MAIT cells play an important role in the effectiveness of adenovirus vector vaccines

In this study, published in the journal Science, UK Coronavirus Immunology Consortium (UK-CIC) researchers, and colleagues from the University of Oxford, tried to understand whether specific immune cells, called mucosal-associated invariant T (MAIT) cells, play a role in our body’s immune response to adenovirus vector vaccines (such as the Oxford/AstraZeneca vaccine).

Viral vector vaccines for COVID-19 use an altered version of a harmless virus to deliver important information about SARS-CoV-2 (the virus that causes COVID-19) to cells in the body. This helps the immune system learn how to detect the virus and prevent future infection. By studying in fine detail how these vaccines train the immune system to protect us from infection with SARS-CoV-2, we can improve the design of future vaccines. 

The researchers of this study wanted to find out if specific immune cells are activated by the viral vectors used in COVID-19 vaccines. MAIT cells are a type of T cell (an immune cell; Mucosal associated invariant T cells) that become activated when our body is infected with a virus. They are found in the blood, in mucosal layers (e.g. in the nose), and the lungs. 

This study focused on MAIT cells specifically and their role in the immune response generated by viral vector vaccines like the Oxford/AstraZeneca COVID-19 vaccine.
Firstly, the researchers found that, when cells were exposed to the viral vector ChAdOx1 (chimpanzee adenovirus Ox1) which was used to make the Oxford/AstraZeneca COVID-19 vaccine, more MAIT cells became activated. This was true in both mice and humans. 

To make sure that this effect was caused by the viral vector (ChAdOx1), and not just by chance, the researchers tracked groups of immune cells to see what happened once the viral vector particles were introduced. The researchers saw that those virus particles caused some of the cells in the groups to respond, and that the signals between them activated the MAIT cells. 

Another part of the study suggested that MAIT cells needed to be activated for other parts of the immune system to respond. Human participants with higher levels of MAIT cell activation tended to have higher T cell responses to the viral vector vaccine. In addition, when vaccines were given to mice genetically modified to lack MAIT cells, they produced fewer T cells compared with normal mice. 

These findings suggest that MAIT cells are an important part of the immune process that creates virus-specific T cells in response to ChAdOx1-based vaccines like the Oxford/AstraZeneca vaccine for COVID-19. More research is needed to understand this process in finer detail, and doing so could help us improve how well these vaccines work.


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