By Maggie Fox, Health and Science Editor
WASHINGTON, May 28 (Reuters) - Blood taken from four Vietnamese survivors of the H5N1 bird flu virus protected mice from several strains of the virus, researchers reported on Monday.
Their finding may offer a new way to treat bird flu infections in people and another potential weapon to stockpile ahead of a feared pandemic of avian influenza.
The researchers created human monoclonal antibodies -- immune system proteins -- trained to recognize the H5N1 virus.
"We have shown that this technique can work to prevent and neutralize infection by the H5N1 bird flu virus in mice," said Dr. Cameron Simmons, of the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam.
The approach is not new. Antibodies taken from human blood can treat or prevent a number of infections, including hepatitis, rabies and respiratory syncytial virus.
"The transfusion of human blood products from patients recovering from the 1918 'Spanish 'flu' was associated with a 50 percent reduction in influenza mortality during the pandemic," the researchers wrote in their study, published in the Public Library of Science journal PLoS Medicine.
Antibodies are immune system proteins that recognize and help orchestrate an immune attack on bacteria, viruses and parasites.
Monoclonal antibodies are specially engineered to attack a certain protein -- in this case, one found in H5N1.
Dr. Kanta Subbarao of the National Institute of Allergy and Infectious Diseases; Dr. Antonio Lanzavecchia of the Institute for Research in Biomedicine in Bellinzona, Switzerland; and Simmons and colleagues worked on the study.
It is freely available online at: here "The four adult blood donors in this study were diagnosed with highly pathogenic avian influenza H5N1 infection between January 2004 and February 2005 at the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam," the researchers wrote.
Lanzavecchia extracted antibody-producing white blood cells, called memory B cells, from the samples. He used a treatment he has developed to make them produce antibodies continuously.
Subbarao's lab screened these for antibodies that could neutralize H5N1. The researchers produced more of these antibodies and then tested mice infected with lethal doses of H5N1.
Most of the mice who got the new antibodies survived, while all untreated mice died, the researchers said.
The antibody treatment protected the mice as late as 72 hours after infection. This is important because antiviral drugs needs to be given quickly after infection -- best within 48 hours -- to be effective.
More tests would be needed but it would be useful to have another treatment alongside Tamiflu and other antiviral drugs in case of a pandemic.
The H5N1 avian influenza virus has killed 186 people out of 307 infected since 2003, according to the World Health Organization.
It mostly affects birds but if it acquires the ability to pass easily from one person to another, it could spark a pandemic that would kill millions.
Vaccines take months to formulate and antivirals are in short supply.