Plant-produced vaccines: promise and reality.

Plant-produced vaccines are a much-hyped development of the past two decades, whose time to embrace reality may have finally come. Vaccines have been developed against viral, bacterial, parasite and allergenic antigens, for humans and for animals; a wide variety of plants have been used for stable transgenic expression as well as for transient expression via Agrobacterium tumefaciens and plant viral vectors. A great many products have shown significant immunogenicity; several have shown efficacy in target animals or in animal models. The realised potential of plant-produced vaccines is discussed, together with future prospects for production and registration.