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Helicobacter pylori Vaccine Development. Catherine O. Johnson March 9, 2006. Pathogen Background. Gram negative bacteria Colonizes the human gastrointestinal tract and stomach Oral-Oral or Oral-Fecal routes of person-to-person transmission. Requisite Nasty Pictures. Nasty Pictures (2).

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Helicobacter pylori vaccine development l.jpg

Helicobacter pylori Vaccine Development

Catherine O. Johnson

March 9, 2006


Pathogen background l.jpg
Pathogen Background

  • Gram negative bacteria

  • Colonizes the human gastrointestinal tract and stomach

  • Oral-Oral or Oral-Fecal routes of person-to-person transmission




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Mechanism of Infection

  • H. pylori is able to establish long-term infection in most individuals

    • Colonizes the mucus layer of the stomach lumen

    • Goes through adherent and non-adherent phases

  • Mechanism used to evade host defenses is not completely understood

    • Able to modulate host immune system to favor a TH1-type inflammatory response; able to specifically modulate the immune responses that would clear the bacteria

    • Extensive intrastrain and interstrain diversity

    • Genetic variation in hosts


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Burden of Disease

  • Most of the time, infected individuals are asymptomatic

  • 15-20% of infected individuals will develop severe gastrointestinal disease

    • Gastric tumors (particularly stomach body)

    • Peptic ulcers & active gastritis

  • Approximately 50% of the global population is infected with H. pylori

    • Higher rates in those of lower SES status

    • 80-90% of persons living in developing countries are infected by early adulthood



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Treatment

  • Triple Therapy

    • Proton pump inhibitor, amoxicillin and clarithromycin

    • Dosed 2 times per day for 1 week

  • Results in eradication of the organism in >80% of individuals

  • Does not prevent recolonization; antibiotic resistance is becoming problematic


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Vaccine Development

  • Interest in both preventive and therapeutic vaccines

  • Relatively good results in animal models

  • Problems with extending vaccines to human subjects

    • Multiple doses required; incomplete protection

    • Route of immunization: oral, rectal, intranasal

    • Genetic diversity of the organism


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Genetic Diversity of H. pylori

  • Most genetically diverse bacterial species

  • Strains differ in

    • Genome size

    • Gene order

    • Genetic content

    • Allelic profile

  • Associations between specific strains and increased incidence of severe sequelae

    • Cag pathogenicity island

    • Specific VacA cytotoxin alleles


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Vaccine Delivery

  • Difficult to generate an immunologic response in the stomach/gut with a systemic inoculation

  • Small studies have shown results with oral vaccines

  • Rectal, intranasal, intrajejunal vaccines are also being explored


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Clinical Trial of Vaccine

  • Trial of an oral therapeutic vaccine

  • Four doses of either 20, 60, or 180mg of recombinant H. pylori urease was given to infected subjects

  • Trial demonstrated immunogenicity of the vaccine; however a high proportion of the subjects reported diarrhea


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