Jahnavi Sarma
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Written By: Jahnavi Sarma | Updated : August 18, 2021 11:15 AM IST
T-cell response in the weeks after mRNA vaccination includes T-cell types normally elicited by natural infection.
Experts have reiterated time and again that getting vaccinated is the only way to fight the deadly COVID-19 virus successfully. Today, we have many vaccines in the market. But each of these vaccines come with different levels of efficacy and safety. Though, by and large, all these vaccines are safe, their level of effectiveness may vary. Now, a new study from the Perelman School of Medicine, University of Pennsylvania, says that Messenger-RNA (mRNA) vaccines against the coronavirus that causes COVID-19 provoke a swift and strong response by the immune system's T cells, which can be called the heavy armour of the immune system. This is published in the journal Immunity.
Most recent studies on COVID-19 vaccine efficacy have concentrated on analysing the antibody response. But the researchers of this study say that the T-cell response is also an important and potentially more durable source of protection. Yet so little has been reported so far on the T-cell response to COVID-19 vaccines.
For the purpose of the study, researchers analyzed the T-cell responses in 36 healthy people without any history of COVID-19, and 11 people who had previously recovered from COVID-19. Both these groups received two doses of the Moderna and Pfizer/BioNTech mRNA vaccines. They saw 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.
But for those without any history of COVID-19 infection, the first vaccine dose elicited a rapid and strong response from helper T cells called CD4 T cells -- some of which help marshal an antibody response, while others stimulate the proliferation of CD8 killer T cells. The strengths of those initial CD4 T cell responses generally predicted the later strengths of antibody and killer T-cell responses. However, the killer T cells tended not to appear in large numbers until after the second vaccine dose -- confirming the importance of that second dose for people with no COVID-19 history.
This reveals the complex details of how the T-cell response to these vaccines unfolds and underlines the importance of a second dose for people with no history of COVID-19.
Based on the findings of this study, researchers say that it is important to look at T cells and not just antibodies to get a complete picture of the vaccine response for those who have not had COIVD-19 and for those who have recovered from the disease. Antibodies are forked proteins secreted by immune cells called B cells. They bind tightly to specific viral structures on virus-infected cells. On the other hand, 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 are also known as the heavy armor of the immune system. Their responses to vaccines are harder to study than antibody responses and, hence, less is known about those responses, including in the case of COVID-19.
The researchers also found that the T-cell response in the weeks after mRNA vaccination includes T-cell types normally elicited by natural infection and, in general, natural viral infection is known to be capable of inducing T-cell protection that lasts years and even decades.
(With inputs from Agencies)
