Immune cells produced during a severe COVID-19 infection may cause cancerous tumors to shrink, research in mice suggests.

The study, published Friday (Nov. 15) in The Journal of Clinical Investigation, found that genetic information from the virus that causes COVID-19 led the immune system to produce special cells with anti-cancer properties. These immune cells, a type of white blood cell called monocytes, helped shrink several types of cancer in mice.

Bharat and his colleagues had noticed that some patients who had both severe COVID-19 and cancer had their tumors shrink after infection.

So they analyzed blood samples from people who had had a bout of severe COVID-19 and found that monocytes produced after severe infection retained a special receptor that bound well to a specific sequence of COVID-19 RNA.