T cells play a decisive role in fighting the coronavirus and preventing infected individuals from becoming seriously ill. They identify and fight the virus directly within the infected cells. Researchers have produced a precise profile of the T cells that respond to SARS-CoV-2 and described them at various stages of the illness. This novel methodological approach may in the future also help to assess the efficacy of SARS-CoV-2 vaccines or in the development of T cell-based treatments for serious cases.