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Scientists hope analysis of T-cells could pave the way for a new generation of Covid-19 vaccines that are more resistant to troubling variants.
A study by Imperial College London looked at T-cells generated by the common cold in 52 people.
All were household contacts of people who had tested positive for Covid-19, and at the start of the study all had tested negative.
Within days, half of this group tested positive.
Researchers then examined blood samples of the 26 who were not infected. Significantly more T-cells were found in this cohort than in the people who caught the virus.
The findings of the study, which began in September 2020, suggest that the T-cells produced in previous infections with the common cold recognise the Sars-CoV-2 virus and help reduce the chance of infection.
“Being exposed to the Sars-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why,” said Rhia Kundu, the study’s lead author and a researcher at Imperial’s National Heart and Lung Institute.
“We found that high levels of pre-existing T-cells, created by the body when infected with other human coronaviruses like the common cold, can protect.”
T-cells are believed to stay in the body longer compared with antibodies.
The authors of the study, published on Monday in Nature Communications, also said that the internal proteins of the Sars-CoV-2 virus, which are targets of the T cells, could be a new target for vaccine makers.
Several current Covid-19 vaccines target the spike protein. But certain mutations, such as those seen in the Delta and Omicron variants, can make the spike harder to recognise, reducing the shots’ efficacy.
“In contrast, the internal proteins targeted by the protective T-cells we identified mutate much less,” Professor Ajit Lalvani, co-author of the study, said.
“Consequently, they are highly conserved between the various Sars-CoV-2 variants, including Omicron. New vaccines that include these conserved, internal proteins would therefore induce broadly protective T-cell responses that should protect against current and future Sars-CoV-2 variants.”
What are T-cells?
T-cells are white blood cells produced in bone marrow. A core component of the immune system, they and work in tandem with antibodies to attack infected cells.
It is believed that humanity’s best vaccines, such as MMR, the combined shot against measles, mumps and rubella, generate both types of immunity but the optimal balance of antibodies and T cells is not known.
Compared with antibodies, T-cells tend to survive longer in the body and continue to kill infected cells, preventing serious illness.
They also tend to attack a wider variety of related pathogens than antibodies, which allows for a greater degree of cross-protection across different viruses or strains, according to the UK’s Science Media Centre.
Immunity against Covid-19 is a complex picture and some evidence has long pointed to waning antibody levels six months after vaccination.
Last year, the chief executive of AstraZeneca, Pascal Soriot, strongly implied, but could not prove, that his company’s viral vector vaccine was likely to produce a more robust T-cell response compared with shots that use mRNA technology.
He suggested that mRNA vaccines showed a waning antibody response may be linked to rising hospital admissions among older people in the EU, where relatively few people aged 60-plus received the AstraZeneca shot. Some scientists have rejected this theory.
