Immunisation against gastric infection with Helicobacter species: first step in the prophylaxis of gastric cancer?

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.

Current Status and Prospects for a Helicobacter pylori Vaccine

Helicobacter pylori infection contributes to a variety of gastric diseases. H pylori-associated gastric cancer is diagnosed in advanced stages, and a vaccine against H pylori is desirable in parts of the world where gastric cancer remains a common form of cancer. Some of the strategies of vaccine development used in animals have been tested in several phase 3 clinical trials; these trials have been largely unsuccessful, although H pylori-specific immune responses have been induced. New insights into promoting immunity and overcoming the immunosuppressive nature of H pylori infection are required to improve the efficacy of an H pylori vaccine.

Vaccinating against Helicobacter pylori in the developing world

Helicobacter pylori infects more than half the world's population and in developing nations the incidence can be over 90%. The morbidity and mortality associated with H. pylori-associated diseases including ulcers and gastric cancer therefore, disproportionately impact the developing world. Mice have been used extensively to demonstrate the feasibility of developing a vaccine for H. pylori infection, and for testing antigens, routes of immunization, dose, and adjuvants. These successes however, have not translated well in clinical trials. Although there are examples where immune responses have been activated, there are few instances of achieving a reduced bacterial load. In vivo and in vitro analyses in both mice and humans demonstrates that the host responds to H. pylori infection through the activation of immunoregulatory mechanisms designed to suppress the anti-H. pylori response. Improved vaccine efficacy therefore, will require the inclusion of factors that over-ride or re-program these immunoregulatory rersponse mechanisms.

Vaccinating against Helicobacter pylori infection

Helicobacter pylori infection of the gastric mucosa remains a cause of significant morbidity and mortality almost 30 years after its discovery. H. pylori infection can lead to several gastric maladies, including gastric cancer, and although antimicrobial therapies for the infection exist, the cost of treatment for gastric cancer and the prognosis of individuals who present with this disease make vaccine development a cost effective alternative to bacterial eradication. Experimental mucosal and systemic H. pylori vaccines in mice significantly reduce bacterial load and sometimes provide sterilizing immunity. Clinical trials of oral vaccines consisting of H. pylori proteins with bacterial exotoxin adjuvants or live attenuated bacterial vectors expressing H. pylori proteins induce adaptive immune mechanisms but fail to consistently reduce bacterial load. Clinical trials and murine studies demonstrate that where H. pylori is killed, either spontaneously or following vaccination, the host demonstrated cellular immunity. Improved efficacy of vaccines may be achieved in new trials of vaccine formulations that include multiple antigens and use methods to optimize cellular immunity. Unfortunately, the industrial sponsors that served as the primary engine for much of the previous animal and human research have withdrawn their support. A renewed or expanded commitment from the biotechnology or pharmaceutical industry that could exploit recent advances in our understanding of the host immune response to H. pylori is necessary for the advancement of an H. pylori vaccine.

Systemic immunization with unadjuvanted whole Helicobacter pylori protects mice against heterologous challenge

BACKGROUND

Adjuvant-free vaccines have many benefits, including decreased cost and toxicity. We examined the protective effect of systemic vaccination with adjuvant-free formalin-fixed Helicobacter pylori or bacterial lysate and the ability of this vaccine to induce protection against heterologous challenge.

MATERIALS AND METHODS

Mice were vaccinated subcutaneously with H. pylori 11637 lysate or formalin-fixed bacteria, with or without ISCOMATRIX adjuvant, then orally challenged with H. pylori SS1. Serum was taken prior to challenge to examine specific antibody levels induced by the vaccinations, and protection was assessed by colony-forming assay.

RESULTS

Vaccination with H. pylori 11637 lysate or formalin-fixed bacteria delivered systemically induced significantly higher levels of Helicobacter-specific serum IgG than the control, unvaccinated group and orally vaccinated group. After heterologous challenge with H. pylori SS1, all vaccinated groups had significantly lower levels of colonization compared with unvaccinated, control mice, regardless of the addition of adjuvant or route of delivery. Protection induced by systemic vaccination with whole bacterial preparations, without the addition of adjuvants, was only associated with a mild cellular infiltration into the gastric mucosa, with no evidence of atrophy.

CONCLUSIONS

Subcutaneous vaccination using unadjuvanted formalin-fixed H. pylori has the potential to be a simple, cost-effective approach to the development of a Helicobacter vaccine. Importantly, this vaccine was able to induce protection against heterologous challenge, a factor that would be crucial in any human Helicobacter vaccine. Further studies are required to determine mechanisms of protection and to improve protective ability.

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.

The nontoxic CTA1-DD adjuvant enhances protective immunity against Helicobacter pylori infection following mucosal immunization

Safe and efficacious adjuvants are much needed to facilitate the development of mucosal vaccines. Here, we have asked whether our nontoxic vaccine adjuvant, CTA1-DD, can enhance protective immunity against Helicobacter pylori infection. Intranasal immunizations with H. pylori lysate together with CTA1-DD-adjuvant induced significant protection in C57Bl/6 mice, almost as strong as similar immunizations using cholera toxin (CT)-adjuvant. Protection remained strong even at 8 weeks postchallenge and the bacterial colonization was reduced by 20-fold compared to lysate-immunized controls. Although CTA1-DD was designed to bind to B cells, microMT mice developed significant, but lower, level of protection following immunization. Intranasal immunizations with CT adjuvant in C57Bl/6 mice resulted in the development of severe postimmunization gastritis at 2 and 8 weeks postchallenge, whereas the degree of gastritis was substantially lower in the CTA1-DD-immunized mice. Protection induced by both CTA1-DD- and CT adjuvant was associated with a strong local infiltration of CD4(+) T cells in the gastric mucosa, and recall responses to specific Ag elicited substantial IFN-gamma production, indicating Th1-dominance. These findings clearly demonstrate that CTA1-DD adjuvant is a promising candidate to be further exploited in the development of a mucosal vaccine against H. pylori infection.

Intranasal CpG-oligodeoxynucleotide is a potent adjuvant of vaccine against Helicobacter pylori, and T helper 1 type response and interferon-gamma correlate with the protection

BACKGROUND

Although a series of vaccines against Helicobacter pylori have emerged in the past 10 years, the mechanism involved in their protective effect is yet to be elucidated, and more effective vaccine adjuvants remain to be developed. In this study, CpG-oligodeoxynucleotide (CpG-ODN) was investigated as a new candidate for a H. pylori vaccine adjuvant. Furthermore, the role of T helper 1 (Th1) type response and interferon (IFN)-gamma in the protective immunity was explored.

METHODS

C57BL/6 mice and IFN-gamma knockout mice were intranasally or orally immunized with H. pylori whole cell sonicate (WCS)/CpG-ODN and challenged with different doses [5 x 10(8) and 5 x 10(6) colony-forming units (CFU)] of H. pylori. The protective effect was assessed as the percentage of noninfected mice. The responsive antibodies and cytokines were analyzed using an enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

The prevention rates against H. pylori infection in mice intranasally immunized with WCS plus CpG-ODN were dramatically higher than those in sham-immunized mice (70% vs. 0%, challenged with 5 x 10(8) CFU H. pylori; 90% vs. 20%, challenged with 5 x 10(6) CFU H. pylori). Significantly higher levels of immunoglobulin G2a (IgG2a) and IFN-gamma were detected in the mice immunized with WCS/CpG than in sham-immunized controls. However, vaccination failed to effectively protect IFN-gamma knockout mice challenged with H. pylori.

CONCLUSIONS

CpG-ODN given intranasally is a potent adjuvant for development of a H. pylori vaccine. Th1-type response and IFN-gamma are involved in the protection.

Protection against Helicobacter pylori infection following immunization is IL-12-dependent and mediated by Th1 cells

The regulatory roles of Th1 and Th2 cells in immune protection against Helicobacter infection are not clearly understood. In this study, we report that a primary H. pylori infection can be established in the absence of IL-12 or IFN-gamma. However, IFN-gamma, but not IL-12, was involved in the development of gastritis because IFN-gamma(-/-) (GKO) mice exhibited significantly less inflammation as compared with IL-12(-/-) or wild-type (WT) mice. Both IL-12(-/-) and GKO mice failed to develop protection following oral immunization with H. pylori lysate and cholera toxin adjuvant. By contrast, Th2-deficient, IL-4(-/-), and WT mice were equally well protected. Mucosal immunization in the presence of coadministered rIL-12 in WT mice increased Ag-specific IFN-gamma-producing T cells by 5-fold and gave an additional 4-fold reduction in colonizing bacteria, confirming a key role of Th1 cells in protection. Importantly, only protected IL-4(-/-) and WT mice demonstrated substantial influx of CD4(+) T cells in the gastric mucosa. The extent of inflammation in challenged IL-12(-/-) and GKO mice was much reduced compared with that in WT mice, indicating that IFN-gamma/Th1 cells also play a major role in postimmunization gastritis. Of note, postimmunization gastritis in IL-4(-/-) mice was significantly milder than WT mice, despite a similar level of protection, indicating that immune protection is not directly linked to the degree of gastric inflammation. Only protected mice had T cells that produced high levels of IFN-gamma to recall Ag, whereas both protected and unprotected mice produced high levels of IL-13. We conclude that IL-12 and Th1 responses are crucial for H. pylori-specific protective immunity.

Safety and efficacy of E coli enterotoxin adjuvant for urease-based rectal immunization against Helicobacter pylori

Low dose E. coli heat-labile enterotoxin (LT), delivered orally or enterically, has been used as an adjuvant for Helicobacter pylori (H. pylori) urease in healthy adults. In this study we aim to test the safety and adjuvant efficacy of LT delivered rectally together with recombinant H. pylori urease. Eighteen healthy adults without present or past H. pylori infection were enrolled in a double blind, randomized, ascending dose study to receive either urease (60 mg), or urease (60 mg) + LT (5 or 25 microg). The immunization preparation was administered per rectum on days 0, 14 and 28. Serum, stool and saliva anti-urease and anti-LT IgG and IgA antibodies (Abs) were measured and urease-specific and LT-specific antigen secreting cells (ASCs) were counted in peripheral blood at baseline and 7 (ASC counts) or 14 days (antibody levels) after each dosing. Peripheral blood lymphoproliferation assays were also performed at baseline and at the end of the study. Rectally delivered urease and LT were well tolerated. Among the 12 subjects assigned to urease+LT, 2 (16.7%) developed anti-urease IgG Abs, 1 (8.3%) developed anti-urease IgA Abs, and 3 (25%) showed urease-specific IgA(+) ASCs. Immune responses to LT were more vigorous, especially in subjects exposed to 5 microg LT. In the urease+ 5 microg LT group, anti-LT IgG and IgA Abs developed in 60 and 80% of the subjects, respectively, while LT-specific IgG(+) and IgA(+) ASCs were detected in all subjects. The magnitude of the anti-LT response was much higher than the response to urease. No IgA anti-urease or anti-LT Abs were detected in stool or saliva and lymphocyte proliferative responses to urease were unsatisfactory. In conclusion, rectal delivery of 5 microg LT is safe and induces vigorous systemic anti-LT immune responses. Further studies are needed to determine if LT can be an effective adjuvant for rectally delivered antigens.

Sterilizing immunity against experimental Helicobacter pylori infection is challenge-strain dependent

The development of a murine model of Helicobacter pylori infection through serial in vivo passage of candidate strains has enabled a quantitative assessment of vaccine efficacy. In this study we compare infection with and protection against challenge from both CagA(+) type I, and CagA(-) type II in vivo adapted isolates. In vivo passage of a type II H. pylori isolate resulted in a highly infectious strain (X47-2AL), capable of reproducibly infecting mice to high density (10(7) CFU/g of gastric tissue). Similarly adapted type I strains were found to colonize mice at a significantly lower level (10(4)-10(5) CFU/g tissue). Mucosal immunization with recombinant urease (rUre) significantly protected animals against both types. Protection against X47-2AL was characterized by a > or =100-fold (or 2 log) reduction in bacterial density. However, the presence of a residual infection highlighted the inability to achieve sterilizing immunity against this strain. The level of protection appeared independent of challenge dose, and was stable for up to 6 months, all animals exhibiting a low-level residual infection that did not recrudesce with time. Similarly immunized mice challenged with isolates representing the residual infection were also protected, confirming that they did not represent a sub-population of H. pylori that could escape immunity. Immunization and challenge studies with type I adapted-isolates, demonstrated a similar 2-3 log reduction in the bacterial burden, but that in this instance resulted in sterilizing immunity. These results suggest varied specificity for the murine host by different Helicobacter strains that can influence the outcome of both infection and immunity.

Emergence of diverse Helicobacter species in the pathogenesis of gastric and enterohepatic diseases

Since Helicobacter pylori was first cultivated from human gastric biopsy specimens in 1982, it has become apparent that many related species can often be found colonizing the mucosal surfaces of humans and other animals. These other Helicobacter species can be broadly grouped according to whether they colonize the gastric or enterohepatic niche. Gastric Helicobacter species are widely distributed in mammalian hosts and are often nearly universally prevalent. In many cases they cause an inflammatory response resembling that seen with H. pylori in humans. Although usually not pathogenic in their natural host, these organisms serve as models of human disease. Enterohepatic Helicobacter species are an equally diverse group of organisms that have been identified in the intestinal tract and the liver of humans, other mammals, and birds. In many cases they have been linked with inflammation or malignant transformation in immunocompetent hosts and with more severe clinical disease in immunocompromised humans and animals. The purpose of this review is to describe these other Helicobacter species, characterize their role in the pathogenesis of gastrointestinal and enterohepatic disease, and discuss their implications for our understanding of H. pylori infection in humans.

Immunology of Helicobacter pylori and prospects for vaccine

Since the initial discovery of H. pylori by Marshall and Warren 17 years ago, much progress has been made in treating this infection. However, as we enter the millennium, H. pylori infection continues to be one of the most common infections of mankind. In addition, eradication of H. pylori still requires multiple antimicrobial agents. A better understanding of the host immune response to H. pylori infection should allow investigators to develop immunotherapies to prevent the acquisition of infection and eradicate existing chronic H. pylori infection.

Gastric mucosal alpha(4)beta(7)-integrin-positive CD4 T lymphocytes and immune protection against helicobacter infection in mice

BACKGROUND & AIMS

The integrin alpha(4)beta(7) mediates homing of effector/memory lymphocytes to the intestine and the mucosa-associated lymphoid tissue. This study examined the ability of alpha(4)beta(7)(hi) CD4(+) T lymphocytes to home to the stomach and their role in immunization-mediated protection against Helicobacter felis infection.

METHODS

Gastric lamina propria and circulating mononucleated cells of naive, infected, and immunized Swiss Webster mice were isolated, and alpha(4)beta(7)-integrin expression was quantified by flow cytometry on CD4(+) T lymphocytes. Anti-alpha(4)beta(7)-integrin antibody was used to block alpha(4)beta(7) function in vivo.

RESULTS

In naive mice, alpha(4)beta(7)(hi) CD4(+) T cells were enriched approximately 10-fold in the gastric mucosa compared with peripheral blood (P<0.0001). Chronic H. felis infection did not alter these proportions, but oral immunization with H. felis sonicate plus cholera toxin (CT) or with CT alone markedly increased gastric alpha(4)beta(7)(hi) CD4(+) T cells compared with naive and infected controls (P = 0.0008 and P = 0.002 for H. felis sonicate and CT, respectively). Anti-alpha(4)beta(7)-integrin antibody blocked the protection induced by oral immunization with H. felis sonicate and CT.

CONCLUSIONS

The integrin alpha(4)beta(7) participates in the homing of CD4(+) T lymphocytes to the stomach and in the protection of the gastric mucosa against H. felis infection.

Further development of the Helicobacter pylori mouse vaccination model

Immunisation against Helicobacter infection in mouse models has thus far produced neither complete protection against the bacteria, nor a complete prevention of the associated gastritis. This study aimed firstly to compare the sensitivities of the various methods used to assess H. pylori infection in the mouse model, and secondly to develop the experimental design to induce a more effective immunity, aimed at further reducing bacterial burden in the gastric tissue. Various mouse strains were prophylactically immunised with whole bacterial sonicate and cholera toxin before challenge with H. pylori-SS1. The relative sensitivities of the urease assay, histological assessment and the colony forming assay to detect levels of H. pylori colonisation were compared. Comparisons of different antigen doses and different timecourses of immunisation were performed. The colony forming assay was found to be far more sensitive than either the urease assay or histological assessment for determining the protective efficacies of immunisation. Mice which had 10(5) H. pylori per gram of stomach by colony assay were negative by histology and urease. Lower doses of whole cell sonicate were more protective than high doses and more effective immunisation was achieved by leaving at least 3 weeks between immunisation instead of weekly immunisations. In conclusion, for assessment of H. pylori colonisation in the mouse model, the colony forming assay should be used. The experimental protocol for immunisation has been altered to produce a significant improvement in protection. However, full protection has still not yet been achieved and more work is still required.

Strategies for developing a Helicobacter pylori vaccine

Novel strategies are needed to control infection with Helicobacter pylori. Prophylactic and therapeutic immunization against this gastric pathogen is possible in animal models, and initial human studies in H. pylori-infected subjects showed that immunization with H. pylori urease is both safe and immunogenic. In rodents, gastric protection against Helicobacter species infection does not depend on the humoral immune response, and a prominent role of the major histocompatibility complex II-restricted CD4(+) T-cell response is recognized; however, much remains to be learned about the mechanisms of effective bactericidal response. A clear understanding of the basic mechanisms of gastric immune protection in humans is of the utmost importance for the development of an effective human vaccine. More potent vaccines are likely to be required to induce protection in humans. The availability of two complete genome sequences of H. pylori represents a unique opportunity to identify novel vaccine antigens. Multivalent vaccines delivered by recombinant attenuated bacteria or administered with nontoxic adjuvants need to be evaluated in relevant models.

Animal models for gastric Helicobacter immunology and vaccine studies

Over the last decade animal models have been used extensively to investigate disease processes and therapy for Helicobacter pylori infections. The H. pylori animal models which have been used in pathogenesis and vaccine studies include the gnotobiotic pig, non-human primates, cats, dogs, and several species of rodents including mice, rats, gerbils and guinea pigs. H. felis infection of mice and H. mustelae infection of ferrets have also been used. Recently, investigators have begun using transgenic mice and gene-targeted 'knock-out' mice to investigate Helicobacter infections. Each of these animal models has distinct advantages and disadvantages which are discussed in this minireview. The choice of an animal model is dictated by factors such as cost and an understanding of how each model will or will not allow fulfillment of experimental objectives.

Oral immunization with urease and Escherichia coli heat-labile enterotoxin is safe and immunogenic in Helicobacter pylori-infected adults

BACKGROUND & AIMS

Oral immunization with Helicobacter pylori urease can cure Helicobacter infection in animals. As a step toward therapeutic immunization in humans, the safety and immunogenicity of oral immunization with recombinant H. pylori urease were tested in H. pylori-infected adults.

METHODS

Twenty-six H. pylori-infected volunteers were randomized in a double-blind study to four weekly oral doses of 180, 60, or 20 mg of urease with 5 microg heat-labile enterotoxin of Escherichia coli (LT), LT alone, or placebo. Side effects and immune responses were evaluated weekly after immunization, and gastric biopsy specimens were obtained after 1 month and 6 months for histology and quantitative cultures.

RESULTS

Diarrhea was noted in 16 of 24 (66%) of the volunteers who completed the study. Antiurease serum immunoglobulin A titers increased 1. 58-fold +/- 0.37-fold and 3.66-fold +/- 1.5-fold (mean +/- SEM) after immunization with 60 and 180 mg urease, respectively, whereas no change occurred in the placebo +/- LT groups (P = 0.005). Circulating antiurease immunoglobulin A-producing cells increased in volunteers exposed to urease compared with placebo (38.9 +/- 13. 6/10(6) vs. 5.4 +/- 3.1; P = 0.018). Eradication of H. pylori infection was not observed, but urease immunization induced a significant decrease in gastric H. pylori density.

CONCLUSIONS

H. pylori urease with LT is well tolerated and immunogenic in H. pylori-infected individuals. An improved vaccine formulation may induce curative immunity.

Host response and vaccine development to Helicobacter pylori infection

Studies in both humans and animals demonstrate that H. pylori is capable of illiciting an innate response that in part is regulated by the genetic makeup of the host. These innate responses includes stimulating immune effector mechanisms at the cellular and biochemical level resulting in the influx of neutrophils into the lamina propria and have even been shown to modify gastric acid secretion. The availability of good animal models of chronic Helicobacter infection has also allowed investigators to begin to examine how the adaptive host immune response prevents and/or exacerbates Helicobacter-induced gastroduodenal disease. The experimental H. felis/mouse model has been utilized by a number of laboratories to investigate mechanisms of host defense against chronic Helicobacter infection. This model and the more recently developed H. pylori rodent model has not only allowed investigators to confirm the feasibility of immunotherapy to prevent and/or cure Helicobacter infection but also to begin to examine how the host immune response prevents and/or exacerbates Helicobacter-induced gastroduodenal disease. Based on these studies a hypothesis is emerging that suggests that protection and/or cure from Helicobacter infection is mediated primarily by an upregulated cellular immune response which may act via an antibody independent mechanism. Paradoxically, following natural infection with H. pylori, a component of the cellular immune response also promotes chronic gastric inflammation without clearance of the organism. The recent development of reliable and reproducible H. pylori/rodent models of disease and the availability of numerous inbred strains, transgenic and knockout animals, will allow investigators to continue to explore the role the host cellular and humoral immune response plays in promoting or preventing this infection.

Rectal and intranasal immunizations with recombinant urease induce distinct local and serum immune responses in mice and protect against Helicobacter pylori infection

To determine the optimal inductive sites for immunization against Helicobacter pylori infection, the protective efficacy of recombinant urease (rUre) was assessed for mice given the vaccine by either the oral (p.o.), intranasal (i.n.), or rectal route. When mice were immunized with rUre (25 microg p.o. or rectally or 10 microg i.n.) plus heat-labile toxin from Escherichia coli as the mucosal adjuvant, all routes afforded protection against challenge with H. pylori, as indicated by a significant reduction in gastric urease activity (P < 0.0005) compared to that of sham-immunized controls. Quantitative H. pylori culture of stomach tissue demonstrated a >97% reduction in bacterial burden in mice immunized by all routes (P < 0.05). Induction of antiurease immunoglobulin A (IgA) levels in gastric luminal secretions after p.o. immunization was greater than after i.n. administration (means, 6.0 and 1.02 ng/ml, respectively) and was dependent upon challenge with H. pylori. However, immunization by the rectal route resulted in the generation of the highest levels of gastric antiurease IgA (mean, 40. 89 ng/ml), which was detectable prior to challenge with H. pylori. Immunohistochemical staining of stomach tissue for cells secreting urease-specific antibody and CD4(+) T cells showed levels of recruitment to be dependent upon challenge with H. pylori and equivalent for all routes. These results identify both the rectum and nasal passages as suitable inductive sites for urease immunization.

Recombinant cholera toxin B subunit is not an effective mucosal adjuvant for oral immunization of mice against Helicobacter felis

Cholera toxin is a potent oral mucosal adjuvant for enteric immunization. Several studies suggest that commercial cholera toxin B subunit (cCTB; purified from holotoxin) may be an effective non-toxic alternative for oral immunization. The present study was performed, using an infectious disease model, to determine if the oral mucosal adjuvanticity of CTB is dependent on contaminating holotoxin. Mice were orally immunized with Helicobacter felis sonicate and either cholera holotoxin, cCTB or recombinant cholera toxin B subunit (rCTB). Serum immunoglobulin G (IgG) and intestinal immunoglobulin A (IgA) antibody responses were determined and the mice were challenged with live H. felis to determine the degree of protective immunity induced. All orally immunized mice responded with serum IgG antibody titres regardless of the adjuvant used. However, only mice immunized with either holotoxin or the cCTB responded with an intestinal mucosal IgA response. Consistent with the production of mucosal antibodies, mice immunized with either holotoxin or cCTB as adjuvants were protected from challenge while mice receiving H. felis sonicate and rCTB all became infected. cCTB induced the accumulation of cAMP in mouse thymocytes at a level equal to 0.1% of that induced by holotoxin, whereas rCTB was devoid of any activity. These results indicate that CTB possesses no intrinsic mucosal adjuvant activity when administered orally. Therefore, when used as an oral adjuvant, CTB should also include small, non-toxic doses of cholera toxin.

Lack of protection following immunisation with H. pylori outer membrane vesicles highlights antigenic differences between H. felis and H. pylori

Helicobacter pylori-induced inflammation is associated with the development of gastritis, peptic ulcer disease and gastric cancer in humans. Immunisation against this bacterium would ultimately have a major impact on H. pylori-related disease, notably global gastric cancer rates. To date, several potential H. pylori vaccine candidates have been identified. In this study, the Helicobacter felis/murine model was used to assess the immunogenicity of a previously undescribed H. pylori outer membrane vesicle fraction in immune protection.

Catalase, a novel antigen for Helicobacter pylori vaccination

The efficacy of an orogastric vaccine comprised of purified Helicobacter pylori catalase plus the mucosal adjuvant cholera toxin (CT) was examined with both the Helicobacter felis and H. pylori mouse models with BALB/c mice. Native H. pylori catalase (200 microg) plus CT was initially used as a vaccine antigen in the H. felis mouse model and protected 80% (8 of 10) of the challenged animals, while all control animals were infected (20 of 20). In a follow-up experiment, recombinant H. pylori catalase plus CT was used for immunization, and groups of mice were challenged with the Sydney strain of H. pylori. Immunization with recombinant catalase protected a significant proportion (9 of 10) of the mice from H. pylori challenge, indicating that this enzyme should be considered as a candidate for a future vaccine. This study provides the first available data on the efficacy of protective immunization with the new Sydney strain of H. pylori in a mouse model. These data also provide indirect evidence that proteins which are normally intracellular, such as catalase, may be present on the surface of H. pylori and thus may provide targets for immunization.

Protective immunization against Helicobacter stimulates long-term immunity

Immunization with an oral vaccine composed of whole cell sonicates of Helicobacter felis plus cholera toxin (CT) can protect mice from H. felis challenge. The aim of this study was to determine whether this protective immunity was long-lived. Mice were given the vaccine then left for up to 15 months before challenge. After 15 months, all mice were still protected from H. felis infection, indicating that oral immunization using bacterial antigens plus CT can stimulate long-term local immunological memory.

Immune and inflammatory responses to Helicobacter pylori infection

The gastroduodenal response to chronic Helicobacter pylori infection is characterized by the infiltration of plasma cells, lymphocytes, neutrophils and monocytes into the mucosa. Eradication studies have shown that this inflammatory response represents a specific reaction to the presence of H. pylori. As well as stimulating specific local T and B cell responses and a systemic antibody response, H. pylori infection also induces a local pro-inflammatory cytokine response. Interleukin-8 (IL-8), which is expressed and secreted by gastric epithelial cells, may be an important host mediator inducing neutrophil migration and activation. IL-8 mRNA and protein secretion in gastric epithelial cell lines can be up-regulated by the cytokines tumour necrosis factor-alpha and IL-1 and also by type I strains of H. pylori (expressing the vacuolating toxin and cytotoxin-associated protein, CagA). The gastric epithelium thus plays an active role in mucosal defence. Neutrophil activation and the production of reactive oxygen metabolites will be induced directly by bacterial factors and indirectly via host-derived cytokines, products of complement activation and bioactive lipids. Strain variation in the induction of both IL-8 from epithelial cells and the oxidative burst in neutrophils may be an important factor determining the extent of mucosal injury. There is now increasing evidence from both in vivo and in vitro studies that type I strains induce an enhanced inflammatory response and mucosal damage. An understanding of the bacterial mediators of mucosal inflammation is important in elucidating the role of chronic H. pylori infection in the pathogenesis of gastroduodenal disease.

Role of the host in pathogenesis of Helicobacter-associated gastritis: H. felis infection of inbred and congenic mouse strains

In humans, Helicobacter pylori establishes a chronic infection which can result in various degrees of gastric inflammation, peptic ulcer disease, and a predisposition to gastric cancer. It has been suggested that bacterial virulence factors such as the vacuolating toxin (VacA) and the cytotoxin-associated gene product (CagA) may play a major role in determining the clinical outcome of Helicobacter infections. The role of host responses in these varied outcomes has received little attention. Helicobacter felis, which does not express CagA or VacA, causes chronic infection and inflammation in a well-characterized mouse model. We have used this model to evaluate the role of host responses in Helicobacter infections. BALB/c, C3H, and C57BL/6 mice were orally infected with a single strain of H. felis, and 2 and 11 weeks after infection, the mice were sacrificed and evaluated histologically for magnitude of H. felis infection. Intensity and extent of inflammation, and cellular composition of the inflammatory infiltrate. All three strains of mice demonstrated comparable levels of infection at 11 weeks, but the pattern and intensity of inflammation varied from minimal in BALB/c mice to severe in C57BL/6 mice. Gastric epithelial erosions were noted in C3H mice, and mucous cell hyperplasia was observed in C3H and C57BL/6 mice. Abundant mucosal mast cells were observed in the gastric tissues of all three mouse strains. Studies using major histocompatibility complex (MHC)-congenic mice revealed probable contributions by both MHC and non-MHC genes to Helicobacter-induced inflammation. Thus, large variations in the severity of disease were observed after infection of different inbred strains and congenic mice with a single isolate of H. felis. These results demonstrate the importance of the host response in disease outcome following gastric Helicobacter infection.

Animal models and vaccine development

Following the demonstration of Helicobacter pylori as a major gastroduodenal pathogen there was a need to develop animal models in order to investigate mechanisms of pathogenesis and to be able to test new treatment strategies. Helicobacter pylori will only colonize a limited number of hosts including non-human primates, germ-free or barrier raised piglets, germ-free dogs and recently laboratory raised cats. Although these models have proved useful there is a need for more convenient small animal models. The ferret infected with its natural gastric organism, Helicobacter mustelae, is the only other animal to show peptic ulceration and has been successfully used to investigate gastritis and antimicrobial agents. The other commonly used animal model is the laboratory mouse or rat infected with either Helicobacter felis or Helicobacter heilmannii, bacteria that normally colonize cat or dog gastric mucosae. Active/chronic gastritis, gastric atrophy, and lymphoma-like lesions have been shown to develop in H. felis infected mice. The most recent and exciting use of an animal model has been the use of the H. felis mouse model in the development of human vaccines against H. pylori. Mice can be protected against infection with large doses of viable H. felis by oral immunization using sonicates of H. felis or H. pylori or recombinant H. pylori urease together with cholera toxin or cholera toxin-B subunit as the mucosal adjuvant. More importantly it has been shown that immunization of already infected animals results in eradication of infection. This raises the intriguing possibility that therapeutic immunization might be a viable option in the management of Helicobacter-associated disease. If immunization as a therapy of peptic ulcers was combined with short-term acid suppression, the possibility of reinfection may also be eliminated. In those countries where H. pylori infection rates are very high and infection occurs at an early age, large scale oral immunization of sections of the community would not only protect the young from the deleterious consequences of long-term H. pylori infection but could also cure existing disease.

The GroES homolog of Helicobacter pylori confers protective immunity against mucosal infection in mice

Helicobacter pylori is an important etiologic agent of gastroduodenal disease. In common with other organisms, H. pylori bacteria express heat shock proteins that share homologies with the GroES-GroEL class of proteins from Escherichia coli. We have assessed the heat shock proteins of H. pylori as potential protective antigens in a murine model of gastric Helicobacter infection. Orogastric immunization of mice with recombinant H. pylori GroES- and GroEL-like proteins protected 80% (n = 20) and 70% (n = 10) of animals, respectively, from a challenge dose of 10(4) Helicobacter felis bacteria (compared to control mice, P = 0.0042 and P = 0.0904, respectively). All mice (n = 19) that were immunized with a dual antigen preparation, consisting of H. pylori GroES-like protein and the B subunit of H. pylori urease, were protected against infection. This represented a level of protection equivalent to that provided by a sonicated Helicobacter extract (P = 0.955). Antibodies directed against the recombinant H. pylori antigens were predominantly of the IgG1 class, suggesting that a type 2 T-helper cell response was involved in protection. This work reports a protein belonging to the GroES class of heat shock proteins that was shown to induce protective immunity. In conclusion, GroES-like and urease B-subunit proteins have been identified as potential components of a future H. pylori subunit vaccine.

Oral immunization with Helicobacter pylori urease B subunit as a treatment against Helicobacter infection in mice

BACKGROUND & AIMS

Eradication of Helicobacter pylori infections in humans results in the healing of gastritis and gastric ulcers. This study used a mouse model to test whether oral vaccination can cure Helicobacter infection and gastritis.

METHODS

Mice were infected with Helicobacter felis. Three weeks after infection, the mice were orally immunized with H. pylori urease B subunit. Control mice were simultaneously infected but sham immunized.

RESULTS

Three to 8 weeks after oral immunization of H. felis-infected mice with recombinant H. pylori urease B subunit, the infection cleared and there was no evidence of gastritis. Vaccinated mice remained protected against two consecutive H. felis challenges.

CONCLUSIONS

These results show that the lack of natural immunity against Helicobacter can be overcome by oral immunization and that vaccination offers a novel therapeutic approach to Helicobacter-induced gastritis.

Effect of oral immunization with recombinant urease on murine Helicobacter felis gastritis

The ability of oral immunization to interfere with the establishment of infection with Helicobacter felis was examined. Groups of Swiss Webster mice were immunized orally with 250 micrograms of Helicobacter pylori recombinant urease (rUrease) and 10 micrograms of cholera toxin (CT) adjuvant, 1 mg of H. felis sonicate antigens and CT, or phosphate-buffered saline (PBS) and CT. Oral immunization with rUrease resulted in markedly elevated serum immunoglobulin G (IgG), serum IgA, and intestinal IgA antibody responses. Challenge with live H. felis further stimulated the urease-specific intestinal IgA and serum IgG and IgA antibody levels in mice previously immunized with rUrease but activated primarily the serum IgG compartment of PBS-treated and H. felis-immunized mice. Intestinal IgA and serum IgG and IgA anti-urease antibody responses were highest in rUrease-immunized mice at the termination of the experiment. Mice immunized with rUrease were significantly protected (P < or = 0.0476) against infection when challenged with H. felis 2 or 6 weeks post-oral immunization in comparison with PBS-treated mice. Whereas H. felis-infected mice displayed multifocal gastric mucosal lymphoid follicles consisting of CD45R+ B cells surrounded by clusters of Thy1.2+ T cells, gastric tissue from rUrease-immunized mice contained few CD45R+ B cells and infrequent mucosal follicles. These observations show that oral immunization with rUrease confers protection against H. felis infection and suggest that gastric tissue may function as an effector organ of the mucosal immune system which reflects the extent of local antigenic stimulation.

Helicobacter-associated gastritis in SCID mice

Immunodeficient (SCID) and immunocompetent mice were infected with Helicobacter felis to address the role of autoimmunity in Helicobacter-associated gastritis. The extents of inflammation were equivalent in the two groups. The numbers of H. felis organisms were marginally increased in the SCID mice but did not achieve statistical significance. These results indicate that autoimmunity is not necessary to induce disease and that the presence of an adaptive immune system does not significantly affect H. felis colonization.

Recombinant antigens prepared from the urease subunits of Helicobacter spp.: evidence of protection in a mouse model of gastric infection

Urease is an important virulence factor for gastric Helicobacter spp. To elucidate the efficacy of individual urease subunits to act as mucosal immunogens, the genes encoding the respective urease subunits (UreA and UreB) of Helicobacter pylori and Helicobacter felis were cloned in an expression vector (pMAL) and expressed in Escherichia coli cells as translational fusion proteins. The recombinant UreA and UreB proteins were purified by affinity and anion-exchange chromatography techniques and had predicted molecular masses of approximately 68 and 103 kDa, respectively. Western blotting (immunoblotting) studies indicated that the urease components of the fusion proteins were strongly immunogenic and were specifically recognized by polyclonal rabbit anti-Helicobacter sp. sera. The fusion proteins (50 micrograms) were used, in combination with a mucosal adjuvant (cholera toxin), to orogastrically immunize mice against H. felis infection. Gastric tissues from H. felis-challenged mice were assessed by the biopsy urease test and by histology. In mice immunized with recombinant H. felis UreB, 60% of animals (n = 7) were histologically negative for H. felis bacteria after challenge at 17 weeks. This compared with 25% (n = 8) for mice immunized with the heterologous H. pylori UreB antigen. Neither the homologous nor the heterologous UreA subunit elicited protective responses against H. felis infection in mice. The study demonstrated that a recombinant subunit antigen could induce an immunoprotective response against gastric Helicobacter infection.

Future research in peptic ulcer disease

For the past 10 years, research into peptic ulcer disease has focused on the surprising suggestion that gastritis and peptic ulcers may be caused by the bacterium Helicobacter pylori. However, the time has now come to reappraise research directions, as a causal link has been established, and even the most ardent sceptics now accept that H. pylori infection is the major factor in most cases of peptic ulcer disease. As with any established microbial disease, we need to understand the epidemiology and mechanisms of pathogenesis, but the major focus should be towards improving therapies and defining the long-term outcome of H. pylori eradication. To devise novel therapeutic agents effectively, we must increase our knowledge of the basic physiology of H. pylori and its ecology in the stomach. This has been a surprisingly neglected area of research and major questions remain. Why does the organism flourish in different areas of the gastric mucosa when gastric pH is increased? Is a change in pH the reason for the potentiating effects of acid-inhibitory agents on anti-H. pylori activity? Will knowledge of the host and bacterial factors that initiate ulcerogenesis allow us to better predict H. pylori-associated ulcers by using non-invasive methods? As H. pylori is a major gastroduodenal pathogen, can we eliminate the infection from selected populations? What are the criteria that will allow therapeutic intervention? The first steps have been taken in the development of an effective vaccine, but who should be immunized?(ABSTRACT TRUNCATED AT 250 WORDS)