SARS-CoV-2-specific T-cells in unexposed humans:presence of cross-reactive memory cells does not equal protective

Using human blood samples obtained from pre-pandemic donors,a recent article by Mateus et al.in Science provided new evidence that SARS-CoV-2-reactive T-cells in unexposed donors are indeed HCoV-specific T-cells.1 The rapid global spread of coronavirus disease 2019(COVID-19),caused by the newly-emerged coronavirus SARS-CoV-2,has led to millions of infections with substantial morbidity and mortality.2 Different clinical manifestations of COVID-19 have been observed:asymptomatic infections,mild self-limiting disease,acute respiratory distress syndrome and death.The determinants underlying disease severity currently remain elusive;since severe patients often present with immune hyperresponsiveness,it is speculated that the host’immune response could be a contributing factor to severe disease.