Scientists have for the first time identified human antibodies that can neutralise different strains of the virus responsible for the outbreaks of severe acute respiratory syndrome (SARS).
Working with collaborators from the United States Army Medical Research Institute of Infectious Diseases (USAMRIID), scientists at the National Institutes of Health conducted in vitro experiments on a mouse model to test the neutralizing activity of the antibodies.
The researchers say that the new findings are important because animal strains of the virus may be capable of triggering a future human outbreak.
"This study is important because the viral strain that caused the outbreak in people in 2002 probably no longer exists in nature," explains Dr. Kanta Subbarao of the National Institute of Allergy and Infectious Diseases (NIAID), whose laboratory verified the efficacy of the anti-SARS antibodies in animal models.
"What we need to prove for any vaccine, therapeutic, antibody, or drug is that it is effective not only against the strain of SARS virus isolated from people, but also against a variety of animal strains, because animals will be a likely source for re-emergence of the SARS virus," added the alumna of Madras University.
The researchers identified two human antibodies that bind to a region on the SARS virus' spike glycoprotein that is called the receptor binding domain (RBD). One of the antibodies, called S230.15, was found in the blood of a patient who had been infected with SARS and later recovered, while the second antibody, m396, was taken from a library of human antibodies the researchers developed from the blood of 10 healthy volunteers.
When tested in cells in the laboratory, both antibodies potently neutralized samples of the virus from the two SARS outbreaks that occurred in 2002-2003 and 2003-2004.
The antibodies also neutralized samples of the virus taken from wild civets, a cat-like mammal in which strains of the virus were found during the outbreaks, although with lower potency.
The researchers say that the antibodies have also been found effective in protecting against human and animal SARS viruses in experiments on mice.
"This antibody neutralizes all strains of SARS we tested and is likely to neutralize all strains of the virus with known sequences. There are no other reports for such antibodies available," said lead researcher Dr. Dimiter S. Dimitrov.
The discovery of two effective antibodies has the advantage that a newly emergent variation of the SARS coronavirus might be insensitive to neutralization with one, but still susceptible to the other.
"Our results demonstrate novel potential antibody-based therapeutics against SARS that could be used alone or in combination...these human antibodies could be also used for diagnosis and as research reagents in the development of vaccines and inhibitors," summarized the authors.
The study has been published in the online edition of the Proceedings of the National Academy of Sciences.