IT SHOULD BE POSSIBLE TO OBTAIN MASS PRODUCTION OF ANTI-VIRAL VACCINES AT LOW COST (BECAUSE THE INSECT CELLS USED FOR THE MULTIPLICATION OF THE BACULOVIRUSES ARE EASY TO CULTIVATE).
Novel sensitive diagnostic antigens have been produced to screen antibodies of all 24 blue tongue virus (BTV) serotypes. Subunit vaccines for 6 serotypes of BTV have been developed. In addition, complete viral like particles have been synthesised by expressing 4 genes of BTV using novel multiple expression vectors. These were shown to be highly immunogenic. For rabies, both diagnostic reagents (eg, N protein) and subunit vaccines (G protein) have been developed.
The project concerned the development and use of baculovirus expression vectors for the preparation of diagnostic reagents and subunit vaccines for 2 economically important viral diseases of livestock and wildlife: rabies and bluetongue (BTV). Expression vectors based on Autographa californica nuclear polyhedrosis virus (AcNPV) were used for the production of proteins that could be used as diagnostic reagents or subunit vaccines. The approach was to clone, sequence then insert cloneddeoxyribonucleic acid (DNA) copies of the relevant viral genes into the AcNPV expression vectors and to characterise the expressed proteins. Specifically for the preparation of subunit vaccines, ribonucleic acid (RNA) segments encoding the outer capsid VP2 protein of 5 serotypes of BTV or rabies G protein, were cloned into AcNPV expression vectors. The expressed VP2 proteins of BTV (10, 11, 13, 17, 2) elicited antibodies that neutralised BTV infectivity. Complete protection of sheep against bluetongue disease was demonstrated by vaccination with 50 ug quantities of the expressed BTV-10 VP2 in conjunction with 20 ug of BTV VP5 protein. In mice the expressed G protein of rabies provided complete protection following vaccination with as little as 10-20 ng of G protein. Protection of dogs was afforded by vaccination with 1 ug of the expressed G protein. Certain of the expressed proteins of BTV were shown to be effective group specific diagnostic reagents. For instance the conserved NS1 protein could be used in the order of 10-50 ng/test. The expressed N protein of rabies was shown to react with antirabies sera (and all the available N monoclonal antibodies) with a high signal to noise ratio. The N antigen has been used as a diagnostic reagent for rabies. An important new development in this research was the coexpression of the BTV VP2, VP5, VP3 and VP7 genes and the formation of immunogenic, structurally complete, virus like particles. The expression of blue tongue proteins has been achieved in Oxford (NERC, project leader P Roy).
THE BACULOVIRUSES ARE SPECIFIC FOR THE CELLS OF SOME INSECTS AND ARE ABLE TO INDUCE THE SYNTHESIS OF A PROTEIN (POLYHEDRIN) IN LARGE QUANTITIES IN INFECTED CELLS (UP TO 25% OF THE TOTAL CELL PROTEIN MASS). THIS PROTEIN IS NON ESSENTIAL FOR THE PRODUCTION OF INFECTIOUS VIRUS IN CELL CULTURE. THIS PROJECT IS THE REPLACEMENT OF THE GENES CODING FOR THIS PROTEIN BY GENES CODING FOR IMMUNIZING ANTIGENS OF BLUETONGUE OR OF RABIES VIRUSES. RNA SEGMENT L22 OF FIVE BLUETONGUE VIRUS SEROTYPES (CODING FOR THE IMMUNIZING PROTEIN VP2), AND THE RABIES GLYCOPROTEIN DNA CLONES WILL BE OBTAINED AND EXPRESSED IN THE BACULOVIRUSES SYSTEM.
Funding SchemeCSC - Cost-sharing contracts