Human protective response induced by meningococcus B vaccine is mediated by the synergy of multiple bactericidal epitopes

4CMenB is the first broad coverage vaccine for the prevention of invasive meningococcal disease caused by serogroup B strains. To gain a comprehensive picture of the antibody response induced upon 4CMenB vaccination and to obtain relevant translational information directly from human studies, we have isolated a panel of human monoclonal antibodies from adult vaccinees. Based on the Ig-gene sequence of the variable region, 37 antigen-specific monoclonal antibodies were identified and produced as recombinant Fab fragments, and a subset also produced as full length recombinant IgG1 and functionally characterized. We found that the monoclonal antibodies were cross-reactive against different antigen variants and recognized multiple epitopes on each of the antigens. Interestingly, synergy between antibodies targeting different epitopes enhanced the potency of the bactericidal response. This work represents the first extensive characterization of monoclonal antibodies generated in humans upon 4CMenB immunization and contributes to further unraveling the immunological and functional properties of the vaccine antigens. Moreover, understanding the mechanistic nature of protection induced by vaccination paves the way to more rational vaccine design and implementation.

HCV E1E2-MF59 vaccine in chronic hepatitis C patients treated with PEG-IFNα2a and Ribavirin: a randomized controlled trial

Hepatitis C virus (HCV) vaccines may be able to increase viral clearance in combination with antiviral therapy. We analysed viral dynamics and HCV-specific immune response during retreatment for experienced patients in a phase Ib study with E1E2MF59 vaccine. Seventy-eight genotype 1a/1b patients [relapsers (30), partial responders (16) and nonresponders (32) to interferon-(IFN)/ribavirin-(RBV)] were randomly assigned to vaccine (V:23), Peg-IFNα2a-180-ug/qw and ribavirin 1000-1200-mg/qd for 48 weeks (P/R:25), or their combination (P/R + V:30). Vaccine (100 μg/0.5 mL) was administered intramuscularly at week 0-4-8-12-24-28-32-36. Neutralizing of binding (NOB) antibodies and lymphocyte proliferation assay (LPA) for E1E2-specific-CD4 + T cells were performed at week 0-12-16-48. Viral kinetics were analysed up to week 16. The vaccine was safe, and a sustained virological response (SVR) was achieved in 4 P/R + V and 2 P/R patients. Higher SVR rates were observed in prior relapsers (P/R + V = 27.3%; P/R = 12.5%). Higher NOB titres and LPA indexes were found at week 12 and 16 in P/R + V as compared to P/R patients (P = 0.023 and 0.025, P = 0.019 and <0.001, respectively). Among the 22 patients with the strongest direct antiviral effects of IFN (ε ≥ 0.800), those treated with P/R + V (10) reached lower HCV-RNA levels (P = 0.026) at week 16. HCV E1E2MF59 vaccine in combination with Peg-IFNα2a + RBV was safe and elicited E1E2 neutralizing antibodies and specific CD4 + T cell proliferation. Upon early response to IFN, vaccinations were associated with an enhanced second phase viral load decline. These results prompt phase II trials in combination with new antiviral therapies.

Deep sequencing in pre- and clinical vaccine research

Vaccine research has experienced a quantum leap after the beginning of the genomics era. High-throughput sequencing techniques, unlimited computing resources, as well as new bioinformatic algorithms are now changing the way we perform genomic studies. Whole genome sequencing will soon become the gold standard for phylogenetic and epidemiology studies and is already shedding new light on the dynamics of bacterial evolution. We believe that deep sequencing projects, together with structural studies on vaccine candidates, will allow targeting constant epitopes and avoid vaccine failure due to antigenic variability. Systems biology, which is expected to revolutionize vaccine research and clinical studies, greatly relies on high-throughput technologies such as RNA-seq. Furthermore, genomics is a key element to develop safer vaccines, and the accuracy of deep sequencing will allow monitoring vaccine coverage after their introduction on the market.

Developing vaccines in the era of genomics: a decade of reverse vaccinology

Vaccines have a significant impact on public health, and vaccinology in the era of genomics is taking advantage of new technologies to tackle diseases for which vaccine development has so far been unsuccessful. Almost all existing vaccines were developed based on traditional vaccinology methods, which relied on empirical screening of a few candidates at a time, based on known features of the pathogen. However, the ability to sequence a pathogen's genome provides access to its entire antigenic repertoire. As such, genomics has catalysed a shift in vaccine development towards sequence-based 'Reverse Vaccinology' approaches, which use high-throughput in silico screening of the entire genome of a pathogen to identify genes that encode proteins with the attributes of good vaccine targets. Furthermore, the increasing availability of genome sequences has led to the development and application of additional technologies to vaccine discovery, including comparative genomics, transcriptomics, proteomics, immunomics and structural genomics. Vaccine candidates identified from a pathogen's genome or proteome can then be expressed as recombinant proteins and tested in appropriate in vitro or in vivo models to assess immunogenicity and protection. The process of reverse vaccinology has been applied to several pathogens, including serogroup B Neisseria meningitidis, Streptococcus agalactiae, Streptococcus pyogenes, Streptococcus pneumoniae and pathogenic Escherichia coli, and has provided scores of new candidate antigens for preclinical and clinical investigation. As novel genome-based technologies continue to emerge, it is expected that new vaccines for unmet diseases will be within reach.

RrgA is a pilus-associated adhesin in Streptococcus pneumoniae

Adherence to host cells is important in microbial colonization of a mucosal surface, and Streptococcus pneumoniae adherence was significantly enhanced by expression of an extracellular pilus composed of three subunits, RrgA, RrgB and RrgC. We sought to determine which subunit(s) confers adherence. Bacteria deficient in RrgA are significantly less adherent than wild-type organisms, while overexpression of RrgA enhances adherence. Recombinant monomeric RrgA binds to respiratory cells, as does RrgC with less affinity, and pre-incubation of epithelial cells with RrgA reduces adherence of wild-type piliated pneumococci. Non-adherent RrgA-negative, RrgB- and RrgC-positive organisms produce pili, suggesting that pilus-mediated adherence is due to expression of RrgA, rather than the pilus backbone itself. In contrast, RrgA-positive strains with disrupted rrgB and rrgC genes exhibit wild-type adherence despite failure to produce pili by Western blot or immunoelectron microscopy. The density of bacteria colonizing the upper respiratory tract of mice inoculated with piliated RrgA-negative pneumococci was significantly less compared with wild-type; in contrast, non-piliated pneumococci expressing non-polymeric RrgA had similar numbers of bacteria in the nasopharynx as piliated wild-type bacteria. These data suggest that RrgA is central in pilus-mediated adherence and disease, even in the absence of polymeric pilus production.

Oral spray immunization may be an alternative to intranasal vaccine delivery to induce systemic antibodies but not nasal mucosal or cellular immunity

Sixty-five healthy adult volunteers were immunized four times at 1-week intervals with an inactivated whole-virus influenza vaccine based on the strain A/New Caledonia/20/99 (H1N1) without adjuvant. The vaccine was administered as nasal spray with a newly developed device to secure intranasal delivery (OptiMist, OptiNose AS, Oslo, Norway), as regular nasal spray, nasal drops or as an oral spray. Significant IgA-antibody responses in nasal secretions were induced in volunteers immunized intranasally but not after oral spray immunization. In saliva, IgA antibodies were only marginally amplified even after oral spray immunizations. At least 73% of the volunteers belonging to any group of vaccine delivery reached serum haemagglutination inhibition titres of 40 or higher, considered protective against influenza, after only two vaccine doses. Those who had the vaccine delivered intranasally also showed evidence from in vitro secretion of granzyme B that cytotoxic T cells had been stimulated. Although immunization with the breath-actuated OptiMist device and nasal drops were superior with respect to both mucosal and systemic immune responses, oral spray immunization might still be considered for studies of mucosal adjuvants that are not yet acceptable for intranasal use.

A pneumococcal pilus influences virulence and host inflammatory responses

Streptococcus pneumoniae (pneumococcus) is a major cause of morbidity and mortality world-wide. The initial event in invasive pneumococcal disease is the attachment of encapsulated pneumococci to epithelial cells in the upper respiratory tract. This work provides evidence that initial bacterial adhesion and subsequent ability to cause invasive disease is enhanced by pili, long organelles able to extend beyond the polysaccharide capsule, previously unknown to exist in pneumococci. These adhesive pili-like appendages are encoded by the pneumococcal rlrA islet, present in some, but not all, clinical isolates. Introduction of the rlrA islet into an encapsulated rlrA-negative isolate allowed pilus expression, enhanced adherence to lung epithelial cells, and provided a competitive advantage upon mixed intranasal challenge of mice. Furthermore, a pilus-expressing rlrA islet-positive clinical isolate was more virulent than a nonpiliated deletion mutant, and it out-competed the mutant in murine models of colonization, pneumonia, and bacteremia. Additionally, piliated pneumococci evoked a higher TNF response during systemic infection, compared with nonpiliated derivatives, suggesting that pneumococcal pili not only contribute to adherence and virulence but also stimulate the host inflammatory response.

SARS: understanding the virus and development of rational therapy

In late 2002 a new disease, severe atypical respiratory syndrome (SARS), emerged in China. A hitherto unknown animal coronavirus (CoV) that had crossed the species barrier through close contact of humans with infected animals was identified as the etiological agent. It rapidly adapted to the new host and not only became readily transmissible between humans but also more pathogenic. Air travel spread it rapidly around the world and ultimately the virus infected 8096 people and caused 774 deaths in 26 countries on 5 continents. Aggressive quarantine measures successfully terminated the disease. Currently, there are no SARS cases recorded and most likely the virus no longer circulates in the human population. In this review we present an overview over SARS-Co virus biology, the disease and discuss strategies to develop antiviral drugs and vaccines.

The response of primary articular chondrocytes to micrometric surface topography and sulphated hyaluronic acid-based matrices

Understanding the response of chondrocytes to topographical cues and chemical patterns could provide invaluable information to advance the repair of chondral lesions. We studied the response of primary chondrocytes to nano- and micro-grooved surfaces, and sulphated hyaluronic acid (HyalS). Cells were grown on grooves ranging from 80 nm to 9 microm in depth, and from 2 microm to 20 microm in width. Observations showed that the cells did not spread appreciably on any groove size, or alter morphology or F-actin organization, although cells showed accelerated movement on 750 nm deep grooves in comparison to flat surfaces. On chemical patterns, the cells migrated onto, and preferentially attached to, HyalS and showed a greater degree of spreading and F-actin re-arrangement. This study shows that 750 nm deep grooves and sulphated hyaluronic acid elicit responses from primary chondrocytes, and this could have implications for the future direction of cartilage reconstruction and orthopaedic treatments in general.

Enhancement of protective efficacy following intranasal immunization with vaccine plus a nontoxic LTK63 mutant delivered with nanoparticles

Most vaccines are still given parenterally. Mucosal vaccination would offer different advantages over parenteral immunization, including blocking of the pathogens at the portal of entry. In this paper, nontoxic Escherichia coli heat-labile enterotoxin (LT) mutants and Supramolecular Biovector systems (SMBV) were evaluated in mice as mucosal adjuvants and delivery systems, respectively, for intranasal immunization with the conjugated group C meningococcal vaccine. The conjugated vaccine formulated together with the LT mutants and the SMBV induced very high titers of serum and mucosal antibodies specific for the group C meningococcal polysaccharide. This vaccination strategy also induced high titers of antibodies with bactericidal activity, which is known to correlate with efficacy. Importantly, the mucosal vaccination, but not the conventional parenteral vaccination, induced bactericidal antibodies at the mucosal level. These data strongly support the feasibility of development of intranasal vaccines with an enhanced protective efficacy against meningococci and possibly against other encapsulated bacteria.

The LTR72 mutant of heat-labile enterotoxin of Escherichia coli enhances the ability of peptide antigens to elicit CD4(+) T cells and secrete gamma interferon after coapplication onto bare skin

Application of antigens with an adjuvant onto bare skin is a needle-free and pain-free immunization procedure that delivers antigens to the immunocompetent cells of the epidermis. We tested here the immunogenicity and adjuvanticity of two mutants of heat-labile enterotoxin (LT) of Escherichia coli, LTK63 and LTR72. Both mutants were shown to be immunogenic, inducing serum and mucosal antibody responses. The application of LTK63 and LTR72 to bare skin induced significant protection against intraperitoneal challenge with a lethal dose of LT. In addition, both LT mutants enhanced the capacity of peptides TT:830-843 and HA:307-319 (representing T-helper epitopes from tetanus toxin and influenza virus hemagglutinin, respectively) to elicit antigen-specific CD4(+) T cells after coapplication onto bare skin. However, only mutant LTR72 was capable of stimulating the secretion of high levels of gamma interferon. These findings demonstrate that successful skin immunization protocols require the selection of the right adjuvant in order to induce the appropriate type of antigen-specific immune responses in a selective and reliable way. Moreover, the use of adjuvants such the LTK63 and LTR72 mutants, with no or low residual toxicity, holds a lot of promise for the future application of vaccines to the bare skin of humans.

The Fur repressor controls transcription of iron-activated and -repressed genes in Helicobacter pylori

The ferric uptake regulator (Fur) protein is known to act as a Fe2+-dependent transcriptional repressor of bacterial promoters. Here, we show that, in Helicobacter pylori, Fur can mediate the regulation of iron-activated genes in contrast to classical Fur regulation, in which iron acts as a co-repressor. Inactivation of the fur gene in the chromosome of H. pylori resulted in the derepression of a 19 kDa protein that was identified by N-terminal sequencing as the non-haem-containing ferritin (Pfr). Growth of the wild-type H. pylori strain on media treated with increasing concentrations of FeSO4 resulted in induction of transcription from the Ppfr promoter and, conversely, depletion of iron resulted in repression of Ppfr, indicating that this promoter is iron activated. In the fur mutant, the Ppfr promoter is constitutively highly expressed and no longer responds to iron, indicating that the Fur protein mediates this type of iron regulation. Footprinting analysis revealed that Fur binds to the Ppfr promoter region and that Fe2+ decreases the efficiency of binding. In contrast, Fe2+ increased the affinity of Fur for a classical Fur-regulated promoter, the iron-repressed frpB gene promoter. To our knowledge, this is the first evidence of direct interaction between the Fur protein and the promoter of an iron-activated (-derepressed) gene. Our results support a model in which the iron status of the Fur protein differentially alters its affinity for operators in either iron-repressed or iron-activated genes.

A novel mimetic antigen eliciting protective antibody to Neisseria meningitidis

Molecular mimetic Ags are of considerable interest as vaccine candidates. Yet there are few examples of mimetic Ags that elicit protective Ab against a pathogen, and the functional activity of anti-mimetic Abs has not been studied in detail. As part of the Neisseria meningitidis serogroup B genome sequencing project, a large number of novel proteins were identified. Herein, we provide evidence that genome-derived Ag 33 (GNA33), a lipoprotein with homology to Escherichia coli murein transglycosylase, elicits protective Ab to meningococci as a result of mimicking an epitope on loop 4 of porin A (PorA) in strains with serosubtype P1.2. Epitope mapping of a bactericidal anti-GNA33 mAb using overlapping peptides shows that the mAb recognizes peptides from GNA33 and PorA that share a QTP sequence that is necessary but not sufficient for binding. By flow cytometry, mouse antisera prepared against rGNA33 and the anti-GNA33 mAb bind as well as an anti-PorA P1.2 mAb to the surface of eight of nine N. meningitidis serogroup B strains tested with the P1.2 serosubtype. Anti-GNA33 Abs also are bactericidal for most P1.2 strains and, for susceptible strains, the activity of an anti-GNA33 mAb is similar to that of an anticapsular mAb but less active than an anti-P1.2 mAb. Anti-GNA Abs also confer passive protection against bacteremia in infant rats challenged with P1.2 strains. Thus, GNA33 represents one of the most effective immunogenic mimetics yet described. These results demonstrate that molecular mimetics have potential as meningococcal vaccine candidates.

Rationally designed strings of promiscuous CD4(+) T cell epitopes provide help to Haemophilus influenzae type b oligosaccharide: a model for new conjugate vaccines

The age-related and T cell-independent immunological properties of most capsular polysaccharides limit their use as vaccines, especially in children under 2 years of age. To overcome these limitations, polysaccharide antigens have been successfully conjugated to a variety of carrier proteins, such as diphtheria toxoid or tetanus toxoid (TT) and the diphtheria mutant (CRM197) to produce very successful glycoconjugate vaccines. The increasing demand for new conjugate vaccines requires the availability of additional carriers providing high and long-lasting T helper cell immunity. Here we describe the design and construction of three recombinant carrier proteins (N6, N10, N19) constituted by strings of 6, 10 or 19 human CD4(+) T cell epitopes from various pathogen-derived antigens, including TT and proteins from Plasmodium falciparum, influenza virus and hepatitis B virus. Each of these epitopes is defined as universal in that it binds to many human MHC class II molecules. When conjugated to Haemophilus influenzae type b (Hib) oligosaccharide, these carriers elicit a potent anti-Hib antibody response in mice. In the case of the N19-Hib conjugate, this response is at least as good as that observed with CRM197-Hib, a conjugate vaccine currently used for mass immunization. We also show that some of the universal epitopes constituting the recombinant carriers are specifically recognized by two human in vitro systems, suggesting that T cell memory is provided by the selected epitopes. The data indicate that rationally designed recombinant polyepitope proteins represent excellent candidates for the development and clinical testing of new conjugate vaccines.

Vacuolation induced by VacA toxin of Helicobacter pylori requires the intracellular accumulation of membrane permeant bases, Cl(-) and water

The protein vacuolating toxin A (VacA) of Helicobacter pylori converts late endosomes into large vacuoles in the presence of permeant bases. Here it is shown that this phenomenon corresponds to an accumulation of permeant bases and Cl(-) in HeLa cells and requires the presence of extracellular Cl(-). The net influx of Cl(-) is due to electroneutral, Na(+), K(+), 2Cl(-) cotransporter-mediated transport. Cell vacuolation leads to cell volume increase, consistent with water flux into the cell, while hyper-osmotic media decreased vacuole formation. These data represent the first evidence that VacA-treated cells undergo an osmotic unbalance, reinforcing the hypothesis that the VacA chloride channel is responsible for cell vacuolation.

The Helicobacter pylori VacA toxin is a urea permease that promotes urea diffusion across epithelia

Urease and the cytotoxin VacA are two major virulence factors of the human pathogen Helicobacter pylori, which is responsible for severe gastroduodenal diseases. Diffusion of urea, the substrate of urease, into the stomach is critically required for the survival of infecting H. pylori. We now show that VacA increases the transepithelial flux of urea across model epithelia by inducing an unsaturable permeation pathway. This transcellular pathway is selective, as it conducts thiourea, but not glycerol and mannitol, demonstrating that it is not due to a loosening of intercellular junctions. Experiments performed with different cell lines, grown in a nonpolarized state, confirm that VacA permeabilizes the cell plasma membrane to urea. Inhibition studies indicate that transmembrane pores formed by VacA act as passive urea transporters. Thus, their inhibition by the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid significantly decreases toxin-induced urea fluxes in both polarized and nonpolarized cells. Moreover, phloretin, a well-known inhibitor of eukaryotic urea transporters, blocks VacA-mediated urea and ion transport and the toxin's main biologic effects. These data show that VacA behaves as a low-pH activated, passive urea transporter potentially capable of permeabilizing the gastric epithelium to urea. This opens the novel possibility that in vivo VacA may favor H. pylori infectivity by optimizing urease activity.

What are the limits of adjuvanticity?

Vaccines developed traditionally following empirical approaches have often limited problems of immunogenicity, probably due to the low level of purity of the active component(s) they contain. The application of new technologies to vaccine development is leading to the production of purer (e.g. recombinant) antigens which, however, tend to have a poorer immunogenicity as compared to vaccines of the previous generation. The search for new vaccine adjuvants involves issues related to their potential limits. Since the introduction of aluminium salts as vaccine adjuvants more than 70 years ago, only one adjuvant has been licensed for human use. The development of some of these new vaccine adjuvants has been hampered by their inacceptable reactogenicity. In addition, some adjuvants work strongly with some antigens but not with others, thus, limiting their potentially widespread use. The need to deliver vaccines via alternative routes of administration (e.g. the mucosal routes) in order to enhance their efficacy and compliance has set new requirements in basic and applied research to evaluate their efficacy and safety. Cholera toxin (CT) and labile enterotoxin (LT) mutants given along with intranasal or oral vaccines are strong candidates as mucosal adjuvants. Their potential reactogenicity is still matter of discussions, although available data support the notion that the effects due to their binding to the cells and those due to the enzymatic activity can be kept separated. Finally, adjuvanticity is more often evaluated in terms of antigen-specific antibody titers induced after parenteral immunization. It is known that, in many instances, antigen-specific antibody titers do not correlate with protection. In addition, very little is known on parameters of cell-mediated immunity which could be considered as surrogates of protection. Tailoring of new adjuvants for the development of vaccines with improved immunogenicity/efficacy and reduced reactogenicity will represent one of the major challenges of the ongoing vaccine-oriented research.

The Helicobacter pylori VacA toxin is a urea permease that promotes urea diffusion across epithelia

Urease and the cytotoxin VacA are two major virulence factors of the human pathogen Helicobacter pylori, which is responsible for severe gastroduodenal diseases. Diffusion of urea, the substrate of urease, into the stomach is critically required for the survival of infecting H. pylori. We now show that VacA increases the transepithelial flux of urea across model epithelia by inducing an unsaturable permeation pathway. This transcellular pathway is selective, as it conducts thiourea, but not glycerol and mannitol, demonstrating that it is not due to a loosening of intercellular junctions. Experiments performed with different cell lines, grown in a nonpolarized state, confirm that VacA permeabilizes the cell plasma membrane to urea. Inhibition studies indicate that transmembrane pores formed by VacA act as passive urea transporters. Thus, their inhibition by the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid significantly decreases toxin-induced urea fluxes in both polarized and nonpolarized cells. Moreover, phloretin, a well-known inhibitor of eukaryotic urea transporters, blocks VacA-mediated urea and ion transport and the toxin's main biologic effects. These data show that VacA behaves as a low-pH activated, passive urea transporter potentially capable of permeabilizing the gastric epithelium to urea. This opens the novel possibility that in vivo VacA may favor H. pylori infectivity by optimizing urease activity.

Neutrophil-activating protein (HP-NAP) versus ferritin (Pfr): comparison of synthesis in Helicobacter pylori

We recently reported that the neutrophil-activating protein (HP-NAP) of Helicobacter pylori is capable of binding iron in vitro. To more fully understand the relationship between iron and HP-NAP the synthesis of HP-NAP was compared to that of Pfr, another iron-binding protein of H. pylori. Synthesis of HP-NAP and Pfr in growing cultures of H. pylori was analysed under iron depletion and iron, copper, nickel and zinc overload. The synthesis of HP-NAP and Pfr in H. pylori was also analysed under conditions of varying pH and oxidative stress. In addition, recombinant HP-NAP and Pfr were produced in Escherichia coli to assess the contribution of the two proteins to increased survival of E. coli under heavy metal overload. Our data reveal that both HP-NAP and Pfr accumulate in the stationary phase of growth. HP-NAP synthesis is not regulated by iron depletion or overload or by the presence of copper, nickel or zinc in liquid medium and it does not confer resistance to these metals when produced in E. coli. Except for an increase in the synthesis of Pfr at pH 5.7 neither the pH or oxidative stress conditions investigated had an affect on the synthesis of either protein. An increase in Pfr synthesis was observed under iron overload and a decrease was observed under conditions of copper, nickel and zinc overload confirming previous reports. Recombinant Pfr, as well as conferring resistance to iron and copper as previously reported, also conferred resistance to zinc overload when produced in E. coli.

The design of vaccines against Helicobacter pylori and their development

Helicobacter pylori is a gram negative, spiral, microaerophylic bacterium that infects the stomach of more than 50% of the human population worldwide. It is mostly acquired during childhood and, if not treated, persists chronically, causing chronic gastritis, peptic ulcer disease, and in some individuals, gastric adenocarcinoma and gastric B cell lymphoma. The current therapy, based on the use of a proton-pump inhibitor and antibiotics, is efficacious but faces problems such as patient compliance, antibiotic resistance, and possible recurrence of infection. The development of an efficacious vaccine against H. pylori would thus offer several advantages. Various approaches have been followed in the development of vaccines against H. pylori, most of which have been based on the use of selected antigens known to be involved in the pathogenesis of the infection, such as urease, the vacuolating cytotoxin (VacA), the cytotoxin-associated antigen (CagA), the neutrophil-activating protein (NAP), and others, and intended to confer protection prophylactically and/or therapeutically in animal models of infection. However, very little is known of the natural history of H. pylori infection and of the kinetics of the induced immune responses. Several lines of evidence suggest that H. pylori infection is accompanied by a pronounced Th1-type CD4(+) T cell response. It appears, however, that after immunization, the antigen-specific response is predominantly polarized toward a Th2-type response, with production of cytokines that can inhibit the activation of Th1 cells and of macrophages, and the production of proinflammatory cytokines. The exact effector mechanisms of protection induced after immunization are still poorly understood. The next couple of years will be crucial for the development of vaccines against H. pylori. Several trials are foreseen in humans, and expectations are that most of the questions being asked now on the host-microbe interactions will be answered.

Iron-dependent transcription of the frpB gene of Helicobacter pylori is controlled by the Fur repressor protein

We have overexpressed and purified the Helicobacter pylori Fur protein and analyzed its interaction with the intergenic regions of divergent genes involved in iron uptake (frpB and ceuE) and oxygen radical detoxification (katA and tsaA). DNase I footprint analysis showed that Fur binds specifically to a high-affinity site overlapping the P(frpB) promoter and to low-affinity sites located upstream from promoters within both the frpB-katA and ceuE-tsaA intergenic regions. Construction of an isogenic fur mutant indicated that Fur regulates transcription from the P(frpB) promoter in response to iron. In contrast, no effect by either Fur or iron was observed for the other promoters.

Living dangerously: how Helicobacter pylori survives in the human stomach

Helicobacter pylori was already present in the stomach of primitive humans as they left Africa and spread through the world. Today, it still chronically infects more than 50% of the human population, causing, in some cases, severe diseases such as peptic ulcers and stomach cancer. To succeed in these long-term associations, H. pylori has developed a unique set of virulence factors, which allow survival in a unique and hostile ecological niche--the human stomach.

Characterization of the antibody response to pneumococcal glycoconjugates and the effect of heat-labile enterotoxin on IGg subclasses after intranasal immunization

The antibody response to pneumococcal glycoconjugate (Pnc) was characterized by analyzing pneumococcal polysaccharide (PPS)-- and protein carrier-specific IgG subclass profiles and their relationship. Mice were immunized intranasally (inl) or subcutaneously (sc) with Pnc with mutants of Escherichia coli heat-labile enterotoxin, LT-R72 and LT-K63, as mucosal adjuvants. Subcutaneous immunization with Pnc alone induced predominantly IgG1, whereas native PPS administered sc induced very low IgG titers that were exclusively of the IgG3 subclass. Compared with sc immunization with Pnc alone, inl immunization with Pnc and LT mutants induced significantly higher systemic IgG2a, IgG3, and IgA antibodies to both PPS and the carrier, whereas the IgG1 titers were comparable. There also was a significant correlation between PPS- and protein carrier--specific antibody responses for all IgG subclasses. This demonstrates that LT mutants can be used to both enhance and modulate the antibody response to the PS moiety of glycoconjugate vaccines.

Physicochemical characterisation of the pertussis vaccine

The characterisation of an acellular pertussis vaccine composed of a genetically modified pertussis toxin, filamentous haemagglutinin and pertactin is described. The three antigens are submitted to a mild treatment with formaldehyde in the presence of lysine before their use in vaccine formulation. Characterisation is performed by amino acid analysis, SDS-PAGE, analytical size exclusion chromatography and, in the case of pertactin, isoelectrofocusing. The effect of some variables on pertactin formaldehyde treatment has been studied by means of isoelectrofocusing and mouse immunogenicity.

Reversal of the CD4(+)/CD8(+) T-cell ratio in lymph node cells upon in vitro mitogenic stimulation by highly purified, water-soluble S3-S4 dimer of pertussis toxin

Pertussis toxin (PT), a holomer consisting of a catalytic S1 subunit and a B oligomer composed of S2-S4 and S3-S4 dimers, held together by the S5 subunit, exerts profound effects on immune cells, including T-cell mitogenicity. While the mitogenic activity of PT was shown to reside fully within the B oligomer, it could not be assigned to any particular B-oligomer component. In this study, we purified the S3-S4 dimer to homogeneity under conditions propitious to maintenance of the native conformation. In contrast to previous reports which suggested that both S3-S4 and S2-S4 dimers are necessary for mitogenic activity, our preparation of the highly purified S3-S4 dimer was as strongly mitogenic as the B oligomer, suggesting that the S3-S4 dimer accounts for the mitogenic activity of the B oligomer. Moreover, in vitro stimulation of naive lymphocytes by the S3-S4 dimer resulted in reversal of the normal CD4(+)/CD8(+) T-cell ratio from approximately 2:1 to 1:2. The reversal of the CD4(+)/CD8(+) T-cell ratio is unlikely to be due to preferential apoptosis-necrosis of CD4(+) T cells, as indicated by fluorescence-activated cell sorter analysis of annexin-stained T-cell subsets, or to preferential stimulation of CD8(+) T cells. The mechanism underlying the reversal requires further investigation. Nevertheless, the data presented indicate that the S3-S4 dimer may have potential use in the context of diseases amenable to immunological modulation.

Helicobacter pylori neutrophil-activating protein stimulates tissue factor and plasminogen activator inhibitor-2 production by human blood mononuclear cells

Helicobacter pylori neutrophil-activating protein (HP-NAP) is a virulence factor that activates phagocytic NADPH-oxidase. The effect of HP-NAP on the production of tissue factor (TF), plasminogen activator inhibitor-2 (PAI-2), and urokinase-type plasminogen activator (u-PA) by human blood mononuclear cells (MNC) was evaluated by using functional and immunological assays and mRNA analysis. HP-NAP induced time- and dose-dependent increases in TF and PAI-2, with a maximal effect at 300 nmol/L (>15-fold increase in antigens). No changes in u-PA were observed. When whole bacteria were used, an H. pylori mutant lacking HP-NAP was significantly less active than the wild-type strain. MNC from a patient with chronic granulomatous disease behaved as do normal cells, which indicates that HP-NAP effects can occur independently of NADPH-oxidase. HP-NAP, by inducing the coordinate expression of cell procoagulant and antifibrinolytic activities, might favor fibrin deposition and contribute to the inflammatory reaction of gastric mucosa elicited by H. pylori.

Mu-like Prophage in serogroup B Neisseria meningitidis coding for surface-exposed antigens

Sequence analysis of the genome of Neisseria meningititdis serogroup B revealed the presence of an approximately 35-kb region inserted within a putative gene coding for an ABC-type transporter. The region contains 46 open reading frames, 29 of which are colinear and homologous to the genes of Escherichia coli Mu phage. Two prophages with similar organizations were also found in serogroup A meningococcus, and one was found in Haemophilus influenzae. Early and late phage functions are well preserved in this family of Mu-like prophages. Several regions of atypical nucleotide content were identified. These likely represent genes acquired by horizontal transfer. Three of the acquired genes are shown to code for surface-associated antigens, and the encoded proteins are able to induce bactericidal antibodies.

Conjugates and reverse vaccinology to eliminate bacterial meningitis

Bacterial meningitis is caused mainly by Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis. Haemophilus influenzae type b vaccines have been extremely successful in eradicating the disease from those countries where the vaccine has been introduced. The recent licensure of the conjugated pneumococcal vaccine suggests that this pathogen also will be soon controlled. Consequently, if we succeed in developing effective vaccines against meningococcus, this will enable us to eliminate bacterial meningitis. The global elimination of bacterial meningitis is a goal which, if appropriate resources are applied, can be reached within the first fifteen years of the 21st century.

Mucosal vaccines: non toxic derivatives of LT and CT as mucosal adjuvants

Most vaccines are still delivered by injection. Mucosal vaccination would increase compliance and decrease the risk of spread of infectious diseases due to contaminated syringes. However, most vaccines are unable to induce immune responses when administered mucosally, and require the use of strong adjuvant on effective delivery systems. Cholera toxin (CT) and Escherichia coli enterotoxin (LT) are powerful mucosal adjuvants when co-administered with soluble antigens. However, their use in humans is hampered by their extremely high toxicity. During the past few years, site-directed mutagenesis has permitted the generation of LT and CT mutants fully non toxic or with dramatically reduced toxicity, which still retain their strong adjuvanticity at the mucosal level. Among these mutants, are LTK63 (serine-to-lysine substitution at position 63 in the A subunit) and LTR72 (alanine-to-arginine substitution at position 72 in the A subunit). The first is fully non toxic, whereas the latter retains some residual enzymatic activity. Both of them are extremely active as mucosal adjuvants, being able to induce very high titers of antibodies specific for the antigen with which they are co-administered. Both mutants have now been tested as mucosal adjuvants in different animal species using a wide variety of antigens. Interestingly, mucosal delivery (nasal or oral) of antigens together with LTK63 or LTR72 mutants also conferred protection against challenge in appropriate animal models (e.g. tetanus, Helicobacter pylori, pertussis, pneumococci, influenza, etc). In conclusion, these LTK63 and LTR72 mutants are safe adjuvants to enhance the immunogenicity of vaccines at the mucosal level, and will be tested soon in humans.

Reverse vaccinology, a genome-based approach to vaccine development

The conventional approach to vaccine development requires cultivation of the pathogenic microorganism and its dissection using biochemical, immunological, and microbiological methods in order to identify the components important for immunity. This method, while successful in many cases, failed to provide a solution for many of those pathogens for which a vaccine is not yet available. Today, the possibility of using genomic information allows us to study vaccine development in silico, without the need of cultivating the pathogen. This approach, which we have named 'reverse vaccinology', reduces the time required for the identification of candidate vaccines and provides new solutions for those vaccines which have been difficult or impossible to develop. The potential of this new approach is illustrated by the use of reverse vaccinology for the development of a vaccine against serogroup B meningococcus. The application of reverse vaccinology to other fields, including viral vaccines is discussed.

Intranasal immunization with SAG1 and nontoxic mutant heat-labile enterotoxins protects mice against Toxoplasma gondii

Effective protection against intestinal pathogens requires both mucosal and systemic immune responses. Intranasal administration of antigens induces these responses but generally fails to trigger a strong protective immunity. Mucosal adjuvants can significantly enhance the immunogenicities of intranasally administered antigens. Cholera toxin (CT) and heat-labile enterotoxin (LT) are strong mucosal adjuvants with a variety of antigens. Moreover, the toxicities of CT and LT do not permit their use in humans. Two nontoxic mutant LTs, LTR72 and LTK63, were tested with Toxoplasma gondii SAG1 protein in intranasal vaccination of CBA/J mice. Vaccination with SAG1 plus LTR72 or LTK63 induced strong systemic (immunoglobulin G [IgG]) and mucosal (IgA) humoral responses. Splenocytes and mesenteric lymph node cells from mice immunized with LTR72 plus SAG1, but not those from mice immunized with LTK63 plus SAG1, responded to restimulation with a T. gondii lysate antigen in vitro. Gamma interferon and interleukin 2 (IL-2) production by splenocytes and IL-2 production by mesenteric lymph node cells were observed in vitro after antigen restimulation, underlying a Th1-like response. High-level protection as assessed by the decreased load of cerebral cysts after a challenge with the 76K strain of T. gondii was obtained in the group immunized with LTR72 plus SAG1 and LTK63 plus SAG1. They were as well protected as the mice immunized with the antigen plus native toxins. This is the first report showing protection against a parasite by using combinations of nontoxic mutant LTs and SAG1 antigen. These nontoxic mutant LTs are now attractive candidates for the development of mucosally delivered vaccines.

Synthesis, chemical and rheological characterization of new hyaluronic acid-based hydrogels

New hyaluronic acid-based hydrogels have been synthesized. The carboxylate groups of hyaluronan were activated in order to bind the amino terminal groups of the di-amine cross-linking reagent. Different hydrogels were obtained according to the different di-amine cross-linking agents (1,3-diaminepropane, 1.6-diaminohexane, PEG500 di-amine. and PEG800 di-amine). The cross-linked polymer (C.L.Hyal) was then sulphated (C.L.HyalS) by a heterogeneous reaction using sulphur trioxide pyridine complex (SO3-Py). The thermo-mechanical properties and swelling degree were evaluated and are discussed in relation to the chemical structure and the hydrophilic character of the gels. The different behaviours of C.L.Hyal and C.L.HyalS indicate the important role of sulphated groups.

The binding subunit of pertussis toxin inhibits HIV replication in human macrophages and virus expression in chronically infected promonocytic U1 cells

We have recently shown that the binding subunit of pertussis toxin (PTX-B) inhibits the entry and replication of macrophage-tropic (R5) HIV-1 strains in activated primary T lymphocytes. Furthermore, PTX-B suppressed the replication of T cell-tropic (X4) viruses at a postentry level in the same cells. In this study we demonstrate that PTX-B profoundly impairs entry and replication of the HIV-1(ADA) (R5), as well as of HIV pseudotyped with either murine leukemia virus or vesicular stomatitis virus envelopes, in primary monocyte-derived macrophages. In addition, PTX-B strongly inhibited X4 HIV-1 replication in U937 promonocytic cells and virus expression in the U937-derived chronically infected U1 cell line stimulated with cytokines such as TNF-alpha and IL-6. Of interest, TNF-alpha-mediated activation of the cellular transcription factor NF-kappaB was unaffected by PTX-B. Therefore, PTX-B may represent a novel and potent inhibitor of HIV-1 replication to be tested for efficacy in infected individuals. In support of this proposition, a genetically modified mutant of PTX (PT-9K/129G), which is safely administered for prevention of Bordetella pertussis infection, showed an in vitro anti-HIV profile superimposable to that of PTX-B.

Induction of neutralizing antibodies against diphtheria toxin by priming with recombinant Mycobacterium bovis BCG expressing CRM(197), a mutant diphtheria toxin

BCG, the attenuated strain of Mycobacterium bovis, has been widely used as a vaccine against tuberculosis and is thus an important candidate as a live carrier for multiple antigens. With the aim of developing a recombinant BCG (rBCG) vaccine against diphtheria, pertussis, and tetanus (DPT), we analyzed the potential of CRM(197), a mutated nontoxic derivative of diphtheria toxin, as the recombinant antigen for a BCG-based vaccine against diphtheria. Expression of CRM(197) in rBCG was achieved using Escherichia coli-mycobacterium shuttle vectors under the control of pBlaF*, an upregulated beta-lactamase promoter from Mycobacterium fortuitum. Immunization of mice with rBCG-CRM(197) elicited an anti-diphtheria toxoid antibody response, but the sera of immunized mice were not able to neutralize diphtheria toxin (DTx) activity. On the other hand, a subimmunizing dose of the conventional diphtheria-tetanus vaccine, administered in order to mimic an infection, showed that rBCG-CRM(197) was able to prime the induction of a humoral response within shorter periods. Interestingly, the antibodies produced showed neutralizing activity only when the vaccines had been given as a mixture in combination with rBCG expressing tetanus toxin fragment C (FC), suggesting an adjuvant effect of rBCG-FC on the immune response induced by rBCG-CRM(197). Isotype analysis of the anti-diphtheria toxoid antibodies induced by the combined vaccines, but not rBCG-CRM(197) alone, showed an immunoglobulin G1-dominant profile, as did the conventional vaccine. Our results show that rBCG expressing CRM(197) can elicit a neutralizing humoral response and encourage further studies on the development of a DPT vaccine with rBCG.

A mucosal vaccine against diphtheria: formulation of cross reacting material (CRM(197)) of diphtheria toxin with chitosan enhances local and systemic antibody and Th2 responses following nasal delivery

The development of new generation vaccines against diphtheria is dependent on the identification of antigens and routes of immunization that are capable of stimulating immune responses similar to, or greater than, those obtained with the parenterally-delivered toxoid vaccine, while reducing the adverse effects that have been associated with the traditional vaccine. In this study, we examined the cellular and humoral immune responses in mice generated after both parenteral and mucosal immunizations with cross-reacting material (CRM(197)) of diphtheria toxin. We found that both native and mildly formaldehyde-treated CRM(197) and conventional diphtheria toxoid (DT) induced mixed Th1/Th2 responses and similar levels of anti-DT serum IgG following parenteral immunization. In contrast, CRM(197) preparations were poorly immunogenic when administered intranasally in solution. However, formulation of the antigens with chitosan significantly enhanced their immunogenicity, inducing high levels of antigen-specific IgG, secretory IgA, toxin-neutralizing antibodies and T cell responses, predominately of Th2 subtype. Furthermore, intranasal immunization with CRM(197) and chitosan induced protective antibodies against the toxin in a guinea pig passive challenge model. We also found that priming parenterally with DT in alum and boosting intranasally with CRM(197) was a very effective method of immunization in mice, capable of inducing high levels of anti-DT IgG and neutralizing antibodies in the serum and secretory IgA in the respiratory tract. Our findings suggest that boosting intranasally with CRM(197) antigen may be very effective in adolescents or adults who have previously been parenterally immunized with a conventional diphtheria toxoid vaccine.

Modulation of innate and acquired immune responses by Escherichia coli heat-labile toxin: distinct pro- and anti-inflammatory effects of the nontoxic AB complex and the enzyme activity

We have examined the roles of enzyme activity and the nontoxic AB complex of heat-labile toxin (LT) from Escherichia coli on its adjuvant and immunomodulatory properties. LTK63, an LT mutant that is completely devoid of enzyme activity, enhanced Th1 responses to coinjected Ags at low adjuvant dose. In contrast, LTR72, a partially detoxified mutant, enhanced Th2 responses and when administered intranasally to mice before infection with Bordetella pertussis suppressed Th1 responses and delayed bacterial clearance from the lungs. LTR72 or wild-type LT inhibited Ag-induced IFN-gamma production by Th1 cells, and LT enhanced IL-5 production by Th2 cells in vitro. Each of the toxins enhanced B7-1 expression on macrophages, but enhancement of B7-2 expression was dependent on enzyme activity. We also observed distinct effects of the nontoxic AB complex and enzyme activity on inflammatory cytokine production. LT and LTR72 suppressed LPS and IFN-gamma induced TNF-alpha and IL-12 production, but enhanced IL-10 secretion by macrophages in vitro and suppressed IL-12 production in vivo in a murine model of LPS-induced shock. In contrast, LTK63 augmented the production of IL-12 and TNF-alpha. Furthermore, LTK63 enhanced NF-kappaB translocation, whereas low doses of LTR72 or LT failed to activate NF-kappaB, but stimulated cAMP production. Thus, E. coli LT appears to be capable of suppressing Th1 responses and enhancing Th2 responses through the modulatory effects of enzyme activity on NF-kappaB activation and IL-12 production. In contrast, the nontoxic AB complex can stimulate acquired immune responses by activating components of the innate immune system.

Reverse vaccinology

Biochemical, serological and microbiological methods have been used to dissect pathogens and identify the components useful for vaccine development. Although successful in many cases, this approach is time-consuming and fails when the pathogens cannot be cultivated in vitro, or when the most abundant antigens are variable in sequence. Now genomic approaches allow prediction of all antigens, independent of their abundance and immunogenicity during infection, without the need to grow the pathogen in vitro. This allows vaccine development using non-conventional antigens and exploiting non-conventional arms of the immune system. Many vaccines impossible to develop so far will become a reality. Since the process of vaccine discovery starts in silico using the genetic information rather than the pathogen itself, this novel process can be named reverse vaccinology.

A structural overview of the Helicobacter cytotoxin

VacA, the major exotoxin produced by Helicobacter pylori, is composed of identical 87-kDa monomers that assemble into flower-shaped oligomers. The monomers can be proteolytically cleaved into two moieties of 37 and 58 kDa, or P37 and P58. The most studied property of VacA is the alteration of intracellular vesicular trafficking in eukaryotic cells leading to the formation of large vacuoles containing markers of late endosomes and lysosomes. However, VacA also causes a reduction in trans-epithelial electrical resistance in polarized monolayers and forms ion channels in lipid bilayers. The ability to induce vacuoles is localized mostly but not entirely in P37, while P58 is involved in cell targeting. Here, we review the structural aspects of VacA biology.

Recombinant Mycobacterium bovis BCG expressing pertussis toxin subunit S1 induces protection against an intracerebral challenge with live Bordetella pertussis in mice

The recent development of acellular pertussis vaccines has been a significant improvement in the conventional whole-cell diphtheria-pertussis-tetanus toxoid vaccines, but high production costs will limit its widespread use in developing countries. Since Mycobacterium bovis BCG vaccination against tuberculosis is used in most developing countries, a recombinant BCG-pertussis vaccine could be a more viable alternative. We have constructed recombinant BCG (rBCG) strains expressing the genetically detoxified S1 subunit of pertussis toxin 9K/129G (S1PT) in fusion with either the beta-lactamase signal sequence or the whole beta-lactamase protein, under control of the upregulated M. fortuitum beta-lactamase promoter, pBlaF*. Expression levels were higher in the fusion with the whole beta-lactamase protein, and both were localized to the mycobacterial cell wall. The expression vectors were relatively stable in vivo, since at two months 85% of the BCG recovered from the spleens of vaccinated mice maintained kanamycin resistance. Spleen cells from rBCG-S1PT-vaccinated mice showed elevated gamma interferon (IFN-gamma) and low interleukin-4 (IL-4) production, as well as increased proliferation, upon pertussis toxin (PT) stimulation, characterizing a strong antigen-specific Th1-dominant cellular response. The rBCG-S1PT strains induced a low humoral response against PT after 2 months. Mice immunized with rBCG-S1PT strains displayed high-level protection against an intracerebral challenge with live Bordetella pertussis, which correlated with the induction of a PT-specific cellular immune response, reinforcing the importance of cell-mediated immunity in the protection against B. pertussis infection. Our results suggest that rBCG-expressing pertussis antigens could constitute an effective, low-cost combined vaccine against tuberculosis and pertussis.

IEM101, a naturally attenuated Vibrio cholerae strain as carrier for genetically detoxified derivatives of cholera toxin

Two mutants of cholera toxin (CTS106 containing a Pro106-->Ser substitution and CTK63 containing a Ser63-->Lys substitution) with greatly reduced or no toxicity respectively, were expressed in the naturally attenuated IEM101 Vibrio cholerae strain (El Tor, Ogawa) which does not express cholera toxin (CT). Expression was driven by the natural promoter of CT, or by a promoter known to induce strong in vivo expression such as nirB. In the rabbit ileal loop assay, where 10(4) wild type bacteria were sufficient to induce fluid accumulation, 10(9) IEM101 expressing CTS106 bacteria were needed to induce some fluid accumulation, while IEM101 expressing CTK63 was inactive, even when 10(10) cells were used. When used to immunize mice intranasally, all bacteria induced vibriocidal antibodies; however, anti-CT antibodies were not induced by bacteria expressing low levels of CTK63 under the control of the ct promoter. Anti-CT antibodies were successfully induced by bacteria expressing high levels of CTK63 under the control of the nirB promoter, or by bacteria expressing low levels of CTS106. These data show that antibodies against cholera toxin can be induced in vivo by high level expression of a non toxic mutant, or by using a mutant with residual ADP-ribosyltransferase activity. In conclusion, we have shown that IEM101, a naturally attenuated Vibrio strain known to be safe and immunogenic in humans, can be engineered to express immunogenic levels of CTK63, and may represent a good candidate for vaccination against cholera.

Immunohistochemical study of lymphocyte populations infiltrating the gastric mucosa of beagle dogs experimentally infected with Helicobacter pylori

Experimental infection of beagle dogs with Helicobacter pylori induces recruitment to the gastric mucosae of neutrophils at early stages and later of mononuclear cells that organize into lymphoid follicles. These structures become macroscopically evident and consist of peripheral CD4(+) T lymphocytes and central CD21(+) B lymphocytes. Furthermore, transient expression of interleukin-8 (IL-8) parallels the presence of neutrophils in the gastric mucosae, whereas expression of IL-6 tends to persist chronically.