An investigation of novel DNA based vaccines for protection against Brucellosis
Commander, Nicola Jane
This thesis describes design, construction and evaluation in a BALB/c mouse model, for five novel Brucella specific DNA vaccines. Brucellosis is worldwide zoonosis of economic significance that poses a significant threat to both animal and human health. Vaccination of livestock can be valuable for reducing transmission and facilitating control. Development of an efficacious non-living vaccine is therefore a valuable goal in brucellosis research. Five candidate antigens were identified within the Brucella melitensis 16M genome. In silico selection was supported by confirming transcription of the selected genes from cultured Brucella, and evidence of candidate protein immunogenicity in Brucella infected sheep. Eukaryotic and prokaryotic expression plasmids were constructed for each candidate antigen. The protective efficacy of six DNA vaccine constructs was evaluated in a BALB/c model of brucellosis. From this evaluation, two protective antigens were identified for further study: Invasion protein B and the 25 kDa outer membrane protein. The DNA vaccines p-omp25 and p-ialB were shown to have equivalent protective efficacy in the mouse model to that achieved through vaccination with the live vaccine strain Rev.1. DNA vaccine mediated protection was associated with production of specific antibodies and priming of both CD4+ and CD8+ IFN-y secreting cells. High numbers of CD8+ cells were observed for the p-omp25 vaccine, whereas CD4+ cells and antibodies were more prevalent following pialB vaccination. The vaccines were found to be most effective when three homologous booster vaccinations were used. Single dose vaccination afforded only modest levels of protection. Attempts to improve delivery of DNA vaccines through adsorption of DNA to cationic liposomes was partially successful in that there was a notable increase in specific humoral immune responses. However, these increases were not associated with increased cell mediated immunity or protective efficacy.