Immunization with recombinant Helicobacter pylori urease decreases colonization levels following experimental infection of rhesus monkeys
Introduction
Helicobacter pylori is the major cause of gastritis, peptic ulcer disease, and gastric carcinoma1, 2, 3. The prevalence of human infection ranges between 30 and 90%, depending on geographic location, and the disease burden is high in both industrialized and developing nations3, 4. It is generally accepted that an effective vaccine to control this infection is a high priority[5].
Experiments using mouse models have definitively shown that mucosal immunization with either crude Helicobacter antigen preparations6, 7or defined native and recombinant H. pylori antigens8, 9, 10, 11, 12protects against primary Helicobacter infection. Furthermore, immunization partially eradicated established Helicobacter infections in mice13, 14, 15and ferrets[16].
Natural immunity to H. pylori appears to be insufficient to prevent reinfection in patients cured of their existing H. pylori infection with antimicrobial therapy[17]. Reinfection with H. pylori after antibiotic therapy can occur rapidly; Gilman et al.[18]reported that 74% of Peruvian adults treated with triple therapy who were free from detectable infection one month after treatment became reinfected in less than a year. Vaccination is one approach to prevent reinfection after effective antimicrobial therapy. Studies in mice have shown that immunization with recombinant H. pylori urease protected against reinfection with H. felis[13].
The majority of colony-raised rhesus monkeys (Macaca mulatta) are infected with H. pylori strains that, by all criteria assessed, are indistinguishable from those isolated from humans19, 20, 21, 22, 23. In these animals, chronic gastritis associated with H. pylori is typified by infiltrates of lymphocytes, plasma cells and histiocytes with no erosions or ulcerations and very few polymorphonuclear leukocytes[19]. In the present study, we investigated the immunogenicity and effectiveness of an H. pylori vaccine in rhesus monkeys as a means to extend the previous findings in mice to a model more relevant to human immunization. The vaccine consisted of recombinant H. pylori urease administered orally together with the Escherichia coli heat-labile enterotoxin (LT) adjuvant.
Section snippets
Monkeys
Colony-raised rhesus monkeys (Macaca mulatta) of Indian origin, 2–3 years of age, were screened for antibodies to H. pylori by ELISA. Animals with the highest serological responses were gastroscoped and biopsied. H. pylori was cultured from 12 seropositive animals, which were selected for study. The animals were randomized to 2 groups. Although all 12 animals started the immunization phase of the experiment, one of the animals in the vaccinated group expired during a gastroscopy procedure and
Results
Since rhesus monkeys bred in captivity are nearly universally infected with H. pylori, we first determined the therapeutic activity of mucosal administration of recombinant H. pylori urease plus LT. Monkeys with documented H. pylori infection at baseline were immunized, and the serological responses to vaccine were determined. Repeated gastroscopy was performed to measure changes in bacterial density and inflammation. The primary immunization regime consisted of six oral doses of vaccine or
Discussion
Colony-raised rhesus monkeys are known to develop chronic H. pylori infections associated with gastritis20, 21, 22. Because the prevalence of naturally-acquired infection is high in these animals[26], and because gastroscopy can be performed to monitor the course of infection, rhesus monkeys would appear to be a suitable model for studies of antibiotic therapy and therapeutic vaccination. Since it is difficult to identify adult rhesus monkeys that are free from infection with H. pylori and
Acknowledgements
We thank P. Didier (Tulane Regional Primate Center) for veterinary assistance; R. Gerety (OraVax) and M.-J. Quentin-Millet (Pasteur Merieux-Connaught, Marcy L'Etoile, France) for critical reading of the manuscript.
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