Updated: March 31, 2021 7:38:15 am
Since new variants of SARS-CoV-emerged in late 2020, there have been concerns about whether these might elude immune responses generated by prior infection or vaccination, potentially making re-infection more likely or vaccination less effective. To investigate this possibility, researchers from the US National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), and other scientists analysed blood cell samples from 30 people who had contracted and recovered from Covid-19 prior to the emergence of virus variants. They found that one key player in the immune response to SARS-CoV-2—the CD8+ T cell—remained active against the virus.
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The research team was led by NIAID’s Andrew Redd, and included scientists from Johns Hopkins University School of Medicine, Johns Hopkins Bloomberg School of Public Health and the company ImmunoScape.
The scientists investigated whether CD8+ T cells in the blood of recovered Covid-19 patients, infected with the initial virus, could still recognise three SARS-CoV-2 variants — B.1.1.7 (which was first detected in the United Kingdom); B.1.351 (originally found in the Republic of South Africa); and B.1.1.248 (first seen in Brazil). Each of these variant has mutations throughout the virus, and, in particular, in the region of the virus’ spike protein that it uses to attach to and enter human cells. Mutations in this spike protein region could make it less recognisable to T cells and neutralising antibodies, which are made by the immune system’s B cells following infection or vaccination.
Although details about the exact levels and composition of antibody and T-cell responses needed to achieve immunity to SARS-CoV-2 are still unknown, scientists assume that strong and broad responses from both antibodies and T cells are required to mount an effective immune response. CD8+ T cells limit infection by recognising parts of the virus protein presented on the surface of infected cells and killing those cells.
In their study of recovered Covid-19 patients, the researchers determined that SARS-CoV-2-specific CD8+ T-cell responses remained largely intact and could recognise virtually all mutations in the variants studied. While acknowledging that larger studies are needed, the researchers note that their findings suggest that the T cell response in convalescent individuals, and most likely in vaccine recipients, are largely not affected by the mutations found in these three variants, and should offer protection against emerging variants.
Optimal immunity to SARS-Cov-2 likely requires strong multivalent T-cell responses in addition to neutralising antibodies and other responses to protect against current SARS-CoV-2 strains and emerging variants, the authors indicate. They stress the importance of monitoring the breadth, magnitude and durability of the anti-SARS-CoV-2 T-cell responses in recovered and vaccinated individuals as part of any assessment to determine if booster vaccinations are needed.
The study has been published in Open Forum Infectious Diseases.
Source: NIH/NIAID (US)
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