MHC class I (MHC-I) multimers were also used to directly detect SARS-CoV-2-specific CD8+ T cells without ex vivo stimulation, and their phenotypes were examined among COVID-19 patients and convalescents.5 Although these studies examined the phenotypes and functions of SARS-CoV-2-reactive T cells, high-dimensional techniques, such as scRNA-seq, could not be combined; thus, the deep profiles of SARS-CoV-2-reactive T cells have not been elucidated. The gene discussed is CD8A; the disease is COVID-19.