Characterization of SARS-CoV-2-specific CD8(+) T cells in COVID-19 convalescent, vaccinated, and individuals with respect to age

Abstract COVID-19, an infectious disease caused by SARS-CoV-2, has given rise to the current global pandemic. Despite the number of infections nearing 300 million people worldwide, CD8+ T cells against SARS-CoV-2 in COVID-19 convalescent, vaccinated, and healthy adults and their changes with age have not been fully characterized. Here, we report the frequency, phenotype, and in vitro expansion capacity of circulating CD8+ T cells recognizing twenty-two epitopes from five SARS-CoV-2 proteins (S, N, M, ORF1ab, and ORF3a). Through multi-color flow cytometry using antigen-specific tetramers, we found that the frequencies of circulating CD8+ T cells ranged from undetectable to 1% in healthy, convalescent, and vaccinated individuals. Analysis of healthy adults ranging from 17 to 98 years of age revealed that the frequency of CD8+ T cells recognizing the epitope N-LLL (N222–230, LLLDRLNQL) is negatively correlated with age, particularly in the frequency of naive N-LLL-specific CD8+ T cells. Furthermore, the percentage of donors which displayed expansion of N-LLL-specific CD8+ T cells in response to in vitro peptide stimulation was significantly higher in convalescent patients than in healthy donors. These preliminary results suggest that there is an age-associated reduction of N-LLL-specific CD8+ T cells and exposure to SARS-CoV-2 primes these cells for robust expansion in response to stimulation with the N-LLL epitope. This work is still ongoing, and we will present the final results during the meeting.