CD4 and infection: We and others previously compared ex vivo SARS-CoV-2-specific CD8+ and CD4+ T cell responses and their TCR repertoires, using peptide/HLA-tetramer enrichment techniques in blood of SARS-CoV-2-infected children and adults (38, –40, 49), blood and tissues of prepandemic children and adults (38, 39) and following COVID-19 mRNA vaccination versus infection (42, 44).