'Cytokine storms' are a deadly problem in COVID-19. Researchers are testing promising solutions.

Some of the worst cases of COVID-19 involve patients who appear to get better then suddenly deteriorate, their lungs and other organs failing under an overwhelming immune response called a "cytokine storm." Cytokines are proteins sent out by a body's adaptive immune system — B and T cells — to recruit other immune cells to fight an infection. When the immune system doesn't shut off the cytokines, a storm of cells overwhelms organs, exhausting a body's immune response, causing dangerous inflammation, and attacking healthy tissues.

In COVID-19, scavenger cells called macrophages apparently attack and inflame the lungs, allowing liquid to fill air sacs and causing acute respiratory distress syndrome. An otherwise healthy woman in her 20s had a double lung transplant because COVID-19 irreparably destroyed her lungs, a Chicago hospital announced Thursday.

"It has become increasingly clear in the past few months that, at least in a subset of people who have the virus, calming the storm is the key to survival," The New York Times reports. Researchers are starting trials on several drugs to prevent or pacify cytokine storms, and others have reported some success with a dialysis-like device called CytoSorb that filters out cytokines from a patient's blood and returns it to the body.

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In China and Italy, doctors had some success with a drug called tocilizumab, marketed as Actemra by Roche, which blocks the cytokine interleukin-6 (IL-6). Another drug, Kineret, blocks a different cytokine, IL-1. A recent study published in the journal Science Immunology reported promising preliminary results from an AstraZeneca cancer drug called Calquence, or acalabrutinib, which aims to stop the cytokines at their root. Using a drug like tocilizumab is "like cutting the branches off a tree," Dr. Louis Staudt, a National Cancer Institute scientist and a lead investigator on the study, tells the Times. "Acalabrutinib is going for the trunk of the tree." AstraZeneca has plans to test the drug in larger trials.