This is why Covid-19 may be life-threatening for some patients

Increasing evidence suggests a significant minority of patients get very ill because of an impaired interferon response. PHOTO: REUTERS

LA JOLLA, CALIFORNIA (BLOOMBERG) - When two brothers fell critically ill with Covid-19 at around the same time in March, their doctors were baffled.

Both were young - 29 and 31 years old - and healthy. Yet within days, they couldn't breathe on their own and, tragically, one of them died.

Two weeks later, when a second pair of Covid-stricken brothers, both in their 20s, also appeared in the Netherlands, geneticists were called in to investigate.

What they uncovered was a path leading from severe cases, genetic variations and gender differences to a loss of immune function that may ultimately yield a new approach to treating thousands of coronavirus patients.

The common thread in the research is the lack of a substance called interferon that helps orchestrate the body's defence against viral pathogens and can be infused to treat conditions such as infectious hepatitis.

Now, increasing evidence suggests that a significant minority of Covid-19 patients get very ill because of an impaired interferon response.

Twin landmark studies published on Thursday (Sept 24) in the journal Science showed that insufficient interferon may lurk at a dangerous turning point in Sars-CoV-2 infections.

"It looks like this virus has one big trick," said Professor Shane Crotty of the Centre for Infectious Disease and Vaccine Research at the La Jolla Institute for Immunology in California.

"That big trick is to avoid the initial innate immune response for a significant period of time and, in particular, avoid an early type-1 interferon response."

The work highlights the potential for interferon-based therapies to enlarge a slowly accumulating range of Covid-19 treatments.

These include Gilead Sciences' remdesivir and convalescent plasma, a component of the blood of recovered patients that may contain beneficial immune factors.

These treatments provide limited benefit and are typically used in very sick, hospitalised patients.

The possibility that interferon may help some people is enticing because it appears most efficacious in the early stages of infection, when life-threatening respiratory failure could still be averted.

Dozens of studies of interferon treatment are now recruiting Covid-19 patients.

"We think timing may be essential because it's only in the very early phase one can really battle the virus particles and defend against infection," said Associate Professor Alexander Hoischen, head of the genomic technologies and immuno-genomics group at Radboud University Medical Centre in Nijmegen that analysed the DNA of the two sets of brothers.

Being male, elderly, and having underlying medical conditions can all raise patients' risk of life-threatening Covid-19.

But even within these groups, disease severity varies widely.

Scientists have speculated that other factors influence susceptibility, including pre-existing levels of inflammation and immunity, the amount of virus that starts an infection, and patients' genetic makeup.

New Nexus Interferon's role represents a new nexus in Covid-19's complex interaction with the human immune system.

Many patients suffer their worst complications because of an immune overreaction sometimes called a cytokine storm, and may benefit from dexamethasone, a cheap generic that calms these storms.

"It's a very interesting disease because too little immunity is no good," Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on Sept 10 in an online briefing for Massachusetts General Hospital staff.

"Too much immunity is really, really bad."

Whether sufficient interferon is available early or late in Covid-19 cases has a major bearing on disease severity, according to Professor Yuen Kwok Yung, chair of infectious diseases in the University of Hong Kong's department of microbiology.

Ideally, production of the antiviral substance would be triggered when immune cells encounter Sars-CoV-2 genetic material, stopping rapid viral reproduction inside the body and averting complications, he said.

"But the Sars-CoV-2 virus has anti-interferon genes which can stop or antagonise the production or effect of interferon," said Prof Yuen, who measured the effects in human lung tissue.

If the interferon response is delayed and the amount of virus in the body peaks at a high level, other parts of the immune system will be "awakened".

'REALLY DISASTROUS'

That may trigger lung-injuring inflammation - collateral damage from an excessive immune reaction to the virus.

"This is really disastrous," he said.

Some people are known to have trouble fighting infections because they make antibodies that deactivate their own interferon.

On Thursday, a global consortium of researchers said such immune reactions to the protein could account for life-threatening Covid-19 pneumonia in at least 2.6 per cent of women and 12.5 per cent of men.

Interferon-blocking antibodies appeared in 101 of 987 patients with severe disease, but none of 663 people with an asymptomatic or mild case, according to the study in Science.

Patients over age 65 were also more likely than younger ones to have the autoimmune abnormality, which was "clinically silent until the patients were infected with Sars-CoV-2", the group of more than 100 scientists said.

'FIRST EXPLANATION'

"These findings provide a first explanation for the excess of men among patients with life-threatening Covid-19 and the increase in risk with age," the researchers led by Professor Jean-Laurent Casanova, head of Rockefeller University's St Giles Laboratory of Human Genetics of Infectious Diseases in New York, said.

"They also provide a means of identifying individuals at risk of developing life-threatening Covid-19."

Genetic analysis of Covid-19 patients published in the same journal revealed two dozen gene mutations that had been "silent" until patients were infected by Sars-CoV-2.

Researchers - many of them also involved in the antibody study - sequenced the genomes of 659 patients with life-threatening cases of the disease; 3.5 per cent carried genetic variations that inhibit interferon production.

Those genetic flaws were similar to the ones that Prof Hoischen and his colleagues from a dozen Dutch centres described in the Journal Of The American Medical Association two months ago.

The two sets of brothers had inherited a gene mutation that impaired the interferon response, keeping their immune systems from fighting the coronavirus until it had replicated for days.

In the Dutch men, the effects were cruel.

The first, a young father from a town in the southern Netherlands, suffered shortness of breath, cough and fever at home for eight days before admission to intensive care.

He was to spend 33 days in the hospital, 10 of them on a ventilator.

RAGING FEVER

His 29-year-old brother succumbed to Covid-19 in an intensive care unit in Rotterdam after being treated for shock and a fever that soared to 44 deg C.

When doctors at Radboud learned of his younger sibling's case, as well as a second pair - 21- and 23-year-old brothers also in respiratory failure - they went looking for a genetic cause.

They found a mutation that was carried on the X chromosome.

Defects on this chromosome are more likely to affect men, who have only one copy, while women have two.

The men's mutations are rare - occurring in 1 in 10,000 people - and an unlikely explanation for the vast majority of severe Covid-19 cases.

But the studies in Science indicate that various forms of interferon dysfunction may underlie as many as 14 per cent of critical patients, and that screening and targeted treatment might prevent severe illnesses and deaths.

"If we manage to get them into our university medical centre early enough," Prof Hoischen said, "our clinicians may be able to treat them with interferons."

Other ways of overcoming auto-immunity, like the removal of antibodies against interferon from the blood, called plasmapheresis, could also help patients.

On the other hand, patients who produce antibodies against interferon shouldn't donate blood products for treating other patients.

"The rare diseases and the more common forms of the same disease may converge, and we can learn from each other," said Prof Hoischen.

"That's the hope."

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