American researchers have succeeded in producing a genetically modified banana, which contains a vaccine for hepatitis B
American researchers have succeeded in producing a genetically modified banana, which contains a vaccine for hepatitis B. In the study, which should be published in a few months, they report that humans who ate the genetically modified bananas developed antibodies to the hepatitis virus.
The countries that will benefit the most from vaccines will be the developing countries. The biggest problem with the vaccination programs conducted by the World Health Organization in these countries is not the cost of the vaccines, but rather the obligation to store injectable vaccines under special refrigeration conditions - an almost impossible task in communities that do not have organized access routes.
Dr. Charles Arentzen, director of the Boyce Thompson Institute for Plant Research, who headed the research, described the process of developing edible vaccines at a conference on the genetic revolution and its impact on humans, which took place last week in Jerusalem.
In the development of the hepatitis B vaccine in the banana, the researchers inserted a gene of the hepatitis B virus into the genome of the plant. The gene is responsible for producing a certain protein in the virus, which does not cause the disease, but the immune system recognizes it as a foreign agent and produces antibodies against it.
In another study, which will be presented this week in Los Angeles at a conference of the American Society for Microbiology, Boyce Thompson Institute researchers were able to induce the production of antibodies against the Norwalk virus in volunteers who ate a potato with a gene of the virus. In industrialized countries, the Norwalk virus, for which there is no vaccine today, causes 90% of stomach and intestinal infections caused by viruses. In developing countries, the severe diarrhea caused by the virus is one of the main causes of infant death. Dr. Arentzen and his colleagues also developed potatoes and tomatoes with a vaccine for hepatitis B and the E. coli bacterium.
For years, scientists struggled to believe that edible vaccines could be produced. The reason for this was that the proteins from which vaccines are made, called peptides, are usually destroyed in the digestive system before they are sufficient to be absorbed and enter the bloodstream. Injection vaccines, on the other hand, reach the bloodstream immediately.
Dr. Arentzen says he and his colleagues don't fully understand how the edible vaccines are preserved, but it turns out that the cells of vegetables and fruits provide good protection for the peptides inside them. "When I eat a tomato, for example, I chew it and break it into pieces. But I don't break down all her cells - the cell slowly breaks down and then the peptide is released. But the amount of peptides in the edible vaccine should be several hundred times greater than in the injected vaccine: about a milligram compared to about ten micrograms (millionths of a gram)."
The first evidence that it is possible to vaccinate humans with vaccines introduced into food was received in 1998, in a study that Dr. Arentzen did together with Dr. Carol Tackett from the University of Maryland in Baltimore. The researchers had the volunteers eat genetically modified potatoes, which contained a vaccine for the E. coli bacteria. The volunteers ate the potatoes in their natural form; It was not possible to cook, bake or fry them, for fear that the heat would destroy the vaccine. The researchers do not intend to use the potatoes outside of the experimental framework: potatoes simply grow relatively quickly, in about four months, which speeds up the experiment, in the case of a banana, on the other hand, from the moment the new gene is inserted into its genome until the fruit is formed, three years pass. "We think of tomatoes and bananas as storage fruits that could be a commercial product," says Dr. Arentzen.
In Israel, the bio-technology company "Terbiot Rahan" registered a patent for potatoes and tobacco plants that, using genetic engineering methods, have been inserted into them with vaccine components for farm animals. In experiments where the vaccines were allowed to live, and then infected with the disease agents, it was found that the vaccine did provide protection. "In the veterinary market, the best thing is to create a vaccine component that farm animals can receive as part of their food," says Dr. Eli Hayit, scientific director of the company. "A good example of this is the vaccination of fish. Today every fish is caught and stored. This is a serious problem, which an edible vaccine could solve."
{Appeared in Haaretz newspaper, 25/5/2000
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