Decreased T cell counts in severe COVID-19 have been associated with reduced T cell activation and function markers, including TCR subunits (CD3ε, CD3γ, CD247, TRAC, TRBC1), surface accessory molecules (CD4, CD8α, CD8β, CD2), T cell migration stimulators (DDP4), TCR signaling kinases (ZAP70, LCK, FYN) and MHC-II molecules (124). This evidence concerns the gene CD4 and COVID-19.