SARS Vaccine Grown
In GM Tomatoes
The Globe and Mail
TORONTO (CP) -- Hold the pickles, hold the lettuce, but if you want immune protection against SARS, don't hold the tomato.
American researchers have managed to grow a SARS vaccine in genetically engineered tomatoes, reporting that mice fed the tomatoes developed antibodies to the coronavirus that killed nearly 800 people in 2003.
Their findings, published Tuesday in the medical journal Proceedings of the National Academy of Sciences, drew interest from others in the scientific community. But experts were quick to caution that vaccine-laden produce isn't heading to your dinner plate anytime soon.
"There's still a long ways to go between knowing whether this is a promising lead and conducting further research or whether other forms of technology would be more likely to be useful," said Dr. Bob Brunham, director of the British Columbia Centre for Disease Control.
Dr. Brunham noted the scientists, from Thomas Jefferson University's Biotechnology Foundation Laboratories, reported only that the mice fed the vaccine-filled tomatoes developed antibodies.
They did not report on whether they "challenged" the mice with the virus to see if those antibodies were the type needed to actually protect against the disease. The simple presence of antibodies can't be assumed to be protective.
"They didn't show ... that their antibodies would neutralize a virus in tissue culture," said Dr. Brunham, who co-chairs the SARS accelerated vaccine initiative or SAVI, a project established in Canada following Toronto's deadly experience with the since-disappeared disease.
The regulatory hurdles such a vaccine would face would be sizeable, given that no vaccine produced in plants has ever been licensed for human use, said Frank Plummer, scientific director of Canada's National Microbiology Laboratory, where researchers have also been working on a SARS vaccine.
"I think there are some practical hurdles for using that kind of thing," Mr. Plummer said. "If they can be overcome, it might be a very cheap way of producing proteins for vaccines. But it hasn't made it there yet."
The notion of growing vaccine in plants " rather than in animal cells or eggs, as is currently the industry norm " dates back to 1992. Biologist Charles Arntzen proposed the idea of genetically modifying bananas to serve as cheap, edible vaccines to protect against a range of infectious diseases.
Others have taken up the notion, including renowned virologist Hilary Koprowski, lead author of this work. Mr. Koprowski produced the first oral polio vaccine (though another, designed by Dr. Albert Sabin, is the one the world uses) and developed the rabies vaccine.
In this work, Mr. Koprowski and his team first genetically engineered a low-nicotine tobacco plant to produce what's called the spike protein of the SARS coronavirus. The spike protein is the key protein on the SARS virus that triggers an immune response.
Tobacco is the easiest plant to genetically modify, co-author Maxim Golovkin explained in an interview from Philadelphia. Once the team was confident they could get tobacco to produce or "express" the SARS protein, they tried the same technique in other vegetables.
"When the best works, you know what to apply to those plants which are recalcitrant and much harder to produce transgenic [models], like tomatoes," Mr. Golovkin said.
While Mr. Arntzen initially thought edible plants could be produced that would immunize simply through consumption, that is no longer considered a viable option.
There would be no way to guarantee that each fruit or vegetable contained enough antigen to provoke immunity; nor would there be any way of ensuring the person ate the whole dose. The picture of an 18-month-old spitting out half his peas comes readily to mind.
"Forget about this," Mr. Golovkin said flatly when asked if a melange of vegetables might one day immunize kids rather than a series of jabs. Government regulators would never allow a vaccine to be licensed without guarantees the dose was standardized, he said.
"How would you normalize the amount of any vaccine or any pharmaceutical drug delivered from eating something?" he noted. "None of the countries of the world would allow you to deliver a drug when it's not normalized."
Instead, Mr. Koprowski's team is freeze-drying produce containing viral antigen, removing the water and grinding what's left into a powder that can be formed into capsules or tablets.
They envisage vaccines that can be taken like a dietary supplement, cheaply produced and stored for long periods of time without suffering degradation.
"It's as easy as putting the seed in the soil and growing the plant up to four or five weeks when it's most potent," Mr. Golovkin said.
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