In DepthCOVID-19

The race is on for antibodies that stop the new coronavirus

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Science  08 May 2020:
Vol. 368, Issue 6491, pp. 564-565
DOI: 10.1126/science.368.6491.564

Science's COVID-19 coverage is supported by the Pulitzer Center.

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An antibody (orange) bound to the surface spike protein of SARS-CoV-2 can block infection.


One of the first people to be diagnosed with COVID-19 in the United States hopes a legacy of her nightmare—the antibodies it left in her blood—will lead to a drug that can help others infected with the novel coronavirus that has now killed more than 250,000 people worldwide.

Early this year, the woman had just learned of the outbreak in Wuhan, China, when she flew to Beijing to celebrate the Lunar New Year with her elderly parents and extended family. A brother from Wuhan joined the gathering on 23 January, catching one of the last flights out before the city went into a lockdown. Days later, her father developed a fever, but the family wasn't concerned. “My dad always has some fever in the winter,” says the woman, a researcher who asked to be called Dr. X to protect her privacy. On 28 January, her brother also developed a fever.

The next day, on her scheduled flight home, a nervous Dr. X wore a mask, brought disinfectant wipes and cleaned everything she touched, and didn't accept any food or drinks from flight attendants. “I treated myself as a potential infectious source.”

Her husband picked her up at the airport, wearing a mask. With the car windows rolled down, they drove to an emergency room to request a coronavirus test. “I didn't have a fever, so they didn't really take me seriously,” she says. But coincidentally, her brother texted as she waited to be seen: He had COVID-19. So she received a test. Days later, after she quarantined herself, developed mild COVID-19 symptoms, and then rebounded, the result came back positive.

By then, her brother and father had both been hospitalized. The brother recovered after 12 days, but her father, a retired scientist in his 80s, went from a ventilator to extracorporeal membrane oxygenation, an artificial lung of sorts. The novel coronavirus, SARS-CoV-2, ultimately infected all seven family members who had gathered for the New Year celebration.

Dr. X could not help her sick family members, but her eagerness to do something grew. She knew that in China, plasma from recovered people, which contains antibodies to the virus, was showing promise as a treatment. Her doctor told her about a project, a collaboration between Vanderbilt University and AstraZeneca, to develop something safer and more powerful. It aims to go beyond the mishmash of antibodies in convalescent plasma and pull out the equivalent of a guided missile: an antibody that “neutralizes” the infectivity of SARS-CoV-2 by binding to the so-called spike protein that enables it to enter human cells. Once one or several neutralizing antibodies have been identified, antibody-producing B cells can be engineered to make them in quantity. These so-called monoclonal antibodies could treat or even prevent COVID-19.

The Vanderbilt-AstraZeneca team is far from the only group trying to identify or engineer monoclonals against SARS-CoV-2. Unlike the many repurposed drugs now being tested in COVID-19 patients, including the modestly effective remdesivir, the immune proteins specifically target this virus. Whereas some groups hope to sieve a neutralizing antibody (a “neut”) from the blood of a survivor like Dr. X, others are trying to produce neuts in mice by injecting them with the spike protein. Still others aim to reengineer an existing antibody or even create one directly from DNA sequences.

Many researchers are optimistic that antibodies will, relatively quickly, prove their worth as a preventive or remedy that buys the world time until a vaccine arrives—if it does. “We've got at least 50—and probably more we don't know about—companies and academic labs that are all racing horses,” says immunologist Erica Ollmann Saphire of the La Jolla Institute for Immunology, who leads an effort to coordinate and evaluate candidate monoclonals. Regeneron Pharmaceuticals, which developed a cocktail of three monoclonal antibodies that worked against the Ebola virus—a notoriously difficult disease to treat—may be out of the gates first with a candidate monoclonal drug entering clinical trials as soon as next month.

Saphire says many questions remain. “We need a sense of the landscape: What are the most effective antibodies against this virus? If we need a cocktail of two, what is the most effective combination?” she asks. “And you might want a very different kind of antibody to prevent infection versus treating an established one.”

John Mascola, an immunologist at the U.S. National Institute of Allergy and Infectious Diseases (NIAID), adds that some antibodies may have nonneutralizing, immune-boosting properties. “The field doesn't know very much about protective immunity to SARS-CoV-2,” Mascola says. “So there's a little bit of scientific guesswork here.”

On a practical level, monoclonals are relatively difficult to make and administer; they have to be given by intravenous drip or injected, and they have traditionally been niche medicines available mainly in wealthy countries. “Monoclonals may well have a very important role,” says Jeremy Farrar, head of the Wellcome Trust charity and an infectious disease specialist. “The big questions will be the capacity to manufacture at scale, distribute, and the cost.”

On 7 March, Dr. X visited the Vanderbilt lab led by James Crowe to donate blood. “I couldn't really help my dad,” the woman says. “It was too late. So I want to make sure that fewer people have to go through what my family has gone through.”

Her father died 9 days later.

From Ebola to COVID-19

Although monoclonal antibodies to treat cancer and autoimmune diseases are a booming business, few for infectious diseases have come to market so far. Regeneron's monoclonal cocktail for Ebola offers an example of their power. It proved its worth during an outbreak in the Democratic Republic of the Congo (DRC) last year and could be approved soon by the U.S. Food and Drug Administration. And a single monoclonal developed by an NIAID team that included Mascola thwarted Ebolavirus in the same DRC study. No other Ebola treatments—including drugs and convalescent plasma—had worked.

Treating millions of people worldwide with a monoclonal isn't far-fetched, Crowe says. “In the past, fully human antibodies were difficult to isolate and expensive to produce,” he notes. But it's getting easier and cheaper. “In the next 5 years, antibodies will become the principal tool used as a medical countermeasure in the event of an epidemic,” he predicts.

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The receptor-binding domain (top) at the tip of SARS-CoV-2's spike protein can be blocked by antibodies targeting several different areas (colors).


It generally takes weeks before an infected person's B cells begin to pump out neuts. Because of the lag, Crowe's team—one of four funded by the Pentagon's Defense Advanced Research Projects Agency (DARPA) to discover monoclonals for emerging infectious threats—sought out early U.S. COVID-19 patients, including Dr. X. The team isolated antibody-producing B cells from the volunteers and used the spike protein, linked to a magnetic bead, as bait for the tiny percentage that produce neuts against SARS-CoV-2.

When they initially bled Dr. X, some 6 weeks after she became infected, those special B cells were only faintly detectable. En route to the airport on a Sunday morning to fly home, Dr. X stopped in the lab for yet another bleed, and they finally struck gold.

A second DARPA-funded group, Canada's AbCellera Biologics, uses a version of spike that Mascola and co-workers engineered as neut bait. To isolate single B cells, copies are placed in 200,000 fluid-filled chambers of a device the size of a credit card. From blood of an early U.S. COVID-19 case in Seattle who had severe disease, AbCellera found 500 candidate antibodies against spike. It whittled them down to 24 leads, selecting those that retain their shape when mass produced and stick longest to the viral protein. (Antibodies bounce on and off their targets.)

Regeneron has similarly bled recovered COVID-19 patients, but it is also injecting spike into mice equipped with human genes for antibody production. From a pool of human- and mouse-derived antibodies, the company plans to select two that neutralize a broad range of SARS-CoV-2 variants. Regeneron is aiming for a pair of antibodies that bind to nonoverlapping sites on spike, Christos Kyratsous, vice president of research at Regeneron, says. This type of antibody cocktail provides an insurance policy against the emergence of mutant strains of SARS-CoV-2 that resist the treatment. “It's unlikely that both sites [on spike] are going to change at the same time,” Kyratsous says.

AstraZeneca, in addition to screening blood from recovered patients and spike-injected mice, is sifting through a massive library of essentially random antibodies created with a method involving viruses called phages. Most groups assume that effective antibodies must target the very tip of the spike, its so-called receptor-binding domain (RBD). But Mark Esser, an AstraZeneca vice president, says, “We have found interesting antibodies that bind to other parts of the spike protein.”

Research groups are also searching for leads from other coronavirus diseases such as severe acute respiratory syndrome (SARS). Vir Biotechnology has found an antibody in a recovered SARS survivor from 2003 that neutralizes SARS-CoV-2. This antibody binds to a region of the RBD that is “highly conserved” between the two coronaviruses, Vir reported in an April preprint.

The company went on to modify the antibody to make it more potent. One modification slows the antibody degradation to give it a longer effective life; another improves the so-called vaccinal effect, which summons T cells—another arm of the immune system—to help destroy infected cells.

Jacob Glanville, an immunologist and computer scientist who runs Distributed Bio, has designed neuts for SARS-CoV-2 in a computer, drawing on genetic sequences and structures of ones known to thwart the SARS virus in cells and even mice. “I'm basically able to get a freebie ride on [past] research in a very brief period,” Glanville says.

With molecular modeling software, Glanville mutated the antibodies to the SARS virus into billions of variants. And using phages as well, Glanville's group created a still larger library of antibodies. The researchers then sorted through what Glanville calls “this vast mutational space” for antibodies predicted to bind to SARS-CoV-2 spike, identifying 50 leads they are testing in vitro. They soon hope to select the best 13 candidates.

Glanville says the aim is to find antibodies that can potently neutralize a broad range of coronaviruses. “The exercise here is to approve one drug that will protect us from this current outbreak but also will enable us to have a tool at our disposal immediately when the next coronavirus outbreak takes place.” That way, he says, “We don't have to play this game every time.”

The burden of choice

With so many COVID-19 monoclonals being developed, “How do you know what is really best and why?” Saphire asks. The Coronavirus Immunotherapy Consortium she leads, funded by $1.7 million from the Bill & Melinda Gates Foundation, is organizing a large-scale, blinded, side-by-side evaluation of candidate monoclonals in test tube studies that gauge their ability to thwart SARS-CoV-2 infection of human cells. The consortium also plans to compare lead candidates in animal models, but needs funding for that costly endeavor.

A doctor in northern Italy who recovered from COVID-19 and has, like Dr. X, contributed his own plasma to AstraZeneca's antibody hunt, stresses that it's far from a given that monoclonals will work. “We don't know the role of neutralizing antibodies in this disease,” says the doctor, who asked not to be named because of his hospital's concerns about publicity. He is also personally familiar with the cost and scarcity of existing monoclonal drugs: His hospital has already had difficulty obtaining immune-calming monoclonals for COVID-19 patients who were having dangerously strong immune reactions to the virus.

A COVID-19 vaccine could, in the long run, do away with the global need for SARS-CoV-2 monoclonals. But Mene Pangalos, AstraZeneca's executive vice president of pharmaceutical R&D, stresses that prospect doesn't concern the company. That would be “fantastic,” he says. “It's important for one of us to solve this pandemic so that we can all get back to some semblance of normality.”

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