Immunization with recombinant Helicobacter pylori urease in specific-pathogen-free rhesus monkeys (Macaca mulatta)

Pivotal role of Helicobacter pylori virulence genes in pathogenicity and vaccine development

One of the most prevalent human infections is Helicobacter pylori (H. pylori), which affects more than half of the global population. Although H. pylori infections are widespread, only a minority of individuals develop severe gastroduodenal disorders. The global resistance of H. pylori to antibiotics has reached concerning levels, significantly impacting the effectiveness of treatment. Consequently, the development of vaccines targeting virulence factors may present a viable alternative for the treatment and prevention of H. pylori infections. This review aims to provide a comprehensive overview of the current understanding of H. pylori infection, with a particular focus on its virulence factors, pathophysiology, and vaccination strategies. This review discusses various virulence factors associated with H. pylori, such as cytotoxin-associated gene A (cagA), vacuolating cytotoxin gene (vacA), outer membrane proteins (OMPs), neutrophil-activated protein (NAP), urease (ure), and catalase. The development of vaccines based on these virulence characteristics is essential for controlling infection and ensuring long-lasting protection. Various vaccination strategies and formulations have been tested in animal models; however, their effectiveness and reproducibility in humans remain uncertain. Different types of vaccines, including vector-based vaccines, inactivated whole cells, genetically modified protein-based subunits, and multiepitope nucleic acid (DNA) vaccines, have been explored. While some vaccines have demonstrated promising results in murine models, only a limited number have been successfully tested in humans. This article provides a thorough evaluation of recent research on H. pylori virulence genes and vaccination methods, offering valuable insights for future strategies to address this global health challenge.

How Long Will It Take to Launch an Effective Helicobacter pylori Vaccine for Humans?

Helicobacter pylori infection often occurs in early childhood, and can last a lifetime if not treated with medication. H. pylori infection can also cause a variety of stomach diseases, which can only be treated with a combination of antibiotics. Combinations of antibiotics can cure H. pylori infection, but it is easy to relapse and develop drug resistance. Therefore, a vaccine is a promising strategy for prevention and therapy for the infection of H. pylori. After decades of research and development, there has been no appearance of any H. pylori vaccine reaching the market, unfortunately. This review summarizes the aspects of candidate antigens, immunoadjuvants, and delivery systems in the long journey of H. pylori vaccine research, and also introduces some clinical trials that have displayed encouraging or depressing results. Possible reasons for the inability of an H. pylori vaccine to be available over the counter are cautiously discussed and some propositions for the future of H. pylori vaccines are outlined.

The impact of ExHp-CD (outer membrane vesicles) released from Helicobacter pylori SS1 on macrophage RAW 264.7 cells and their immunogenic potential

Bacterial-derived extracellular vesicles could play a major role in attenuating and treating diseases. They play a major anti-infection role by modulating immune responses against pathogens and preventing infection by inhibiting pathogen localization and proliferation. In this study, outer membrane vesicles (ExHp-CD) released by Helicobacter pylori SS1 (H. pylori) and total antigens isolated from H. pylori SS1 (AgHp) were evaluated for their immunogenic potential and their effect on macrophage RAW 264.7 cells. Results demonstrated that both ExHp-CD and AgHp induced T helper 2 (Th2) immune response, which was reported to be important in immune protection against H. pylori infections. Both ExHp-CD and AgHp produced high levels of IL-10 and IL-4, while no significant levels of IL-12 p70 or IFN-γ were detected. However, ExHp-CD showed a better effect on macrophage RAW 264.7 cells compared to AgHp. Macrophage RAW 264.7 cells stimulated with 5, and 10 μg/mL of ExHp-CD showed an increased ratio of CD206 (M2 phenotype marker) and a decreased ratio of CD86 (M1 phenotype marker). Moreover, results suggested that the immunogenic effect that ExHp-CD possesses was attributed to their cargo of Epimerase_2 domain-containing protein (Epi_2D), Probable malate:quinone oxidoreductase (Pro_mqo), and Probable cytosol aminopeptidase (Pro_ca). Results demonstrated that ExHp-CD possesses an immunological activity to induce Th2 immune response against H. pylori infection with results comparable to AgHp. However, ExHp-CD showed higher efficacy regarding safety, biocompatibility, lack of toxicity, and hemocompatibility. Thus, it could serve as an immunogenic candidate with more desired characteristics.

Gastric eosinophils are detrimental for Helicobacter pylori vaccine efficacy

Helicobacter pylori (Hp) colonizes the human gastric mucosa with a high worldwide prevalence. Currently, Hp can be eradicated by the use of antibiotics. Due to the increase of antibiotic resistance, new therapeutic strategies need to be devised: one such approach being prophylactic vaccination. Pre-clinical and clinical data showed that a urease-based vaccine is efficient in decreasing Hp infection through the mobilization of T helper (Th)-dependent immune effectors, including eosinophils. Preliminary data have shown that upon vaccination and subsequent Hp infection, eosinophils accumulate in the gastric mucosa, suggesting a possible implication of this granulocyte subset in the vaccine-induced reduction of Hp infection. In our study, we confirm that activated eosinophils, expressing CD63, CD40, MHCII and PD-L1 at their cell surface, infiltrate the gastric mucosa during vaccine-induced reduction of Hp infection. Strikingly, we provide evidence that bone marrow derived eosinophils efficiently kill Hp in vitro, suggesting that eosinophils may participate to the vaccine-induced reduction of Hp infection. However, conversely to our expectations, the absence of eosinophils does not decrease the efficacy of this Hp vaccine in vivo. Indeed, vaccinated mice that have been genetically ablated of the eosinophil lineage or that have received anti-Sialic acid-binding immunoglobulin-like lectin F eosinophil-depleting antibodies, display a lower Hp colonization when compared to their eosinophil sufficient counterparts. Although the vaccine induces similar urease-specific humoral and Th responses in both eosinophil sufficient and deficient mice, a decreased production of anti-inflammatory cytokines, such as IL-10, TGFβ, and calgranulin B, was specifically observed in eosinophil depleted mice. Taken together, our results suggest that gastric eosinophils maintain an anti-inflammatory environment, thus sustaining chronic Hp infection. Because eosinophils are one of the main immune effectors mobilized by Th2 responses, our study strongly suggests that the formulation of an Hp vaccine needs to include an adjuvant that preferentially primes Hp-specific Th1/Th17 responses.

Pathogenicity of Helicobacter pylori in cancer development and impacts of vaccination

Helicobacter pylori affect around 50% of the population worldwide. More importantly, the gastric infection induced by this bacterium is deemed to be associated with the progression of distal gastric carcinoma and gastric mucosal lymphoma in the human. H. pylori infection and its prevalent genotype significantly differ across various geographical regions. Based on numerous virulence factors, H. pylori can target different cellular proteins to modulate the variety of inflammatory responses and initiate numerous "hits" on the gastric mucosa. Such reactions lead to serious complications, including gastritis and peptic ulceration, gastric cancer and gastric mucosa-associated lymphoid structure lymphoma. Therefore, H. pylori have been considered as the type I carcinogen by the Global Firm for Research on Cancer. During the two past decades, different reports revealed that H. pylori possess oncogenic potentials in the gastric mucosa through a complicated interplay between the bacterial factors, various facets, and the environmental factors. Accordingly, numerous signaling pathways could be triggered in the development of gastrointestinal diseases (e.g., gastric cancer). Therefore, the main strategy for the treatment of gastric cancer is controlling the disease far before its onset using preventive/curative vaccination. Increasing the efficiency of vaccines may be achieved by new trials of vaccine modalities, which is used to optimize the cellular immunity. Taken all, H. pylori infection may impose severe complications, for resolving of which extensive researches are essential in terms of immune responses to H. pylori. We envision that H. pylori-mediated diseases can be controlled by advanced vaccines and immunotherapies.

Status of vaccine research and development for Helicobacter pylori

Gastric adenocarcinoma is globally the third leading cause of death due to malignancy, with the bulk of this disease burden being suffered by low and middle income countries (LMIC), especially in Asia. The majority of these cancers develop as a result of a chronic gastritis that arises in response to infection with the stomach-dwelling bacterium, Helicobacter pylori. A vaccine against this pathogen would therefore be a powerful tool for preventing gastric adenocarcinoma. However, notwithstanding a proof-of-concept that vaccination can protect children from acquisition of H. pylori infection, there are currently no advanced vaccine candidates with only a single vaccine in Phase I clinical trial. Further, the development of a vaccine against H. pylori is not a current strategic priority of major pharmaceutical companies despite the large global disease burden. Given the involvement of such companies is likely to be critical for late stage development, there is therefore a need for an increased appreciation of the burden of this disease in LMIC and more investment to reinvigorate research in H. pylori vaccine Research and Development.

The Human Stomach in Health and Disease: Infection Strategies by Helicobacter pylori

Helicobacter pylori is a bacterial pathogen which commonly colonizes the human gastric mucosa from early childhood and persists throughout life. In the vast majority of cases, the infection is asymptomatic. H. pylori is the leading cause of peptic ulcer disease and gastric cancer, however, and these outcomes occur in 10-15% of those infected. Gastric adenocarcinoma is the third most common cause of cancer-associated death, and peptic ulcer disease is a significant cause of morbidity. Disease risk is related to the interplay of numerous bacterial host and environmental factors, many of which influence chronic inflammation and damage to the gastric mucosa. This chapter summarizes what is known about health and disease in H. pylori infection, and highlights the need for additional research in this area.

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.

Gastric helicobacters in domestic animals and nonhuman primates and their significance for human health

Helicobacters other than Helicobacter pylori have been associated with gastritis, gastric ulcers, and gastric mucosa-associated lymphoid tissue lymphoma in humans. These very fastidious microorganisms with a typical large spiral-shaped morphology were provisionally designated "H. heilmannii," but in fact they comprise at least five different Helicobacter species, all of which are known to colonize the gastric mucosa of animals. H. suis, which has been isolated from the stomachs of pigs, is the most prevalent gastric non-H. pylori Helicobacter species in humans. Other gastric non-H. pylori helicobacters colonizing the human stomach are H. felis, H. salomonis, H. bizzozeronii, and the still-uncultivable "Candidatus Helicobacter heilmannii." These microorganisms are often detected in the stomachs of dogs and cats. "Candidatus Helicobacter bovis" is highly prevalent in the abomasums of cattle but has only occasionally been detected in the stomachs of humans. There are clear indications that gastric non-H. pylori Helicobacter infections in humans originate from animals, and it is likely that transmission to humans occurs through direct contact. Little is known about the virulence factors of these microorganisms. The recent successes with in vitro isolation of non-H. pylori helicobacters from domestic animals open new perspectives for studying these microorganisms and their interactions with the host.

Protection against Helicobacter pylori infection in mongolian gerbil by intragastric or intramuscular administration of H. pylori multicomponent vaccine

BACKGROUND

Development of Helicobacter pylori vaccine would be a new effective strategy for prevention and treatment of H. pylori infection. Recombinant H. pylori vaccine comprising a single subunit antigen can only induce immune response with limited protection efficiency. In this study, the protective effect of H. pylori multicomponent vaccines consisting of three recombinant subunit antigens was investigated using the Mongolian gerbil model.

MATERIALS AND METHODS

Mongolian gerbils were immunized with different formulations of three recombinant H. pylori antigens (UreB, HspA, and HpaA) with two different adjuvants (Al(OH)3, LT(R72DITH)) by intragastric (i.g.) or intramuscular (i.m.) routes. The protective effects of multicomponent vaccines were assessed after H. pylori challenge in different studies. The specific IgG antibodies in serum were monitored by ELISA, and the mRNA expressions of IL-4 and IFN-gamma in spleen tissue were detected by reverse transcribed polymerase chain reaction (RT-PCR).

RESULTS

The protective effect against H. pylori challenge in gerbils immunized with three recombinant antigens and LT(R72DITH) or Al(OH)3 was significantly higher than that in single- or double-antigen vaccine-immunized and control gerbils. Furthermore, the protective effect of the triple-antigen vaccine combined with the LT(R72DITH) adjuvant (average 86.3%) was significantly greater than that of vaccine combined with the Al(OH)3 adjuvant (average 53.4%). After the first immunization, the anti-UreB/HspA/HpaA serum IgG level in gerbils immunized with triple-antigen vaccine combined with Al(OH)3 was higher than that in gerbils immunized with the vaccine combined with LT(R72DITH). Splenic interferon (IFN)-gamma and interleukin (IL)-4 transcript levels were significantly increased in LT(R72DITH) vaccine-immunized gerbils as compared to the Al(OH)3 vaccine group. Moreover, splenic IL-4 mRNA levels were higher than IFN-gamma in gerbils immunized with triple-antigen vaccine with either LT(R72DITH) or Al(OH)3.

CONCLUSIONS

This study indicated that the recombinant multicomponent vaccine provided effective protection against H. pylori infection as compared to the single-antigen vaccine. This protective immunity would be closely associated with a predominant Th2-type response.

Culture of Helicobacter pylori and purification of antigen protein

Helicobacter pylori (H. pylori) live in the stomach of human. It is a kind of curve bacteria which can lead to chronic gastritis, peptic ulcer and gastric cancer. Usually, antibiotics are used to treat the patients, but they have a lot of side effects. Milk of milch cow immunized with H. pylori vaccine can prevent and treat the infection of H. pylori without side effects. During the production of immune milk, the basic work is to prepare vaccine. During the preparation of sub-unit vaccine, key is to isolate and purify the antigen protein. In this article, we discuss the culture of H. pylori (solid and liquid culture), the recombinant expression and purification of its antigen protein (urease, VacA, CagA and lipopolysaccharide).

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.

Possible correlates of long-term protection against Helicobacter pylori following systemic or combinations of mucosal and systemic immunizations

The ability to induce long-term immunity to Helicobacter pylori is necessary for an effective vaccine. This study was designed to establish the most efficient route(s) (systemic, mucosal, or a combination) of immunization for induction of long-term immunity and to define correlates of protection. Mice were immunized orally alone (oral group), intramuscularly (i.m.) alone (i.m. group), orally followed by i.m. (oral/i.m. group), or i.m. followed by orally (i.m./oral group). Long-term protective immunity to oral H. pylori challenge was observed 3 months after immunization through the i.m. or oral/i.m. route. Protection correlated with an increase in H. pylori-specific interleukin-12 and both immunoglobulin G1 (IgG1) and IgG2a serum titers following challenge. Mice that were not protected (oral or i.m./oral) had increased levels of IgA in both sera and Peyer's patches. This study demonstrates the ability to induce long-term immunity against H. pylori, provides correlates of protection, and illustrates the crucial role of the immunization route(s).

The inflammatory and immune response to Helicobacter pylori infection

Lifelong Helicobacter pylori infection and its associated gastric inflammation underlie peptic ulceration and gastric carcinogenesis. The immune and inflammatory responses to H. pylori are doubly responsible: gastric inflammation is the main mediator of pathology, and the immune and inflammatory response is ineffective, allowing lifelong bacterial persistence. However, despite inducing gastric inflammation, most infections do not cause disease, and bacterial, host and environmental factors determine individual disease risk. Although H. pylori avoids many innate immune receptors, specific virulence factors (including those encoded on the cag pathogenicity island) stimulate innate immunity to increase gastric inflammation and increase disease risk. An acquired T helper 1 response upregulates local immune effectors. The extent to which environmental factors (including parasite infection), host factors and H. pylori itself influence T-helper differentiation and regulatory T-cell responses remains controversial. Finally, effective vaccines have still not been developed: a better understanding of the immune response to H. pylori may help.

Molecular analysis of Helicobacter pylori-associated gastric inflammation in naïve versus previously immunized mice

To identify mechanisms of immunity against Helicobacter pylori, we performed microarray analysis on gastric tissue from infected mice and mice vaccinated prior to challenge. RNA from gastric tissue was used to screen over 10,000 genes. MHC antigens and GTP binding proteins were upregulated in both groups. Infected mice were characterized by expression of innate host defense markers while immune mice expressed many IFN-gamma response genes and T cell markers. Results were confirmed for several genes by RT-PCR. CD4+ spleen cells from immune mice produced significantly more IFN-gamma than from infected mice. These results support a role for T cell regulated inflammation in H. pylori immunity.

Identification and characterization of macaque CD89 (immunoglobulin A Fc receptor)

The interaction of the immunoglobulin A (IgA) molecule with its specific cellular receptor is necessary to trigger a variety of effector functions able to clear IgA-opsonized antigens. The human IgA-specific Fc receptor, FcalphaRI or CD89, is expressed on cells of the myeloid lineage. Recently, CD89 homologues have been identified in rats and cattle. Because non-human primates represent well established models for a variety of human diseases and for the testing of immunotherapeutic strategies, we cloned and sequenced cDNAs corresponding to the CD89 gene from rhesus (Macaca mulatta) and cynomolgus (Macaca fascicularis) macaques. Macaque sequences of full-length CD89 consist of five exons of length identical to the corresponding human CD89 exons. The rhesus and cynomolgus macaque derived amino acid sequences are highly homologous to each other (99.3% identity) and exhibit 86.5% and 86.1% identity to the human counterpart, respectively. Transfection of HeLa cells with plasmids containing the cloned macaque cDNAs resulted in the expression of surface molecules recognized by an anti-human CD89 antibody. Five splice variants were identified in rhesus macaques. Three of the five variants are similar to described human CD89 splice variants, whereas two variants have not been described in humans. Three splice variants were identified in cynomolgus macaques. Of the three variants, one is present also in humans and rhesus macaques, whereas the other two are shared with rhesus macaques but not humans. Similarly to the human CD89, macaque CD89 is expressed on myeloid cells from peripheral blood. The characterization of macaque CD89 represents an essential step in establishing a non-human primate model for the testing of immunotherapeutic approaches based on the manipulation of the IgA/CD89 interaction.

Cloning and expression and immunogenicity of Helicobacter pylori BabA2 gene

AIM: To construct a recombinant strain which expresses BabA of Helicobacter pylori (H pylori) and to study the immunogenicity of BabA.

METHODS: BabA₂ DNA was amplified by PCR and inserted into the prokaryotie expression vector pET-22b (+) and expressed in the BL21 (DE3) E.coli strain. Furthermore, BabA immunogenicity was studied by animal test.

RESULTS: DNA sequence analysis showed the sequence of BabA₂ DNA was the same as the one published by GenBank. The BabA recombinant protein accounted for 34.8% of the total bacterial protein. The serum from H pylori infected patients and Balb/c miced immunized with BabA itself could recognize rBabA.

CONCLUSION: BabA recombinant protein may be an potential vaccine for control and treatment of H pylori infection.

Quantitative detection for low levels of Helicobacter pylori infection in experimentally infected mice by real-time PCR

Accurate diagnosis of Helicobacter pylori infection is important in both clinical practice and clinical research. Molecular methods are highly specific and sensitive, and various PCR-based tests have been developed to detect H. pylori in gastric biopsy specimens. We optimized a sensitive and specific quantitative SYBR Green I real-time PCR assay for detection of H. pylori based on amplification of the fragment of a 26-kDa Helicobacter species-specific antigen gene that allows for detection of 5 bacterial cells per PCR sample. Under the assay conditions, SYBR Green I real-time PCR is highly reproducible with a precise log-linear relation in the range of six orders of magnitude of bacterial DNA concentrations. For accurate comparison of H. pylori infection in different tissue samples, the amount of total host DNA in each sample is normalized by TaqMan real-time PCR of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) pseudogenes. The developed method was validated in prophilactically immunized and experimentally infected mice and revealed a level of H. pylori gastric colonisation that was below the limit of detection for a rapid urease test. This new method established for a quantitative analysis of H. pylori in the host's stomach may be useful in experimental studies evaluating new anti-H. pylori drugs and vaccines.

Expression of Helicobacter pylori Hsp60 protein and its immunogenicity

AIM: To express Hsp60 protein of H pylori by a constructed vector and to evaluate its immunogenicity.

METHODS: Hsp60 DNA was amplified by PCR and inserted into the prokaryotie expression vector pET-22b (+), which was transformed into BL21 (DE3) E.coli strain to express recombinant protein. Immunogenicity of expressed Hsp60 protein was evaluated with animal experiments.

RESULTS: DNA sequence analysis showed Hsp60 DNA was the same as GenBank’s research. Hsp60 recombinant protein accounted for 27.2% of the total bacterial protein, and could be recognized by the serum from H pylori infected patients and Balb/c mice immunized with Hsp60 itself.

CONCLUSION: Hsp60 recombinant protein might become a potential vaccine for controlling and treating H pylori infection.

Cloning, expression and antigenic analysis of heat shock protein A gene of human Helicobacter pylori

AIM

To construct a recombinant vector containing gene encoding heat shock protein A with a Mr of 13 000 from human Helicobacter pylori (H pylori) and express it in E. coli BL21, and to explore the antigenicity.

METHODS

The target gene was amplified from H pylori chromosome by PCR, and then inserted into the prokaryotic expression vector pET32a (+) digested by restrictive endonuclease enzymes of kpn I, BamH I simultaneously. The recombinant vector was transformed and expressed in E.coli BL21.The antigenicity of recombinant fusion protein was analysed by Western blot.

RESULTS

Enzyme digestion and sequencing analysis showed that the target gene has been inserted into the recombinant vector, but as compared with the gene reported by GenBank, 1.6% of gene mutation and 1.6% of amino acid residues change in H pylori occurred, respectively. SDS-PAGE analysis showed that the recombinant vector could be expressed in E.coli BL21, the relative molecular mass (Mr) of expressed product was 33×10³, while Mr of protein expressed by pET32a (+) was about 20×10³, and soluble fusion expression product accounted for 18.96% of total bacterial protein. After purification with Ni+-NTA agarose resin, the purity of recombinant fusion protein was about 95%. Western blot result showed that recombinant fusion protein could be recognized by anti-H pylori positive serum, suggesting that the protein had good antigenicity.

CONCLUSION

The gene encoding H pylori heat shock protein A has been cloned and expressed successfully. The results lay the foundation for development of H pylori protein vaccine and a quick diagnostic kit for detection of H pylori infection.

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Construction and characterization of bivalent vaccine candidate expressing HspA and Mr18000 OMP from Helicobacter pylori

AIM: To construct a recombinant vector which can express outer membrane protein (OMP) with M_r18000 and heat shock protein A (HspA) from Helicobacter pylori (H. pylori) in E. coli BL21, and to exploit the possibility for obtaining the vaccine conferring protection from H. pylori infection.

METHODS: The target gene of HspA was amplified from H. pylori chromosome by PCR, and then inserted into the prokaryotic expression vector pET32a (+) by restrictive endonuclease enzyme kpn I, BamH I simultaneously. The recombinant vector was used to sequence, and then together with pET32a (+)/Omp₁₈, digested by restrictive endonuclease enzyme Hind III and BamH I simultaneously. pET32a(+)/ HspA and Omp₁₈ were recovered from 1% agarose gel by gel kit, and ligated with T₄ ligase by BamH I digested viscidity end. The recombinant plasmid of pET32a(+)/HspA/Omp₁₈ was transformed and expressed in E. coli BL21 (DE3) under induction of IPTG. After purification, its antigenicity of the fusion protein was detected by Western blot.

RESULTS: Enzyme digestion analysis and sequencing showed that the target genes were inserted into the recombinant vector, composed of 891 base pairs, encoded objective polypeptides of 297 amino acid residues. Compared with GenBank reported by Tomb et al there were 1.3% and 1.4% differences in obtained H. pylori nucleotide sequence and amino acid residues, respectively. SDS-PAGE analysis showed that relative molecule mass (M_r) of the expressed product was M_r 51000, M_r of protein expressed by pET32a (+) was about M_r 20000, and soluble expression product accounted for 18.96% of total bacterial protein. After purification with Ni⁺²-NTA agarose resins, the purification of recombinant fusion protein was about 95%. Western blot showed that recombinant fusion protein could be recognized by the patients’ serum infected with H. pylori and anti-Omp₁₈ monoclone, suggesting that this protein had good antigenicity.

CONCLUSION: The gene coding for H. pylori M_r18000 OMP and HspA was cloned and expressed successfully. The results obtained lay the foundation for development of H. pylori protein vaccine and a quick diagnostic kit.

Attenuated Salmonella enterica serovar Typhi expressing urease effectively immunizes mice against Helicobacter pylori challenge as part of a heterologous mucosal priming-parenteral boosting vaccination regimen

Recombinant vaccine strains of Salmonella enterica serovar Typhi capable of expressing Helicobacter pylori urease were generated by transforming strains CVD908 and CVD908-htrA with a plasmid harboring the ureAB genes under the control of an in vivo-inducible promoter. The plasmid did not interfere with the ability of either strain to replicate and persist in human monocytic cells or with their transient colonization of mouse lungs. When administered to mice intranasally, both recombinant strains elicited antiurease immune responses skewed towards a Th1 phenotype. Vaccinated mice exhibited strong immunoglobulin G2a (IgG2a)-biased antiurease antibody responses as well as splenocyte populations capable of proliferation and gamma interferon (IFNgamma) secretion in response to urease stimulation. Boosting of mice with subcutaneous injection of urease plus alum enhanced immune responses and led them to a more balanced Th1/Th2 phenotype. Following parenteral boost, IgG1 and IgG2a antiurease antibody titers were raised significantly, and strong urease-specific splenocyte proliferative responses, accompanied by IFNgamma as well as interleukin-4 (IL-4), IL-5, and IL-10 secretion, were detected. Neither immunization with urease-expressing S. enterica serovar Typhi alone nor immunization with urease plus alum alone conferred protection against challenge with a mouse-adapted strain of H. pylori; however, a vaccination protocol combining both immunization regimens was protective. This is the first report of effective vaccination against H. pylori with a combined mucosal prime-parenteral boost regimen in which serovar Typhi vaccine strains are used as antigen carriers. The significance of these findings with regard to development of a human vaccine against H. pylori and modulation of immune responses by heterologous prime-boost immunization regimens is discussed.

Helicobacter pylori: consensus and controversy

Helicobacter pylori is uniquely adapted to colonize the human stomach. Infection leads to a range of subclinical and clinical outcomes that depend on properties of the infecting strain, the host, and the environment. Eradication therapy is indicated for infected persons who develop peptic ulcer disease or gastric lymphoma or who are beginning long-term treatment with nonsteroidal anti-inflammatory drugs. However, treatment may worsen gastroesophageal reflux disease and increase the risk of esophageal cancer. H. pylori infections can be diagnosed noninvasively and can be eradicated with approximately 85% success by a variety of multidrug, 7-14-day regimens. Unfortunately, antibiotic resistance is affecting treatment effectiveness in the United States and abroad. A more complete understanding of the variation in H. pylori pathogenesis should lead to clearer recommendations about treatment for infected persons who have neither peptic ulcer disease nor gastric lymphoma.

[14C]Urea breath test is not sensitive for detection of acute Helicobacter pylori infection in rhesus monkeys (Macaca mulatta)

The urea breath test is sensitive and specific for detection of chronic infection with H. pylori. We sought to determine the sensitivity of the [14C]urea breath test for detection of acute H. pylori infection using experimentally infected rhesus monkeys. Eighteen monkeys were inoculated with H. pylori. Serial [14C]urea breath tests and cultures of gastric biopsies were performed before and up to 10 weeks after inoculation. Cultures from all 18 monkeys were positive for H. pylori at each time point. The sensitivity of the [14C]urea breath test increased systematically from 43% at two weeks after inoculation up to 93% at 10 weeks after inoculation. Quantitative cultures of H. pylori showed a tendency to decline over time following inoculation. We conclude that the [14C]urea breath test is not sensitive for detection of acute H. pylori infection in rhesus monkeys until 10 weeks after inoculation. While this may reflect a gradual increase in bacterial load that was not detected by limited sampling, our data are not consistent with this hypothesis.

Determination of the infectious dose of Helicobacter pylori during primary and secondary infection in rhesus monkeys (Macaca mulatta)

We sought to determine the infectious dose of Helicobacter pylori during primary and secondary infection in the rhesus monkey and to determine whether preinoculation acid suppression is necessary to produce colonization. Mixed inoculation with three human-derived strains showed that H. pylori J166 is particularly adapted to colonization of rhesus monkeys, since it outcompeted two other strains. The minimum infectious dose of H. pylori J166 was 10(4) bacteria in specific-pathogen (H. pylori)-free monkeys. Rechallenge of these monkeys after antibiotic therapy was characterized by a 10- to 100-fold decrease in bacterial load compared to primary infection, but with little change in the infectious dose. Acid suppression prior to inoculation was not necessary for colonization to occur. These results provide a basis for future animal experiments using more ecologically relevant conditions of inoculation and suggest that reduction in bacterial load rather than complete protection may be a more realistic goal for H. pylori vaccination.

Vaccines: an ongoing promise?

Over the past decade, intensive research has focused on developing a vaccine therapy for Helicobacter pylori. Substantial unresolved questions cloud the current approach, and the development of a vaccine against this unique organism has proved very challenging. Many candidate vaccines have been tested in animal models. The immunogenicity and the safety of some vaccine formulations have been recently evaluated through clinical trials, and the efficacy of these vaccine therapies in humans will be determined in the near future. This article will provide an overview of the current knowledge of natural and vaccine-induced immune responses to H. pylori infection. It will also review past vaccine successes and failures in animal models and the limited experience to date in using vaccine therapy in humans. Several obstacles to H. pylori vaccine development efforts along with the future direction of these efforts will be discussed.

The design of vaccines against Helicobacter pylori and their development

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

Vaccination against Helicobacter pylori in non-human primate models and humans

Several vaccination studies have been performed in monkeys and humans testing the feasibility of prophylactic and therapeutic immunizations against Helicobacter pylori. The monkey studies showed that immune responses were induced by oral vaccination with the mucosal adjuvant LT (Escherichia coli heat-labile enterotoxin), parenteral administration with a cationic lipid adjuvant, and by mucosal priming followed by parenteral boosts. Both prophylactic and therapeutic activities were demonstrated in monkeys, providing a strong impetus for human vaccine trials. Preliminary studies in humans were undertaken in order to identify a tolerable dose of LT adjuvant or to test the effectiveness of mutant atoxic LT adjuvants. The results from these preliminary studies suggest that native LT causes diarrhoea at doses required for adjuvanticity while a mutant LT does not. In one study in which infected human subjects were vaccinated with orally administered urease antigen with native LT, there was a modest reduction in the level of H. pylori gastric colonization. A second clinical study employing H. pylori whole cell antigen and a mutant LT in infected subjects showed immune responses and although the subjects remained infected, the study was not designed to measure reduction in H. pylori colonization. Recombinant Salmonella expressing urease and other H. pylori antigens have been effective in mice (see accompanying Frontlines Topic Review by John O. Nedrud [1]), but monkey studies are not possible because of host range restriction. Human trials of parenteral immunization, mucosal immunization with mutant LT and live Salmonella vectors are needed to fully assess the ability of vaccines to prevent or treat H. pylori infections.

Selection for urease activity during Helicobacter pylori infection of rhesus macaques (Macaca mulatta)

Helicobacter pylori strain J166 recovered from experimentally inoculated rhesus monkeys had up to a 250-fold-increased urease activity over that before inoculation. This was found to result from the selection of urease positive J166 clones from a heterogeneous inoculum, which was predominantly urease negative due to a 1-bp insertion in the ureA gene. These results confirm the importance of urease for H. pylori colonization. Strain J166 is particularly well adapted to the rhesus monkey, since it colonized preferentially despite the fact that less than 0.1% of the inoculum was urease positive.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infects over half of the world population. Infection with the bacterium causes gastritis and peptic ulcer disease and is associated with the development of gastric cancers. However, only a small proportion of individuals develop these complications of infection. Therefore, identification of both host and bacterial factors that mediate disease is an intense area of current research interest. This review highlights recent advances in understanding of the mechanisms underlying disease pathophysiology following infection with H. pylori.

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.

Review article: Helicobacter pylori vaccines-the current status

In this review, we take a look at the current status in the development of a vaccine against the human pathogenic bacterium, Helicobacter pylori, a major aetiological factor in peptic ulcer disease and gastric adenocarcinoma. Various animal models are now in use from mice infected with H. pylori, through gnotobiotic pigs and primates to ferrets naturally infected with their own Helicobacter, H. mustelae. A significant problem remains the requirement for a suitable mucosal adjuvant. Detoxification or the use of low doses of adjuvants already available may provide a solution and new immune stimulating compounds have been tested with some success. New approaches include the delivery of Helicobacter antigens by DNA immunization, microparticles or live vectors such as attenuated salmonella and the examination of alternative routes of vaccine administration. The phenomenon of post-immunization gastritis and improvements in vaccine efficacy are also discussed. A major area of interest is the mechanism by which immunization actually influences Helicobacter colonization. This remains a mystery: antibodies appear to be unimportant whereas CD4+ T-cells essential. Finally, a viewpoint is given on whom should be immunized when a final vaccine becomes available.