Determination of t cell immune response to SARS-CoV-2 coronavirus based on induced γ-interferon production by specific T cells upon their stimulation by viral antigen

The aim of this work was to study the capacity of human T cells immune for SARS-CoV-2, to produce IFNγ, a marker of T cell immunity, in response to stimulation by a peptide pool in whole blood. Eighty samples of whole blood were received from the volunteers with known medical history in 2021, and 258 volunteers were examined in September-October 2022. In this study, 2 detection techniques were used, i.e.: (1) solid-phase enzyme immunoassay to determine antibodies of class G to RBD SARS-CoV-2; (2) IGRA test to determine IFNγ produced by antigen-specific lymphocytes in response to their stimulation by viral antigen. The parameters of the IGRA test were optimized with a sample of 80 specimens from the volunteers. The threshold value of the IFNγ level was determined (4.85 pg/mL), at the diagnostic specificity of 100% (80.6-100), and diagnostic sensitivity of 92.19% (83-96.6%), 95% CI. The study was further continued with a sample of 258 volunteers. Of them, 28.7%, did not exceed the threshold level of IFNγ after stimulation, according to results of the IGRA test. Meanwhile, all volunteers exhibited class G antibodies to RBB SARS-CoV-2. There was no correlation between the levels of antibodies and the level of interferon response in the entire group. When comparing IgG antibody levels and the amplitude of IFNγ (if exceeding the baseline level) in the groups differing in the time of the last vaccination, the median values of the parameters were slightly higher for the subgroup which was revaccinated 1-2 months before the study, while a significant difference between these subgroups was revealed only when evaluating IFNγ, pg/mL (Mann–Whitney criterion, p = 0.0321). According to the results of the study, it can be assumed that all the patients in the sample who were vaccinated and had COVID-19 infection, showed a humoral immune response. However, about a third of them lacked cellular immunity to SARS-CoV-2. There was no correlation between the levels of antibodies and the level of interferon response (Spearman’s criterion). Revaccination within previous 1-2 months has been shown to promote the increased amplitude of interferon response.