Chimaeric Rift Valley fever virus-like particle vaccine candidate production in Nicotiana benthamiana.

Rift valley fever virus (RVFV) is an emerging mosquito borne virus and haemorrhagic fever agent, which causes abortion storms in farmed small ruminants and potentially causes miscarriages in humans. Although live-attenuated vaccines are available for animals, they can only be used in endemic areas and there are currently no commercially available vaccines for humans. Here we describe the production of chimaeric RVFV virus-like particles transiently expressed in Nicotiana benthamiana by Agrobacterium tumefaciens-mediated gene transfer. The glycoprotein (Gn) gene was modified by removing its ectodomain (Gne) and fusing it to the transmembrane domain and cytosolic tail-encoding region of avian influenza H5N1 haemagglutinin. This was expressed transiently in N. benthamiana with purified protein yields calculated to be ∼ 57 mg/kg fresh weight. Transmission electron microscopy showed putative chimaeric RVFV Gne-HA particles of 49-60 nm which were immunogenic, eliciting Gn-specific antibody responses in vaccinated mice without the use of adjuvant. To our knowledge, this is the first demonstration of the synthesis of Gne-HA chimaeric RVFV VLPs and the first demonstration of a detectable yield of RVFV Gn in plants.