Forget about painful shots or bitter pills--if vaccine-makers' plans come to fruition, people will eat vaccines in vegetables. A new report in the June issue of Nature Medicine suggests that plant geneticists have gone a long way toward that goal, at least for mice. A weekly meal of genetically engineered potatoes protects the rodents against three deadly stomach bugs at once.
The idea of making edible vaccines has been around since the mid-80s, when tools for genetically modifying plants emerged. But making crops produce proteins that elicit an immune response is easier dreamed of than done: Ingested proteins usually disintegrate in the stomach before they reach the intestine's immune system.
A clever solution is to hurry the vaccine toward its target with the help of the toxin that causes cholera. This new strategy was tried by plant molecular biologist William Langridge of Loma Linda University in California and his team. The researchers stitched genes together from three stomach bugs: rotavirus, toxic Escherichia coli, and Vibrio cholerae, which causes cholera.
When the researchers served the transgenic potatoes to mice, the animals produced antibodies against all three bacterial and viral proteins. So far so good--but, as Langridge points out, "you can make antibodies against all sorts of antigens, but those antibodies don't necessarily protect the animals" from infections, as has been the case in previous studies with transgenic plant vaccines. But when the researchers injected the mice with cholera toxin or infected them with rotavirus, about 50% of the animals remained healthy. And in those that did get sick, the diarrhea was about half as severe and lasted about half as long as in nonimmunized mice.
"This is really great stuff. It's another important step forward in the development of plant-based vaccines," says plant biologist Charles Arntzen of Arizona State University in Tempe, who, in 1992, pioneered the production of viral proteins in plants for vaccine purposes. The new study, Arntzen adds, is the most recent in a series of papers that show that plant-based vaccines are "a viable strategy."