Just as vaccines were developed and were being deployed for mass inoculation, the COVID-19 virus started mutating. Today, we have many variants of this pathogen, some more lethal than others. This was expected as all viruses mutate. But the worry here was how will it affect the global fight against the pandemic? As variants of SARS-CoV-2 provoke concern that they might elude protective immune responses generated by prior infection or vaccination, researchers from the National Institute of Allergy and Infectious Diseases (NIAID) have found that a key player in the immune response remained mostly unaffected. According to them, one key player in the immune response to SARS-CoV-2 -- the CD8+ T cell -- remained active against the virus.
Mutations in spike protein neutralize antibodies
To come to this conclusion, researchers looked at the blood cell samples from 30 people who had contracted and recovered from COVID-19 prior to the emergence of virus variants. The investigators asked whether CD8+ T cells in the blood of recovered COVID-19 patients, infected with the initial virus, could still recognize three SARS-CoV-2 variants -- B.1.1.7, which was first detected in the UK; B.1.351, originally found in South Africa; and B.1.1.248, first seen in Brazil. They saw that each 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 cells. Mutations in this spike protein region could make it less recognisable to T cells and neutralise antibodies, which are made by the immune system's B cells following infection or vaccination, the researchers said.
Both T cells and antibodies response needed for immunity
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, the researchers 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.
Mutations do not affect T cell response in convalescing patients
In this study, researchers determined that SARS-CoV-2-specific CD8+ T-cell responses remained largely intact and could recognise virtually all mutations in the variants studied. But they agree that larger studies are needed to validate these findings. The findings of this study suggest that the T cell response in convalescent individuals, and most likely in vaccinees, are largely not affected by the mutations found in these three variants, and should offer protection against emerging variants.