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Immune Protein Might Fight SARS

'Good fortune' leads to promising therapy against killer virus

MONDAY, Feb. 2, 2004 (HealthDayNews) -- A protein pulled from a vast "library" of immune system chemicals blocks infection with the deadly SARS virus.

The protein, called an antibody, prevented the virus from entering cells in a lab dish so well that researchers are now testing the molecule in small animals. If those experiments are effective, they say, the antibody could be tried in people as a possible emergency treatment for or vaccine against SARS, which killed 774 people last year and sickened nearly 8,100, according to the World Health Organization.

So far this year, at least four people have fallen ill with SARS, a highly contagious respiratory infection caused by a new form of coronavirus. So far, all the patients are in China, though last year's outbreak spread to dozens of countries, including the United States and Canada.

The spread of SARS in China has been tentatively linked to civets, a species of wild cat prized as a culinary delicacy. Last month, U.S. health officials banned the importation of civets, both alive and dead, into this country over concerns they might spread the disease. The embargo doesn't apply to trophy animals that have been stuffed for display or to cats that have been approved for use by educators or scientists.

The new study appears in this week's issue of the Proceedings of the National Academy of Sciences. Robert Lamb, a molecular biologist at Northwestern University, says the antibody isn't the "cure for tomorrow" and will take time to develop. However, it does validate the method the researchers used to find the molecule: making proteins in the laboratory instead of isolating them from infected patients.

"It's an approach showing that neutralizing antibodies to this virus can be made," says Lamb, who edited the journal article.

In the study, scientists at the Dana-Farber Center for Cancer Immunology and AIDS in Boston culled through a catalogue of some 27 billion antibodies to find eight that showed promise in fighting SARS. Specifically, the proteins targeted a protein in the SARS virus called S1, a key feature of the structure that helps it penetrate host cells.

The researchers shipped the eight antibodies off to the National Center for Infectious Diseases, a division of the U.S. Centers for Disease Control and Prevention. There, scientists found one of the proteins, called 80R, prevented the virus from entering human cells in a dish.

"You can get complete inhibition" of infection, says study co-author Dr. Wayne Marasco, an immune system expert at Dana-Farber. "The data looked quite good."

Marasco oversees the antibody library, and says the success of the SARS protein owes a certain amount to good fortune. "We pulled out eight and only one of them worked," he says. "As it turns out, that portion of the virus is well exposed. That does not have to be the case."

Antibody therapy already plays a role in treating severe lung disease, including cytomegalovirus and respiratory syncytial virus (RSV), the leading causes of lower respiratory tract infections in young children.

SARS patients do mount an antibody response to the virus, but it's typically too late to prevent lung damage, Marasco says. Ideally, doctors could administer the SARS antibody to infected people early in the course of their illness to prevent airway destruction. Similarly, the protein could be used as a vaccine in people exposed to "super spreaders," people who pass the disease along to many others.

Marasco's group has identified roughly a dozen potentially useful antibodies in their collection, including proteins that might help fight HIV, the virus that causes AIDS, as well as several forms of cancer. But the SARS protein is the most advanced in terms of its clinical progress, he says. "This is perhaps the one that we think we'd like to develop," he says.

More information

For more on SARS, visit the World Health Organization or the U.S. Centers for Disease Control and Prevention.

SOURCES: Wayne Marasco, M.D., Ph.D., associate professor, Dana-Farber Cancer Institute, Harvard Medical School, Boston; Robert Lamb, Ph.D., Sc.D., professor, biochemistry, molecular biology, and cell biology, Northwestern University, Evanston, Ill.; Feb. 2-6, 2004, Proceedings of the National Academy of Sciences
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