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CRISPR-Based Anti-Viral Therapy Could One Day Foil the Flu—and COVID-19

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Artistic rendering of CRISPR Cas13a as scissors

CRISPR gene-editing technology has tremendous potential for making non-heritable DNA changes that can treat or even cure a wide range of devastating disorders, from HIV to muscular dystrophy Now, a recent animal study shows that another CRISPR system—targeting viral RNA instead of human DNA—could work as an inhaled anti-viral therapeutic that can be preprogrammed to seek out and foil potentially almost any flu strain and many other respiratory viruses, including SARS-CoV-2, the coronavirus that causes COVID-19.

How can that be? Other CRISPR gene-editing systems rely on a sequence-specific guide RNA to direct a scissor-like, bacterial enzyme (Cas9) to just the right spot in the genome to cut out, replace, or repair disease-causing mutations. This new anti-viral CRISPR system also relies on guide RNA. But the guide instead directs a different bacterial enzyme, called Cas13a, to the right spot in the viral genome to bind and cleave viral RNA and stop viruses from replicating in lung cells.

The findings, recently published in the journal Nature Biotechnology [1], come from the lab of Philip Santangelo, Georgia Institute of Technology and Emory University, Atlanta. Earlier studies by other groups had shown the potential of Cas13 for degrading the RNA of influenza viruses in a lab dish [2,3]. In this latest work, Santangelo and colleagues turned to mice and hamsters to see whether this enzyme could actually work in the lung tissue of a living animal.

What’s interesting is how Santangelo’s team did it. Rather than delivering the Cas13a protein itself to the lungs, the CRISPR system works by supplying a messenger RNA (mRNA) with the instructions to make the anti-viral Cas13a protein. This is the same idea as the Pfizer and Moderna mRNA-based COVID-19 vaccines, which temporarily direct your muscle cells to produce viral spike proteins that launch an immune response. In this case, the lung cells translate the Cas13a mRNA to produce the protein. Directed by the guide RNA that was also delivered to the same cells, Cas13a degrades the viral RNA and stops the infection. Because mRNA doesn’t enter the cell’s nucleus, it doesn’t interact with DNA and raise potential concerns about causing unwanted genetic changes.

The researchers designed guide RNAs that were specific to a shared, highly conserved portion of influenza viruses involved in replicating their genome and infecting other cells. They also designed another set directed to key portions of SARS-CoV-2.

Next, they delivered the Cas13a mRNA and guides straight to the lungs of animals using an adapted nebulizer, just like those used to deliver medicines to the lungs of people. In mice with influenza, Cas13a degraded influenza RNA in the lungs and the animals recovered without any apparent side effects. In SARS-CoV-2-infected hamsters, the same approach limited the virus’s ability to replicate in cells as the animals COVID-19-like symptoms improved.

The findings are the first to show that mRNA can be used to express the Cas13a protein in living lung tissue, not just in cells in a dish. It’s also the first to show that the bacterial Cas13a protein is effective at slowing or stopping replication of SARS-CoV-2. The latter raises hope that this CRISPR system could be quickly adapted to fight any future novel coronaviruses that develop the ability to infect humans.

The researchers report that this approach has potential to work against the vast majority—99 percent—of the flu strains that have circulated around the world over the last century. It also should be equally effective against the new and more contagious variants of SARS-CoV-2 now circulating around the globe. While more study is needed to understand the safety of such an anti-viral approach before trying it in humans, what’s clear is basic research advances like this one hold great potential for helping us to fight life-threatening respiratory viruses of the past, present, and future.

References:

[1] Treatment of influenza and SARS-CoV-2 infections via mRNA-encoded Cas13a in rodents. Blanchard EL, Vanover D, Bawage SS, Tiwari PM, Rotolo L, Beyersdorf J, Peck HE, Bruno NC, Hincapie R, Michel F, Murray J, Sadhwani H, Vanderheyden B, Finn MG, Brinton MA, Lafontaine ER, Hogan RJ, Zurla C, Santangelo PJ. Nat Biotechnol. 2021 Feb 3. [Published online ahead of print.]

[2] Programmable inhibition and detection of RNA viruses using Cas13. Freije CA, Myhrvold C, Boehm CK, Lin AE, Welch NL, Carter A, Metsky HC, Luo CY, Abudayyeh OO, Gootenberg JS, Yozwiak NL, Zhang F, Sabeti PC. Mol Cell. 2019 Dec 5;76(5):826-837.e11.

[3] Development of CRISPR as an antiviral strategy to combat SARS-CoV-2 and influenza. Abbott TR, Dhamdhere G, Liu Y, Lin X, Goudy L, Zeng L, Chemparathy A, Chmura S, Heaton NS, Debs R, Pande T, Endy D, La Russa MF, Lewis DB, Qi LS. Cell. 2020 May 14;181(4):865-876.e12.

Links:

COVID-19 Research (NIH)

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

Santangelo Lab (Georgia Institute of Technology, Atlanta)


To Beat COVID-19, Social Distancing is a Must

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Teleworking with family at home
gettyimages/SDI Productions

Even in less challenging times, many of us try to avoid close contact with someone who is sneezing, coughing, or running a fever to avoid getting sick ourselves. Our attention to such issues has now been dramatically heightened by the emergence of a novel coronavirus causing a pandemic of an illness known as COVID-19.

Many have wondered if we couldn’t simply protect ourselves by avoiding people with symptoms of respiratory illness. Unfortunately, the answer is no. A new study shows that simply avoiding symptomatic people will not go far enough to curb the COVID-19 pandemic. That’s because researchers have discovered that many individuals can carry the novel coronavirus without showing any of the typical symptoms of COVID-19: fever, dry cough, and shortness of breath. But these asymptomatic or only mildly ill individuals can still shed virus and infect others.

This conclusion adds further weight to the recent guidance from U.S. public health experts: what we need most right now to slow the stealthy spread of this new coronavirus is a full implementation of social distancing. What exactly does social distancing mean? Well, for starters, it is recommended that people stay at home as much as possible, going out only for critical needs like groceries and medicines, or to exercise and enjoy the outdoors in wide open spaces. Other recommendations include avoiding gatherings of more than 10 people, no handshakes, regular handwashing, and, when encountering someone outside of your immediate household, trying to remain at least 6 feet apart.

These may sound like extreme measures. But the new study by NIH-funded researchers, published in the journal Science, documents why social distancing may be our best hope to slow the spread of COVID-19 [1]. Here are a few highlights of the paper, which looks back to January 2020 and mathematically models the spread of the coronavirus within China:

• For every confirmed case of COVID-19, there are likely another five to 10 people with undetected infections.
• Although they are thought to be only about half as infectious as individuals with confirmed COVID-19, individuals with undetected infections were so prevalent in China that they apparently were the infection source for 86 percent of confirmed cases.
• After China established travel restrictions and social distancing, the spread of COVID-19 slowed considerably.

The findings come from a small international research team that included NIH grantee Jeffrey Shaman, Columbia University Mailman School of Public Health, New York. The team developed a computer model that enabled researchers to simulate the time and place of infections in a grid of 375 Chinese cities. The researchers did so by combining existing data on the spread of COVID-19 in China with mobility information collected by a location-based service during the country’s popular 40-day Spring Festival, when travel is widespread.

As these new findings clearly demonstrate, each of us must take social distancing seriously in our daily lives. Social distancing helped blunt the pandemic in China, and it will work in other nations, including the United States. While many Americans will likely spend weeks working and studying from home and practicing other social distancing measures, the stakes remain high. If this pandemic isn’t contained, this novel coronavirus could well circulate around the globe for years to come, at great peril to us and our loved ones.

As we commit ourselves to spending more time at home, progress continues to be made in using the power of biomedical research to combat this novel coronavirus. A notable step this week was the launch of an early-stage human clinical trial of an investigational vaccine, called mRNA-1273, to protect against COVID-19 [2]. The vaccine candidate was developed by researchers at NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and their collaborators at the biotechnology company Moderna, Inc., Cambridge, MA.

This Phase 1 NIAID-supported trial will look at the safety of the vaccine—which cannot cause infection because it is made of RNA, not the whole coronavirus—in 45 healthy adults. The first volunteer was injected this past Monday at Kaiser Permanente Washington Health Research Institute, Seattle. If all goes well and larger follow-up clinical studies establish the vaccine’s safety and efficacy, it will then be necessary to scale up production to make millions of doses. While initiating this trial in record time is reason for hope, it is important to be realistic about all of the steps that still remain. If the vaccine candidate proves safe and effective, it will likely take at least 12–18 months before it would be widely available.

In the meantime, social distancing remains one of the best weapons we have to slow the silent spread of this virus and flatten the curve of the COVID-19 pandemic. This will give our health-care professionals, hospitals, and other institutions more valuable time to prepare, protect themselves, and aid the many people whose lives may be on the line from this coronavirus.

Importantly, saving lives from COVID-19 requires all of us—young, old and in-between—to take part. Healthy young people, whose risk of dying from coronavirus is not zero but quite low, might argue that they shouldn’t be constrained by social distancing. However, the research highlighted here demonstrates that such individuals are often the unwitting vector for a dangerous virus that can do great harm—and even take the lives of older and more vulnerable people. Think about your grandparents. Then skip the big gathering. We are all in this together

References:

[1] Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2). Li R, Pei S, Chen B, Song Y, Zhang T, Yang W, Shaman J. Science. 16 March 2020. [Preprint ahead of publication]

[2] NIH clinical trial of investigational vaccine for COVID-19 begins. NIH News Release, March 16, 2020.

Links:

Coronavirus (COVID-19) (NIH)

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

Coronavirus (COVID-19) (Centers for Disease Control and Prevention, Atlanta)

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


These Oddball Cells May Explain How Influenza Leads to Asthma

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Cells of a mouse lung after an H1N1 infection
Credit: Andrew Vaughan, University of Pennsylvania, Philadelphia

Most people who get the flu bounce right back in a week or two. But, for others, the respiratory infection is the beginning of lasting asthma-like symptoms. Though I had a flu shot, I had a pretty bad respiratory illness last fall, and since that time I’ve had exercise-induced asthma that has occasionally required an inhaler for treatment. What’s going on? An NIH-funded team now has evidence from mouse studies that such long-term consequences stem in part from a surprising source: previously unknown lung cells closely resembling those found in taste buds.

The image above shows the lungs of a mouse after a severe case of H1N1 influenza infection, a common type of seasonal flu. Notice the oddball cells (green) known as solitary chemosensory cells (SCCs). Those little-known cells display the very same chemical-sensing surface proteins found on the tongue, where they allow us to sense bitterness. What makes these images so interesting is, prior to infection, the healthy mouse lungs had no SCCs.

SCCs, sometimes called “tuft cells” or “brush cells” or “type II taste receptor cells”, were first described in the 1920s when a scientist noticed unusual looking cells in the intestinal lining [1] Over the years, such cells turned up in the epithelial linings of many parts of the body, including the pancreas, gallbladder, and nasal passages. Only much more recently did scientists realize that those cells were all essentially the same cell type. Owing to their sensory abilities, these epithelial cells act as a kind of lookout for signs of infection or injury.

This latest work on SCCs, published recently in the American Journal of Physiology–Lung Cellular and Molecular Physiology, adds to this understanding. It comes from a research team led by Andrew Vaughan, University of Pennsylvania School of Veterinary Medicine, Philadelphia [2].

As a post-doc, Vaughan and colleagues had discovered a new class of cells, called lineage-negative epithelial progenitors, that are involved in abnormal remodeling and regrowth of lung tissue after a serious respiratory infection [3]. Upon closer inspection, they noticed that the remodeling of lung tissue post-infection often was accompanied by sustained inflammation. What they didn’t know was why.

The team, including Noam Cohen of Penn’s Perelman School of Medicine and De’Broski Herbert, also of Penn Vet, noticed signs of an inflammatory immune response several weeks after an influenza infection. Such a response in other parts of the body is often associated with allergies and asthma. All were known to involve SCCs, and this begged the question: were SCCs also present in the lungs?

Further work showed not only were SCCs present in the lungs post-infection, they were interspersed across the tissue lining. When the researchers exposed the animals’ lungs to bitter compounds, the activated SCCs multiplied and triggered acute inflammation.

Vaughan’s team also found out something pretty cool. The SCCs arise from the very same lineage of epithelial progenitor cells that Vaughan had discovered as a post-doc. These progenitor cells produce cells involved in remodeling and repair of lung tissue after a serious lung infection.

Of course, mice aren’t people. The researchers now plan to look in human lung samples to confirm the presence of these cells following respiratory infections.

If confirmed, the new findings might help to explain why kids who acquire severe respiratory infections early in life are at greater risk of developing asthma. They suggest that treatments designed to control these SCCs might help to treat or perhaps even prevent lifelong respiratory problems. The hope is that ultimately it will help to keep more people breathing easier after a severe bout with the flu.

References:

[1] Closing in on a century-old mystery, scientists are figuring out what the body’s ‘tuft cells’ do. Leslie M. Science. 2019 Mar 28.

[2] Development of solitary chemosensory cells in the distal lung after severe influenza injury. Rane CK, Jackson SR, Pastore CF, Zhao G, Weiner AI, Patel NN, Herbert DR, Cohen NA, Vaughan AE. Am J Physiol Lung Cell Mol Physiol. 2019 Mar 25.

[3] Lineage-negative progenitors mobilize to regenerate lung epithelium after major injury. Vaughan AE, Brumwell AN, Xi Y, Gotts JE, Brownfield DG, Treutlein B, Tan K, Tan V, Liu FC, Looney MR, Matthay MA, Rock JR, Chapman HA. Nature. 2015 Jan 29;517(7536):621-625.

Links:

Asthma (National Heart, Lung, and Blood Institute/NIH)

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

Vaughan Lab (University of Pennsylvania, Philadelphia)

Cohen Lab (University of Pennsylvania, Philadelphia)

Herbert Lab (University of Pennsylvania, Philadelphia)

NIH Support: National Heart, Lung, and Blood Institute; National Institute on Deafness and Other Communication Disorders


Possible Explanation for Why Some People Get More Colds

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Cough

Getty Images/yourstockbank

Colds are just an occasional nuisance for many folks, but some individuals seem to come down with them much more frequently. Now, NIH-funded researchers have uncovered some new clues as to why.

In their study, the researchers found that the cells that line our airways are quite adept at defending against cold-causing rhinoviruses. But there’s a tradeoff. When these cells are busy defending against tissue damage due to cigarette smoke, pollen, pollutants, and/or other airborne irritants, their ability to fend off such viruses is significantly reduced [1].

The new findings may open the door to better strategies for preventing the common cold, as well as other types of respiratory tract infections caused by non-flu viruses. Even small improvements in prevention could have big implications for our nation’s health and economy. Every year, Americans come down with more than 500 million colds and similar infections, leading to reduced work productivity, medical expenses, and other costs approaching $40 billion [2].