Tiny antibodies naturally generated by llamas may be effective against COVID-19

As the fight against COVID-19 continues, scientists have turned to an unlikely source for a potentially effective treatment: tiny antibodies naturally generated by llamas.

While the world has welcomed the news of several COVID-19 vaccines, the search for effective treatments for those who contract the virus is underway. Now scientists are looking for what might appear to be an unlikely source: the South American Lama.

Researchers are using ultra-bright x-rays from the Advanced Photon Source (APS), a user facility from the US Department of Energy’s (DOE) Office of Science at the DOE’s Argonne National Laboratory, to help transform naturally generated llama antibodies in potentially effective therapies against SARS. CoV-2, the virus that causes COVID-19. Antibodies are the immune system’s natural defense against infection and, when taken from the blood, can be used to design treatments and vaccines.

Llamas generate these nanobodies naturally in high yields, and they fit into the surface pockets of proteins that larger antibodies cannot access. “

Jason McLellan, University of Texas, Austin

“We have received over 50 llama antibodies containing several SARS-CoV-2 proteins,” said Andrzej Joachimiak, director of the Center for Structural Biology (SBC) at APS and co-director of the Center for Structural Genomics of Infectious Diseases. (The APS researchers are not working with the live virus, but with crystals from simulated proteins.)

These antibodies are part of ongoing collaborations with several partners, including researchers from the National Institutes of Health (NIH) and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), Joachimiak said, and will be analyzed using PSA to see if they fight the infectivity of the virus.

While it may seem surprising that scientists are turning to llamas, there is a very good reason for this.

Llamas belong to a group of mammals called camels, a group that also includes camels and alpacas. Thanks to a quirk of nature, camels produce a unique type of antibody against the disease. These antibodies, often called nanobodies, are about half the size of antibodies produced by humans. They are also remarkably stable and easy to handle for scientists.

This genetic oddity, which causes camels like llamas to produce these smaller antibodies with unique protein chains, was discovered by accident in the late 1980s by Belgian scientists. Since then, scientists have worked with camelid nanobodies to create treatments for several diseases with great success. Their small size allows them to bind to areas of viral proteins that larger antibodies cannot integrate into, preventing these proteins from connecting to cells.

“Llamas generate these nanobodies naturally in high yields, and they fit into the surface pockets of proteins that larger antibodies cannot access,” said Jason McLellan, associate professor at the University of the Texas to Austin.

McLellan has years of experience working with camelid nanobodies. He and his graduate student Daniel Wrapp, along with Xavier Saelens’ group in Belgium, have isolated nanobodies that have been shown to be effective against respiratory syncytial virus (RSV) and two coronaviruses: severe acute respiratory syndrome (SARS) and the syndrome. Middle East Respiratory System (MERS). .

When the genetic sequence for SARS-CoV-2 was released in January 2020, McLellan, Wrapp and Saelens worked quickly to test whether any of the antibodies they had previously isolated against the original SARS-CoV (taken from a llama Belgian named Winter) could also bind and neutralize SARS-CoV-2.

They discovered that one of these nanobodies, which they had characterized using SBC beamlines at APS, could be effective against SARS-CoV-2. McLellan said this nan person – called VHH72 – is now in development as a treatment for COVID-19. He and Wrapp received a 2020 Golden Goose Award for this research.

McLellan will tell you that if his results were good, his hopes were a little higher.

“We were looking for a strong antibody that neutralized all coronaviruses,” he said. “We immunized Winter in the hopes of arousing this nan person. And maybe we provoked her, but we didn’t isolate her.”

Isolating these tiny nanobodies is tricky because the body generates huge numbers of them and only a small fraction is meant to fight a particular virus. This is exactly the problem that Yi Shi, professor of cell biology at the University of Pittsburgh, is trying to solve.

In an article published in Science, Shi and his colleagues unveiled an advanced new method of mass spectroscopy to analyze these nanobodies from llama blood samples. The result, according to Shi and research assistant Yufei Xiang (the lead author of the article), is a large set of nanobodies that bind well to the SARS-CoV-2 virus.

“It’s thousands of times better than current technology, especially in its breeding properties,” Shi said. “We want nanobodies that bind tightly to SARS-CoV-2, and with this method we can get a drug-grade nanobodies that are up to 10,000 times more potent.”

As with McLellan’s research, Shi’s experience began with a llama, this one named Wally because he looks like (and therefore shares a name with) his black Labrador. The team immunized Wally against SARS-CoV-2, waiting for the generation of nanobodies for two months, then Xiang used his new method to analyze the nanobodies, identify them and quantify them. They ended up with 10 million nan person sequences.

These nanobodies can stay at room temperature for six weeks and are small enough to vaporize, meaning that therapeutics made from them can be inhaled directly into the lungs instead of moving through the bloodstream. To confirm the effectiveness of nanobodies, Cheng Zhang, assistant professor at the University of Pittsburgh, determined the structures of nanobodies linked to the SARS-CoV-2 virus at the National Institute of General Medical Sciences and the Center for Structural Biology of the National Cancer Institute (GM / CA) at APS.

“With this method, we can discover thousands of distinct nanobodies with very high affinity for specific antigen binding,” Shi said. “These nanobodies may or may not provide a treatment for COVID-19, but the technology used to isolate them will be important in the future.”

More recently, a team of scientists led by the University of Bonn in Germany reported newly discovered nanobodies that bind to SARS-CoV-2 and can prevent what is called “mutational escape”. It is the ability of a virus to avoid immune responses by mutating, and treatment that prevents the virus from doing so would protect against reinfection.

This research team has combined several nanobodies into molecules that simultaneously attack different parts of the virus, thus helping to prevent viral mutations from reducing therapeutic efficacy. These nanobodies were taken from a llama and an alpaca immune to the SARS-CoV-2 virus, and out of several million candidates, they ended up with four molecules that were found to be effective.

Ian Wilson, professor of structural biology at the Scripps Research Institute in California, led the team that conducted X-ray diffraction studies at APS GM / CA to determine the structures of these virus-bound molecules.

“From the crystal structures determined from the data collected at APS and the Stanford synchrotron light source (SSRL), we were able to identify the binding sites of nanobodies on the binding domain of the SARS-CoV receptor. -2, ”Wilson said. “X-ray structural information, combined with cryoelectron microscopy data, has been used to help design even more potent multivalent antibodies to prevent infection with COVID-19. The structural x-ray work was greatly facilitated by immediate access to the PSA.

Only time (and other tests) will tell if the different nanobodies will result in effective treatments for COVID-19. But if they do, we’ll have the adorable llama to thank for it.