Abstract for non-specialists

Bacteria Helicobacter pylori infects half of the world population causing gastritis and contributing to increased incidence of ulcers and gastric malignancies. This infection can be treated with multi-drug regime, but this is often associated with induced antibiotic resistance and does not protect individuals from re-infections. Vaccination against H. pylori can therefore be a viable alternative to control this widespread infection. However, developing an effective vaccine against H. pylori has presented a challenge because H. pylori or its components, which have frequently been used as parts of vaccines, are modified by bacteria such that they evade host defense mechanisms. Using synthetic biology approaches we managed to assemble functional “immunobricks” into a designer vaccine with a goal to activate both innate and acquired immune response to H. pylori. We successfully developed two forms of such designer vaccines. One was based on modifying H. pylori component (flagellin) such that it can now be recognized by the immune system. The other relied upon linking H. pylori components to certain molecules of the innate immune response (so called Toll-like receptors) to activate and guide H. pylori proteins to relevant compartments within the immune cell causing optimal innate and acquired immune response. Both types of vaccines have been thoroughly characterized in vitro (in test tubes or cells) as well as in vivo (laboratory mice) exhibiting substantial antibody response. Our strategy of both vaccines’ design is not limited to H. pylori and can be applied to other pathogens. Additionally, our vaccines can be delivered using simple and inexpensive vaccination routes, which could be suitable also in third world countries.
Scientific abstract

Almost half of the world's population is infected with bacteria Helicobacter pylori, which colonize gastric mucosa, causing gastritis and ulcers and is recognized as a type I carcinogen by WHO. An effective vaccine against H. pylori is not available, although it would be a durable solution, particularly in a formulation affordable to the third world population. H. pylori evades the immune surveillance by modifying several of its components including flagellin to avoid detection by several Toll-like receptors. The goal of our project was to prepare a modular designer vaccine, using the principles of synthetic immunology. An effective vaccine has to trigger activation of adaptive immunity, which is directed against microbial proteins or polysaccharides as well as of innate immunity, which is usually achieved by the addition of adjuvants of whole microbes. We prepared a set of “immunobricks” with defined functions in activation of the immune system and can be combined to achieve a desired response. In the first approach we have modified H. pylori flagellin to be able to activate TLR5, making it »visible« to the immune system. To this chimeric flagellin we attached either complete protein or a designed a multiepitope of several virulence factors of H. pylori. We prepared three implementations of this system in the form of recombinant proteins, engineered bacteria and DNA vaccines, demonstrated responsiveness of each of them in cell culture assays, cellular localization and even obtained significant antibody response in laboratory animals only weeks after vaccination. The second approach was to extend the range of activation of innate immune response to different Toll-like receptors by linking antigen to different TLR segments, which are constitutively activated by the addition of a dimerization domain. In this case we could direct localization of resulting fusion receptors to either cell membrane or cellular vesicles, which should assist in proper antigen processing and presentation. The power of this approach is that we could mimic synergistic activation of several TLRs by pathogenic microbes, while having the advantage of safety of a defined subunit vaccine.

Experimental work on this project was performed by seven undergraduate students between june and october 2008, supported by their mentors.

Department of Biotechnology
National Institute of Chemistry, Slovenia

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