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Genes, Blood Type Tied to Risk of Severe COVID-19

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SARS-CoV-2 virus particles
Caption: Micrograph of SARS-CoV-2 virus particles isolated from a patient.
Credit: National Institute of Allergy and Infectious Diseases, NIH

Many people who contract COVID-19 have only a mild illness, or sometimes no symptoms at all. But others develop respiratory failure that requires oxygen support or even a ventilator to help them recover [1]. It’s clear that this happens more often in men than in women, as well as in people who are older or who have chronic health conditions. But why does respiratory failure also sometimes occur in people who are young and seemingly healthy?

A new study suggests that part of the answer to this question may be found in the genes that each one of us carries [2]. While more research is needed to pinpoint the precise underlying genes and mechanisms responsible, a recent genome-wide association (GWAS) study, just published in the New England Journal of Medicine, finds that gene variants in two regions of the human genome are associated with severe COVID-19 and correspondingly carry a greater risk of COVID-19-related death.

The two stretches of DNA implicated as harboring risks for severe COVID-19 are known to carry some intriguing genes, including one that determines blood type and others that play various roles in the immune system. In fact, the findings suggest that people with blood type A face a 50 percent greater risk of needing oxygen support or a ventilator should they become infected with the novel coronavirus. In contrast, people with blood type O appear to have about a 50 percent reduced risk of severe COVID-19.

These new findings—the first to identify statistically significant susceptibility genes for the severity of COVID-19—come from a large research effort led by Andre Franke, a scientist at Christian-Albrecht-University, Kiel, Germany, along with Tom Karlsen, Oslo University Hospital Rikshospitalet, Norway. Their study included 1,980 people undergoing treatment for severe COVID-19 and respiratory failure at seven medical centers in Italy and Spain.

In search of gene variants that might play a role in the severe illness, the team analyzed patient genome data for more than 8.5 million so-called single-nucleotide polymorphisms, or SNPs. The vast majority of these single “letter” nucleotide substitutions found all across the genome are of no health significance, but they can help to pinpoint the locations of gene variants that turn up more often in association with particular traits or conditions—in this case, COVID-19-related respiratory failure. To find them, the researchers compared SNPs in people with severe COVID-19 to those in more than 1,200 healthy blood donors from the same population groups.

The analysis identified two places that turned up significantly more often in the individuals with severe COVID-19 than in the healthy folks. One of them is found on chromosome 3 and covers a cluster of six genes with potentially relevant functions. For instance, this portion of the genome encodes a transporter protein known to interact with angiotensin converting enzyme 2 (ACE2), the surface receptor that allows the novel coronavirus that causes COVID-19, SARS-CoV-2, to bind to and infect human cells. It also encodes a collection of chemokine receptors, which play a role in the immune response in the airways of our lungs.

The other association signal popped up on chromosome 9, right over the area of the genome that determines blood type. Whether you are classified as an A, B, AB, or O blood type, depends on how your genes instruct your blood cells to produce (or not produce) a certain set of proteins. The researchers did find evidence suggesting a relationship between blood type and COVID-19 risk. They noted that this area also includes a genetic variant associated with increased levels of interleukin-6, which plays a role in inflammation and may have implications for COVID-19 as well.

These findings, completed in two months under very difficult clinical conditions, clearly warrant further study to understand the implications more fully. Indeed, Franke, Karlsen, and many of their colleagues are part of the COVID-19 Host Genetics Initiative, an ongoing international collaborative effort to learn the genetic determinants of COVID-19 susceptibility, severity, and outcomes. Some NIH research groups are taking part in the initiative, and they recently launched a study to look for informative gene variants in 5,000 COVID-19 patients in the United States and Canada.

The hope is that these and other findings yet to come will point the way to a more thorough understanding of the biology of COVID-19. They also suggest that a genetic test and a person’s blood type might provide useful tools for identifying those who may be at greater risk of serious illness.

References:

[1] Characteristics of and important lessons from the Coronavirus Disease 2019 (COVID-19) outbreak in China: Summary of a report of 72 314 cases from the Chinese Center for Disease Control and Prevention. Wu Z, McGoogan JM, et. al. 2020 Feb 24. [published online ahead of print]

[2] Genomewide association study of severe Covid-19 with respiratory failure. Ellinghaus D, Degenhardt F, et. a. NEJM. June 17, 2020.

Links:

The COVID-19 Host Genetics Initiative

Andre Franke (Christian-Albrechts-University of Kiel, Germany)

Tom Karlsen (Oslo University Hospital Rikshospitalet, Norway)


Searching for Ways to Prevent Life-Threatening Blood Clots in COVID-19

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At Home with Gary Gibbons

Six months into the coronavirus disease 2019 (COVID-19) pandemic, researchers still have much to learn about the many ways in which COVID-19 can wreak devastation on the human body. Among the many mysteries is exactly how SARS-CoV-2, which is the novel coronavirus that causes COVID-19, triggers the formation of blood clots that can lead to strokes and other life-threatening complications, even in younger people.

Recently, I had a chance to talk with Dr. Gary Gibbons, Director of NIH’s Heart, Lung, and Blood Institute (NHLBI) about what research is being done to tackle this baffling complication of COVID-19. Our conversation took place via videoconference, with him connecting from his home in Washington, D.C., and me linking in from my home just up the road in Maryland. Here’s a condensed transcript of our chat:

Collins: I’m going to start by asking about the SARS-CoV-2-induced blood clotting not only in the lungs, but in other parts of the body. What do we know about the virus that would explain this?

Gibbons: It seems like every few weeks another page gets turned on COVID-19, and we learn even more about how this virus affects the body. Blood clots are one of the startling and, unfortunately, devastating complications that emerged as patients were cared for, particularly in New York City. It became apparent that certain individuals had difficulty getting enough oxygen into their system. The difficulty couldn’t be explained entirely by the extent of the pneumonia affecting the lungs’ ability to exchange oxygen.

It turned out that, in addition to the pneumonia, blood clots in the lungs were compromising oxygenation. But some patients also had clotting, or thrombotic, complications in their veins and arteries in other parts of the body. Quite puzzling. There were episodes of relatively young individuals in their 30s and 40s presenting with strokes related to blood clots affecting the arterial circulation to the brain.

We’re still trying to understand what promotes the clotting. One clue involves the endothelial cells that form the inner lining of our blood vessels. These cells have on their surface a protein called the angiotensin-converting enzyme 2 (ACE2) receptor, and this clue is important for two reasons. One, the virus attaches to the ACE2 receptor, using it as an entry point to infect cells. Two, endothelial-lined blood vessels extend to every organ in the body. Taken together, it seems that some COVID-19 complications relate to the virus attaching to endothelial cells, not only in the lungs, but in the heart and multiple organs.

Collins: So, starting in the respiratory tree, the virus somehow breaks through into a blood vessel and then gets spread around the body. There have been strange reports of people with COVID-19 who may not get really sick, but their toes look frostbitten. Is “COVID toes,” as some people call it, also part of this same syndrome?

Gibbons: We’re still in the early days of learning about this virus. But I think this offers a further clue that the virus not only affects large vessels but small vessels. In fact, clots have been reported at the capillary level, and that’s fairly unusual. It’s suggestive that an interaction is taking place between the platelets and the endothelial surface.

Normally, there’s a tightly regulated balance in the bloodstream between pro-coagulant and anticoagulant proteins to prevent clotting and keep the blood flowing. But when you cut your finger, for example, you get activation for blood clots in the form of a protein mesh. It looks like a fishing net that can help seal the injury. In addition, platelets in the blood stream help to plug the holes in that fishing net and create a real seal of a blood vessel.

Well, imagine it happening in those small vessels, which usually have a non-stick endothelial surface, almost like Teflon, that prevents clotting. Then the virus comes along and tips the balance toward promoting clot formation. This disturbs the Teflon-like property of the endothelial lining and makes it sticky. It’s incredible the tricks this virus has learned by binding onto one of these molecules in the endothelial lining.

Collins: Who are the COVID-19 patients most at risk for this clotting problem?

Gibbons: Unfortunately, it appears right now that older adults are among the most vulnerable. They have a lot of the risks for the formation of these blood clots. What’s notable is these thrombotic complications are also happening to relatively young adults or middle-aged individuals who don’t have a lot of other chronic conditions, or comorbidities, to put them at higher risk for severe disease. Again, it’s suggestive that this virus is doing something that is particular to the coagulation system.

Collins: We’d love to have a way of identifying in advance the people who are most likely to get into trouble with blood clotting. They might be the ones you’d want to start on an intervention, even before you have evidence that things are getting out of control. Do you have any kind of biomarker to tell you which patients might benefit from early intervention?

Gibbons: Biomarkers are being actively studied. What we do know from some earlier observations is that you can assess the balance of clotting and anticlotting factors in the blood by measuring a biomarker called D-dimer. It’s basically a protein fragment, a degradation product, from a prior clot. It tells you a bit about the system’s activity in forming and dissolving clots.
If there’s a lot of D-dimer activity, it suggests a coagulation cascade is jazzed up. In those patients, it’s probably a clue that this is a big trigger in terms of coagulation and thrombosis. So, D-dimer levels could maybe tell us which patients need really aggressive full anticoagulation.

Collins: Have people tried empirically using blood thinners for people who seem to be getting into trouble with this clotting problem?

Gibbons: There’s a paper out of the Mount Sinai in New York City that looked at thousands of patients being treated for COVID-19 [1]. Based on clinical practice and judgments, one of the striking findings is that those who were fully anticoagulated had better survival than those who were not. Now, this was not a randomized, controlled clinical trial, where some were given full anticoagulation and others were not. It was just an observational study that showed an association. But this study indicated indirectly that by giving the blood thinners, changing that thrombotic risk, maybe it’s possible to reduce morbidity and mortality. That’s why we need to do a randomized, controlled clinical trial to see if it can be used to reduce these case fatality rates.

Collins: You and your colleagues got together and came up with a design for such a clinical trial. Tell us about that.

Gibbons: My institute studies the heart, lung, and blood. The virus attacks all three. So, our community has a compelling need to lean in and study COVID-19. Recently, NIH helped to launch a public-private partnership called Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV). As the name spells out, this initiative provides is a clinical platform to generate life-saving treatments as we wait for the development of a vaccine.

Through ACTIV, a protocol is now in the final stages of review for a clinical trial that will involve a network of hospitals and explore the question: is it sufficient to try a low-dose thrombo-prophylactic, or clot preventative, approach versus full anticoagulation? Some think patients ought to have full anticoagulation, but that’s not without risk. So, we want to put that question to the test. As part of that, we’ll also learn more about biomarkers and what could be predictive of individuals getting the greatest benefit.

If we find that fully anticoagulating patients prevents clots, then that’s great. But it begs the question: what happens when patients go home? Is it sufficient to just turn off the drip and let them go their merry way? Should they have a low dose thrombo-prophylactic regimen for a period of time? If so, how long? Or should they be fully anticoagulated with oral anticoagulation for a certain period of time? All these and other questions still remain.

Collins: This can make a huge difference. If you’re admitted to the hospital with COVID-19, that means you’re pretty sick and, based on the numbers that I’ve seen, your chance of dying is about 12 percent if nothing else happens. If we can find something like an anticoagulant that would reduce that risk substantially, we can have a huge impact on reducing deaths from COVID-19. How soon can we get this trial going, Gary?

Gibbons: We have a sense of urgency that clearly this pandemic is taking too many lives and time is of the essence. So, we’ve indeed had a very streamlined process. We’re leveraging the fact that we have clinical trial networks, where regardless of what they were planning to do, it’s all hands on deck. As a result, we’re able to move faster to align with that sense of urgency. We hope that we can be off to a quick launch within the next two to three weeks with the anticoagulation trials.

Collins: This is good because people are waiting on the vaccines, but realistically we won’t know whether the vaccines are working for several more months, and having them available for lots of people will be at the very end of this year or early 2021 at best. Meanwhile, people still are going to be getting sick with COVID-19. We want to be able to have as many therapeutic options as possible to offer to them. And this seems like a pretty exciting one to try and move forward as quickly as possible. You and your colleagues deserve a lot of credit for bringing this to everybody’s attention.

But before we sign off, I have to raise another issue of deep significance. Gary, I think both of us are struggling not only with the impact of COVID-19 on the world, but the profound sorrow, grief, frustration, and anger that surrounds the death of George Floyd. This brings into acute focus the far too numerous other circumstances where African Americans have been mistreated and subjected to tragic outcomes.

This troubling time also shines a light on the health disparities that affect our nation in so many ways. We can see what COVID-19 has done to certain underrepresented groups who have borne an undue share of the burden, and have suffered injustices at the hands of society. It’s been tough for many of us to admit that our country is far from treating everyone equally, but it’s a learning opportunity and a call to redouble our efforts to find solutions.

Gary, you’ve been a wonderful leader in that conversation for a long time. I want to thank you both for what you’re doing scientifically and for your willingness to speak the truth and stand up for what’s right and fair. It’s been great talking to you about all these issues.

Gibbons: Thank you. We appreciate this opportunity to fulfill NIH’s mission of turning scientific discovery into better health for all. If there’s any moment that our nation needs us, this is it.

Reference:

[1] Association of Treatment Dose Anticoagulation With In-Hospital Survival Among Hospitalized Patients With COVID-19. Paranjpe I, Fuster V, Lala A, Russak A, Glicksberg BS, Levin MA, Charney AW, Narula J, Fayad ZA, Bagiella E, Zhao S, Nadkarni GN. J Am Coll Cardiol. 2020 May 5;S0735-1097(20)35218-9.

Links:

Coronavirus (COVID-19) (NIH)

Rising to the Challenge of COVID-19: The NHLBI Community Response,” Director’s Messages, National Heart, Lung, and Blood Institute/NIH, April 29, 2020.

Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) (NIH)


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.

References:

[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.

Links:

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


The Prime Cellular Targets for the Novel Coronavirus

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Credit: NIH

There’s still a lot to learn about SARS-CoV-2, the novel coronavirus that causes COVID-19. But it has been remarkable and gratifying to watch researchers from around the world pull together and share their time, expertise, and hard-earned data in the urgent quest to control this devastating virus.

That collaborative spirit was on full display in a recent study that characterized the specific human cells that SARS-CoV-2 likely singles out for infection [1]. This information can now be used to study precisely how each cell type interacts with the virus. It might ultimately help to explain why some people are more susceptible to SARS-CoV-2 than others, and how exactly to target the virus with drugs, immunotherapies, and vaccines to prevent or treat infections.

This work was driven by the mostly shuttered labs of Alex K. Shalek, Massachusetts Institute of Technology, Ragon Institute of MGH, MIT, and Harvard, and Broad Institute of MIT and Harvard, Cambridge; and Jose Ordovas-Montanes at Boston Children’s Hospital. In the end, it brought together (if only remotely) dozens of their colleagues in the Human Cell Atlas Lung Biological Network and others across the U.S., Europe, and South Africa.

The project began when Shalek, Ordovas-Montanes, and others read that before infecting human cells, SARS-CoV-2 docks on a protein receptor called angiotensin-converting enzyme 2 (ACE2). This enzyme plays a role in helping the body maintain blood pressure and fluid balance.

The group was intrigued, especially when they also learned about a second enzyme that the virus uses to enter cells. This enzyme goes by the long acronym TMPRSS2, and it gets “tricked” into priming the spike proteins that cover SARS-CoV-2 to attack the cell. It’s the combination of these two proteins that provide a welcome mat for the virus.

Shalek, Ordovas-Montanes, and an international team including graduate students, post-docs, staff scientists, and principal investigators decided to dig a little deeper to find out precisely where in the body one finds cells that express this gene combination. Their curiosity took them to the wealth of data they and others had generated from model organisms and humans, the latter as part of the Human Cell Atlas. This collaborative international project is producing a comprehensive reference map of all human cells. For its first draft, the Human Cell Atlas aims to gather information on at least 10 billion cells.

To gather this information, the project relies, in part, on relatively new capabilities in sequencing the RNA of individual cells. Keep in mind that every cell in the body has essentially the same DNA genome. But different cells use different programs to decide which genes to turn on—expressing those as RNA molecules that can be translated into protein. The single-cell analysis of RNA allows them to characterize the gene expression and activities within each and every unique cell type. Based on what was known about the virus and the symptoms of COVID-19, the team focused their attention on the hundreds of cell types they identified in the lungs, nasal passages, and intestines.

As reported in Cell, by filtering through the data to identify cells that express ACE2 and TMPRSS2, the researchers narrowed the list of cell types in the nasal passages down to the mucus-producing goblet secretory cells. In the lung, evidence for activity of these two genes turned up in cells called type II pneumocytes, which line small air sacs known as alveoli and help to keep them open. In the intestine, it was the absorptive enterocytes, which play an important role in the body’s ability to take in nutrients.

The data also turned up another unexpected and potentially important connection. In these cells of interest, all of which are found in epithelial tissues that cover or line body surfaces, the ACE2 gene appeared to ramp up its activity in concert with other genes known to respond to interferon, a protein that the body makes in response to viral infections.

To dig further in the lab, the researchers treated cultured cells that line airways in the lungs with interferon. And indeed, the treatment increased ACE2 expression.

Earlier studies have suggested that ACE2 helps the lungs to tolerate damage. Completely missed was its connection to the interferon response. The researchers now suspect that’s because it hadn’t been studied in these specific human epithelial cells before.

The discovery suggests that SARS-CoV-2 and potentially other coronaviruses that rely on ACE2 may take advantage of the immune system’s natural defenses. When the body responds to the infection by producing more interferon, that in turn results in production of more ACE2, enhancing the ability of the virus to attach more readily to lung cells. While much more work is needed, the finding indicates that any potential use of interferon as a treatment to fight COVID-19 will require careful monitoring to determine if and when it might help patients.

It’s clear that these new findings, from data that weren’t originally generated with COVID-19 in mind, contained several potentially important new leads. This is another demonstration of the value of basic science. We can also rest assured that, with the outpouring of effort from members of the scientific community around the globe to meet this new challenge, progress along these and many other fronts will continue at a remarkable pace.

Reference:

[1] SARS-CoV-2 receptor ACE2 is an interferon-stimulated gene in human airway epithelial cells and is detected in specific cell subsets across tissues. Ziegler, CGK et al. Cell. April 20, 2020.

Links:

Coronaviruses (National Institute of Allergy and Infectious Diseases/NIH)

Human Cell Atlas (Broad Institute, Cambridge, MA)

Shalek Lab (Harvard Medical School and Massachusetts Institute of Technology, Cambridge)

Ordovas-Montanes Lab (Boston Children’s Hospital, MA)

NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of General Medical Sciences; National Heart, Lung, and Blood Institute


Antibody Points to Possible Weak Spot on Novel Coronavirus

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Credit: Meng Yuan and Nicholas Wu, Wilson Lab, The Scripps Research Institute, La Jolla, CA

Researchers are working hard to produce precise, 3D molecular maps to guide the development of safe, effective ways of combating the coronavirus disease 2019 (COVID-19) pandemic. While there’s been a lot of excitement surrounding the promise of antibody-based tests and treatments, this map you see above highlights another important use of antibodies: to inform efforts to design a vaccine.

This image shows the crystal structure of a human antibody (heavy chain in orange, light chain in yellow), which is a blood protein our immune systems produce to attack viruses and other foreign invaders. This particular antibody, called CR3022, is bound to a key surface protein of the novel coronavirus (white).

The CR3022 antibody actually doesn’t come from someone who has recovered from COVID-19. Instead, it was obtained from a person who, nearly two decades ago, survived a bout of severe acute respiratory syndrome (SARS). The SARS virus, which disappeared in 2004 after a brief outbreak in humans, is closely related to the novel coronavirus that causes COVID-19.

In a recent paper in the journal Science, the NIH-funded lab of Ian Wilson, The Scripps Research Institute, La Jolla, CA, along with colleagues at The University of Hong Kong, sought to understand how the human immune system interacts with and neutralizes this highly infectious virus [1]. The lab did so by employing high-resolution X-ray crystallography tools [2]. They captured the atomic structure of this antibody bound to its target by shooting X-rays through its crystallized form. (An antibody measures about 10 nanometers; a nanometer is 1 billionth of a meter.)

Other researchers had shown previously that CR3022 cross-reacts with the novel coronavirus, although the antibody doesn’t bind tightly enough to neutralize and stop it from infecting cells. So, Wilson’s team went to work to learn precisely where the antibody attaches to the novel virus. Those sites are of special interest because they highlight spots on a virus that are vulnerable to attack—and, as such, potentially good targets for vaccine designers.

A key finding in the new paper is that the antibody binds a highly similar site on both the SARS and novel coronaviruses. Those sites differ in each virus by just four amino acids, the building blocks of a protein.

This is particularly interesting because the antibody pictured above is bound to a spike protein, which is the appendage on both the SARS and novel coronavirus that enables them to bind to a key receptor protein on the surface of human cells, called ACE2. This binding activity marks the first step for these viruses in gaining entry into human cells and infecting them.

The human antibody shown in this image locks onto the virus’s spike protein at a different location than where the human ACE2 protein binds to the novel coronavirus. Intriguingly, the antibody binds to a spot on the novel coronavirus that is usually hidden, except for when virus shapeshifts its structure in order to infect a cell.

The findings suggest that a successful vaccine may be one that elicits antibodies that targets this same spot, but binds more tightly than the one seen above, thereby protecting human cells against the virus that causes COVID-19. However, Wilson notes that this study has just uncovered one potential vulnerability of the novel coronavirus, and it is likely the virus likely has many more that could be revealed with further study.

To continue in this quest to design a safe and effective vaccine, Wilson and his colleagues are now gathering blood samples to collect antibodies from people who’ve recovered from COVID-19. So, we can look forward to seeing some even more revealing images soon.

References:

[1] A highly conserved cryptic epitope in the receptor-binding domains of SARS-CoV-2 and SARS-CoV. Yuan M, Wu NC, Zhu X, Lee CD, So RTY, Lv H, Mok CKP, Wilson IA. Science. 2020 Apr 3.

[2] 100 Years Later: Celebrating the Contributions of X-ray Crystallography to Allergy and Clinical Immunology. Pomés A, Chruszcz M, Gustchina A, Minor W, Mueller GA, Pedersen LC, Wlodawer A, Chapman MD. J Allergy Clin Immunol. 2015 Jul;136(1):29-37.

Links:

Coronaviruses (National Institute of Allergy and Infectious Diseases/NIH)

Coronavirus (COVID-19) (NIH)

Ian Wilson (The Scripps Research Institute, La Jolla, CA)

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


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