SARS-CoV-2 infection is characterized by an excessive inflammatory response associated with a cytokine storm and a prominent lymphopenia affecting CD4+ T cells, CD8+ T cells, B cells and natural killer cells. Both lymphopenia and the cytokine storm determine increased COVID-19 disease severity and enhanced mortality. Cysteine supplementation will improve immunological functions by enhancing GSH levels (Dröge and Breitkreutz, 2000; Ghezzi, 2011). This evidence concerns the gene CD4 and COVID-19.