Abstract

Background: T-cell response against SARS-CoV-2 is essential for disease control and to understand correlates of protection against various disease outcomes in COVID-19. This makes T-cell measurement an important tool for clinical management.

Aims: To evaluate the IFN-?-releasing T-cell response against spike (S), nucleocapsid (N) and membrane (M) SARS-CoV-2 antigens using an ELISPOT-based assay in acute, convalescent, and vaccinated individuals.

Methods: Blood samples were collected from acute (n=71) and convalescent (n=59) individuals classified according to severity; and from vaccinated (n=48) and non-vaccinated (n=80) controls. After stimulating with S, N and M antigens overnight, T-cell response was measured (T-SPOT® Discovery SARS-CoV-2. Oxford Immunotec, UK). IgG against S and N were also measured.

Results: S antigen triggered the highest number of T-cell responses (46%), although responses against N and M were in a large percentage of individuals. The majority of convalescent individuals (93%) had a reactive T-cell response more than 200 days after diagnosis. Such response increased with severity. Acute patients had fewer positive responses (68%). S antigen triggered most responses in vaccinated controls, but only in half of them T-cell response was observed after the second dose. A higher percentage of individuals showed IgG response compared to IFN-?-releasing T-cell responses, and moderate correlations between both quantitative responses were seen.

Conclusions: T-cell response against SARS-CoV-2 is low during acute phase but may increase over time, as seen in convalescent individuals. Regarding vaccinated individuals, half had a positive test result after the second dose.