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Antibody neutralizes SARS and COVID-19 coronaviruses

While it hasn't yet been tested in humans, its ability to target multiple coronaviruses shows early promise.

Jeff Lagasse, Associate Editor

An antibody first identified in a blood sample from a patient who recovered from Severe Acute Respiratory Syndrome, or SARS, in 2003 inhibits related coronaviruses, including the cause of COVID-19, according to a new report.

The antibody, called S309, is now on a fast-track development and testing path at Vir Biotechnology in the next step towards possible clinical trials. Laboratory research findings on the S309 antibody are reported in the May 18 edition of Nature.

While biochemists still need to show that the antibody is protective in living systems, the antibody could become part of the coronavirus pandemic response if it's shown to work against COVID-19 in people – which would be a major step, considering there are still no approved licensed therapeutics proven to fight the virus.

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While the University of Washington School of Medicine isn't the only lab seeking neutralizing antibodies to treat the coronavirus, this antibody differs in that its search did not take place in people who had COVID-19, but in someone who had been infected 17 years ago during a SARS epidemic, which allowed the team to move more quickly than other groups.

The scientists identified several monoclonal antibodies of interest from memory B cells of the SARS survivor. Memory B cells form following an infectious illness. Their lineage can last for life in some cases. They usually remember a pathogen, or one similar to it, that the body has ousted in the past, and launch an antibody defense against a reinfection.

Several of the antibodies from the SARS survivor's memory B cells are directed at a protein structure on coronaviruses. This structure is critical to the coronaviruses' ability to recognize a receptor on a cell, fuse to it and inject their genetic material into the cell. This infectivity machinery is located in the spikes that crown the coronavirus.

The S309 antibody is particularly potent at targeting and disabling the spike protein that promotes the coronavirus entry into cells. It was able to neutralize SARS CoV-2 by engaging with a section of the spike protein near the attachment site to the host cell.

Through their cryo-electron microscopy studies and binding assays, the researchers learned that the S309 antibody recognizes a binding site on the coronavirus that is conserved across many sarbecoviruses, not just the SARS and COVID-19 viruses. That is probably why this antibody, instead of being single-minded, is able to act against related coronaviruses.

Combining the S309 antibody with other, though weaker, antibodies identified in the recovered SARS patient enhanced the neutralization of the COVID-19 coronavirus.

This multiple antibody cocktail approach might help limit the coronavirus' ability to form mutants capable of escaping a single-ingredient antibody treatment, according to the researchers.

The scientists said they hope these initial results pave the way for using the S309 antibody, alone or in a mixture, as a preventive measure for people at a high risk of exposure to the COVID-19 coronavirus or as post-exposure therapy to limit or treat severe illness.


The antibody therapy being tested is one of a handful of potential treatments being investigated for COVID-19. A randomized trial of a triple combination therapy with interferon beta-1b, lopinavir-ritonavir and ribavirin is being tested in Hong Kong, and when started within seven days of showing COVID-19 symptoms, is safe and more effective at reducing the duration of viral shedding than lopinavir-ritonavir alone in patients with mild to moderate illness, according to early results.

Secondary outcomes – planned outcome measures that are not as important as the primary outcome measure, but are still of interest in evaluating the effect of an intervention – suggest that clinical improvement and length of stay may be significantly shorter in people treated with the triple combination fewer than seven days after showing symptoms, compared to lopinavir-ritonavir alone.

Twitter: @JELagasse

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