What is the specificity of the T-cell response generated in COVID-19 patients?
Circulating SARS-CoV-2−specific CD8+ and CD4+ T cells have been reported in ∼70% and 100% of COVID-19 convalescent patients, respectively.62 CD4+ T cell responses to spike were robust and correlated with SARS-CoV-2-specific-IgG and -IgA titers. The M, spike and N proteins each accounted for 11-27% of the total CD4+ response, with additional responses commonly targeting nsp3, nsp4, ORF3a and ORF8, among others. For CD8+ T cells, spike and M proteins were recognized, with at least 8 SARS-CoV-2 ORFs targeted. Interestingly, SARS-CoV-2−reactive CD4+ T cells were detected in ∼40-60% of unexposed individuals, which indicate cross-reactive T cell recognition between circulating ‘common cold’ coronaviruses and SARS-CoV-2.62