Clinical development of plant-produced recombinant pharmaceuticals: Vaccines, antibodies and beyond

In the last few years, plants have become an increasingly attractive platform for recombinant protein production. This builds on two decades of research, starting with transgenic approaches to develop oral vaccines in which antigens or therapeutics can be delivered in processed plant biomass, and progressing to transient expression approaches whereby high yields of purified targets are administered parenterally. The advantages of plant-based expression systems include high scalability, low upstream costs, biocontainment, lack of human or animal pathogens, and ability to produce target proteins with desired structures and biological functions. Using transgenic and transient expression in whole plants or plant cell culture, a variety of recombinant subunit vaccine candidates, therapeutic proteins, including monoclonal antibodies, and dietary proteins have been produced. Some of these products have been tested in early phase clinical trials, and show safety and efficacy. Among those are mucosal vaccines for diarrheal diseases, hepatitis B and rabies; injectable vaccines for non-Hodgkin's lymphoma, H1N1 and H5N1 strains of influenza A virus, and Newcastle disease in poultry; and topical antibodies for the treatment of dental caries and HIV. As lead plant-based products have entered clinical trials, there has been increased emphasis on manufacturing under current Good Manufacturing Practice (cGMP) guidelines, and the preparation and presentation to the relevant government agencies of regulatory packages.