The United Kingdom scientists are to begin testing a treatment that said could counteract the effects of COVID-19 in patients who are most severely ill.
Those with the severest form of the disease have been found to have meager numbers of an immune cell called a T-cell.
The clinical trial will determine whether a drug called Interleukin 7, believed to raise T-cell numbers, will improve recovery for patients.
This includes researchers from the Francis Crick Institute, King's College London, and the Hospital of Guy and St Thomas.
Crashing T-cells
Researchers believe that checking patients for immune problems at hospital entry could help doctors identify those most likely to decline.
They have looked at 60 COVID-19 patients' immune cells in the blood and found an apparent crash in the number of T-cells.
The team found in their study that patients who do worse have a problem with a particular type of T-cell that usually eradicates cells infected with viruses. They also have far fewer immune cells that can be involved in tissue repair, called basophils.
It indicates that the virus skews the immune response in critically ill patients, and takes out one of the most important natural defenses of the body.
Adrian Hayday, who manages Crick's Immunosurveillance Laboratory, said the changes they witnessed in the blood are "not subtle." He added patients with these features seem more likely to experience severe disease, requiring intensive management.
Hayday, who also serves as a Crick Institute professor, said it was a "great surprise" to see what was going on with the immune cells.
"They're trying to protect us, but the virus seems to be doing something that's pulling the rug from under them because their numbers have declined dramatically," he told BBC.
The finding could also be of assistance to researchers developing new treatments and vaccines. If scientists were able to discover what causes the immune cells to disappear and malfunction, they could hunt for a drug to stop it.
The team suggests that supplying patients with recombinant IL-7 (Interleukin 7), a natural protein that promotes T cell function, could help with the issue. It has called for immediate trials to see if it will work, the researchers added.
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Coronavirus doesn't discriminate
Professor Hayday said coronavirus also doesn't simply discriminate according to age and underlying condition.
"Although in smaller numbers, younger, healthy individuals can also be struck down with severe symptoms," he said.
Hayday said clinical treatment decisions can be guided by the state-of-the-art knowledge of the immune system.
Manu Shankar-Hari, an intensive care medicine consultant at the Guy's and St Thomas' NHS Foundation Trust, told The Telegraph health workers routinely measure white blood cell counts in all hospitalized patients.
"Our new study clearly underlines the enormous potential for measuring the status of particular types of immune cells involved in fighting the virus."
