Plant-made vaccines and reagents for the One Health initiative

Rybicki, Edward Peter

Vaccines to protect against rabies viruses were an early target of molecular farming: as early as 2003, 15 it was suggested that plant-made rabies vaccines could be a useful tool for wildlife immunisation, specifically in the context of fruit bats in the genus Pteropus. These are hosts of many potentially humaninfecting viruses, including the henipaviruses Hendra and Nipah; Menangle and Tioman rubulaviruses, and Australian bat lyssavirus, which is a close relative of rabies virus. 15 Indeed, intraperitoneal immunisation of mice with purified extracts of transgenic tobacco (Nicotiana tabacum) expressing high concentrations of rabies virus G protein elicited comparable levels of immune response to the inactivated conventional vaccine, and complete protective immunity in mice against intracerebral lethal challenge with live rabies virus. 16 In a more recent study, sheep were protected from live virus challenge by oral immunisation with a single dose of transgenic maize kernels containing 2 mg of G protein. 17 The Canadian biotech company Medicago Inc. has also patented a rabies virus-like particle vaccine made in in plants, 18 and announced an expansion of their vaccine pipeline to include the new product. 19 It is also possible to produce effective anti-rabies monoclonal antibodies (MAbs) in plants: 20 The potential of such biologics to replace the rabies immunoglobulin (RIG) of either equine or human origin that is normally used for rabies immunotherapy, and which is prohibitively expensive for developing countries, is a highly attractive prospect for future development. In a response to what is seen as a pressing health need in a rabiesendemic developing country, the Council for Scientific and Industrial Research in South Africa is producing a soon-to-be commercialised anti-rabies MAb called Rabivir in transgenic tobacco, which they claim is 10 times cheaper than the conventional alternative. 21