A New Line of Defense Against Bird Flu
un article du ScienceNOW Daily News
By Martin Enserink
ScienceNOW Daily News
29 May 2007
Physicians may someday get an extra tool to deal with a global outbreak of bird flu in humans. In laboratory experiments, antibodies from patients who successfully battled avian influenza protected mice from the virus, researchers say in a paper published in this month's issue of Public Library of Science (PloS) Medicine. Although less practical than antiviral drugs, antibodies could provide crucial help, says Albert Osterhaus, a virologist at Erasmus Medical Center in Rotterdam, the Netherlands.
Industrially produced antibodies are already used against a variety of diseases, including rabies and hepatitis A and B. But they may be useful in influenza as well. During the 1918 influenza pandemic, some doctors experimentally treated patients by transfusing them with blood products from recovered patients; a review study published last year suggested that such treatments may have cut mortality in half.
For the new study, researchers at the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, took blood samples from four patients as they recovered from infection with H5N1--the virus that causes avian influenza--in 2004 and 2005. Scientists at the Institute for Research in Biomedicine (IRB) in Bellinzona, Switzerland, then isolated the so-called memory B cells, which produce antibodies; using a special trick that employs the Epstein-Barr virus, they "immortalized" these cells to make them crank out antibodies indefinitely. Finally, researchers at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, tested four of these antibodies in a mouse strain highly susceptible to H5N1 infection.
All four antibodies saved the lives of mice infected with an H5N1 strain isolated in Vietnam in 2004. The antibodies even worked when given 3 days after infection. Three of the four also protected against a strain found in 2005 in Indonesia that is a genetically distinct form of the virus. Further studies showed that the antibodies limited viral replication in the lungs as well as lung damage and slowed down the virus's spread out of the lungs.
That means the antibodies could form an additional line of defense--besides drugs like Tamiflu, which carry the risk of resistance--during an influenza pandemic, says IRB Director Antonio Lanzavecchia. Because flu viruses change constantly, it's uncertain whether any of these four antibodies would still work if a new H5N1 strain unleashes a pandemic; it may be necessary to start anew with antibodies from future patients. But the study shows that this can be done quickly, Lanzavecchia says.
"It's a beautiful paper," says Osterhaus. The broad protection seen with the three antibodies and the fact that the antibodies worked even 3 days after infection are both "hopeful findings," he says. But a key question will be how fast antibody production can be scaled up, he adds, and the fact that the antibodies need to be injected--versus given as pills--is a drawback.