New York Times
May 14, 2000
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 in Ithaca, N.Y., developed the anti-Norwalk-virus potato and has done early clinical trials on potatoes containing vaccines for hepatitis B and for the diarrhea-causing illness known as travelers disease. Scientists in Poland working with Dr. Hilary Koprowski of Thomas Jefferson University in Philadelphia have tested a hepatitis B vaccine contained in lettuce.
Numerous obstacles must still be overcome, so it is likely to be several years 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 extremely low levels, and proteins are destroyed by acids in the stomach. Such factors could make it hard, particularly for infants, to eat enough to get a proper dose. Assuring a consistent dose is another problem.
For these reasons, some scientists say that using a raw fruit or vegetable as a vaccine is impractical. Some processing will be necessary to concentrate the vaccine and assure a consistent dose, said Dr. Hugh S. Mason, who has been developing the vaccines at Boyce Thompson.
Its next trials will use tomatoes ground into powder and then turned into a paste or juice by adding water. This concentrated tomato juice would have to be pasteurized and maybe refrigerated to keep out other harmful organisms. That could limit the practicality of the vaccine in the developing world.
Dr. Shengwu Ma of the London Health Sciences Center in London, Ontario, hopes to use edible vaccines to treat autoimmune diseases, in which the immune system attacks the body's own tissues. He wants to induce what is known as oral tolerance, the tendency of the body generally not to mount an immune attack on foods.
Dr. Ma has developed genetically modified potatoes containing a protein known as GAD, which is found in the pancreas cells that are attacked by the immune system of people with juvenile diabetes. The idea is that if the immune system thinks GAD is food, it might reduce its attacks on the GAD-containing pancreas cells. Tests on mice have been promising.
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Last Updated on 5/15/00
By Karen Lutz