T cell response to Covid may remain potent after vaccination: Study

Some of the concerning variants of the Sars-Cov-2, such as those first found in the UK, South Africa, Brazil and California, appear to have little resistance to the last line of the body's immune defences trained by a vaccine or a past infection, according to a study by a group of US-based researchers.

The authors say that the findings suggest that even if a variant is successful in infecting a person after they have been vaccinated or infected by the Sars-Cov-2 once before, the immune system's T cell response is likely to be potent enough in order to reduce the severity. The team was led by researchers from California's La Jolla Institute for Immunology.

T cells are what are loosely considered the third line of the body's defence, along with B cells. There are two types of T cells, helper (CD4) and killer (CD8). Helper cells aid in drawing the attention of the other components of the immune response (such as B cells), while killer T cells destroy any infected human cells.

Scientists believe protection from re-infection may be dependent on the volume and nature of antibodies, which are a manifestation of B cells. They, however, taper in volume once an infection is over but the body can quickly churn out large numbers again since memory T cells and memory B cells retain a blueprint of the virus.

The study found that this blueprint retains large details of the virus in general, and the mutations are not too significant to make this memory redundant.

"Overall, reactivity to the peptide pools spanning the variant genomes was found to be similar to that against the ancestral Wuhan strain. When the sum total of reactivity throughout the genome was considered, no differences or decreases in reactivity compared to the ancestral were noted for the variant pools ," the authors said, when they analysed the four variants with that of the T cell responses created by those who recovered from the a previous bout of Covid-19.

This may be of significant for India since one of these variants is the one first seen in California with the L452R mutation, which has been found in the B.1.617 that has arisen in several Indian states.

The authors found such similarities in people who received the mRNA vaccines by Moderna and Pfizer-BioNTech, except for a slight decrease in reactivity in the case of the South African variant B.1.351.

The authors see their findings as positive news in light of the concern over the impact of variants. "Undoubtedly, several of the variants are associated with increased transmissibility, and also have been associated with decreased susceptibility to neutralizing antibodies from infected or vaccinated individuals. In contrast, the data presented here suggests that T cell responses are largely unaffected by the variants," the paper added.

"A booster vaccine against those VOCs (variants of concern) makes sense, and is likely to be highly effective, and those efforts are hurtling forwards," said Shane Crotty of La Jolla Institute in a tweet in reference to the study.