Evaluation of specific T cell immune response to SARS-CoV-2 in COVID-19 infection and following Gam-COVID-Vac vaccine prophylaxis

An aberrant immune response during SARS-CoV-2 infection has been shown to determine the clinical features, disease severity, and progression of COVID-19 infection. This work aimed for comprehensive assessment of the immune response by comparative evaluation of diagnostic significance of the antibodies to RBD domain of the SARS-CoV-2 spike protein, as well as detection of effector CD4+ and CD8+T cells specific to SARS-CoV-2 antigens. The study was performed in unvaccinated persons, healthy individuals vaccinated with Gam-COVID-Vac, and in the patients who have had COVID-19 infection. We have found that IgG antibodies to the RBD domain of the SARS-CoV-2 spike protein are detectable at a frequency of 73% to 92% of cases in vaccinated persons and COVID-19 reconvalescents. The numbers of effector CD4+ and CD8+T lymphocytes responding to stimulation with SARS-CoV-2 antigens by producing the IFN cytokine varied depending on the introduced antigen and tended to be higher in vaccinated individuals. In non-vaccinated healthy persons who contacted with COVID-19 patients, T cell response to the SARS-CoV-2 nucleoproteins was revealed. For adequate assessment of antiviral and post-vaccination immune response to COVID-19, it would be necessary to study not only humoral immune response by the presence of antibodies, but also functionally active specific T lymphocytes directed for SARS-CoV-2 protein antigens.