Genetic sequencing of the SARS virus reveals a pathogen that began its life in an animal, then mutated before it picked up the power to infect people.
Health officials have a strong need for vaccines that are both economical and easily administered. Plants have long been seen as an attractive source for vaccines, since plants can be grown inexpensively on a large scale.
The easiest plant to genetically modify is tobacco. For the SARS study, Koprowski and his colleagues engineered low-nicotine plants to produce a so-called spike protein of the SARS virus. The protein is used to trigger an immune response in the human body.
Once the researchers showed that tobacco could produce the SARS virus spike protein, they applied the same technique to tomatoes. Mice that were fed genetically modified tomatoes developed antibodies to the virus that causes SARS.
However, the scientists did not report whether they injected the mice with the SARS virus.
"It does not show that the antibody offers any protection," said Michael Lai, a virologist at the University of Southern California in Los Angeles.
Don't expect to see "vaccine vegetables" anytime soon. Researchers say it would be impossible to standardize the amount of vaccine in a vegetable. In fact no vaccine produced in plants has ever been licensed for human use.
However, the scientists envision that the SARS vaccine could be ground into a powder, formed into capsules, and consumed as a dietary supplement.
Another team of scientists, meanwhile, is claiming a breakthrough in the battle against Ebola and Marburg, two related viruses that have struck central Africa several times in recent years.
Ebola and Marburg are hemorrhagic fevers, meaning they cause major internal and external bleeding. They kill 50 to 90 percent of their victims within a few days. There is no cure for either virus.
Scientists based the new vaccines on a virus called vesicular stomatitis virus (VSV). The virus was "rewired" to carry a gene that encoded a protein from either the Ebola or Marburg virus.
When monkeys were inoculated with the vaccines, the primates' immune systems mounted a response against either the Ebola or Marburg virus.
With their immune systems accordingly "primed," the monkeys were able to fend off authentic doses of Ebola or Marburg virus that they were later exposed to.
"This is the first vaccine system that has been shown to protect monkeys against both Ebola and Marburg viruses," said Tom Geisbert of the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland.
Geisbert, who was one of the lead researchers of the study, says he expects the vaccine to work in people because monkeys are even more sensitive to the viruses than humans are.
"The fact that we could completely protect monkeys against such a high-challenge dose given by a very lethal route is very encouraging," Geisbert said. "[It] bodes well for future use in humans."
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