Development of an edible (needle-free) plant-based vaccine for bovine pneumonic pasteurellosis
This ongoing research targets development of an edible vaccine platform for cattle, in a collaborative program involving three laboratories in three Colleges at the University of Guelph: R. Lo’s lab in Biological Sciences, J. Strommer’s lab in OAC and P. Shewen’s lab in OVC. Specifically, it focuses on production of alfalfa that expresses proteins with a role in protection against pneumonia caused by bacteria in the Pasteurella family, and feeding of this alfalfa to ruminating calves to stimulate immunity. Natural cudding activity is used to expose tissues in the throat to the vaccine. Such exposure should induce immunity in the respiratory tract in particular. This OCA grant supported a graduate student who worked on assessing immune response to alfalfa expressed antigens, in particular the leukotoxin and GS60 surface proteins, of Mannheimia haemolytica and response to experimental challenge, as a measure of vaccine efficacy. Two vaccination and challenge experiments were conducted during the course of this project. The first, involving 30 calves, was completed in summer 2007. Twenty vaccinates were fed alfalfa expressing recombinant leukotoxin (rLkt50), surface antigen (rGs60) and glycoprotease (rGcp), and 10 unvaccinated controls were fed wild-type alfalfa. A second trial compared 3 groups of 6 animals. One group was fed alfalfa expressing the three antigens, one was vaccinated subcutaneously with the commercial vaccine Presponse SQ, and one served as unvaccinated controls. In the first trial vaccinated calves responded to vaccination and produced serum and mucosal antibodies to Lkt, but challenge was too severe to demonstrate protective efficacy. Nevertheless, it was found that levels of IgA antibodies to Lkt in nasal secretions correlated with protection against pneumonia, providing an important parameter for monitoring immunogenicity, a major hurtle in mucosal vaccination. There was no significant difference in serum antibody response to Gs60 comparing vaccinates and controls, but there was an association between a high antibody titer, acquired by natural exposure or vaccination, and protection against pneumonia. Assay for mucosal antibodies to Gs60 is in progress. The second vaccination and challenge trial was completed in August 2008. Circulating and mucosal antibody responses will be evaluated in the coming months. Although we did not demonstrate protective efficacy in either challenge trial, analysis of serological samples should furnish new information about immunogenicity that will be valuable for advancing this research program.
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