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10 Mar 2023

T cells are first responders against breakthrough COVID infection, study finds

B cells, which produce antibodies, and T cells play a vital role in the immune response against viral infections, but how quickly do these different parts of the immune system kick in once you get a breakthrough SARS-CoV-2 infection?

To that end, researchers from the Doherty Institute studied the immune response to COVID infections in people who were previously vaccinated by collecting blood samples and nasal swabs over the first weeks after their symptoms began.

University of Melbourne’s Dr Marios Koutsakos, a Research Fellow at the Doherty Institute and lead author of the study, explained.

“This study is relatively unique because there are not many cohorts in the world that collect samples so early after infection, and where we have both immunology information and information about the virus,” Dr Koutsakos said.

“We looked at two things: 1) how quickly antibodies are recalled or start to increase, and 2) how quickly do the T cells start to respond, so that we understand the timing for each component of immune memory.”

And what they found surprised them.

They discovered that T cells responded very quickly and strongly to the virus – even faster than neutralising antibodies.

“We were quite excited to see that, even just one day after the symptoms started, T cells had detected the infection, became activated, and started to increase in numbers” University of Melbourne’s Dr Jennifer Juno, a Group Leader and Post-doctoral Fellow at the Doherty Institute and senior author of the paper, said.

“In contrast, we found that it takes between one to two weeks for the levels of antibodies to start to increase.”

Understanding and developing strategies to enhance T cell responses could be important for protecting against SARS-CoV-2 variants that are able to escape neutralising antibody responses.

Interestingly, the study also found that people who had higher levels of CD8+ T cell activation at the beginning of the infection had lower levels of the virus in their nasal swabs and cleared the virus more quickly.

“We hope additional work will help to clarify the extent to which CD8 T cells can help to clear the virus during infection,” Dr Juno said.

The study was published in Immunity.

Funding: Morningside Foundation, National Health and Medical Research Council (NHMRC), Medical Research Future Fund (MRFF)

Peer review: Immunity (DOI: 10.1016/j.immuni.2023.02.017)