CD4 and viral infectious disease: In the former group, SARS-CoV-2–specific CD4+ T cells almost exclusively displayed an early differentiated memory phenotype and limited capacity to produce IFN-γ; in the latter group, SARS-CoV-2–responsive CD4+ T cells preferentially exhibited a late differentiated memory phenotype and were enriched in GrB, suggesting that cytotoxic memory CD4+ T cells could be a relevant component in SARS-CoV-2 immunity, as previously described for other viral infections (48).