Popeye would be stunned to discover what scientists have in mind for spinach.
If researchers can turn a fanciful idea into reality, people could get vaccinated against any number of diseases by eating genetically engineered vegetables.
“Imagine, public-health clinics which have jars of vaccines with spinach,” said Hilary Koprowski, a prominent virologist who launched the plant-vaccine research at Thomas Jefferson University.
Researchers at Jefferson and several other medical centers are experimenting with vegetables and fruit as vehicles for delivering vaccines against diseases as varied as rabies and HIV, the virus that causes AIDS.
They say the approach could be particularly useful in Third World countries, potentially allowing for the immunization of millions of people at a cost cheaper than traditional vaccine shots.
So far, the idea of edible vaccines has been tested only in animals. But this month, researchers at the University of Maryland’s Center for Vaccine Development were to conduct the first tests on human subjects. They will see whether genetically altered potatoes will stimulate the immune system to produce antibodies that protect against what is known as traveler’s diarrhea.
Maurice Hilleman, a director of the Merck Institute and a leading vaccine researcher for 50 years, called the approach “futuristic.” He added: “It deserves support, and it deserves pursuit. But there are difficult problems that need to be resolved.”
Among the key questions are not only whether genetically altered vegetables can stimulate the human immune system but also how long the immune response would last and whether there would be any undesirable side effects.
If the experimental approach pans out, it could mean more affordable and more widely available vaccines around the world, experts say. Vaccinations also help prevent medical costs down the line.
The novel approach could overcome many logistical problems inherent in the health-care systems of poor countries. Medical workers to administer inoculations are often in short supply. So are syringes and needles. And many vaccines must be refrigerated or they lose their potency.
Roy Widdus, coordinator of the international Children’s Vaccine Initiative in Geneva, said finding simpler ways to deliver vaccines is an important long-term research goal. About 20 percent of the world’s children are not fully immunized by age 1 against diphtheria, tetanus, whooping cough, polio and measles.
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While edible vaccines are an appealing idea, Widdus said, they also would pose new challenges for distribution. For instance, he said, how would the edible vaccines be packaged? What kind of shelf life would they have? And what happens if someone eats too many vegetables?
Today, nearly all vaccines are delivered directly into the body with an injection. Typically, they are made of killed viruses, live but weakened viruses or genetically engineered viral proteins. Depending on the disease being targeted, some vaccines are derived from bacteria.
While vaccines don’t cause disease, they establish a small but passing infection. The infection triggers an immune response, marshaling antibodies and certain types of white blood cells to fight the virus. When a vaccinated person encounters that same virus later, the body “remembers” the initial infection and produces another immune response to prevent the virus from establishing itself.
The experimental vegetable-based vaccines are meant to do the same thing. But instead of being injected, the vaccine would be swallowed.
The 5-year-old program at Jefferson is supported by the Biotechnology Foundation Inc. in Philadelphia. The non-profit corporation receives money from the Commonwealth of Pennsylvania.
The Jefferson scientists are trying to develop such immunity-inducing vegetables by infecting spinach plants with viruses that normally grow in tobacco and alfalfa plants. These plant viruses are not harmful to the health of humans, according to the researchers.
The scientists have tinkered with the tobacco and alfalfa viruses, inserting into their genetic material certain proteins from viruses that can infect people, including the rabies virus and HIV.
When these plant viruses reproduce, they churn out millions of copies of the human viral proteins as well. When someone eats the spinach containing these genetically engineered viruses, scientists hope the proteins will elicit an immune response.
Although a goal is to deliver vaccines via common vegetables, the Jefferson scientists are, as a first step, testing the effectiveness of the purified plant virus to see if it stimulates immunity in animals.
Mice injected with genetically engineered fragments of rabies and HIV viruses produced antibodies to the diseases.