Blood taken from four Vietnamese survivors of the bird flu virus protected mice from several strains of the virus, researchers have revealed.
Their finding may offer a new way to treat H5N1 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 recognise the H5N1 virus.
"We have shown that this technique can work to prevent and neutralise 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 per cent 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 recognise 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.