New study suggests ‘robust’ coronavirus T cell response

Our immune systems have several different ways of protecting us. Memory T cells can recognize pathogens we’ve encountered in the past, which can give us long-term immunity. A new study on COVID-19 patients and people exposed to the coronavirus suggests that there is a “robust” T cell response that may protect them.

In the study, which was accepted this month for publication in Cell, researchers measured the T cell response in people who had severe cases of COVID-19 as well as exposed family members and people who were asymptomatic or had mild cases. They took blood samples and looked for many types and markers of T cells.

The team found SARS-CoV-2 specific T cell responses in both people who had tested positive for antibodies to the virus and those who didn’t. They also found the T cell response was stronger for exposed family members than unexposed people. This study suggests that people who are exposed, asymptomatic or have mild disease may be protected against SARS-CoV-2 because the T cells were reactive to the virus.

This could mean that long-term immunity may be achievable because of T cells.

“There’s a lot of hot stuff going on right now” in T cell research, says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), in a Facebook Live interview. “People who don’t seem to have high titers of antibodies, but who are infected or have been infected, have good T-cell responses.”

Although there are other studies on T cells for the coronavirus, more research needs to be done to understand this better and gather more evidence to support that T cells can provide a long term immunity to the coronavirus. 

What is cross reactivity

One potential explanation for why some people may have a T cell response even with low exposure is that some T cells may be cross-reactive to a range of similar pathogens. Another study published Aug. 4 in Science shows that there’s a T cell response in unexposed people. They had preexisting T cells that were cross-reactive to SARS-CoV-2 and a handful of common cold coronaviruses. This could be how the immune system broadly protects us from infection, although we do not yet have evidence that the T cell response would be enough to protect against SARS-CoV-2 when exposed to it.

What this means

We don’t know what T cells and long-term immunity mean in this case. “We’re just now hitting the point of relevance” to be able to think about longer timelines, says immunologist Deepta Bhattacharya of the University of Arizona to The New York Times. We’ll find out more as longer term studies get published and people are exposed a second time to the virus.

Some cases of reinfection are starting to be reported. Researchers in Hong Kong reported today a case where someone was infected a second time but did not develop symptoms.

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We don’t know yet if having reactive T cells will fully protect you from SARS-CoV-2 infection, but it’s something to investigate further.

For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.

You can follow Chia-Yi Hou on Twitter.

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