produced, expressed, and attached to a lipoamino acid based adjuvant (lipid core peptide; LCP). Nanoparticles (40 nm diameter) of an optimal size for stimulating antibody-mediated immunity were formed upon the addition of these lipoproteins to aqueous buffer (PBS). Systemic antigen-specific IgG antibodies were raised against all eight antigens in C57BL/6J mice, without the need to formulate with additional adjuvant. These antibodies bound cell surface M proteins of S. pyogenes strains represented within the polytope sequence, with higher antibody levels observed where a dendritic cell targeting peptide (DCpep) was incorporated within the LCP adjuvant.

FROM THE CLINICAL EDITOR

In this study, a novel vaccine development system is presented, combining adjuvants with recombinant protein antigens, and presenting the antigen in a nanoparticle system optimized for antibody production. They demonstrate efficient vaccination in a murine model system without the need for additional adjuvants.

Long-term antibody memory induced by synthetic peptide vaccination is protective against Streptococcus pyogenes infection and is independent of memory T cell help

Streptococcus pyogenes (group A Streptococcus [GAS]) is a leading human pathogen associated with a diverse array of mucosal and systemic infections. Vaccination with J8, a conserved region synthetic peptide derived from the M-protein of GAS and containing only 12 aa from GAS, when conjugated to diphtheria toxoid, has been shown to protect mice against a lethal GAS challenge. Protection has been previously shown to be Ab-mediated. J8 does not contain a dominant GAS-specific T cell epitope. The current study examined long-term Ab memory and dissected the role of B and T cells. Our results demonstrated that vaccination generates specific memory B cells (MBC) and long-lasting Ab responses. The MBC response can be activated following boost with Ag or limiting numbers of whole bacteria. We further show that these memory responses protect against systemic infection with GAS. T cell help is required for activation of MBC but can be provided by naive T cells responding directly to GAS at the time of infection. Thus, individuals whose T cells do not recognize the short synthetic peptide in the vaccine will be able to generate a protective and rapid memory Ab response at the time of infection. These studies significantly strengthen previous findings, which showed that protection by the J8-diphtheria toxoid vaccine is Ab-mediated and suggest that in vaccine design for other organisms the source of T cell help for Ab responses need not be limited to sequences from the organism itself.

Induction of anti-Plasmodium immunity following subpatent infection with live erythrocytic stages and drug cure

An effective malaria vaccine remains an important priority for the millions of people living in malaria endemic regions. Subambitious goals for the development of a vaccine have been set, which aim to achieve a licensed first-generation P. falciparum malaria vaccine with more than 50% protective efficacy against severe disease and death, lasting for at least 1 year by 2015. These goals were set in the context of a subunit vaccine. However, a whole-parasite vaccine might be expected to induce substantially superior protection. Our group has been focusing on low dose blood-stage parasites as a valid vaccine approach, and we present here the relevant methodology for this.

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

Vaccine development for Group A streptococcal (GAS) infection has been extensively focused on the N-terminal hypervariable or the C-terminal conserved regions of the M protein, a major virulence factor of GAS. We evaluated the immunogenicity and functional activity of the conserved C-terminal peptide vaccine candidate, J8, conjugated to CRM197, in two mouse strains: C3H (H2(k)) and Balb/c (H2(d)), and in rhesus macaques. Mice were immunized with J8-CRM197 formulated with Amorphous Aluminum Hydroxyphosphate Sulfate Adjuvant (AAHSA), and non-human primates were immunized with J8-CRM197 formulated with AAHSA, ISCOMATRIX (TM) adjuvant, or AAHSA/ISCOMATRIX adjuvant. J8-CRM197 was immunogenic in mice from both H2(k) and H2(d) backgrounds, and the antibodies generated bound to the surface of four different GAS serotypes and had functional bacterial opsonic activity. Mice immunized with J8-CRM197/AAHSA demonstrated varying degrees of protection from lethal challenge. We also demonstrated that J8-CRM197 is immunogenic in non-human primates. Our data confirm the utility of J8 as a potential GAS vaccine candidate and demonstrate that CRM197 is an acceptable protein carrier for this peptide.

Immunological evaluation of lipopeptide group A streptococcus (GAS) vaccine: structure-activity relationship

Streptococcus pyogenes (group A streptococcus, GAS) is a Gram-positive bacterial pathogen responsible for a wide variety of diseases. To date, GAS vaccine development has focused primarily on the M-protein. The M-protein is highly variable at the amino (N)-terminus (determining serotype) but is conserved at the carboxyl (C)-terminus. Previously a 29 amino acid peptide (named J14) from the conserved region of the M-protein was identified as a potential vaccine candidate. J14 was capable of eliciting protective antibodies that recognized many GAS serotypes when co-administered with immuno-stimulants. This minimal epitope however showed no immunogenicity when administered alone. In an attempt overcome this immunological non-responsiveness, we developed a self-adjuvanting vaccine candidate composed of three components: the B-cell epitope (J14), a universal helper T-cell epitope (P25) and a lipid moiety consisting of lipoamino acids (Laas) which target Toll-like receptor 2 (TLR2). Immunological evaluation in B10.BR (H-2k) mice demonstrated that the epitope attachment to the point of lipid moiety, and the length of the Laa alkyl chain have a profound effect on vaccine immunogenicity after intranasal administration. It was demonstrated that a vaccine featuring C-terminal lipid moiety containing alkyl chains of 16 carbons, with P25 located at the N-terminus, and J14 attached to the side chain of a central lysine residue was capable of inducing optimal antibody response. These findings have considerable relevance to the development of a broad spectrum J14-based GAS vaccine and in particular provided a rational basis for peptide vaccine design based on this self-adjuvanting lipopeptide technology.

Experimental asexual blood stage malaria immunity

Immunity to asexual blood stages of malaria is complex, involving both humoral and cell-mediated immune mechanisms. The availability of murine models of malaria has greatly facilitated the analysis of immune mechanisms involved in resistance to the asexual blood stages. This unit details the materials and methods required for inducing protective immunity toward experimental blood stage malaria parasites by vaccination, repeated infection, and drug cure, as well as adoptive transfer of antigen-specific T cells.

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

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

A whole parasite vaccine to control the blood stages of Plasmodium: the case for lateral thinking

Now, 27 years following the cloning of malaria antigens with the promise of the rapid development of a malaria vaccine, we face significant obstacles that are belatedly being addressed. Poor immunogenicity of subunit vaccine antigens and significant antigenic diversity of target epitopes represent major hurdles for which there are no clear strategies for a way forward within the current paradigm. Thus, a different paradigm - a vaccine that uses the whole organism - is now being examined. Although most advances in this approach relate to a vaccine for the pre-erythrocytic stages (sporozoites, liver stages), this opinion paper will outline the possibilities of developing a whole parasite vaccine for the blood stage and address some of the challenges for this strategy, which are entirely different to the challenges for a subunit vaccine. It is the view of the author that both vaccine paradigms should be pursued, but that success will come more quickly using the paranormal approach of exposing individuals to ultra-low doses of whole attenuated or killed parasites.

Our impasse in developing a malaria vaccine

Malaria presents a challenge to world health that to date has been beyond the abilities of researchers to conquer. This critique presents some of the strategies employed by the parasite to overcome immunity and the immunological challenges that we face to develop vaccines. A conclusion is that a vaccine must identify novel antigens or epitopes that are not normally immunogenic and which are therefore not under immune pressure and most likely to be conserved between different strains. Such antigens are most likely to be targets of cellular immunity. The case for a whole parasite blood stage vaccine is presented based on these premises.

A vaccine to provide strain-transcending immunity to group A streptococci

Organisms such a Streptococcus pyogenes (group A streptococcus), Plasmodium spp parasites and HIV present significant obstacles to vaccine development. They can subvert the immune system and present dominant antigens that can display a vast array of allelic types of variants. In spite of these obvious decoys, the main strategy to develop vaccines for these organisms has been to focus on dominant antigens or epitopes. The obvious reason for this approach is that such antigens and epitopes are easy to define. Early successes are often posted largely because homologous organisms are typically used to challenge animals post-vaccination. However, success in efficacy trials with heterologous challenge is yet to be seen.

Immune-mediated mechanisms of parasite tissue sequestration during experimental cerebral malaria

Cerebral malaria is a severe complication of malaria. Sequestration of parasitized RBCs in brain microvasculature is associated with disease pathogenesis, but our understanding of this process is incomplete. In this study, we examined parasite tissue sequestration in an experimental model of cerebral malaria (ECM). We show that a rapid increase in parasite biomass is strongly associated with the induction of ECM, mediated by IFN-gamma and lymphotoxin alpha, whereas TNF and IL-10 limit this process. Crucially, we discovered that host CD4(+) and CD8(+) T cells promote parasite accumulation in vital organs, including the brain. Modulation of CD4(+) T cell responses by helminth coinfection amplified CD4(+) T cell-mediated parasite sequestration, whereas vaccination could generate CD4(+) T cells that reduced parasite biomass and prevented ECM. These findings provide novel insights into immune-mediated mechanisms of ECM pathogenesis and highlight the potential of T cells to both prevent and promote infectious diseases.