Of the distinct arms of adaptive immunity, CD4+ T cell responses against epitopes conserved across SARS-CoV-2 and other coronaviruses are present in COVID-19 convalescent patients [650,689,690,691] and more importantly, often in unexposed healthy individuals [689,692,693,694,695] as well, with proportions up to 50–80% in some of the unexposed populations analyzed [650,690,696]. The gene discussed is CD4; the disease is COVID-19.