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Although previous research had shown that T cells induced by other coronaviruses can recognize SARS-CoV-2, the new study examines for the first time how the presence of these T cells at the time of exposure to SARS-CoV-2 influences whether someone gets infected or not.
The researchers emphasize that their findings provide a model for the design of a universal second-generation vaccine that could prevent infection of current and future variants of SARS-CoV-2, including Omicron.
“Being exposed to the SARS-CoV-2 virus is not always synonymous with infection. Now we have seen why. The cause is that high levels of pre-existing T cells, created by the body when it becomes infected with other
Human coronaviruses such as the common cold can protect against Covid-19 infection, ”explains Rhia Kundu, first author of the study.
Although this is an important discovery, he adds, “it is just a form of protection. The best way to protect against Covid-19 is to get vaccinated».
The study began in September 2020 when the majority of people in the UK had not been infected or vaccinated against SARS-CoV-2.
It included 52 persons who lived with a person infected with PCR-confirmed SARS-CoV-2 infection and who had therefore been exposed to the virus. Participants performed PCR tests at the beginning and 4 and 7 days later, to determine if they developed an infection.
Blood samples were obtained from the 52 participants within 1 to 6 days of being exposed to the virus. This allowed the researchers to analyze the levels of pre-existing T cells induced by previous common cold coronavirus infections that also cross-recognize SARS-CoV-2 virus proteins.
They found that there were significantly higher levels of these cross-reactive T cells in the 26 people who did not get infected, compared to the 26 people who did. These T cells targeted internal proteins within the SARS-CoV-2 virus, rather than the spike protein on the surface of the virus, to protect against infection.
Current vaccines do not induce a immune response to these internal proteins. The researchers believe that, in conjunction with our existing vaccines targeting effective spike proteins, these proteins offer a new target for a vaccine that could provide long-lasting protection because T-cell responses persist longer than antibody responses, which decline. a few months after vaccination.
For Ajit Lalvani, lead author of the study published in «
Nature Communications»,« The work provides the clearest evidence to date that the T cells induced by the common cold coronaviruses play a protective role against SARS-CoV-2. These T cells – he emphasizes – provide protection by attacking proteins within the virus, rather than the spike protein on its surface.
Lalvani explains that the spike protein are under a lot of immune pressure from vaccine-induced antibodies that drives the evolution of vaccine escape mutants. However, “the internal proteins targeted by the protective T cells we identified mutate much less.”
For this reason, he continues, “they are highly conserved among the different SARS -Variants of CoV-2, including Omicron.”
Therefore, he notes, “new vaccines that include these conserved internal proteins would induce broadly protective T cell responses that should protect against current and future SARS-CoV-2 variants.”
The researchers point to some limitations of their study: a sample is small and the fact that 88% of the participants were of white European ethnicity.
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