Relevance of Helicobacter pylori virulence factors for vaccine development

Helicobacter pylori infection increases the risk for a wide spectrum of clinical outcomes, ranging from peptic ulcer disease to gastric cancer. However, the infection induces gastric and duodenal ulceration or gastric cancer in only a minority of infected subjects because H. pylori strains are genetically diverse and express different virulence factors. Individuals infected with strains that express these virulence factors probably develop severe diseases such as gastric cancer. Nevertheless, the ancient relationship between H. pylori and humans suggests that some strains could be beneficial to human health, which means that generalized administration of antibiotic therapy could eventually cause problems. The development of vaccines based on virulence factors that provide long-term protection is the best strategy for control and/or elimination of pathogenic strains. The different immunization schemes and formulations designed to evaluate the vaccines based on virulence factors in animal models have offered promising results. However, it is necessary to determine whether or not these results can be reproduced in humans. This article reviews recent vaccination studies that explore this possibility: oral vaccines using urease or inactivated whole cells plus LT as adjuvant and urease expressed in Salmonella spp. vectors, as well as a parenteral multicomponent vaccine plus aluminum hydroxide as adjuvant. Although these studies have achieved limited success,they have established support for the development of an effective vaccine against this infection.