Antibodies from people who recovered from SARS — a deadly respiratory disease caused by a coronavirus that emerged nearly 20 years ago — may be critical to fighting COVID-19, according to a study in the journal Nature.
The peer-reviewed paper reveals how an antibody discovered in a person infected by the severe acute respiratory syndrome virus in 2003 acted as a potent blocker against SARS-CoV-2, the closely related coronavirus that causes COVID-19.
A team of international researchers, including scientists from San Francisco’s Vir Biotechnology and the University of Washington, conducted the study, which was published in May.
Their finding is part of a ballooning area of inquiry by researchers, universities and drug companies around the world, and in the Bay Area, to develop antibody treatments for COVID-19, and to prevent people from getting sick in the first place.
Vir Biotechnology, whose stock shot up after the paper was published, plans to start clinical trials this summer on two treatments related to the SARS antibody discovery.
The immune system forms antibodies, which are y-shaped proteins, to disable specific pathogens it encounters. Vaccines spur the immune system into producing these antibodies without causing a person to become sick. Antibody therapies for viruses are mostly made by finding antibodies in people who were previously infected. These antibodies are then generally used to treat disease early in infection by preventing more cells from becoming infected or destroying those that already are.
In February, the team of scientists from Vir Biotechnology and the University of Washington began to look for SARS coronavirus antibodies that could work against the new coronavirus because antibodies to that virus weren’t readily available for study. Since the two viruses are closely related — akin to viral cousins — it made sense to search for antibodies that would work for both, said David Veesler, a senior author on the paper and a virologist at the University of Washington who had been studying SARS.
Still, it was a long shot. So scientists were surprised by the strength of the antibody they discovered, which blocked not only the SARS and COVID-19 coronaviruses in the lab, but a third coronavirus found in bats.
“Looking for effective antibodies is like looking for a needle in a haystack,” Veesler said. “So this was very, very exciting because this antibody has the potential to have a high public health impact.”
Viruses are snippets of genetic code wrapped in protein. The genetic material is an instruction manual for manufacturing more viruses. But a virus must first infect and then hijack the protein-making assembly lines of a living cell — be it in a tomato plant, a bat or a human being — before it can start building more viruses.
“Wherever you find life, you find viruses,” Veesler said.
As with any parasite, gaining entry into a host is the most crucial step. The new coronavirus does this through the spiky proteins on its surface that give the virus its eponymous crown-like appearance. The spike protein acts like a key that fits snugly into a specific protein on a human cell and lets the virus in.
Antibodies are just one component of a person’s immune response. But some antibodies that glom onto the spike protein appear to thwart this cellular invasion.
These so-called virus “neutralizing” antibodies were what Veesler and his team went looking for in old blood samples from the person infected with the SARS coronavirus. Following infection, the immune system stores the blueprints for various antibodies in memory B cells, the body’s equivalent of a storage locker full of weapons it has previously forged to help fight pathogens.
In this locker, Veesler’s team unearthed the antibody S309. The lab results were stark: Whenever S309 was added, SARS-CoV-2 couldn’t enter cells and replicate. It also appeared to effectively obstruct the SARS coronavirus and the related bat coronavirus from entering cells. But how?
The group of scientists used molecular imaging technology to visualize what was happening at the atomic level. What they discovered was both surprising and helped explain why this particular antibody appeared so effective.
Not only did it bind to the spike protein, but also to carbohydrates on the spike that the virus uses to try to “trick” the immune system into thinking it’s just a normal human molecule, Veesler said.
If the virus is the wolf, then the carbohydrates are the sheep’s clothing.
“But this antibody saw right through that,” Veesler said.
The team is still researching exactly how that interaction blocks the virus from entering cells. Perhaps even more intriguing, however, is that the antibody binds to a specific area of the spike protein that is almost identical among the SARS virus, SARS-CoV-2, and related coronaviruses.
“To hit a spot like that was fairly fortuitous,” said Anthony Fehr, a virologist and coronavirus expert at the University of Kansas, who is researching other therapies for the new virus. “This probably won’t be the last time that a SARS-like virus is going to emerge in the human population. So having something like this could be a really useful tool.”
Unlike drugs made of chemical compounds, antibody therapeutics are quicker to develop, test and get approved, said National Institutes of Health Director Dr. Francis Collins in a recent blog post. They also can be used to target vaccine development.
“Because of these and other factors, many experts think antibody-based therapies may offer one of the best near-term options for developing safe, effective treatments for COVID-19,” he said.
The gold standard for viruses, however, is still a vaccine. Although antibodies are used to lessen the severity of symptoms after exposure to viruses like rabies and hepatitis B, they have generated disappointing results with other diseases. In addition, any prophylactic antibody therapy for people in high-risk settings like nursing homes would have to be taken regularly, an expensive and less efficient method than using a vaccine to prompt a person’s immune system into building its own antibodies.
“It is not a substitute for a vaccine,” Fehr said. “Antibody therapy is more transient in nature. It is not a permanent fix.”
Cynthia Dizikes is a San Francisco Chronicle staff writer. Email: cdizikes@sfchronicle.com Twitter: @CDizikes
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