2.4 SARS-CoV-2-specific T cell responses
Enzyme-linked immunospot (ELISpot) assay (BD, USA) and intracellular
cytokine staining (ICS) were used to test SARS-CoV-2-specific T cell
reaction in 2-year COVID-19 convalescents and health controls, as
described in our previous study (Supplementary
Methods).3