People infected with the coronavirus carry immune cells known as T cells that help the body fight off the infection, a study suggests. These cells may help people recover from COVID-19, but their exact role is still unknown.
Researchers found T cells that target SARS-CoV-2, the virus that causes COVID-19, in the blood of people who had recovered from a coronavirus infection. Some people who had never been exposed to the virus also had T cells that could recognize the virus, researchers report May 14 in Cell. That finding suggests that previous infections with other coronaviruses, like the ones that cause common colds, could provide some level of protection against the new coronavirus, such as keeping people from developing severe disease.
It remains unclear whether these defenses can protect people from a reinfection with SARS-CoV-2, and, if so, for how long.
A key part of the immune system, T cells can recognize fragments of viruses. When the cells identify a viral protein, helper T cells release chemical signals that trigger other parts of the immune system to kick into gear. Others, called killer T cells, hunt down and kill infected cells.
The team first predicted which viral proteins from SARS-CoV-2 might represent the best target for T cells to recognize. Then it mixed those viral fragments with immune cells extracted from blood samples from 10 COVID-19 patients who had recovered from the disease as well as 11 healthy people. Those healthy people had participated in unrelated studies from 2015 to 2018 — before the pandemic began — and could not have been previously exposed to the coronavirus when their blood was sampled.
Around 70 percent of the COVID-19 patients harbored the cell-killing T cells, and all carried helper T cells. The immune cells recognized a variety of proteins from the coronavirus, including ones that help it break into cells or coat its genetic material.
About half of the healthy people also had helper T cells that recognized bits of SARS-CoV-2, and about a third had the killer T cells. All of these people tested positive for antibodies that attach to two coronaviruses that cause common colds, a sign the participants had been previously infected by those viruses.
It’s “tempting to speculate” that the cells could help people never exposed to the new coronavirus, the researchers write. But to know for sure, experts would need to test T cells from someone both before and after a SARS-CoV-2 infection.