Plant-Produced Vaccines for Protection from Human and Veterinary Coronaviruses

Coronaviruses are responsible for numerous diseases causing substantial morbidity and mortality to both humans and animals. In particular, they have caused three significant outbreaks in humans including severe acute respiratory syndrome 1 (SARS-CoV-1), Middle East respiratory syndrome (MERS-CoV), and, most recently, the severe acute respiratory syndrome 2 (SARS-CoV-2) pandemic. Two relevant veterinary diseases are porcine transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV), which cause severe losses in the pork industry. While efficacious vaccines were developed in an unprecedented timeframe for COVID-19, vaccines have not been commercialized for other human coronaviruses and vaccines against animal coronaviruses have limited efficacy and logistical challenges in administration. There is a clear need for more efficacious vaccines with simpler methods of delivery and administration for both human and veterinary use. The production of subunit vaccines in plant systems holds great promise in addressing the current challenges and facilitate the preparation for future potential outbreaks and new viruses. This review will summarize the state of development of vaccines in plant systems including tobacco, rice, maize, and others.