CD4 and COVID-19: 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(Chen and Wherry, 2020; Labarrere and Kassab, 2021). Both lymphopenia and the cytokine storm determine increased COVID-19 disease severity and enhanced mortality (Labarrere and Kassab, 2021). Cysteine supplementation improves T-cell functions by enhancing GSH levels (Dröge and Breitkreutz, 2000; Ghezzi, 2011)