Immune responses in mice to intranasal and intracutaneous administration of a DNA vaccine encoding Helicobacter pylori-catalase

Outer Membrane Vesicles (OMVs) as Biomedical Tools and Their Relevance as Immune-Modulating Agents against H. pylori Infections: Current Status and Future Prospects

Outer membrane vesicles (OMVs) are lipid-membrane-bounded nanoparticles that are released from Gram-negative bacteria via vesiculation of the outer membrane. They have vital roles in different biological processes and recently, they have received increasing attention as possible candidates for a broad variety of biomedical applications. In particular, OMVs have several characteristics that enable them to be promising candidates for immune modulation against pathogens, such as their ability to induce the host immune responses given their resemblance to the parental bacterial cell. Helicobacter pylori (H. pylori) is a common Gram-negative bacterium that infects half of the world's population and causes several gastrointestinal diseases such as peptic ulcer, gastritis, gastric lymphoma, and gastric carcinoma. The current H. pylori treatment/prevention regimens are poorly effective and have limited success. This review explores the current status and future prospects of OMVs in biomedicine with a special focus on their use as a potential candidate in immune modulation against H. pylori and its associated diseases. The emerging strategies that can be used to design OMVs as viable immunogenic candidates are discussed.

IgY antibodies: The promising potential to overcome antibiotic resistance

Antibiotic resistant bacteria are a growing threat to global health security. Whilst the emergence of antimicrobial resistance (AMR) is a natural phenomenon, it is also driven by antibiotic exposure in health care, agriculture, and the environment. Antibiotic pressure and inappropriate use of antibiotics are important factors which drive resistance. Apart from their use to treat bacterial infections in humans, antibiotics also play an important role in animal husbandry. With limited antibiotic options, alternate strategies are required to overcome AMR. Passive immunization through oral, nasal and topical administration of egg yolk-derived IgY antibodies from immunized chickens were recently shown to be effective for treating bacterial infections in animals and humans. Immunization of chickens with specific antigens offers the possibility of creating specific antibodies targeting a wide range of antibiotic-resistant bacteria. In this review, we describe the growing global problem of antimicrobial resistance and highlight the promising potential of the use of egg yolk IgY antibodies for the treatment of bacterial infections, particularly those listed in the World Health Organization priority list.

Potential Therapeutic Effects of Egg Yolk Antibody (IgY) in Helicobacter pylori Infections─A Review

Currently, the infection with Helicobacter pylori affects about half of the world's population, and the most common therapy to treat H. pylori is the first line clarithromycin-based triple therapy or the quadruple therapy. However, drug resistance, eradication in a low level, high rate of reinfection, and gastrointestinal side effects among the causative organisms for H. pylori infection pose a critical challenge to the global health care community. Therefore, new approaches to treat H. pylori infections are urgently needed. Chicken egg yolk constituting a source of immunoglobulin Y (IgY) has attracted noticeable attention for its advantages of cost-effective extraction, minimization of animal harm and suffering, and induction of no specific resistance and is, therefore, being regarded as an alternative therapy for H. pylori infection. This review is intended to summarize various H. pylori antigens for IgY preparation in terms of their application, mechanism, and limitations.

Designing and development of epitope-based vaccines against Helicobacter pylori

Helicobacter pylori infection is the principal cause of serious diseases (e.g. gastric cancer and peptic ulcers). Antibiotic therapy is an inadequate strategy in H. pylori eradication because of which vaccination is an inevitable approach. Despite the presence of countless vaccine candidates, current vaccines in clinical trials have performed with poor efficacy which makes vaccination extremely challenging. Remarkable advancements in immunology and pathogenic biology have provided an appropriate opportunity to develop various epitope-based vaccines. The fusion of proper antigens involved in different aspects of H. pylori colonization and pathogenesis as well as peptide linkers and built-in adjuvants results in producing epitope-based vaccines with excellent therapeutic efficacy and negligible adverse effects. Difficulties of the in vitro culture of H. pylori, high genetic variation, and unfavourable immune responses against feeble epitopes in the complete antigen are major drawbacks of current vaccine strategies that epitope-based vaccines may overcome. Besides decreasing the biohazard risk, designing precise formulations, saving time and cost, and induction of maximum immunity with minimum adverse effects are the advantages of epitope-based vaccines. The present article is a comprehensive review of strategies for designing and developing epitope-based vaccines to provide insights into the innovative vaccination against H. pylori.

Evaluation of an attenuated Listeria monocytogenes as a vaccine vector to control Helicobacter pylori infection

The increasing resistance of Helicobacter pylori (H. pylori) to antibiotics has limited the efficacy of antibiotic therapy in the treatment of H. pylori-associated gastric diseases. The vaccine as an alternative method is becoming a safe and effective way to address this problem. In previous studies, live vector vaccines have proved to be effective in controlling H. pylori infection. Attenuated Listeria monocytogenes (L. monocytogenes) is a potential candidate vector applied in clinical trials, which can deliver foreign antigens and induce a broad immune response. To further explore the effectiveness of L. monocytogenes as a vaccine vector against H. pylori, attenuated L. monocytogenes-based vaccine EGDeΔactA/inlB(EGDeAB)-MECU was constructed to secrete a multi-epitope chimeric antigen (MECU) containing multiple B cell epitopes from H. pylori antigens. EGDeAB-MECU could secrete MECU stably. After immunized by gavage and intravenous injection, both EGDeAB and EGDeAB-MECU could significantly decrease gastric H. pylori colonization and induce a high level of specific antibodies against H. pylori. In conclusion, attenuated L. monocytogenes had an immunotherapeutic effect on H. pylori-infected mice, indicating its further development as a promising candidate vaccine vector for the H. pylori vaccine.

Secretory System Components as Potential Prophylactic Targets for Bacterial Pathogens

Bacterial secretory systems are essential for virulence in human pathogens. The systems have become a target of alternative antibacterial strategies based on small molecules and antibodies. Strategies to use components of the systems to design prophylactics have been less publicized despite vaccines being the preferred solution to dealing with bacterial infections. In the current review, strategies to design vaccines against selected pathogens are presented and connected to the biology of the system. The examples are given for Y. pestis, S. enterica, B. anthracis, S. flexneri, and other human pathogens, and discussed in terms of effectiveness and long-term protection.

Helicobacter pylori Virulence Factors-Mechanisms of Bacterial Pathogenicity in the Gastric Microenvironment

Gastric cancer constitutes one of the most prevalent malignancies in both sexes; it is currently the fourth major cause of cancer-related deaths worldwide. The pathogenesis of gastric cancer is associated with the interaction between genetic and environmental factors, among which infection by Helicobacter pylori (H. pylori) is of major importance. The invasion, survival, colonization, and stimulation of further inflammation within the gastric mucosa are possible due to several evasive mechanisms induced by the virulence factors that are expressed by the bacterium. The knowledge concerning the mechanisms of H. pylori pathogenicity is crucial to ameliorate eradication strategies preventing the possible induction of carcinogenesis. This review highlights the current state of knowledge and the most recent findings regarding H. pylori virulence factors and their relationship with gastric premalignant lesions and further carcinogenesis.

Effect of the cagW-based gene vaccine on the immunologic properties of BALB/c mouse: an efficient candidate for Helicobacter pylori DNA vaccine

BACKGROUND

Helicobacter pylori (H. pylori) infect more than half of the world population, and they cause different serious diseases such as gastric carcinomas. This study aims to design a vaccine on the basis of cagW against H. pylori infection. After pcDNA3.1 (+)-cagW-CS-NPs complex is produced, it will be administered into the muscles of healthy BALB/c mice in order to study the effect of this DNA vaccine on the interleukin status of mice, representing its effect on the immune system. After that, the results will be compared with the control groups comprising the administration of cagW-pCDNA3.1 (+) vaccine, the administration of chitosan and the administration of PBS in the muscles of mice.

METHODS

The cagW gene of H. pylori was amplified by employing PCR, whose product was then cloned into the pcDNA3.1 (+) vector, and this cloning was confirmed by PCR and BamHI/EcoRV restriction enzyme digestion. CagW gene DNA vaccine was encapsulated in chitosan nanoparticles (pcDNA3.1 (+)-cagW-CS-NPs) using a complex coacervation method. The stability and in vitro expression of chitosan nanoparticles were studied by DNase I digestion and transfection, and the immune responses elicited in specific pathogen-free (SPF) mice by the pcDNA3.1 (+)-cagW-CS-NPs were evaluated. Apart from that, the protective potential pcDNA3.1 (+)-cagW-CS-NPs was evaluated by challenging with H. pylori.

RESULTS

The pcDNA3.1 (+)-cagW-CS-NPs comprises cagW gene of H. pylori that is encapsulated in chitosan nanoparticles, produced with good morphology, high stability, a mean diameter of 117.7 nm, and a zeta potential of + 5.64 mV. Moreover, it was confirmed that chitosan encapsulation protects the DNA plasmid from DNase I digestion, and the immunofluorescence assay showed that the cagW gene could express in HDF cells and maintain good bioactivity at the same time. In comparison to the mice immunized with the control plasmid, in vivo immunization revealed that mice immunized with pcDNA3.1 (+)-cagW-NPs showed better immune responses and prolonged release of the plasmid DNA.

CONCLUSIONS

This research proves chitosan-DNA nanoparticles as potent immunization candidates against H. pylori infection and paves the way for further developments in novel vaccines encapsulated in chitosan nanoparticles.

Immunologic properties and therapeutic efficacy of a multivalent epitope-based vaccine against four Helicobacter pylori adhesins (urease, Lpp20, HpaA, and CagL) in Mongolian gerbils

BACKGROUND

Therapeutic vaccination is a desirable alternative for controlling Helicobacter pylori (H. pylori) infection. Attachment to the gastric mucosa is the first step in establishing bacterial colonization, and adhesins, which are on the surface of H. pylori, play a pivotal role in binding to human gastric mucosa.

MATERIALS AND METHODS

In the present study, we constructed a multivalent epitope-based vaccine named CFAdE with seven carefully selected antigenic fragments from four H. pylori adhesins (urease, Lpp20, HpaA and CagL). The specificity, immunogenicity and ability to produce neutralizing antibodies of CFAdE were evaluated in BALB/c mice. After that, its therapeutic efficacy and protective immune mechanisms were explored in H. pylori-infected Mongolian gerbils.

RESULTS

The results indicated that CFAdE could induce comparatively high levels of specific antibodies against urease, Lpp20, HpaA and CagL. Additionally, oral therapeutic immunization with CFAdE plus polysaccharide adjuvant (PA) significantly decreased H. pylori colonization compared with oral immunization with urease plus PA, and the protection was correlated with IgG and sIgA antibody and antigen-specific CD4⁺ T cells.

CONCLUSIONS

This study indicated that the multivalent epitope-based vaccine, which targeted multiple adhesins in adherence of H. pylori to the gastric mucosa, is more effective than the univalent vaccine targeting urease only. This multivalent epitope-based vaccine may be a promising therapeutic candidate vaccine against H. pylori infection.

Identification of novel Haemophilus parasuis serovar 5 vaccine candidates using an immunoproteomic approach

Haemophilus parasuis is the aetiological agent of Glässer's disease, which is responsible for cases of fibrinous polyserositis, polyarthritis and meningitis. No vaccine is known that provides cross-protection against all serovars. The identification of novel immunoprotective antigens would undoubtedly contribute to the development of efficient subunit vaccines. In the present study, an immunoproteomic approach was used to analyze secreted proteins of H. parasuis and six proteins with high immunogenicity were identified. Five of them were successfully expressed, and their immunogenicity and protective efficacy were assessed in a mouse challenge model. All five proteins elicited strong humoral antibody and cellular immune responses in mice. They all effectively reduced the growth of H. parasuis in mouse organs and conferred different levels of protection (40-80%) against challenge. IgG subtype analysis revealed that the five proteins induce a bias toward a Th1-type immune response, and a significant increase was observed in the cytokine levels of IL-2, IFN-γ and Th2-specific IL-4 in the culture supernatants of splenocytes isolated from immunized mice. The results suggest that both Th1 and Th2 responses are involved in mediating protection. These data suggest that the five proteins could be potential subunit vaccine candidates for use to prevent H. parasuis infection.

BIOLOGICAL SIGNIFICANCE

Haemophilus parasuis can cause huge financial loss in the swine industry worldwide. There are still no vaccines which can provide cross-protection against all serovars. To address this need, we applied an immunoproteomic approach involving 2-DE, MALDI-TOF/TOF MS and Western-blot to identify the secreted proteins which may be able to provide immunoprotection to this disease. We identified six immunogenic proteins, and the immunogenicity and protective efficacy were validated. This result provides a foundation for developing novel subunit vaccines against Haemophilus parasuis.

Helicobacter Catalase Devoid of Catalytic Activity Protects the Bacterium against Oxidative Stress

Catalase, a conserved and abundant enzyme found in all domains of life, dissipates the oxidant hydrogen peroxide (H₂O₂). The gastric pathogen Helicobacter pylori undergoes host-mediated oxidant stress exposure, and its catalase contains oxidizable methionine (Met) residues. We hypothesized catalase may play a large stress-combating role independent of its classical catalytic one, namely quenching harmful oxidants through its recyclable Met residues, resulting in oxidant protection to the bacterium. Two Helicobacter mutant strains (katA^H56A and katA^Y339A) containing catalase without enzyme activity but that retain all Met residues were created. These strains were much more resistant to oxidants than a catalase-deletion mutant strain. The quenching ability of the altered versions was shown, whereby oxidant-stressed (HOCl-exposed) Helicobacter retained viability even upon extracellular addition of the inactive versions of catalase, in contrast to cells receiving HOCl alone. The importance of the methionine-mediated quenching to the pathogen residing in the oxidant-rich gastric mucus was studied. In contrast to a catalase-null strain, both site-change mutants proficiently colonized the murine gastric mucosa, suggesting that the amino acid composition-dependent oxidant-quenching role of catalase is more important than the well described H₂O₂-dissipating catalytic role. Over 100 years after the discovery of catalase, these findings reveal a new non-enzymatic protective mechanism of action for the ubiquitous enzyme.

Antibody Production and Th1-biased Response Induced by an Epitope Vaccine Composed of Cholera Toxin B Unit and Helicobacter pylori Lpp20 Epitopes

BACKGROUND

The epitope vaccine is an attractive potential for prophylactic and therapeutic vaccination against Helicobacter pylori (H. pylori) infection. Lpp20 is one of major protective antigens which trigger immune response after H. pylori invades host and has been considered as an excellent vaccine candidate for the control of H. pylori infection. In our previous study, one B-cell epitope and two CD4(+) T-cell epitopes of Lpp20 were identified.

OBJECTIVE

In this study, an epitope vaccine composed of mucosal adjuvant cholera toxin B subunit (CTB) and these three identified Lpp20 epitopes were constructed to investigate the efficacy of this epitope vaccine in mice.

METHODS

The epitope vaccine including CTB, one B-cell, and two CD4(+) T-cell epitopes of Lpp20 was constructed and named CTB-Lpp20, which was then expressed in Escherichia coli and used for intraperitoneal immunization in BALB/c mice. The immunogenicity, specificity, and ability to induce antibodies against Lpp20 and cytokine secretion were evaluated. After that, CTB-Lpp20 was intragastrically immunized to investigate the prophylactic and therapeutic efficacy in infected mice.

RESULTS

The results indicated that the epitope vaccine CTB-Lpp20 possessed good immunogenicity and immunoreactivity and could elicit specific high level of antibodies against Lpp20 and the cytokine of IFN-γ and IL-17. Additionally, CTB-Lpp20 significantly decreased H. pylori colonization in H. pylori challenging mice, and the protection was correlated with IgG, IgA, and sIgA antibody and Th1-type cytokines.

CONCLUSION

This study will be better for understanding the protective immunity of epitope vaccine, and CTB-Lpp20 may be an alternative strategy for combating H. pylori invasion.

Production of IFN-γ and IL-4 Against Intact Catalase and Constructed Catalase Epitopes of Helicobacter pylori From T-Cells

Background:

Helicobacter pylori infection is highly prevalent in the developing countries. It causes gastritis, peptic ulcer disease, and gastrocarcinoma. Treatment with drugs and antibiotics is problematic due to the following reasons: cost, resistance to antibiotics, prolonged treatment and using multiple drugs. Catalase is highly conserved among the Helicobacter species and is important to the survival of the organism. It is expressed in high amounts and is exposed to the surface of this bacterium; therefore it represents a suitable candidate vaccine antigen.

Objectives:

A suitable approach in H. pylori vaccinology is the administration of epitope based vaccines. Therefore the responses of T-cells (IFN-γ and IL-4 production) against the catalase of H. pylori were determined. Then the quality of the immune responses against intact catalase and three epitopes of catalase were compared.

Materials and Methods:

In this study, a composition of three epitopes of the H. pylori catalase was selected based on Propred software. The effect of catalase epitopes on T-cells were assayed and immune responses identified.

Results:

The results of IFN-γ, IL-4 production against antigens, epitopes, and recombinant catalase by T-cells were compared for better understanding of epitope efficiency.

Conclusions:

The current research demonstrated that epitope sequence stimulates cellular immune responses effectively. In addition, increased safety and potency as well as a reduction in time and cost were advantages of this method. Authors are going to use this sequence as a suitable vaccine candidate for further research on animal models and humans in future.

Therapeutic efficacy of the multi-epitope vaccine CTB-UE against Helicobacter pylori infection in a Mongolian gerbil model and its microRNA-155-associated immuno-protective mechanism

Vaccination is an effective means of preventing infectious diseases, including those caused by Helicobacter pylori. In this study, we constructed a novel multi-epitope vaccine, CTB-UE, composed of the cholera toxin B subunit and tandem copies of the B and Th cell epitopes from the H. pylori urease A and B subunits. We evaluated the therapeutic efficacy of the multi-epitope vaccine CTB-UE against H. pylori infection in a Mongolian gerbil model and studied its immuno-protective mechanisms. The experimental results indicated that urease activity, H. pylori colonisation density, the levels of IL-8 and TNF-α in the serum, and the levels of COX-2 and NAP in gastric tissue were significantly lower and the IgG level in the serum and the IFN-γ level in spleen lymphocytes were significantly higher in the vaccinated group compared with the model control group; additionally, gastric mucosal inflammation was notably alleviated following vaccination. The results showed that CTB-UE had a good therapeutic effect on H. pylori infection. The immuno-protective mechanism was closely related to the immune response mediated by microRNA-155, the expression of which was strongly up-regulated after CTB-UE administration. The expression levels of the microRNA-155 target proteins IFN-γRα, AID, and PU.1 were significantly down-regulated; these results indicated that CTB-UE induced an immune response biased towards Th1 cells by up-regulating microRNA-155 to inhibit IFN-γRα expression and induced a humoral immune response towards B cells by up-regulating microRNA-155 to inhibit PU.1 and AID expression. These results demonstrate that the multi-epitope vaccine CTB-UE may be a promising therapeutic vaccine against H. pylori infection and is a new therapeutic tool for human use.

Immunological features and efficacy of the reconstructed epitope vaccine CtUBE against Helicobacter pylori infection in BALB/c mice model

Urease is an essential virulence factor and colonization factor for Helicobacter pylori, of which the urease B subunit (UreB) is considered as an excellent vaccine candidate antigen. In previous study, an epitope vaccine with cholera toxin B subunit (CTB) and an epitope (UreB321-339) named CtUBE was constructed and the mice were protected significantly after intragastric vaccination with the CtUBE liposome vaccine. However, the fusion protein CtUBE was expressed as inclusion bodies and was difficultly purified. Besides, the immunogenicity and specificity of the CtUBE vaccine was not investigated in a fairly wide and detailed way. In this study, the fusion peptide CtUBE was reconstructed and expressed as a soluble protein with pectinase signal peptide at the N terminus and the 6-his tag at its C-terminal, and then the immunogenicity, specificity, prophylactic, and therapeutic efficacy of the reconstructed CtUBE (rCtUBE) vaccine were evaluated in BALB/c mice model after purification. The experimental results indicated that mice immunized with rCtUBE could produce comparatively high level of specific antibodies which could respond to natural H. pylori urease, UreB, or the minimal epitope UreB327-334 involved with the active site of urease, and showed effectively inhibitory effect on the enzymatic activity of urease. Besides, oral prophylactic or therapeutic immunization with rCtUBE significantly decreased H. pylori colonization compared with oral immunization with rCTB or PBS, and the protection was correlated with antigen-specific IgG, IgA, and mucosal sIgA antibody responses, and a Th2 cells response. This rCtUBE vaccine may be a promising vaccine candidate for the control of H. pylori infection.

Enhancement of Helicobacter pylori outer inflammatory protein DNA vaccine efficacy by co-delivery of interleukin-2 and B subunit heat-labile toxin gene encoded plasmids

Development of an effective vaccine for controlling H. pylori-associated infection, which is present in about half the people in the world, is a priority. The H. pylori outer inflammatory protein (oipA) has been demonstrated to be a potential antigen for a vaccine. In the present study, use of oipA gene encoded construct (poipA) for C57BL/6 mice vaccination was investigated. Whether co-delivery of IL-2 gene encoded construct (pIL-2) and B subunit heat-labile toxin of Escherichia coli gene encoded construct (pLTB) can modulate the immune response and enhance DNA vaccine efficacy was also explored. Our results demonstrated that poipA administered intradermally ('gene gun' immunization) promoted a strong Th2 immune response, whereas co-delivery of either pIL-2 or pLTB adjuvant elicited a Th1-biased immune response. PoipA administered with both pIL-2 and pLTB adjuvants promoted a strong Th1 immune response. Regardless of the different immune responses promoted by the various vaccination regimes, all immunized mice had smaller bacterial loads after H. pylori challenge than did PBS negative and pVAX1 mock controls. Co-delivery of adjuvant(s) enhances poipA DNA vaccine efficacy by shifting the immune response from being Th2 to being Th1-biased, which results in a greater reduction in bacterial load after H. pylori challenge. Both prophylactic and therapeutic vaccination can achieve sterile immunity in some subjects.

Prophylactic and therapeutic efficacy of the epitope vaccine CTB-UA against Helicobacter pylori infection in a BALB/c mice model

Epitope vaccine based on the enzyme urease of Helicobacter pylori is a promising option for prophylactic and therapeutic vaccination against H. pylori infection. In our previous study, the epitope vaccine CTB-UA, which was composed of the mucosal adjuvant cholera toxin B subunit (CTB) and an epitope (UreA₁₈₃₋₂₀₃) from the H. pylori urease A subunit (UreA) was constructed. This particular vaccine was shown to have good immunogenicity and immunoreactivity and could induce specific neutralizing antibodies, which exhibited effectively inhibitory effects on the enzymatic activity of H. pylori urease. In this study, the prophylactic and therapeutic efficacy of the epitope vaccine CTB-UA was evaluated in a BALB/c mice model. The experimental results indicated that oral prophylactic or therapeutic immunization with CTB-UA significantly decreased H. pylori colonization compared with oral immunization with PBS. The results also revealed that the protection was correlated with antigen-specific IgG, IgA, and mucosal secretory IgA antibody responses. CTB-UA may be a promising vaccine candidate for the control of H. pylori infection.

Antigenic diversity among Portuguese clinical isolates of Helicobacter pylori

BACKGROUND

 The human gastroduodenal pathogen, Helicobacter pylori, is characterized by an unusual extent of genetic heterogeneity. This dictates differences in the antigenic pattern of strains resulting in heterogeneous human humoral immune responses. Here, we examined the antigenic variability among a group of 10 strains isolated from Portuguese patients differing in age, gender, and H. pylori-associated gastric diseases.

MATERIAL AND METHODS

 Immunoassays were performed on two-dimensional electrophoresis gels obtained for the proteome of each strain, using a commercial pool of antibodies produced in rabbit, against the whole cell lysate of an Australian H. pylori strain. Relevant proteins were identified by mass spectrometry.

RESULTS

Immunoproteomes of the Portuguese strains showed no correlation between the number of antigenic proteins or the antigenic profile, and the disease to which each strain was associated. The Heat shock protein B was the unique immunoreactive protein common to all of them. Additionally, seven proteins were found to be antigenic in at least 80% of strains: enoyl-(acyl-carrier-protein) reductase (NADH); Catalase; Flagellin A; 2 isoforms of alkyl hydroperoxide reductase; succinyl-CoA transferase subunit B; and an unidentified protein. These proteins were present in the proteome of all tested strains, suggesting that differences in their antigenicity are related to antigenic variance.

CONCLUSIONS

 This study showed evidence of the variability of antigenic pattern among H. pylori strains. We believe that this fact contributes to the failure of anti-H. pylori vaccines and the low accuracy of serological tests based on a low number of proteins or antigens of only one strain.

DNA vaccines for targeting bacterial infections

DNA vaccination has been of great interest since its discovery in the 1990s due to its ability to elicit both humoral and cellular immune responses. DNA vaccines consist of a DNA plasmid containing a transgene that encodes the sequence of a target protein from a pathogen under the control of a eukaryotic promoter. This revolutionary technology has proven to be effective in animal models and four DNA vaccine products have recently been approved for veterinary use. Although few DNA vaccines against bacterial infections have been tested, the results are encouraging. Because of their versatility, safety and simplicity a wider range of organisms can be targeted by these vaccines, which shows their potential advantages to public health. This article describes the mechanism of action of DNA vaccines and their potential use for targeting bacterial infections. In addition, it provides an updated summary of the methods used to enhance immunogenicity from codon optimization and adjuvants to delivery techniques including electroporation and use of nanoparticles.

Immunogenicity of Helicobacter pylori urease B protein and DNA vaccines in a mouse model

A vaccine could alleviate major morbidity and mortality associated with Helicobacter pylori infection. We immunized BALB/c mice with 3 doses of a protein or DNA vaccine based on H pylori urease B. Protein alone was immunogenic even after the first dose, whereas DNA did not elicit antibodies after 3 doses. DNA preceding protein (D-P-P) appeared to blunt the response to protein, whereas DNA following protein (P-D-D) shifted from a predominantly T helper 2 (Th2) profile to a balanced Th1:Th2 profile. These preliminary findings may have important implications for the development of an H pylori vaccine.

Immunology of Helicobacter pylori: insights into the failure of the immune response and perspectives on vaccine studies

Helicobacter pylori infects the stomach of half of the human population worldwide and causes chronic active gastritis, which can lead to peptic ulcer disease, gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. The host immune response to the infection is ineffective, because the bacterium persists and the inflammation continues for decades. Bacterial activation of epithelial cells, dendritic cells, monocytes, macrophages, and neutrophils leads to a T helper cell 1 type of adaptive response, but this remains inadequate. The host inflammatory response has a key functional role in disrupting acid homeostasis, which impacts directly on the colonization patterns of H pylori and thus the extent of gastritis. Many potential mechanisms for the failure of the host response have been postulated, and these include apoptosis of epithelial cells and macrophages, inadequate effector functions of macrophages and dendritic cells, VacA inhibition of T-cell function, and suppressive effects of regulatory T cells. Because of the extent of the disease burden, many strategies for prophylactic or therapeutic vaccines have been investigated. The goal of enhancing the host's ability to generate protective immunity has met with some success in animal models, but the efficacy of potential vaccines in humans remains to be demonstrated. Aspects of H pylori immunopathogenesis are reviewed and perspectives on the failure of the host immune response are discussed. Understanding the mechanisms of immune evasion could lead to new opportunities for enhancing eradication and prevention of infection and associated disease.

Construction of targeted DNA vaccine of H pylori and immune test in BALB/c mice

AIM: To construct DNA vaccine targeted on antigen-presenting cells for the purpose of increasing the immunogenecity of Helicobacter pylori DNA vaccine.

METHODS: DNA vaccine was constructed by combining the targeted DNA sequence with katA. Whether or not the DNA vaccine could be expressed in the mammalian cells was detected by indirect immunofluorescence assay of 293T cells transfected with DNA vaccine. The IgG, IgG1 and IgG2a antibody titers of BALB/c mice immunized with DNA vaccine were also determined.

RESULTS: It was indicated in the immunofluorescence assay of 293T cells transfected with DNA vaccine that the KatA protein could be expressed in these cells. Enzyme-linked immunosorbent assay (ELISA) also showed that the transfected cells with pcDNAkathIgz had a higher affinity for IgG. The IgG antibody titer of BALB/c mice immunized with targeted DNA vaccine was significantly higher than that of mice immunized with pcDNAkatA, and a shift form (Th2 response to Th1 response) was achieved in the mice immunized with DNA vaccine.

CONCLUSION: DNA vaccine targeted on antigen-presenting cells is constructed successfully, which can evoke a higher IgG antibody titer than non-targeted DNA vaccine.

The current status of Helicobacter pylori vaccines: a review

Helicobacter pylori, a Gram-negative flagellate bacterium that infects the stomach of more than half of the global population, is regarded as the leading cause of chronic gastritis, peptic ulcer disease, and even gastric adenocarcinoma in some individuals. Although the bacterium induces strong humoral and cellular immune responses, it can persist in the host for decades. It has several virulence factors, some of them having vaccine potential as judged by immunoproteomic analysis. A few vaccination studies involving a small number of infected or uninfected humans with various H. pylori formulations such as the recombinant urease, killed whole cells, and live Salmonella vectors presenting the subunit antigens have not provided satisfactory results. One trial that used the recombinant H. pylori urease coadministered with native Escherichia coli enterotoxin (LT) demonstrated a reduction of H. pylori load in infected participants. Although extensive studies in the mouse model have demonstrated the feasibility of both therapeutic and prophylactic immunizations, the mechanism of vaccine-induced protection is poorly understood as several factors such as immunoglobulin and various cytokines do not contribute to protection. Transcriptome analyses in mice have indicated the role of nonclassical immune factors in vaccine-induced protection. The role of regulatory T cells in the persistence of H. pylori infection has also been suggested. A recently developed experimental H. pylori infection model in humans may be used for testing several new adjuvants and vaccine delivery systems that have been currently obtained. The use of vaccines with appropriate immunogens, routes of immunization, and adjuvants along with a better understanding of the mechanism of immune protection may provide more favorable results.

Construction of an oral recombinant DNA vaccine from H pylori neutrophil activating protein and its immunogenicity

AIM: To construct a live attenuated Salmonella typhimurium (S. typhimurium) strain harboring the H pylori neutrophil activating protein (HP-NAP) gene as an oral recombinant DNA vaccine, and to evaluate its immunogenicity.

METHODS: By genetic engineering methods, the genomic DNA of H pylori was extracted as a template. The total length of the HP-NAP gene was amplified by polymerase chain reaction (PCR) and cloned into pBT vector for sequencing and BLAST analysis, then subcloned into a eukaryotic expression vector pIRES followed by PCR identification and restriction enzyme digestion. The identified recombinant plasmid pIRES-NAP was transfected into COS-7 cells for target fusion protein expression, and its antigenicity was detected by Western blotting. Then the recombinant plasmid was transformed into a live attenuated S. typhimurium strain SL7207 as an oral vaccine strain, and its immunogenicity was evaluated with animal experiments.

RESULTS: A 435 bp product was cloned using high homology with HP-NAP gene in GenBank (more than 98%). With identification by PCR and restriction enzyme digestion, a recombinant eukaryotic expression plasmid pIRES-NAP containing the HP-NAP gene of H pylori was successfully constructed. The expressed target protein had a specific reaction with H pylorii whole cell antibody and showed a single strip result detected by Western blotting. Oral immunization of mice with recombinant DNA vaccine strain SL7207 (pIRES-NAP) also induced a specific immune response.

CONCLUSION: The successful construction of HP-NAP oral DNA vaccine with good immunogenicity may help to further investigate its immunoprotection effects and develop vaccine against H pylori infection.

Specific T cell responses to Helicobacter pylori predict successful eradication therapy

OBJECTIVE

The aim of our prospective study was to test a specific T cell response to Helicobacter pylori before therapy and compare it to the success of H. pylori eradication 12 months later.

METHODS

A total of 14 dyspeptic patients and 10 patients with previous H. pylori eradication failure were recruited into the study; before therapy their gastric samples for H. pylori cultivation and blood samples for dendritic cell cultivation were obtained. H. pylori antigens were produced to prime dendritic cells for stimulation of T lymphocyte response.

RESULTS

The level of cytokine response by T cells was measured and results were compared with the success of H. pylori eradication one year later. There was a significantly increased response in expression of IFN-gamma and IL-4 molecules by DCs stimulated T cells in subjects that successfully eradicated H. pylori compared with those who failed to eradicate the infection. Our results support the hypothesis that successful H. pylori eradication requires established anti-H. pylori immune response besides antibiotic treatment.

CONCLUSION

Effective IFN-gamma cytokine response to H. pylori antigens seems to be of particular importance. Immunisation could be therefore beneficial for H. pylori eradication, while immunodeficiency could cause the failure in H. pylori eradication.

DNA vaccines against enteric infections

The first DNA vaccines for prevention of infectious diseases were described in 1993 and have since been shown to generate protective humoral and cellular immune responses to numerous infectious agents. For enteric infections, protective immunity has been obtained with DNA vaccines against several enteric viral, bacterial, and parasitic agents. Inoculation of DNA vaccines has generally been by intramuscular injection or by gene gun delivery of vaccine DNA-coated gold microparticles into the skin. Administration of DNA vaccines by the oral route would target the vaccines to enteric mucosal tissues, as well as providing a convenient means for vaccine delivery. Orally administered plasmid DNAs encapsulated in polymeric microparticles or inserted in live bacterial vectors have been effective in animal models for rotavirus DNA vaccines and Listeria monocytogenes DNA vaccines, respectively. Human trials of enteric DNA vaccines have not been initiated, but trials of veterinary vaccines have shown promise.

Mucosal immunization with a urease B DNA vaccine induces innate and cellular immune responses against Helicobacter pylori

BACKGROUND

Helicobacter pylori is recognized as a major risk factor for recurrent gastroduodenal inflammatory diseases and gastric adenocarcinoma. The high prevalence of H. pylori infection worldwide, the risks of side-effects from antibiotic therapy, and increasing resistance to antibiotics are the main primers for the development of improved H. pylori vaccines. The antigenic potential of its urease enzyme, a critical virulence factor required for colonization of the gastric mucosa, has been demonstrated in animal and human studies. An important but controversial issue in H. pylori vaccine studies is the type of immune response required to control infection. A new approach in H. pylori vaccinology is the administration of DNA vaccines, which has included heat-shock protein and catalase DNA vaccines.

MATERIALS AND METHODS

The H. pylori urease subunit B construct or vector alone was administered to mice via the intranasal route. Spleens and stomachs were examined on day 0 and weeks 3, 6, and 12 after immunization. Proliferation of spleen cells was assessed using the carboxyfluorescein diacetate succinimidyl ester-based flow cytometry assay and cytokine secretion from cultured spleen cells was detected by ELISA, after stimulation with the urease subunit B recombinant antigen. Total RNA was isolated from stomach and spleen tissue and the expression of beta-defensin and cytokine genes was monitored by reverse transcription followed by polymerase chain reaction (RT-PCR). Immunized mice were challenged with H. pylori and bacterial DNA quantified by TaqMan PCR.

RESULTS

The urease B subunit DNA vaccine increased INF-gamma secretion and splenocyte proliferation without inducing adverse effects in the spleen. Increase in gastric beta-defensin 1 and marked induction in local IL-10 : IFN-gamma ratio up to 12 weeks post-immunization suggest a potential role for local innate immune responses in protection at the site of infection. Although significant bacterial reduction in the stomachs of urease B subunit DNA-immunized mice was observed, intermediate reduction was also noted in the vector group. Increased defensin expression and adjuvant effects of the cytosine preceding guanosine motifs may contribute to this phenomenon. Our data confirm that cytosine preceding guanosine motifs, even without coadministration with antigen, can reduce extracellular bacterial load.

CONCLUSIONS

In this study, a DNA construct encoding the urease B subunit was assessed for its immune profile and its ability to reduce bacterial colonization in the murine stomach. Our studies suggest that local innate immune responses may play a greater role than previously supposed in limiting H. pylori colonization in the gastric mucosa.

A plasmid immunization construct encoding urease B of Helicobacter pylori induces an antigen-specific antibody response and upregulates the expression of beta-defensins and IL-10 in the stomachs of immunized mice

The objectives of this study were to investigate the efficacy of a prototype DNA immunization construct encoding the urease B subunit enzyme of Helicobacter pylori (H. pylori) for inducing adaptive and innate immune responses in mice immunized via intramuscular or subcutaneous routes and to further explore the adjuvant effects of the CpG motifs in the vector. Antibody, cytokine, and beta-defensin profiles were assessed in the stomachs of immunized animals: experiments were terminated 3 months after immunization because there was a significant increase in the anti-H. pylori urease B antibody response at Week 6 in mice immunized with the urease B construct. A long lasting expression of IL-10 mRNA was noted. Furthermore, a marked and sustained increase in the mRNA expression of beta-defensins was also observed, particularly beta1. This study demonstrates that an H. pylori urease B DNA construct can induce innate as well as adaptive immune responses in the stomachs of immunized mice. Upregulation of beta-defensin gene expression followed immunization and we believe that this is the first report of a DNA vaccine inducing innate anti-microbial responses. Such complex molecular interactions that modulate both innate and adaptive immune responses may be of critical importance in the control of mucosal pathogens, such as H. pylori.

Diagnosis of Helicobacter pylori infection and diseases associated with Helicobacter pylori by Helicobacter pylori outer membrane proteins

AIM: To examine the serological response of patients with upper gastrointestinal diseases and Helicobocter pylori (H pylori) infection to two H pylori outer membrane proteins (OMPs) (M_r18000 and M_r26000) acquired by gene recombinant technique, and to determine the diagnostic significance of serological tests derived from these OMPs.

METHODS: Recombinant vectors encoding the two H pylori OMPs were used to transform and express in BL21 (DE3) E.coli. After purification with Ni²⁺-NTA agarose resin, colloid gold kits were prepared with purified recombinant proteins to detect H pylori infection and H pylori-associated diseases by the immunity-marker technology. We selected 150 patients with H pylori infection and digestive symptoms without previous treatment, including chronic gastritis (n = 60), duodenal ulcer (n = 30), gastric ulcer (n = 30), and gastric cancer (n = 30). As controls, 33 H pylori-negative healthy volunteers were also recruited. Serum samples were collected from all subjects, and the antibodies to specific proteins of H pylori were tested with the colloid gold test kits. The sensitivity, specificity and accuracy of the colloid gold tests were evaluated, by using the combination of standard diagnostic methods (¹³C urea breath test and bacteria culture) and classic enzyme-linked immunosorbent assay (ELISA) as reference.

RESULTS: After purification with Ni²⁺-NTA agarose resin, the purity of recombinant fusion proteins was about 95%. The recombinant fusion proteins were recognized by the specific monoclonal antibodies against the two H pylori OMPs, as demonstrated by the ELISA. Of the 150 serum samples from patients infected with H pylori 141 (94.0%) responded positively to the recombinant protein with M_r26000, while the seropositive rates were 95.0%, 96.7%, 96.7% and 90.0% for patients with H pylori-associated chronic gastritis, duodenal ulcer, gastric ulcer, and gastric cancer respectively. The sensitivity, specificity, and accuracy of the colloid gold kit with M_r26000 protein were 94.0%, 97.0%, and 94.5%, respectively. Compared with the classic ELISA, bacteria culture and ¹³C urea breath test results in detecting H pylori-infection, there was no significant difference (P > 0.05). For the colloid gold kit with M_r18000, the seropositive rates were 52.0%, 40.0%, 40.0%, 53.3% and 86.7%, respectively, in H pylori-infected patients, and those with H pylori-associated chronic gastritis, duodenal ulcer, gastric ulcer, and gastric cancer. There was a significant difference (P < 0.05) in seropositivity between patient with gastric cancer (86.7%) and those with other diseases (43.3%).

CONCLUSION: The two colloid gold kits derived from the recombinant OMPs are useful tools either for detecting H pylori infection, or for, predicting H pylori-associated gastric malignancy.

Expression and immunocompetence of HspA-UreB fusion protein of Helicobacter pylori

AIM: To construct recombinant expression vector expressing HspA-UreB fusion protein of Helicobacter pylori (H. pylori), and to determine its immunoreactivity, in order to develop gene recombinant vaccine against H. pylori infection.

METHODS: The hspA and ureB genes were amplified by PCR from H. pylori MEL-HP27 isolated in Zhengzhou and cloned directionally into vector pNEB193. These two genes were restricted by using two corresponding restriction enzyme separately and cloned together into the fusion expression vector pET-30 (a), and the recombinant plasmid was then used to transform E.coli BL21 (DE3). The positive clones were identified by PCR and restriction enzyme digestion. The recombinant fusion protein HspA-UreB was induced to express from E.coli by IPTG and was analyzed by SDS-PAGE. The fusion protein was purified by use of Ni²⁺ affinity chromatography and then used to immunize mice. The immunogenecity and immunoreactivity of the fusion protein were analyzed by Western blot.

RESULTS: The hspA-ureB fusion gene was amplified from the recombinant fusion expression plasmid pET-HU27 (pET-HspA-UreB) by PCR, and also the hspA-ureB fusion gene fragment was produced from these plasmids after restriction enzyme digestion. SDS-PAGE and optical density scanning indicated that the fusion protein was expressed in the recombinant vaccine strain BL21 (pET-HU27) as a protein with 82.1 KDa of molecular weight that accounted for 21% of the total bacterial protein. The purity of fusion protein was 91%. Western blot analysis of the purified fusion protein confirmed that it could specifically be recognized by mouse serum.

CONCLUSION: A recombinant vaccine candidate strain expression fusion protein HspA-UreB of H. pylori is constructed and identified successfully, and purified fusion protein has strong immunoreactivity.

Defensive applications of gene transfer technology in the face of bioterrorism: DNA-based vaccines and immune targeting

Gene transfer involves the introduction of an engineered gene into a person's cells with the expectation that the protein expressed from the gene will produce a therapeutic benefit. Strategies based on this principle have led to the approval of > 600 clinical trials and enrollment of approximately 3500 subjects worldwide in attempts to treat diseases ranging from cancer to AIDS to cystic fibrosis. While gene therapy has met with limited success and still has many hurdles to overcome before it sees wide application, it may be useful as a defensive strategy against bioterrorism agents including infectious microbes and toxins. Although many defensive strategies are possible, immunological strategies are currently the most developed and are being actively applied to the development of strategies against several of the most virulent potential bio-weapons. While most of these strategies are not yet ready for human application, DNA-based vaccines appear to be among the most promising in the fight against bioterrorism.

Helicobacter pylori- inflammation, immunity and vaccines

The mechanisms by which Helicobacter pylori escape the host immune response remains an important topic. Regulatory T cells appear to play a role in the persistence of the infection and the control of tissue damage. In the thought that the host genetic background influences the cross-talk between pathogens and hosts, the impact of cytokine polymorphisms on the outcome of H. pylori has been further delineated in the review period. On the other hand, several additional genes of H. pylori have been shown to participate in the pro-inflammatory cytokine and chemokine response to the infection. Finally, progress has been achieved in vaccine development, with new vaccine delivery systems and routes of immunization tested in animal models and human volunteers.