Toward Development of an Oral, Plant-Based Vaccine Against Escherichia coli O157:H7
UNIFORMED SERVICES UNIV OF THE HEALTH SCIENCES BETHESDA MD DEPT OF MICROBIOLOGY AND IMMUNOLOGY
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Enterohemorrhagic Escherichia coli EHEC O157H7 is the most common infectious cause of bloody diarrhea in the United States, and a sequela of this infection, the hemolytic uremic syndrome HUS, is the primary cause of acute renal failure in children in the U.S. The majority of U.S. cases of EHEC O157H7 have occurred as a consequence of ingestion of undercooked, contaminated hamburger or produce andor water contaminated with bovine manure. Intimin is the primary adhesin of EHEC O157H7, and is required for colonization of neonatal calves. I hypothesized that an intimin-based vaccination strategy in calves might reduce colonization of cattle with EHEC O157H7. To test this concept in a small animal model, I developed transgenic tobacco plant cells that expressed the full length or carboxy-terminal portion Int261 of EHEC O157H7 intimin and then immunized mice parenterally with intimin expressed from the plant cells, or fed mice the transgenic plant cells, or both. I was able to show that these mice not only generated an intimin-specific mucosal immune response when primed parenterally and boosted orally but also exhibited a reduced duration of EHEC O157H7 fecal shedding after challenge. These results suggest that transgenic plants are attractive and feasible production and delivery systems for an intimin-based vaccine for cattle, and such a vaccine can reduce the duration of EHEC O157H7 shedding in a small animal model. In addition, Shiga toxin type 2 Stx2 is another important EHEC O157H7 virulence factor that plays a critical role in the development of potentially fatal HUS in humans. I developed a toxoid of Stx2 by making site-directed changes to the nucleotide sequence of the Stx2 A subunit gene that abrogated cytotoxcity in vitro and in vivo. The Stx2 toxoid elicited toxin-neutralizing antibody when parenterally injected in mice.
- Genetic Engineering and Molecular Biology