Mutations leading to Omicron variant did not enable virus to fully escape immune system

However, the researchers caution that their finding only relates to one type of cell-mediated immunity — the body’s defense against invaders that doesn’t involve circulating antibodies — and that it may be the antibody-related immune response (known as humoral immunity) that fails when omicron causes so-called breakthrough infections.

The team’s study was published March 1, 2022, in mBio, a journal from the American Society for Microbiology.

“We found in a January 2021 study that in people previously infected with the original COVID strain, specific epitopes [portions of a protein that elicit an immune response] from the virus are recognized by immune system cells known as CD8+ T lymphocytes, or killer T cells, and that this recognition enables a cell-mediated attack on COVID,” says study lead author Andrew Redd, Ph.D., assistant professor of medicine at the Johns Hopkins University School of Medicine and staff scientist at NIAID. “In our latest work, we found that these epitopes remained virtually untouched by the mutations found in the omicron variant. Therefore, the CD8+ T cell response to omicron should be virtually as strong as it was to the initial form of SARS-CoV-2.”

Other research groups in the United States and South Africa have demonstrated very similar results for people previously infected by or vaccinated against the original SARS-CoV-2 strain.

CD8+ T cells are nicknamed killer T cells (they’re also known as cytotoxic T cells) for their ability to eliminate foreign invaders such as bacteria and viruses from the body. The T cells used in the latest study were from blood samples collected in 2020 from 30 patients who had recovered from mild to moderate cases of COVID-19. The convalescent plasma donors had six human leukocyte antigens (cell-surface proteins that regulate the immune system and are part of each person’s genetic profile), Redd says, that are representative of greater than 73% of the U.S. population.

“This suggests that a significant portion of Americans who have been vaccinated against or exposed to the original strain of SARS-CoV-2 might have cytotoxic T cells that can produce an immune response to omicron,” says study senior author Aaron Tobian, M.D., Ph.D., director of the transfusion medicine division and professor of pathology at the Johns Hopkins University School of Medicine.

Source: Johns Hopkins Medicine