PDCD1 and COVID-19: While it has been reported that dexamethasone upregulated CTLA-4 abundance in lymphocytes in vitro, in our cohort of severe COVID-19 patients, dexamethasone suppressed the gene encoding for CTLA-4, as well as other exhaustion signature genes TIGIT, LAG3, PD1, FASL, Eomesodermin and CD86 (40, 57, 58).