Memory T cells may provide long-term protection against SARS-CoV-2 even if antibodies wane. Screening 26 convalescent patients and 25 healthy donors, the authors of this preprint identified immunodominant SARS-CoV-2 epitopes that elicit pre-existing and newly induced CD8+ T cell responses and measured the frequency, immunophenotype and function of these T cells. Notably, SARS-CoV-2-specific T cells were present even in seronegative convalescent patients. Longitudinal analyses in one patient showed in vivo priming and rapid expansion of SARS-CoV-2-specific CD8+ T cells, followed by a long contraction phase, with T cells but not antibodies still detectable 109 days post infection. Therefore, T cells might help to control SARS-CoV-2 infection and serve as correlates of protective immunity. Further studies are needed to evaluate T cell-mediated protection from reinfection.