An impaired count of natural killer (NK) immune cells and reduced ability to destroy infected cells are key characteristics of severe COVID-19 infection, according to newly published research in the journal Blood Advances.
A team of researchers at the University of Alberta and University of Calgary followed 12 patients with severe COVID-19 symptoms at hospitals in Edmonton. They found that the patients had a reduced number of NK cells and that cytokines—molecules that aid cell-to-cell communication in immune responses and stimulate the movement of cells toward sites of inflammation, infection and trauma—were also markedly reduced.
“This suggests there’s something in particular about how this virus triggers the immune system, but also how it changes how the immune system can self-regulate,” said Mohamed Osman, a rheumatologist and immunologist and assistant professor of medicine in the U of A’s Faculty of Medicine & Dentistry.
A substantial proportion of COVID-19 patients admitted to intensive care die of pneumonia due to a cytokine storm, where the body’s immune system goes into overdrive and attacks itself rather than fighting off the illness. NK cells are a key regulator of the immune response, controlling how active it becomes.
According to Osman, the findings of the study were confirmed with the help of Faisal Khan, director of the Hematology Translational Lab at the University of Calgary and associate professor at the Cumming School of Medicine. Since the initial publication of the findings, Osman said the team has also added data from an additional 18 patients showing similar results.
The team is now working to get a better sense of whether the dampened NK cells are unique to the virus when it causes severe COVID-19. They are seeking to compare their findings with those from patients who have mild COVID-19 symptoms and others who have respiratory infections unrelated to COVID-19. If it is unique to severe COVID-19, the team hopes in future studies to identify genetic signatures that may exacerbate the problem and could be used as a biomarker to identify patients who may be at higher risk of developing severe symptoms.
The team is also paying close attention to clinical trials of potential COVID-19 therapies that boost NK cell function, said Osman. One such ongoing trial is for the drug tocilizumab.
“They’ve found that in those people who responded to tocilizumab, the NK cell function was restored,” said Osman. “That suggests this is a very nice biomarker that can be used to tell you whether the immune response to COVID-19 is actually resolving or not.”