Recent studies has shown that moderate and severe symptoms in patients with COVID-19 are associated with a drastic reduction in the numbers of both CD4+ and CD8+ T cells.9,10 We have recently demonstrated that a balance between T-cell immunity and neutralizing antibodies is required for COVID-19 recovery.11 Additionally, Son et al.12 uncovered the presence of a tissue-resident helper T-cell population in the lung, which plays a critical role in promoting the development of protective B and CD8+ T-cell responses. This evidence concerns the gene CD4 and COVID-19.