Oral immunization of rabbits with VP60 particles confers protection against rabbit hemorrhagic disease

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Abstract
Rabbit hemorrhagic disease virus (RHDV) causes more than 90% mortality in adult rabbits. In this study, the cDNA of the VP60 coding sequence of RHDV was cloned under the control of the polyhedrin and p10 promoters of baculovirus to be expressed in insect cells. The expression of RHDV VP60 under the control of the p10 promoter was 5–10 times higher than using the polyhedrin promoter. The p10-derived VP60 was able to assemble into virus-like particles (VLPs). RHDV VLPs were successfully used to protect rabbits against the disease even at doses as low as 0.5 µg when injected intramuscularly or sub-cutaneously. The ability to elicit an immune response was independent of the adjuvant or the route of immunization. Remarkably, oral administration of RHDV VLPs efficiently induced protecting antibodies to RHD at doses as low as 3 µg. The use of binary ethylenimine for the stabilization of the VLPs was decisive for eliciting a good oral immunity. This report demonstrates the potential use of these procapsids in obtaining RHD oral vaccines and opens the door to the use of these capsids for the prevention of the disease in wild animals. Therefore, a new, and potentially important application of recombinant VLPs in the induction of protective immunity by the oral route is foreseen.