Plant Vaccine Targets SARS

Cheap and easy to give, the vaccine could prevent another outbreak

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By
HealthDay Reporter

MONDAY, June 13, 2005 (HealthDay News) -- Tomato and tobacco plants can be engineered to make a vaccine against the virus that causes SARS, a new study claims.

Severe acute respiratory syndrome (SARS) was first reported in Asia in February 2003. Over the next few months, the illness spread to more than two dozen countries in North America, South America, Europe and Asia before the global outbreak was contained.

According to the World Health Organization, 8,098 people worldwide became sick with SARS during the outbreak, and 774 died. Since that time, there has not been another SARS outbreak.

However, that first outbreak increased demand for a vaccine that is economical and easily administered.

"I thought there was a need to prepare quickly a vaccine that is inexpensive and safe," said lead researcher Dr. Hilary Koprowski, director of the Center for Neurovirology at Thomas Jefferson University.

The report appears in this week's online issue of the Proceedings of the National Academy of Sciences.

Developing vaccines this way has been shown to be safe, and is potentially inexpensive. "Plants have an advantage over all other methods of vaccine production because of the fact that the production is much safer and is much less expensive, and is much easier to administer because it is orally administered," he said.

Moreover, vaccines can be produced by other plants, as well. "To my great surprise, almost any plant will support growth of material for production of viruses and production of vaccines," Koprowski said.

Koprowski noted that using plants to develop vaccines has been tested in many other diseases. But, so far, there hasn't been support from the pharmaceutical industry to use this method for developing vaccines, he added. Trials using plant-derived vaccines for hepatitis B and rabies have already been done.

To test whether a successful SARS vaccine could be produced by plants, Koprowski's team engineered tomato and low-nicotine tobacco plants to produce a fragment of the SARS-CoV protein. Several of the engineered plants successfully expressed high levels of the protein. These levels could be increased through selective plant breeding, Koprowski noted.

To see if the vaccine was effective, the research team fed mice tomatoes that contained the protein. The mice did, in fact, develop antibodies for the SARS virus.

They also treated mice with a tobacco-derived protein. In this case, the mice were injected with the protein or received it through a feeding tube. The injected mice produced SARS-CoV antibodies. However, direct delivery of the protein to the stomach didn't produce antibodies. Koprowski's team speculates that swallowing the tobacco vaccine directly to the stomach did not provide enough exposure to produce antibodies.

Growing plants that produce vaccines is the wave of the future. "Making products in plants is cheap, easy to distribute, easy to administer," Koprowski said. "Therefore, the future is with plants."

One expert thinks Koprowski is on the right track. "I'm a fan of plant-derived vaccines," said Robert Garry, a professor of microbiology at Tulane University. "It's going to be important for a lot of viruses and bacteria that need vaccines."

However, Garry is cautious about the findings. "There is a bit of a step in producing an immune response," he said. "There is a difference between getting an antibody response, as these investigators were able to measure, and getting a protective response, but it's a good first step."

Although there hasn't been a new SARS outbreak, that doesn't mean there won't be one, Garry noted. "The virus is still present in animal reservoirs. We are not going to be able to eradicate the virus in the way that has been done for smallpox and measles," he said.

Garry thinks that spending money to stockpile a SARS vaccine is money well spent, given the cost of the last SARS outbreak. "No matter what you spend on a vaccine, you probably will be saving money just on the chance that it might come again," he said.

"SARS is out there as a threat," Garry said. "Whether there's another outbreak is anybody's guess."

According to another report, a prototype drug created by researchers at the University of Illinois at Chicago shows promise in slowing production of the SARS virus.

Based on their early work, the researchers have received an $8 million grant from the National Institute of Allergy and Infectious Diseases to develop protease inhibitors to treat SARS. Protease inhibitors are drugs that disrupt enzymes that digest proteins and have been successful in treating HIV/AIDS.

More information

The CDC can tell you more about SARS.

SOURCES: Hilary Koprowski, M.D., director, Center for Neurovirology, Thomas Jefferson University, Philadelphia; Robert Garry, Ph.D., professor, microbiology, Tulane University, New Orleans; June 13-17, 2005, Proceedings of the National Academy of Sciences online; news release, University of Illinois at Chicago

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