Baculovirus-mediated delivery of viral hemorrhagic septicemia virus G protein in forms of envelope-spiked protein and a CMV promoter-driven expression cassette

Abstract

Viral hemorrhagic septicemia virus (VHSV) has been a main cause of morbidity and mortality in cultured olive flounder (Paralichthys olivaceus) in Korea. The aim of the present study was to construct recombinant baculovirus-based VHSV G protein delivery tools for the immunization of olive flounder. We rescued recombinant A. californica multiple nucleopolyhedrovirus (AcMNPV) i) displaying VHSV G protein on the viral envelop, ii) harboring a CMV promoter-driven VHSV G protein gene cassette, or iii) having a bicistronic construct equipped with both envelope-spiked G protein and a CMV promoter driven G protein cassette. In the immunization experiment, groups of olive flounder immunized with recombinant baculoviruses carrying VHSV G protein on the envelope showed significantly higher survival rates than groups of fish in the control group (medium only) and the control recombinant baculovirus (expressing green florescent protein) immunized group, suggesting the possible use of recombinant baculoviruses carrying foreign antigens on the envelope for the development of fish vaccines. The survival rate of fish immunized with a recombinant baculovirus having a CMV-driven VHSV G protein expressing cassette was higher than that of fish immunized with a baculovirus having a reporter protein-expressing cassette, but was much lower compared to previously reported results of VHSV G protein-based DNA vaccines, suggesting that the delivery efficiency of the present baculovirus-mediated VHSV G protein gene into olive flounder cell's nucleus might not be high compared to plasmid-based DNA vaccines. Although the group of fish immunized with the recombinant baculovirus equipped with both envelope-spiked G protein and a CMV promoter driven G protein cassette showed the highest survival rate against VHSV challenge, further elaborate studies are needed to uncover the synergic effect of the two forms of VHSV G protein delivered by recombinant baculoviruses.