Oral vaccination of BacFish-vp6 against grass carp reovirus evoking antibody response in grass carp

To obtain a vaccine and evaluate its immune efficacy as an oral vaccine against Grass Carp Reovirus (GCRV), a donor vector pFastBac-FA-VP6-ph-VP6 containing two GCRV vp6 genes, one driven by the Megalobrama amblycephala β-actin promoter and another one controlled by baculovirus polyhedrin promoter was constructed to generate the recombinant baculovirus BacFish-vp6. From the hemolymph of 5th instar silkworm inoculated with BacFish-vp6, a 53 kDa recombinant VP6 protein could be detected. And the infected pupae collected at 120 h post-inoculation with BacFish-vp6 were used to make freeze-dried powder as an oral vaccine. When the grass carps were orally administrated with feed containing 1%, 5% and 10% of the freeze-dried powder, their specific antibody against VP6 could be detected. Further studies showed that vp6 has been transcripted in the grass carp kidney (CIK) cells infected with BacFish-vp6 and the different tissues of orally vaccinated fish. All the results suggested the powder of the silkworm pupae infected with BacFish-vp6 could possibly be used as an orally administered vaccine.

► GCRV vp6 was cloned and expressed by baculovirus expression system in silkworm.
► The freeze-dried powder infected with BacFish-vp6 could induce specific antibody after orally administrated in grass carp.
► The powder may possess simultaneously the roles of subunit vaccine and DNA vaccine.