Plant-made vaccines and reagents for the One Health initiative

Rybicki, Edward Peter

Ebolaviruses have been part of One Health thinking for some time: several reviews have, in recent years, discussed the control of the viruses' emergence in the context of One Health, and in the context of zoonotic threats and the exotic animal practice. [22] [23] [24] An obvious target for their control, in humans but also possibly in other primates at risk like chimpanzees and gorillas, are vaccinesand this is one area of hope after the recent West African epidemic, where accelerated licensure and testing threw up several likely candidates, but one real success in recombinant vesicular stomatitis virus (rVSV-ZEBOV). 25 This notwithstanding, subunit vaccines may yet be useful, for Zaire and other ebola-and marburgvirusesand investigations have been done on the vaccine potential of different viral proteins to throw up useful candidates, including as well as the obvious GP1 envelope glycoprotein, VP24, VP30, and VP40. 26 Toward this goal, several plant-made antigens have been shown to have potential. One novel approach was the expression of an Ebola immune complex (EIC) in N benthamiana, using a replicating geminivirus-derived vector. 27 The GP1 protein of Zaire ebolavirus was C-terminus fused to the heavy chain of a humanised 6D8 IgG mAb antibody, which specifically binds GP1: this was co-expressed with the 6D8 light chain and the assembled mAb::GP1 chimaera was purified by ammonium sulfate precipitation and protein G affinity chromatography. The mAb was functional in terms of binding C1q, and the chimaera formed a cross-linked immune complex with itself. BALB/C mice immunised subcutaneously with purified EIC produced anti-GP1 antibodies at levels similar to those elicited using a GP1 VLP vaccine. Another very recent approach was to make the ebolavirus matrix protein VP40 in plants: 28 this protein is highly multifunctional and elicits protective immunity in mice. 26, 29 Transgenic tobacco plants expressed an ER-targetted VP40 at levels of »3 mg/kg fresh weight of plant tissue. The protein was given orally or subcutaneously to BALB/C mice in 3 low-dose preparations (125 ng oral, 25 ng s/c) without adjuvants, and elicited reasonable responses. Both these proteins are candidate vaccines, and candidate low-cost reagents for ebolavirus diagnostic kits.