Construction and immunogenicity of novel bivalent virus-like particles bearing VP60 genes of classic RHDV(GI.1) and RHDV2(GI.2)

Rabbit hemorrhagic disease (RHD) is an acute, inflammatory, septic, and devastating infectious disease caused by Rabbit hemorrhagic disease virus (RHDV), which poses a serious threat to the rabbit industry. RHDV2 (GI.2/RHDVb), a recently reported new variant could cause RHD in wild populations, but also RHDV-vaccinated rabbits. For now, both RHDV and RHDV2 are the main causes of RHD. To develop a new subunit vaccine that could protect rabbits against both classic RHDV and RHDV2 infections, we constructed a recombinant baculovirus (Bac-classic RHDV VP60-RHDV2 VP60) containing the VP60 genes of classic RHDV and RHDV2. Both VP60 genes were well expressed simultaneously in Spodoptera frugiperda cells (Sf9) after infection with the recombinant baculovirus. Transmission electron microscopy showed that the recombinant VP60 self-assembled into virus-like particles (VLPs). The antigenicity and immunogenicity of the bivalent VLPs vaccine were examined with animal experiments. Our results demonstrated that both the humoral and cellular immune responses were efficiently induced in rabbits by a subunit vaccine based on the recombinant baculovirus. In addition, all rabbits immunized with the bivalent VLPs vaccine survived after challenged with classic RHDV, and showed no clinical signs of RHD, whereas all the rabbits in the negative control group died from classic RHDV infection and showed typical clinical signs of RHD. In summary, our results indicated that the recombinant baculovirus carrying two VP60 genes is a candidate construct from which to develop a bivalent VLPs vaccine against both classic RHDV and RHDV2 infections.