Scientists have identified an antibody from the blood sample of a person who recovered from severe acute respiratory syndrome (SARS) which appears to neutralise the virus that causes COVID-19, SARS-CoV-2. This individual had the infection 17 years ago in the SARS outbreak of 2002–2004 and eventually recovered from it. Researchers from the University of Washington School of Medicine (UW Medicine) have been studying SARS-CoV antibodies from this individual – the SARS infection results from a virus that is closely related to SARS-CoV-2, but there are no proven treatments for COVID-19 as yet. The antibody, or a combination of different antibodies, could then serve to treat newly-infected cases of COVID-19 or as a prophylactic in people at high risk of infection.

Looking for antibodies in someone who had an infection with SARS-CoV rather than SARS-CoV-2 is what “allowed us to move so fast compared to other groups,” said David Veesler, an Assistant professor of biochemistry at UW Medicine.Apart from neutralising SARS-CoV and SARS-CoV-2, the antibody may also neutralise other coronaviruses in the same subgenus.

The researchers at UW Medicine claimed that “passive administration of monoclonal antibodies (mAbs) could have a major impact on controlling the SARS-CoV-2 pandemic by providing immediate protection, and could be ready for clinical trials in 5–6 months compared to the traditional timeline of 10–12 months.”

The researchers previously identified several mAbs for SARS-CoV that originated from “memory B cells” in the blood of the same individual. Memory B cells are immune cells that can “remember” a particular infection and will launch a rapid antibody defense when the body encounters the pathogen again. Of the candidate antibodies that were screened from the blood sample, one named S309 was found to be highly effective at inactivating both SARS-CoV and SARS-CoV-2.

The researchers then used cryo-electron microscopy, an imaging technique, to investigate the structure of S309 and the mechanism by which it inactivates SARS-CoV-2. They discovered that S309 binds to a site near the apex of the spikes that the virus uses to invade human cells; the antibody binding site (epitope) is close to the part of the spike that latches onto a receptor called ACE2, which is present in particularly high concentrations on the outer membranes of cells in the lungs, blood vessels, and gut.

The epitope to which S309 binds similarly exists on the spikes of several closely related coronaviruses. This suggests that a “crucial, conserved” part of the viruses has changed little in their evolution. It also reduces the likelihood that SARS-CoV-2 will evolve much differently.

The researchers additionally report that variants of S309 that are more stable and effective have already entered an “accelerated development path.” Clinical trials will test whether the S309 antibody is safe and neutralises the virus in people – researchers may combine S309 with other antibodies to make a more effective treatment and further disable the ability of SARS-CoV-2 to evolve an escape mechanism.