38th Annual Meeting of the Society for Invertebrate Pathology

The baculovirus-insect cell expression system is widely used for the production of recombinant proteins. Membrane proteins, likely candidates for subunit vaccines against enveloped viruses and protozoan parasites, are often more troublesome to produce than cytoplasmic proteins. A protein expressed at low levels and in non-native forms is the Theileria parva sporozoite surface protein p67. T. parva is a protozoan parasite which causes the fatal cattle disease East Coast fever. Different parts of p67 were produced as fusions to GFP or to the baculovirus envelope glycoprotein GP64, resulting either in cytoplasmic expression or surface display. In this way, stable and more-authentic p67 antigens were obtained. By testing these antigens in different animal models highly immunogenic vaccine candidates were obtained, which were efficacious against ECF in cattle at much lower doses than with previously produced recombinant p67 and with a single boost immunization. By replacing the p67 signal peptide with the honeybee mellitin signal surface and by removing its transmembrane domain, a secreted form was obtained. The integrity of this secreted protein was further improved by deleting the chitinase and v-cathepsin genes from the baculovirus vector. These deletions were performed in a bacmid setup, allowing broad scale application of this novel vector.