Many vaccines are difficult and expensive to make, store, and administer to patients, especially in developing nations where they're needed most. If Charles Arntzen's work pans out, though, vaccines will become a lot easier to produce and deliver. He has developed a "vegetable vaccine"-specifically, a genetically engineered potato. When eaten, the potato provokes an immune response to some strains of E. coli, a bacterium that can cause fatal cases of food poisoning and diarrhea. Arntzen, a plant biologist at the Boyce Thompson Institute for Plant Research in Ithaca, New York, hopes his potato will be the forerunner of many edible vaccines that will protect against a wide range of diseases, including cholera and hepatitis B.
Arntzen began his project six years ago by transferring a gene from E. coli into the DNA of potato plants. His strategy was to trick the potato into producing bits of E. coli protein. When the potato was eaten, a person's immune system would churn out antibodies.
But Arntzen had trouble getting the plants to produce enough E. coli protein to provoke an immune response. Apparently the potato plant could not effectively "read" the genetic instructions in the E. coli gene. So Arntzen built an artificial gene-a chemical sequence of instructions that cause the potato to produce a protein identical to the one made by the bacterium.
When 14 volunteers ate small chunks of raw potato impregnated with the synthetic E. coli gene, antibodies against the bacterium appeared in their guts and bloodstreams. Their immune response was just as strong as that of people who were exposed to the bacterium itself. Antibodies in gut secretions are the first line of defense against viruses and bacteria that cause severe diarrhea. An oral vaccine, which goes straight to the gut, would be more efficient than an injection for such diseases.
Later this year, Arntzen hopes to test a potato vaccine for Norwalk virus, another cause of gastrointestinal disease, and he has begun working on vaccines for cholera and hepatitis B. An uncooked potato, however, is not his ideal delivery system. He's experimenting with tomatoes, but what he really wants is a banana vaccine. Bananas grow in much of the developing world, and they're a natural baby food. Arntzen says there seems to be no limit to the types of vaccines plants can create. "This is going to be a very effective strategy for delivering oral vaccines."