The idea of using plants to produce human and other therapeutic proteins is intriguing because plants potentially can produce so much product so cheaply. Transgenic plants that produce insect toxins and other proteins also are commonplace, providing proof-of-concept. Now plant-produced proteins have been successfully tested in humans as both a prophylactic against infection and as a vaccine.

The vaccine, given orally when volunteers ate plant tissue, also has shown the viability of using a vaccination pathway that acts via the gut.