Vaccine-laced potato stirs immune system

Monday, July 17th 2000, 12:00 am
By: News On 6

Suddenly, the idea of a vaccinating potato doesn't sound so half-baked.

Volunteers who ate chunks of such a potato have, for the first time, developed an immune reaction to a disease-causing virus. If all goes well, researchers may one day grow vaccine crops that protect against infection with a few bites. No shots, no syringes, not even special cooking instructions.

"Everything we dreamed of has been working out," said Charles Arntzen of Cornell University. "I want within my scientific career to see someone immunized with this."

He'd actually like to offer every developing nation edible vaccines for their most troubling diseases. Immunization rates are highest in countries that have nurses and refrigerators in every neighborhood. Poorer countries would welcome a vaccine that doesn't call for sterile handling or meticulous storage.

The prospects ripened a bit this month, with the publication of the Journal of Infectious Diseases. In it, scientists describe their latest success with the vaccinating potato. The potato looks and tastes like an ordinary spud. But each bite stows bits of genetic material from the Norwalk virus, the most common cause of food poisoning in the United States.

After a raw potato snack, 19 of 20 volunteers were left with an immune system armed against Norwalk. The study was a safety test of the vaccine, so researchers didn't try to actually protect people from infection. That's a matter for future studies.

Like a conventional vaccine, the potatoes contain just enough of the Norwalk virus to get the body's attention. Under a microscope, the virus looks a bit like a teeny tennis ball. Researchers inserted into the potato's cells the gene that codes for the protein on the ball's outer fuzz. In the potato, the gene awakens and starts churning out hollow shells of Norwalk virus. The body's immune system doesn't know the particles are only decoys. Confronted with a real infection, however, the immune system would be ready for a fight.

"It was absolutely delightful to us to know that humans would recognize this protein," said Dr. Arntzen, who works at Cornell's Boyce Thompson Institute for Plant Research.

Dr. Arntzen and his colleagues demonstrated in 1998 that they could perform the same trick using genes from a bacterium. In this case, the potato produced an immune response to a strain of E. coli. For the most part, though, Dr. Arntzen plans to concentrate on viruses. As simpler microbes, viruses are the most likely to be folded into a plant vaccine.

Researchers used Norwalk virus for this experiment because some of the collaborators, who work at Baylor College of Medicine in Houston, were already developing a Norwalk vaccine. But scientists are also making a plant vaccine for hepatitis B.

A hepatitis B vaccine already exists, a fact that provides an advantage in the plant studies. Researchers know exactly what a protecting immune response to hepatitis B needs to look like, said Yasmin Thanavala of the Roswell Park Cancer Institute in Buffalo, N.Y. An edible hepatitis B vaccine would also be a major scientific achievement. Hepatitis B is spread through contact with contaminated blood. The current hepatitis B vaccine is given by injection – directly into the blood – because that's where the immune cells need to patrol.

If an edible vaccine can enter the body through the digestive tract, yet still cause immune cells to appear in the blood, "It's a great example of the power of immunization orally," Dr. Thanavala said.

But if a potato provoked immunity only in the stomach and intestine, the achievement would be little more than a quaint curiosity.

The first experiments with the hepatitis potato are finished, but the data are still not completely analyzed.

The progress so far, though, is getting the attention of more and more scientists. Dr. Thanavala said that when she first started work on edible vaccines, many of her colleagues were doubtful. "Now, when I meet people, they say, 'That's the coolest thing.'"

One interested scientist is Robert Rose of the University of Rochester Medical Center in New York. Dr. Rose is one of the researchers developing a vaccine for human papilloma virus, considered the most important risk factor for developing cervical cancer. When Dr. Rose first heard about the vaccinating potato, "it was shocking to think it might be possible," he said.

Now, he is working with Dr. Arntzen and his colleagues to insert a papilloma virus vaccine into a plant. "I'm optimistic," he said, "but the nature of the business is that you run into pitfalls."

And he said he's encouraged by the Norwalk experiment.

"It's a very important paper," Dr. Rose said, because it is further evidence of the promise of edible vaccines.

Dr. Arntzen's ultimate goal is to develop a vaccinating banana. Bananas are eaten worldwide, uncooked. The idea of putting vaccines in food first came to him as he watched a child eating a banana. For the time being, though, bananas grow too slowly to make them practical for research. That's why current experiments involve raw potatoes.

The scientists stress that they are not developing a designer food. Never mind that the delivery device happens to taste good fried, with a side of ketchup. "This is a drug, and it will be dispensed as a drug," Dr. Thanavala said.

The first experimental bananas, containing foreign genes, are now growing in a greenhouse. From the time Dr. Arntzen began the project in the early 1990s, progress has come swifter than he imagined. "I'm convinced now this is going to be a viable method," he said, with no fear that he would ever have to eat his words.