In the continuing hunt for antibodies that could fight the novel coronavirus SARS-CoV-2, researchers have mostly looked at people who have already contracted Covid-19. There have been at least two exceptions, both of which have looked at antibodies developed by survivors of another outbreak, SARS, 17 years ago.
One antibody, called S309, taken from a SARS survivor from 2003, has been shown in the lab to neutralise SARS-CoV-2. The results were reported in Nature this week.
The other antibody, called CR3022, was first isolated in 2006, again from a SARS survivor of the early 2000s. CR3022 may hold clues to the vulnerability of SARS-CoV-2, researchers reported in Science last month.
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S309: The newer of the two studies has reported the more definite findings, although more research is still required. An international team of scientists isolated antibodies from a SARS survivor’s “memory B cells” Memory B cells form after an infectious illness, and usually remember the pathogen (or a similar one) that it had fought it back earlier. If a new infection happens, these cells launch an antibody counterattack again.
From the SARS survivor’s memory B cells, the scientists identified a number of monoclonal antibodies. Several of these antibodies target a protein structure on coronaviruses (SARS and Covid-19 are caused by different but related coronaviruses). This protein structure is located in the spikes in the crown — the “corona” of the virus. The spike is a crucial tool in infection; this is what attaches to human cells.
Among the antibodies, S309 was found to be particularly potent at targeting and disabling the spike protein. It was able to neutralise SARS CoV-2 by engaging with a section of the spike protein near the site where it attaches to the host cell, the researchers said.
Miles to go: It is important to note that the action of S309 has only been demonstrated in the lab. “We still need to show that this antibody is protective in living systems, which has not yet been done,” biochemist David Veesler, one of the senior authors of the study, said in a statement released by the University of Washington School of Medicine.
The scientists noted, however, that they hope these initial results will pave the way for using S309, alone or in a mixture, as a preventive measure for people at high-risk of exposure to SARS-CoV-2 or as post-exposure therapy. The antibody is now on a fast-track development and testing path at the company Vir Biotechnology in the next step toward possible clinical trials, the University said.
CR3022: The action of this antibody from a SARS survivor was described by Chinese scientists earlier this year, indicating that it cross-reacts against SARS-CoV-2, too. Citing this report, the Scripps Institute in the US said in April that its researchers have now done structural mapping to determine how the antibody binds to SARS-CoV-2.
The antibody’s binding site was found highly similar between the two coronaviruses. However, the antibody binds much less tightly to SARS-CoV-2 than it does to the SARS virus. And CR0322 cannot neutralise SARS-CoV-2 in lab as it does SARS-CoV.
The takeaway is that the binding site, as identified, is a site of vulnerability for SARS-CoV-2. Other antibodies binding it more tightly would plausibly succeed in neutralising the virus, the Scripps Institute said.
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