Raw potatoes might not be most people's idea of a delicious meal, especially if the potatoes have been genetically modified to contain a protein from the Norwalk virus, which causes vomiting and diarrhea. But when 20 volunteers in Baltimore ate such potatoes, the viral protein not only did no harm; it stimulated an immune response in 19 of them that might prevent them from becoming sick if they ever encounter the real virus.
The test, conducted last year, was one of the first clinical trials of a so-called edible vaccine. Some day, some scientists say, people might be protected from disease by eating special bananas, tomato paste or crackers.
"Would you rather eat a candy bar or would you rather get a needle?" said John A. Howard, chief executive of ProdiGene, a company in College Station, Tex., that is working on edible vaccines in corn.
Edible vaccines could be especially important for developing countries, which often lack resources to distribute and preserve injectable vaccines.
The Boyce Thompson Institute for Plant Research at Cornell University inIthaca, N.Y., developed the anti-Norwalk-virus potato and has done earlyclinical trials on potatoes containing vaccines for hepatitis B and for thediarrhea-causing illness known as travelers disease. Scientists in Polandworking with Dr. Hilary Koprowski of Thomas Jefferson University in Philadelphiahave tested a hepatitis B vaccine contained in lettuce.
Numerous obstacles must still be overcome, so it is likely to be severalyears before such vaccines reach the market.
One challenge will be to shift to foods that are more commonly eaten raw,since cooking could destroy the vaccine.
In addition, the desired protein is often produced in the food at extremelylow levels, and proteins are destroyed by acids in the stomach. Such factorscould make it hard, particularly for infants, to eat enough to get a properdose. Assuring a consistent dose is another problem.
For these reasons, some scientists say that using a raw fruit or vegetable asa vaccine is impractical. Some processing will be necessary to concentrate thevaccine and assure a consistent dose, said Dr. Hugh S. Mason, who has beendeveloping the vaccines at Boyce Thompson.
Its next trials will use tomatoes ground into powder and then turned into apaste or juice by adding water. This concentrated tomato juice would have to bepasteurized and maybe refrigerated to keep out other harmful organisms. Thatcould limit the practicality of the vaccine in the developing world.
Dr. Shengwu Ma of the London Health Sciences Center in London, Ontario, hopesto use edible vaccines to treat autoimmune diseases, in which the immune systemattacks the body's own tissues. He wants to induce what is known as oraltolerance, the tendency of the body generally not to mount an immune attack onfoods.
Dr. Ma has developed genetically modified potatoes containing a protein knownas GAD, which is found in the pancreas cells that are attacked by the immunesystem of people with juvenile diabetes. The idea is that if the immune systemthinks GAD is food, it might reduce its attacks on the GAD-containing pancreascells. Tests on mice have been promising.