Development and evaluation of a subunit DIVA vaccine against bluetongue virus serotype 8 in cattle
Abstract: Bluetongue virus (BTV) causes the primarily vector-borne bluetongue disease of ruminants, which poses a permanent threat to Europe since new serotypes and strains are frequently introduced. Vaccination of cattle is essential to control BTV outbreaks. Commercial attenuated and inactivated vaccines are efficacious in reducing BTV spread and disease, but do not fulfil all safety, adaptability, or production requirements. Additionally, no current vaccines allow the differentiation of infected from vaccinated animals (DIVA). DIVA vaccines enable surveillance of BTV epidemiology and vaccine efficacy, and facilitate a quick return for countries to a BTV-free status. This thesis presents the development and evaluation of a novel subunit DIVA vaccine against BTV serotype 8 (BTV-8) in cattle. Five His-tagged recombinant BTV proteins (VP2, VP5 of BTV-8; NS1, NS2, NS3 of BTV-2) were produced in baculovirus or E. coli expression systems. Purification protocols were optimized for all but VP5. Based on the feasibility of protein production and the capability of the remaining four proteins to induce humoral or cellular immune responses in mice, VP2, NS1, and NS2 were selected to formulate an experimental vaccine combined to an ISCOM-matrix adjuvant (SubV). Next, cattle were immunized twice at a three-week interval with SubV, a commercial inactivated vaccine, or a placebo. SubV induced humoral immune responses, including virus-neutralizing antibodies, against all three proteins, as well as a cellular immune response directed against NS1. These responses were of similar type and comparable magnitude between both vaccines, suggesting that SubV might provide protection that is at least as effective as the commercial vaccine. Finally, the protective efficacy of SubV was evaluated and complete virological and clinical protection against virulent BTV-8 challenge was observed following vaccination in calves. This was likely due to the induction of virus-neutralizing antibodies directed against VP2 of BTV-8 and cross-serotype T cell responses directed against NS1 and NS2 of BTV-2. Furthermore, SubV was shown to be DIVA-compliant based on the detection of antibodies directed against VP7, by using commercially-available diagnostic assays. This novel BTV subunit vaccine is a promising candidate and should be further developed.
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