Differences in Characteristics of T-Cell Immunity to SARS-CoV-2 in Clinically Healthy Subjects.

We studied the differences in the characteristics of T-cell immunity in clinically healthy volunteers of three groups: "no previous COVID-19, not vaccinated", "recovered", and "vaccinated" as well as the relationship between the presence of IFNγ-releasing T cells in response to stimulation with peptide pools overlapping the main S, N, M, ORF3, and ORF7 protein sequences and the presence of IgG to the SARS-CoV-2 S protein. In the "no previous COVID-19, non-vaccinated" group, T cells specific to both S protein and other virus proteins were absent in 95% subjects. In the "recovered from COVID-19" group, T cells specific to the spike protein were present in samples from 39% subjects. In the same group, T-cell immunity to other viral proteins was present in 58% subjects. In vaccinated subjects, specific T cells responding to stimulation with S protein peptides were found in 47% cases and Т cells specific to N, M, ORF3, ORF7 proteins were detected in only 22% subjects.