Development of a VLP-based vaccine in silkworm pupae against rabbit hemorrhagic disease virus.

Rabbit hemorrhagic disease virus (RHDV) is the etiological agent behind rabbit hemorrhagic disease (RHD), which is lethal and contagious in rabbits. The virus does not replicate in cell culture and the only commercial inactivated vaccine available is derived from infected rabbit livers. RHDV capsid protein, VP60, is the main antigen comprising the virion. We used a baculovirus-silkworm pupae system to express VP60, which self-assembled into virus-like particles (VLPs) with a similar size and morphology to RHDV. Hemagglutination assays (HAs) showed that VP60 expression levels of VP60 reached as high as 10(7)HA units (HAU) per pupa. A single intramuscular injection with 10(4)HAU of VLPs completely protected rabbits for at least 180days against RHDV challenge, and for at least 360days when the VLPs were emulsified with Freund's complete adjuvant. These data suggest that silkworm pupae can be used to develop VLP-based vaccines which confer durable protection against RHD.