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Caught on Camera: Neutralizing Antibodies Interacting with SARS-CoV-2

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Caption: Illustration showing the binding regions for the four classes of SARS-CoV-2 neutralizing antibodies. They bind to a part of the virus’s spike protein called the receptor binding domain (gray). Credit: Christopher Barnes, California Institute of Technology, Pasadena

As this long year enters its final month, there is good reason to look ahead to 2021 with optimism that the COVID-19 pandemic will finally be contained. The Food and Drug Administration is now reviewing the clinical trial data of the Pfizer and Moderna vaccines to ensure their safety and efficacy. If all goes well, emergency use authorization could come very soon, allowing immunizations to begin.

Work also continues on developing better therapeutics against SARS-CoV-2, the novel coronavirus that causes COVID-19. Though we’ve learned a great deal about this coronavirus in a short time, structural biologists continue to produce more detailed images that reveal more precisely where and how to target SARS-CoV-2. This research often involves neutralizing antibodies that circulate in the blood of most people who’ve recovered from COVID-19. The study of such antibodies and how they interact with SARS-CoV-2 offers critical biological clues into how to treat and prevent COVID-19.

A recent study in the journal Nature brings more progress, providing the most in-depth analysis yet of how human neutralizing antibodies physically grip SARS-CoV-2 to block it from binding to our cells [1]. To conduct this analysis, a team of NIH-supported structural biologists, led by postdoc Christopher Barnes and Pamela Björkman, California Institute of Technology, Pasadena, used the power of cryo-electron microscopy (cryo-EM) to capture complex molecular interactions at near-atomic scale.

People infected with SARS-CoV-2 (or any foreign substance, for that matter) generate thousands of different versions of attack antibodies. Some of these antibodies are very good at sticking to the coronavirus, while others attach only loosely. Barnes used cryo-EM to capture highly intricate pictures of eight different human neutralizing antibodies bound tightly to SARS-CoV-2. Each of these antibodies, which had been isolated from patients a few weeks after they developed symptoms of COVID-19, had been shown in lab tests to be highly effective at blocking infection.

The researchers mapped all physical interactions between several human neutralizing antibodies and SARS-CoV-2’s spike protein that stud its surface. The virus uses these spiky extensions to infect a human cell by grabbing on to the angiotensin-converting enzyme 2 (ACE2) receptor. The molecular encounter between the coronavirus and ACE2 takes place via one or more of a trio of three protein domains, called receptor-binding domains (RBDs), that jut out from its spikes. RBDs flap up and down in the fluid surrounding cells, “reaching up” to touch and enter, or “laying down” to hide from an infected person’s antibodies and immune cells. Only an “up” RBD can attach to ACE2 and get into a cell.

Taken together with other structural information known about SARS-CoV-2, Barnes’ cryo-EM snapshots revealed four different types of shapes, or classes, of antibody-spike combinations. These high-resolution molecular views show that human neutralizing antibodies interact in many different ways with SARS-CoV-2: blocking access to either one or more RBDs in their “up” or “down” positions.

These results tell us a number of things, including underscoring why strategies that combine multiple types of antibodies in an “antibody cocktail” might likely offer broader protection against infection than using just a single type of antibody. Indeed, that approach is currently being tested in patients with COVID-19.

The findings also provide a molecular guide for custom-designing synthetic antibodies in the lab to foil SARS-CoV-2. As one example, Barnes and his team observed that one antibody completely locked all three RBDs into closed (“down”) positions. As you might imagine, scientists might want to copy that antibody type when designing an antibody-based drug or vaccine.

It is tragic that hundreds of thousands of people have died from this terrible new disease. Yet the immune system helps most to recover. Learning as much as we possibly can from those individuals who’ve been infected and returned to health should help us understand how to heal others who develop COVID-19, as well as inform precision design of additional vaccines that are molecularly targeted to this new foe.

While we look forward to the arrival of COVID-19 vaccines and their broad distribution in 2021, each of us needs to remember to practice the three W’s: Wear a mask. Watch your distance (stay 6 feet apart). Wash your hands often. In parallel with everyone adopting these critical public health measures, the scientific community is working harder than ever to meet this moment, doing everything possible to develop safe and effective ways of treating and preventing COVID-19.

Reference:

[1] SARS-CoV-2 neutralizing antibody structures inform therapeutic strategies. Barnes CO, Jette CA, Abernathy ME, et al. Nature. 2020 Oct 12. [Epub ahead of print].

Links:

Coronavirus (COVID-19) (NIH)

Combat COVID (U.S. Department of Health and Human Services, Washington, D.C.)

Freezing a Moment in Time: Snapshots of Cryo-EM Research (National Institute of General Medical Sciences/NIH)

Björkman Lab (California Institute of Technology, Pasadena)

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


Mini-Lungs in a Lab Dish Mimic Early COVID-19 Infection

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Credit: Arvind Konkimalla, Tata Lab, Duke University, Durham, NC

Researchers have become skilled at growing an array of miniature human organs in the lab. Such lab-grown “organoids” have been put to work to better understand diabetes, fatty liver disease, color vision, and much more. Now, NIH-funded researchers have applied this remarkable lab tool to produce mini-lungs to study SARS-CoV-2, the coronavirus that causes COVID-19.

The intriguing bubble-like structures (red/clear) in the mini-lung pictured above represent developing alveoli, the tiny air sacs in our lungs, where COVID-19 infections often begin. In this organoid, the air sacs consist of many thousands of cells, all of which arose from a single adult stem cell isolated from tissues found deep within healthy human lungs. When carefully nurtured in lab dishes, those so-called alveolar epithelial type-2 cells (AT2s) begin to multiply. As they grow, they spontaneously assemble into structures that closely resemble alveoli.

A team led by Purushothama Rao Tata, Duke University School of Medicine, Durham, NC, developed these mini-lungs in a quest to understand how adult stem cells help to regenerate damaged tissue in the deepest recesses of the lungs, where SARS-CoV-2 attacks. In earlier studies, the researchers had shown it was possible for these cells to produce miniature alveoli. But there was a problem: the “soup” they used to nurture the growing cells included ingredients that weren’t well defined, making it hard to characterize the experiments fully.

In the study, now reported in Cell Stem Cell, the researchers found a way to simplify and define that brew. For the first time, they could produce mini-lungs consisting only of human lung cells. By growing them in large numbers in the lab, they can now learn more about SARS-CoV-2 infection and look for new ways to prevent or treat it.

Tata and his collaborators at the University of North Carolina, Chapel Hill, have already confirmed that SARS-CoV-2 infects the mini-lungs via the critical ACE2 receptor, just as the virus is known to do in the lungs of an infected person.

Interestingly, the cells also produce cytokines, inflammatory molecules that have been tied to tissue damage. The findings suggest the cytokine signals may come from the lungs themselves, even before immune cells arrive on the scene.

The heavily infected lung cells eventually self-destruct and die. In an unexpected turn of events, they even induce cell death in some neighboring healthy cells that are not infected. The relevance of the studies to the clinic was boosted by the finding that the gene activity patterns in the mini-lungs are a close match to those found in samples taken from six patients with severe COVID-19.

Now that he’s got the recipe down, Tata is busy making organoids and helping to model COVID-19 infections, with the hope of identifying and testing promising new treatments. It’s clear these mini-lungs are breathing some added life into the basic study of COVID-19.

Reference:

[1] Human lung stem cell-based alveolospheres provide insights into SARS-CoV-2-mediated interferon responses and pneumocyte dysfunction. Katsura H, Sontake V, Tata A, Kobayashi Y, Edwards CE, Heaton BE, Konkimalla A, Asakura T, Mikami Y, Fritch EJ, Lee PJ, Heaton NS, Boucher RC, Randell SH, Baric RS, Tata PR. Cell Stem Cell. 2020 Oct 21:S1934-5909(20)30499-9.

Links:

Coronavirus (COVID-19) (NIH)

Tata Lab (Duke University School of Medicine, Durham, NC)

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


What We Know About COVID-19’s Effects on Child and Maternal Health

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At Home with Diana Bianchi

There’s been a lot of focus, and rightly so, on why older adults and adults with chronic disease appear to be at increased risk for coronavirus disease 2019 (COVID-19). Not nearly as much seems to be known about children and COVID-19.

For example, why does SARS-CoV-2, the novel coronavirus that causes COVID-19, seem to affect children differently than adults? What is the psychosocial impact of the pandemic on our youngsters? Are kids as infectious as adults?

A lot of interesting research in this area has been published recently. That includes the results of a large study in South Korea in which researchers traced the person-to-person spread of SARS-CoV-2 in the early days of the pandemic. The researchers found children younger than age 10 spread the virus to others much less often than adults do, though the risk is not zero. But children age 10 to 19 were found to be just as infectious as adults. That obviously has consequences for the current debate about opening the schools.

To get some science-based answers to these and other questions, I recently turned to one of the world’s leading child health researchers: Dr. Diana Bianchi, Director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). Dr. Bianchi is a pediatrician with expertise in newborn medicine, neonatology, and reproductive genetics. Here’s a condensed transcript of our chat, which took place via videoconference, with Diana linking in from Boston and me from my home in Chevy Chase, MD:

Collins: What is the overall risk of children getting COVID-19? We initially heard they’re at very low risk. [NOTE: Since the recording of this interview, new data has emerged from state health departments that suggest that as much as 10 percent of new cases of COVID-19 occur in children.]

Bianchi: Biological factors certainly play some role. We know that the virus often enters the body via cells in the nasal passage. A recent study showed that, compared to adults, children’s nasal cells have less of the ACE2 receptor, which the virus attaches to and uses to infect cells. In children, the virus probably has less of an opportunity to grab onto cells and get into the upper respiratory tract.

Importantly, social reasons also play a role in that low percentage. Children have largely been socially isolated since March, when many schools shut down. By and large, young kids have been either home or playing in their backyards.

Collins: If kids do get infected with SARS-CoV-2, the virus that causes COVID-19, what kind of symptoms are displayed?

Bianchi: Children tend to be affected mildly. Relatively few children end up in intensive care units. The most common symptoms are: fever, in about 60 percent of children; cough; and a mild respiratory illness. It’s a different clinical presentation. Children seem to be more prone to vomiting, diarrhea, severe abdominal pain, and other gastrointestinal problems.

Collins: Are children as infectious as adults?

Bianchi: We suspect that older kids probably are. A recently published meta-analysis, or systematic review of the medical literature, also found about 20 percent of infected kids are asymptomatic. There are probably a lot of kids out there who can potentially infect others.

Collins: Do you see a path forward here for schools in the fall?

Bianchi: I think the key word is flexibility. We must remain flexible in the months ahead. Children have struggled from being out of school, and it’s not just the educational loss. It’s the whole support system, which includes the opportunity to exercise. It includes the opportunity to have teachers and school staff looking objectively at the kids to see if they are psychologically well.

The closing of schools has also exacerbated disparities. Schools provide meals for many kids in need, and some have had a lot of food insecurity for the past several months. Not to mention kids in homeless situations often don’t have access to the internet and other learning tools. So, on the whole, being in school is better for children than not being there. That’s how most pediatricians see it. However, we don’t want to put children at risk for getting sick.

Collins: Can you say a little bit more about the consequences, particularly for young children, of being away from their usual areas of social interaction? That’s true this summer as well. Camps that normally would be a place where lots of kids would congregate have either been cancelled or are being conducted in a very different way.

Bianchi: Thus far, most of the published information that we have has really been on the infection and the clinical presentations. Ultimately, I think there will be a lot of information about the behavioral and developmental consequences of not being exposed to other children. I think that older children are also really suffering from not having a daily structure, for example, through sports.

For younger children, they need to learn how to socialize. There are advantages to being with your parents. But there are a lot of social skills that need to be learned without them. People talk about the one-eyed babysitter, YouTube. The American Academy of Pediatrics has issued recommendations for limiting screen time. That’s gone out the window. I’ve talked with a lot of my staff members who are struggling with this balance between educating or entertaining their children and having so-called quality time, and the responsibility to do their jobs.

Collins: What about children with disabilities? Are they in a particularly vulnerable place?

Bianchi: Absolutely. Sadly, we don’t hear a lot about children with disabilities as a vulnerable population. Neither do we hear a lot about the consequences of them not receiving needed services. So many children with disabilities rely on people coming into their homes, whether it’s to help with respiratory care or to provide physical or speech therapy. Many of these home visits are on hold during the pandemic, and that can cause serious problems. For example, you can’t suction a trachea remotely. Of course, you can do speech therapy remotely, but that’s not ideal for two reasons. First, face-to-face interactions are still better, and, secondly, disparities can factor into the equation. Not all kids with disabilities have access to the internet or all the right equipment for online learning.

Collins: Tell me a little bit more about a rare form of consequences from COVID-19, this condition called MIS-C, Multi-System Inflammatory Syndrome of Children. I don’t think anybody knew anything about that until just a couple of months ago.

Bianchi: Even though there were published reports of children infected with SARS-CoV-2 in China in January, we didn’t hear until April about this serious new inflammatory condition. Interestingly, none of the children infected with SARS-CoV-2 in China or Japan are reported to have developed MIS-C. It seemed to be something that was on the European side, predominantly the United Kingdom, Italy, and France. And then, starting in April and May, it was seen in New York and the northeastern United States.

The reason it’s of concern is that many of these children are gravely ill. I mentioned that most children have a mild illness, but the 0.5 percent who get the MIS-C are seriously ill. Almost all require admission to the ICU. The scary thing is they can turn on a dime. They present with more of a prolonged fever. They can have very severe abdominal pain. In some cases, children have been thought to have appendicitis, but they don’t. They have serious cardiac issues and go into shock.

The good news is the majority survive. Many require ventilators and blood-pressure support. But they do respond to treatment. They tend to get out of the hospital in about a week. However, in two studies of MIS-C recently published in New England Journal of Medicine, six children died out of 300 children. So that’s what we want to avoid.

Collins: In terms of the cause, there’s something puzzling about MIS-C. It doesn’t seem to be a direct result of the viral infection. It seems to come on somewhat later, almost like there’s some autoimmune response.

Bianchi: Yes, that’s right. MIS-C does tend to occur, on an average, three to four weeks later. The NIH hosted a conference a couple weeks ago where the top immunologists in the world were talking about MIS-C, and everybody has their piece of the elephant in terms of a hypothesis. We don’t really know right now, but it does seem to be associated with some sort of exuberant, post-infectious inflammatory response.

Is it due to the fact that the virus is still hiding somewhere in the body? Is the body reacting to the virus with excessive production of antibodies? We don’t know. That will be determined, hopefully, within weeks or months.
Collins: And I know that your institute is taking a leading role in studying MIS-C.

Bianchi: Yes. Very shortly after the first cases of MIS-C were being described in the United States, you asked me and Gary Gibbons, director of NIH’s National Heart Lung and Blood Institute, to cochair a taskforce to develop a study designed to address MIS-C. Staff at both institutes have been working, in collaboration with NIH’s National Institute of Allergy and Infectious Diseases, to come up with the best possible way to approach this public health problem.

The study consists of a core group of kids who are in the hospital being treated for MIS-C. We’re obtaining biospecimens and are committed to a central platform and data-sharing. There’s an arm of the study that’s looking at long-term issues. These kids have transient coronary artery dilation. They have a myocarditis. They have markers of heart failure. What does that imply long-term for the function of their hearts?

We will also be working with several existing networks to identify markers suggesting that a certain child is at risk. Is it an underlying immune issue, or is it ethnic background? Is it this a European genomic variant? Exactly what should we be concerned about?

Collins: Let me touch on the genomics part of this for a minute, and that requires a brief description. The SARS-CoV-2 novel coronavirus is crowned in spiky proteins that attach to our cells before infecting them. These spike proteins are made of many amino acids, and their precise sequential order can sometimes shift in subtle ways.

Within that sequential order at amino acid 614, a shift has been discovered. The original Chinese isolate, called the D version, had aspartic acid there. It seems the virus that spread from Asia to the U.S. West Coast also has aspartic acid in that position. But the virus that traveled to Italy and then to the East Coast of the U.S. has a glycine there. It’s called the G version.

There’s been a lot of debate about whether this change really matters. More data are starting to appear suggesting that the G version may be more infectious than the D version, although I’ve seen no real evidence of any difference in severity between the two.

Of course, if the change turned out to be playing a role in MIS-C, you would expect not to have seen so many cases on the West Coast. Has anyone looked to see if kids with the D version of the virus ever get MIS-C?

Bianchi: It hasn’t been reported. You could say that maybe we don’t get all the information from China. But we do get it from Japan. In Japan, they’ve had the D version, and they haven’t had MIS-C.

Collins: Let’s talk about expectant mothers. What is the special impact of COVID-19 on them?

Bianchi: Recently, a lot of information has come out about pregnant women and the developing fetus. A recent report from the Centers for Disease Control and Prevention suggested that pregnant women are at a greatly increased risk of hospitalization. However, the report didn’t divide out hospitalizations that would be expected for delivering a baby from hospitalizations related to illness. But the report did show that pregnant women are at a higher risk of needing respiratory support and having serious illness, particularly if there is an underlying chronic condition, such as chronic lung disease, diabetes or hypertension.

Collins: Do we know the risk of the mother transmitting the coronavirus to the fetus?

Bianchi: What we know so far is the risk of transmission from mother to baby appears to be small. Now, that’s based on the fact that available studies seem to suggest that the ACE2 receptor that the virus uses to bind to our cells, is not expressed in third trimester placental tissue. That doesn’t mean it’s not expressed earlier in gestation. The placenta is so dynamic in terms of gene expression.

What we do know is there’s a lot of ACE2 expression in the blood vessels. An interesting recent study showed in the third trimester placenta, the blood vessels had taken a hit. There was actual blood vessel damage. There was evidence of decreased oxygenation in the placenta. We don’t know the long-term consequences for the baby, but the placentas did not look healthy.

Collins: I have a friend whose daughter recently was ready to deliver her baby. As part of preparing for labor, she had a COVID-19 test. To her surprise and dismay, she was positive, even though she had no symptoms. She went ahead with the delivery, but then the baby was separated from her for a time because of a concern about the mother transmitting the virus to her newborn. Is separation widely recommended?

Bianchi: I think most hospitals are softening on this. [NOTE: The American Academy of Pediatrics recently issued revised recommendations about labor and delivery, as well as about breastfeeding, during COVID-19]

In the beginning, hospitals took a hard line. For example, no support people were allowed into the delivery room. So, women were having more home deliveries, which are far more dangerous, or signing up to give birth at hospitals that allowed support people.

Now more hospitals are allowing a support person in the room during delivery. But, in general, they are recommending that the mother and the support person get tested. If they’re negative, everything’s fine. If the support person is positive, he or she’s not allowed to come in. If the mother is positive, the baby is separated, generally, for testing. In many hospitals, mothers are given the option of reuniting with the baby.

There’s also been a general discussion about mothers who test positive breastfeeding. The more conservative recommendation is to pump the milk and allow somebody else to bottle-feed the baby while the mother recovers from the infection. I should also mention a recent meta-analysis in the United Kingdom. It suggested that a cesarean section delivery is not needed because of SARS-CoV-2 positivity alone. It also found there’s no reason for SARS-CoV-2 positive women not to breast feed.

Collins: Well, Diana, thank you so much for sharing your knowledge. If there’s one thing you wanted parents to take away from this conversation, what would that be?

Bianchi: Well, I think it’s natural to be concerned during a pandemic. But I think parents should be generally reassuring to their children. We’ll get through this. However, I would also say that if a parent notices something unusual going on with a child—skin rashes, the so-called blue COVID toes, or a prolonged fever—don’t mess around. Get your child medical attention as soon as possible. Bad things can happen very quickly to children infected with this virus.

For the expectant parents, hopefully, their obstetricians are counseling them about the fact that they are at high risk. I think that women with chronic conditions really need to be proactive. If they’re not feeling well, they need to go to the emergency room. Again, things can happen quickly with this virus.

But the good news is the babies seem to do very well. There’s no evidence of birth defects so far, and very limited evidence, if at all, of vertical transmission. I think they can feel good about their babies. They need to pay attention to themselves.

Collins: Thank you, Diana, for ending on those wise words.

Bianchi: Thanks, Francis.

Links:

Coronavirus (COVID-19) (NIH)

Diana W. Bianchi, MD, Biosketch of the NICHD Director (Eunice Kennedy Shriver National Institute of Child Health and Human Development/NIH)

Responding to COVID-19, Director’s Corner, NICHD, June 3, 2020

National Child & Maternal Health Education Program (NICHD)

Pregnancy (NICHD)


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)


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