Study results underline the importance of a second dose booster of mRNA COVID-19 vaccines and T-Cell response

Aug. 17, 2021

Messenger-RNA (mRNA) vaccines against the coronavirus that causes COVID-19 provoke a swift and strong response by the immune system’s T cells—the heavy armor of the immune system—according to a study reported by researchers in the Perelman School of Medicine at the University of Pennsylvania.

Although recent studies of vaccines tend to focus on the antibody response, the T-cell response is also an important and potentially more durable source of protection—yet little has been reported so far on the T-cell response to COVID-19 vaccines.

In the new study, which appears in the journal Immunity, the Penn Medicine researchers analyzed the T-cell responses in 47 healthy people who received two doses of the Moderna and Pfizer/BioNTech mRNA vaccines.

The results reveal the complex details of how the T-cell response to these vaccines unfolds, and underline the importance of a second dose for people with no history of COVID-19. The findings showed, however, that in people with a history of COVID-19, the T-cell response was already robust after the first vaccine dose, with no significant increase after the second dose, which may have implications for potential future booster shots.

“Our findings underscore the fact that we need to look at T cells, not just antibodies, if we want a complete picture of the vaccine response for those who have not had COIVD-19 and for those who have recovered from the disease,” said senior author E. John Wherry, PhD, chair of the department of Systems Pharmacology and Translational Therapeutics and director of the Penn Institute of Immunology in the Perelman School of Medicine at the University of Pennsylvania.

Antibodies are forked proteins secreted by immune cells called B cells; they can bind tightly to specific viral structures on virus-infected cells. T cells also have antibody-like receptors that enable tight binding to specific viral structures, but they are whole cells, some of which—called “killer” T-cells—are capable of directly killing virus-infected cells they encounter. T cells therefore have long been regarded as the heavy armor of the immune system. Their responses to vaccines are harder to study than antibody responses, though, so less is known about those responses, including in the case of COVID-19.

Perelman School of Medicine report

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