PDCD1 and COVID-19: Indeed, the phenotype of exhausted NK cells from COVID-19 cases was represented with a higher expression of inhibitory markers, such as PD1, Tim-3, NKG2A, LAG3, PDCD1, and HAVCR2 on NK cells, leading to a decreased expression of IFN-γ, IL-2 and TNF-α as well as reduced granzyme B levels via inflammatory regulating pathway, like NF-κB-dependent upregulation of ICAM-1 expression in target cells [66–68].