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Finding Antibodies that Neutralize SARS-CoV-2

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Neutralizing Antibodies
Caption: Model of three neutralizing antibodies (blue, purple and orange) bound to the spike protein, which allows SARS-CoV-2 attach to our cells. Credit: Christopher Barnes and Pamela Bjorkman, California Institute of Technology, Pasadena.

It’s now clear that nearly everyone who recovers from coronavirus disease 2019 (COVID-19) produces antibodies that specifically target SARS-CoV-2, the novel coronavirus that causes the infection. Yet many critical questions remain. A major one is: just how well do those particular antibodies neutralize the virus to fight off the infection and help someone recover from COVID-19? Fortunately, most people get better—but should the typical antibody response take the credit?

A new NIH-funded study of nearly 150 people who recovered from COVID-19 offers some essential insight. The study, published in the journal Nature, shows that most people, in fact, do produce antibodies that can effectively neutralize SARS-CoV-2. But there is a catch: 99 percent of the study’s participants didn’t make enough neutralizing antibodies to mount an ideal immune response.

The good news is that when researchers looked at individuals who mounted a strong immune response, they were able to identify three antibodies (depicted above) that were extremely effective at neutralizing SARS-CoV-2. By mass-producing copies of these antibodies as so-called monoclonal antibodies, the researchers can now better evaluate their potential as treatments to help people who don’t make strongly neutralizing antibodies, or not enough of them.

These findings come from a team led by Michel Nussenzweig, Paul Bieniasz, and Charles Rice at The Rockefeller University, New York, and Pamela Bjorkman at the California Institute of Technology, Pasadena. In the Nussenzweig lab, the team has spent years searching for broadly neutralizing antibodies against the human immunodeficiency virus (HIV). In response to the COVID-19 pandemic and its great urgency, Nussenzweig and team shifted their focus recently to look for promising antibodies against SARS-CoV-2.

Antibodies are blood proteins that the immune system makes to neutralize viruses or other foreign invaders. The immune system doesn’t make just one antibody to thwart an invader; it makes a whole family of antibodies. But not all antibodies in that family are created equal. They can vary widely in where they latch onto a virus like SARS-CoV-2, and that determines how effective each will be at blocking it from infecting human cells. That’s one reason why people respond differently to infections such as COVID-19.

In early April, Nussenzweig’s team began analyzing samples from volunteer survivors who visited The Rockefeller Hospital to donate plasma, which contains the antibodies. The volunteers had all recovered from mild-to-severe cases of COVID-19, showing their first signs of illness about 40 days prior to their first plasma collection.

Not surprisingly, all volunteers had produced antibodies in response to the virus. To test the strength of the antibodies, the researchers used a special assay that shows how effective each one is at blocking the virus from infecting human cells in lab dishes.

Overall, most of the plasma samples—118 of 149—showed at best poor to modest neutralizing activity. In about one-third of individuals, their plasma samples had below detectable levels of neutralizing activity. It’s possible those individuals just resolved the infection quickly, before more potent antibodies were produced.

More intriguing to the researchers were the results from two individuals that showed an unusually strong ability to neutralize SARS-CoV-2. Among these two “elite responders” and four other individuals, the researchers identified 40 different antibodies that could neutralize SARS-CoV-2. But again, not all antibodies are created equal. Three neutralized the virus even when present at extremely low levels, and they now will be studied further as possible monoclonal antibodies.

The team determined that those strongly neutralizing antibodies bind three distinct sites on the receptor-binding domain (RBD) of the coronavirus spike protein. This portion of the virus is important because it allows SARS-CoV-2 to bind and infect human cells. Importantly, when the researchers looked more closely at plasma samples with poor neutralizing ability, they found that they also contained those RBD-binding antibodies, just not in very large numbers.

These findings help not only to understand the immune response to COVID-19, they are also critical for vaccine design, revealing what a strong neutralizing antibody for SARS-CoV-2 should look like to help the immune system win. If a candidate vaccine can generate such strongly neutralizing antibodies, researchers will know that they are on the right track.

While this research showed that there’s a lot of variability in immune responses to SARS-CoV-2, it appears that most of us are inherently capable of producing antibodies to neutralize this devastating virus. That brings more reason for hope that the many vaccines now under study to elicit such neutralizing antibodies in sufficient numbers may afford us with much-needed immune protection.


[1] Convergent antibody responses to SARS-CoV-2 in convalescent individuals. Robbiani DF, Gaebler C, Muecksch F, et al. Nature. 2020 Jun 18. [Published online ahead of print].


Coronavirus (COVID-19) (NIH)

Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV)

Nussenzweig Lab (The Rockefeller University, New York)

Bjorkman Lab (California Institute of Technology, Pasadena)

NIH Support: National Institute of Allergy and Infectious Diseases

Enlisting Monoclonal Antibodies in the Fight Against COVID-19

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B38 Antibody and SARS-CoV-2 wtih ACE2 Receptor
Caption: Antibody Binding to SARS-CoV-2. Structural illustration of B38 antibody (cyan, green) attached to receptor-binding domain of the coronavirus SARS-CoV-2 (magenta). B38 blocks SARS-CoV-2 from binding to the ACE2 receptor (light pink) of a human cell, ACE2 is what the virus uses to infect cells. Credit: Y. Wu et a. Science, 2020

We now know that the immune system of nearly everyone who recovers from COVID-19 produces antibodies against SARS-CoV-2, the novel coronavirus that causes this easily transmitted respiratory disease [1]. The presence of such antibodies has spurred hope that people exposed to SARS-CoV-2 may be protected, at least for a time, from getting COVID-19 again. But, in this post, I want to examine another potential use of antibodies: their promise for being developed as therapeutics for people who are sick with COVID-19.

In a recent paper in the journal Science, researchers used blood drawn from a COVID-19 survivor to identify a pair of previously unknown antibodies that specifically block SARS-CoV-2 from attaching to human cells [2]. Because each antibody locks onto a slightly different place on SARS-CoV-2, the vision is to use these antibodies in combination to block the virus from entering cells, thereby curbing COVID-19’s destructive spread throughout the lungs and other parts of the body.

The research team, led by Yan Wu, Capital Medical University, Beijing, first isolated the pair of antibodies in the laboratory, starting with white blood cells from the patient. They were then able to produce many identical copies of each antibody, referred to as monoclonal antibodies. Next, these monoclonal antibodies were simultaneously infused into a mouse model that had been infected with SARS-CoV-2. Just one infusion of this combination antibody therapy lowered the amount of viral genetic material in the animals’ lungs by as much as 30 percent compared to the amount in untreated animals.

Monoclonal antibodies are currently used to treat a variety of conditions, including asthma, cancer, Crohn’s disease, and rheumatoid arthritis. One advantage of this class of therapeutics is that the timelines for their development, testing, and approval are typically shorter than those for drugs made of chemical compounds, called small molecules. 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.

So, what exactly led up to this latest scientific achievement? The researchers started out with a snippet of SARS-CoV-2’s receptor binding domain (RBD), a vital part of the spike protein that protrudes from the virus’s surface and serves to dock the virus onto an ACE2 receptor on a human cell. In laboratory experiments, the researchers used the RBD snippet as “bait” to attract antibody-producing B cells in a blood sample obtained from the COVID-19 survivor. Altogether, the researchers identified four unique antibodies, but two, which they called B38 and H4, displayed a synergistic action in binding to the RBD that made them stand out for purposes of therapeutic development and further testing.

To complement their lab and animal experiments, the researchers used a particle accelerator called a synchrotron to map, at near-atomic resolution, the way in which the B38 antibody locks onto its viral target. This structural information helps to clarify the precise biochemistry of the complex interaction between SARS-CoV-2 and the antibody, providing a much-needed guide for the rational design of targeted drugs and vaccines. While more research is needed before this or other monoclonal antibody therapies can be used in humans suffering from COVID-19, the new work represents yet another example of how basic science is expanding fundamental knowledge to advance therapeutic discovery for a wide range of health concerns.

Meanwhile, there’s been other impressive recent progress towards the development of monoclonal antibody therapies for COVID-19. In work described in the journal Nature, an international research team started with a set of neutralizing antibodies previously identified in a blood sample from a person who’d recovered from a different coronavirus-caused disease, called severe acute respiratory syndrome (SARS), in 2003 [3]. Through laboratory and structural imaging studies, the researchers found that one of these antibodies, called S309, proved particularly effective at neutralizing the coronavirus that causes COVID-19, SARS-CoV-2, because of its potent ability to target the spike protein that enables the virus to enter cells. The team, which includes NIH grantees David Veesler, University of Washington, Seattle, and Davide Corti, Humabs Biomed, a subsidiary of Vir Biotechnology, has indicated that S309 is already on an accelerated development path toward clinical trials.

In the U.S. and Europe, the Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) partnership, which has brought together public and private sector COVID-19 therapeutic and vaccine efforts, is intensely pursuing the development and testing of therapeutic monoclonal antibodies for COVID-19 [4]. Stay tuned for more information about these potentially significant advances in the next few months.


[1] Humoral immune response and prolonged PCR positivity in a cohort of 1343 SARS-CoV 2 patients in the New York City region. Wajnberg A , Mansour M, Leven E, Bouvier NM, Patel G, Firpo A, Mendu R, Jhang J, Arinsburg S, Gitman M, Houldsworth J, Baine I, Simon V, Aberg J, Krammer F, Reich D, Cordon-Cardo C. medRxiv. Preprint Posted May 5, 2020.

[2] A noncompeting pair of human neutralizing antibodies block COVID-19 virus binding to its receptor ACE2. Wu Y. et al., Science. 13 May 2020 [Epub ahead of publication]

[3] Cross-neutralization of SARS-CoV-2 by a human monoclonal SARS-CoV antibody. Pinto D, Park YJ, Beltramello M, Veesler D, Cortil D, et al. Nature. 18 May 2020 [Epub ahead of print]

[4] Accelerating COVID-19 therapeutic interventions and vaccines (ACTIV): An unprecedented partnership for unprecedented times. Collins FS, Stoffels P. JAMA. 2020 May 18.


Coronavirus (COVID-19) (NIH)

Monoclonal Antibodies (National Cancer Institute/NIH)

Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV)

NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of General Medical Sciences

Bringing Needed Structure to COVID-19 Drug Development

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SARS-Cov-2 Molecular Map
Caption: Molecular map showing interaction between the spike protein (gold) of the novel coronavirus and the peptidase domain (blue) of human angiotensin-converting enzyme 2 (ACE2). Credit: Adapted from Yan R., Science, 2020.

With so much information swirling around these days about the coronavirus disease 2019 (COVID-19) pandemic, it would be easy to miss one of the most interesting and significant basic science reports of the past few weeks. It’s a paper published in the journal Science [1] that presents an atomic-scale snapshot showing the 3D structure of the spike protein on the novel coronavirus attached to a human cell surface protein called ACE2, or angiotensin converting enzyme 2. ACE2 is the receptor that the virus uses to gain entry.

What makes this image such a big deal is that it shows—in exquisite detail—how the coronavirus attaches to human cells before infecting them and making people sick. The structural map of this interaction will help guide drug developers, atom by atom, in devising safe and effective ways to treat COVID-19.

This new work, conducted by a team led by Qiang Zhou, Westlake Institute for Advanced Study, Hangzhou, China, took advantage of a high-resolution imaging tool called cryo-electron microscopy (cryo-EM). This approach involves flash-freezing molecules in liquid nitrogen and bombarding them with electrons to capture their images with a special camera. When all goes well, cryo-EM can solve the structure of intricate macromolecular complexes in a matter of days, including this one showing the interaction between a viral protein and human protein.

Zhou’s team began by mapping the structure of human ACE2 in a complex with B0AT1, which is a membrane protein that it helps to fold. In the context of this complex, ACE2 is a dimer—a scientific term for a compound composed of two very similar units. Additional mapping revealed how the surface protein of the novel coronavirus interacts with ACE2, indicating how the virus’s two trimeric (3-unit) spike proteins might bind to an ACE2 dimer. After confirmation by further research, these maps may well provide a basis for the design and development of therapeutics that specifically target this critical interaction.

The ACE2 protein resides on the surface of cells in many parts of the human body, including the heart and lungs. The protein is known to play a prominent role in the body’s complex system of regulating blood pressure. In fact, a class of drugs that inhibit ACE and related proteins are frequently prescribed to help control high blood pressure, or hypertension. These ACE inhibitors lower blood pressure by causing blood vessels to relax.

Since the COVID-19 outbreak, many people have wondered whether taking ACE inhibitors would be helpful or detrimental against coronavirus infection. This is of particular concern to doctors whose patients are already taking the medications to control hypertension. Indeed, data from China and elsewhere indicate hypertension is one of several coexisting conditions that have consistently been reported to be more common among people with COVID-19 who develop life-threatening severe acute respiratory syndrome.

In a new report in this week’s New England Journal of Medicine, a team of U.K. and U.S. researchers, partly supported by NIH, examined the use of ACE inhibitors and other angiotensin-receptor blockers (ARBs) in people with COVID-19. The team, led by Scott D. Solomon of Brigham and Women’s Hospital and Harvard Medical School, Boston, found that current evidence in humans is insufficient to support or refute claims that ACE inhibitors or ARBs may be helpful or harmful to individuals with COVID-19.

The researchers concluded that these anti-hypertensive drugs should be continued in people who have or at-risk for COVID-19, stating: “Although additional data may further inform the treatment of high-risk patients … clinicians need to be cognizant of the unintended consequences of prematurely discontinuing proven therapies in response to hypothetical concerns.” [2]

Research is underway to generate needed data on the use of ACE inhibitors and similar drugs in the context of the COVID-19 pandemic, as well as to understand more about the basic mechanisms underlying this rapidly spreading viral disease. This kind of fundamental research isn’t necessarily the stuff that will make headlines, but it likely will prove vital to guiding the design of effective drugs that can help bring this serious global health crisis under control.


[1] Structural basis for the recognition of the SARS-CoV-2 by full-length human ACE2. Yan R, Zhang Y, Li Y, Xia L, Guo Y, Zhou Q. Science. 27 March 2020. [Epub ahead of publication]

[2] Renin–Angiotensin–Aldosterone System Inhibitors in Patients with Covid-19. Vaduganathan M, Vardeny O, Michel T, McMurray J, Pfeffer MA, Solomon SD. 30 NEJM. March 2020 [Epub ahead of Publication]


Coronavirus (COVID-19) (NIH)

COVID-19, MERS & SARS (National Institute of Allergy and Infectious Diseases/NIH)

Transformative High Resolution Cryo-Electron Microscopy (Common Fund/NIH)

Qiang Zhou (Westlake Institute for Advanced Study, Zhejiang Province)

Scott D. Solomon (Brigham and Women’s Hospital, Boston)

NIH Support: National Center for Advancing Translational Sciences; National Heart, Lung, and Blood Institute

Body-on-a-Chip Device Predicts Cancer Drug Responses

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Credit: McAleer et al., Science Translational Medicine, 2019

Researchers continue to produce impressive miniature human tissues that resemble the structure of a range of human organs, including the livers, kidneys, hearts, and even the brain. In fact, some researchers are now building on this success to take the next big technological step: placing key components of several miniature organs on a chip at once.

These body-on-a-chip (BOC) devices place each tissue type in its own pea-sized chamber and connect them via fluid-filled microchannels into living, integrated biological systems on a laboratory plate. In the photo above, the BOC chip is filled with green fluid to make it easier to see the various chambers. For example, this easy-to-reconfigure system can make it possible to culture liver cells (chamber 1) along with two cancer cell lines (chambers 3, 5) and cardiac function chips (chambers 2, 4).

Researchers circulate blood-mimicking fluid through the chip, along with chemotherapy drugs. This allows them to test the agents’ potential to fight human cancer cells, while simultaneously gathering evidence for potential adverse effects on tissues placed in the other chambers.

This BOC comes from a team of NIH-supported researchers, including James Hickman and Christopher McAleer, Hesperos Inc., Orlando, FL. The two were challenged by their Swiss colleagues at Roche Pharmaceuticals to create a leukemia-on-a-chip model. The challenge was to see whether it was possible to reproduce on the chip the known effects and toxicities of diclofenac and imatinib in people.

As published in Science Translational Medicine, they more than met the challenge. The researchers showed as expected that imatinib did not harm liver cells [1]. But, when treated with diclofenac, liver cells on the chip were reduced in number by about 30 percent, an observation consistent with the drug’s known liver toxicity profile.

As a second and more challenging test, the researchers reconfigured the BOC by placing a multi-drug resistant vulva cancer cell line in one chamber and, in another, a breast cancer cell line that responded to drug treatment. To explore side effects, the system also incorporated a chamber with human liver cells and two others containing beating human heart cells, along with devices to measure the cells’ electrical and mechanical activity separately.

These studies showed that tamoxifen, commonly used to treat breast cancer, indeed killed a significant number of the breast cancer cells on the BOC. But, it only did so after liver cells on the chip processed the tamoxifen to produce its more active metabolite!

Meanwhile, tamoxifen alone didn’t affect the drug-resistant vulva cancer cells on the chip, whether or not liver cells were present. This type of cancer cell has previously been shown to pump the drug out through a specific channel. Studies on the chip showed that this form of drug resistance could be overcome by adding a second drug called verapamil, which blocks the channel.

Both tamoxifen alone and the combination treatment showed some off-target effects on heart cells. While the heart cells survived the treatment, they contracted more slowly and with less force. The encouraging news was that the heart cells bounced back from the tamoxifen-only treatment within three days. But when the drug-drug combination was tested, the cardiac cells did not recover their function during the same time period.

What makes advances like this especially important is that only 1 in 10 drug candidates entering human clinical trials ultimately receives approval from the Food and Drug Administration (FDA) [2]. Often, drug candidates fail because they prove toxic to the human brain, liver, kidneys, or other organs in ways that preclinical studies in animals didn’t predict.

As BOCs are put to work in testing new drug candidates and especially treatment combinations, the hope is that we can do a better job of predicting early on which chemical compounds will prove safe and effective in humans. For those drug candidates that are ultimately doomed, “failing early” is key to reducing drug development costs. By culturing an individual patient’s cells in the chambers, BOCs also may be used to help doctors select the best treatment option for that particular patient. The ultimate goal is to accelerate the translation of basic discoveries into clinical breakthroughs. For more information about tissue chips, take a look at NIH’s Tissue Chip for Drug Screening program.


[1] Multi-organ system for the evaluation of efficacy and off-target toxicity of anticancer therapeutics. McAleer CW, Long CJ, Elbrecht D, Sasserath T, Bridges LR, Rumsey JW, Martin C, Schnepper M, Wang Y, Schuler F, Roth AB, Funk C, Shuler ML, Hickman JJ. Sci Transl Med. 2019 Jun 19;11(497).

[2] Clinical development success rates for investigational drugs. Hay M, Thomas DW, Craighead JL, Economides C, Rosenthal J. Nat Biotechnol. 2014 Jan;32(1):40-51.


Tissue Chip for Drug Screening (National Center for Advancing Translational Sciences/NIH)

James Hickman (Hesperos, Inc., Orlando, FL)

Hesperos, Inc.

NIH Support: National Center for Advancing Translational Sciences

Oral Insulin Delivery: Can the Tortoise Win the Race?

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Turtle shape compared to capsule shape
Caption: The African leopard tortoise’s shape inspired a new insulin-injecting “pill” (right). Credit: Alex Abramson

People with diabetes often must inject insulin multiple times a day to keep their blood glucose levels under control. So, I was intrigued to learn that NIH-funded bioengineers have designed a new kind of “pill” that may someday reduce the need for those uncomfortable shots. The inspiration for their design? A tortoise!

The new “pill”—actually, a swallowable device containing a tiny injection system—is shaped like the shell of an African leopard tortoise. In much the same way that the animal’s highly curved shell enables it to quickly right itself when flipped on its back, the shape of the new device is intended to help it land in the right position to inject insulin or other medicines into the stomach wall.

The hunt for a means to deliver insulin in pill form has been on ever since insulin injections first were introduced, nearly a century ago. The challenge in oral delivery of insulin and other “biologic” drugs—including therapeutic proteins, peptides, or nucleic acids—is how to get these large biomolecules through the highly acidic stomach and duodenum, where multiple powerful digestive enzymes reside, and into the bloodstream unscathed. Past efforts to address this challenge have met with only limited success.

In a study published in the journal Science, a team, led by Robert Langer at Massachusetts Institute of Technology, Cambridge, and Giovanni Traverso, Brigham and Women’s Hospital, Harvard Medical School, Boston, took a new approach to the problem by developing a tiny, ingestible injection system [1]. They call their pea-sized device SOMA, short for “self-orienting millimeter-scale applicator.”

In designing SOMA, the researchers knew they had to come up with a design that would orient the injection apparatus correctly. So they looked to the African leopard tortoise. They knew that, much like a child’s “weeble-wobble” toy, this tortoise can easily right its body if tipped over due to its low center of gravity and highly curved shell. With the shape of the tortoise shell as a starting point, the researchers used computer modeling to perfect their design. The final result features a partially hollowed-out, polymer-and-steel capsule that houses a tiny, spring-loaded needle tipped with compressed, freeze-dried insulin. There is also a dissolvable sugar disk to hold the needle in place until the time is right.

Here’s how it works: once a SOMA is swallowed and reaches the stomach, it quickly orients itself in a way that its needle-side rests against the stomach wall. After the protective sugar disk dissolves in stomach acid, the spring-loaded needle tipped with insulin is released, injecting its load of insulin into the stomach wall, from which it enters the bloodstream. Meanwhile, the spent SOMA device passes on through the digestive system.

The researchers’ tests in pigs have shown that a single SOMA can successfully deliver insulin doses of up to 3 milligrams, comparable to the amount a human with diabetes might need to inject. The tests also showed that the device’s microinjection did not damage the animals’ stomach tissue or the muscles surrounding the stomach. Because the stomach is known for being insensitive to pain, researchers expect that people receiving insulin via SOMA wouldn’t feel a thing, but much more research is needed to confirm both the safety and efficacy of the new device for human use.

Meanwhile, this fascinating work serves as a reminder that when it comes to biomedical science, inspiration sometimes can come from the most unexpected places.


[1] An ingestible self-orienting system for oral delivery of macromolecules. Abramson A, Caffarel-Salvador E, Khang M, Dellal D, Silverstein D, Gao Y, Frederiksen MR, Vegge A, Hubálek F, Water JJ, Friderichsen AV, Fels J, Kirk RK, Cleveland C, Collins J, Tamang S, Hayward A, Landh T, Buckley ST, Roxhed N, Rahbek U, Langer R, Traverso G. Science. 2019 Feb 8;363(6427):611-615.


Diabetes (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)

Langer Lab (MIT, Cambridge)

Giovanni Traverso (Brigham and Women’s Hospital, Harvard Medical School, Boston)

NIH Support: National Institute of Biomedical Imaging and Bioengineering

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