PDCD1 and COVID-19: Further studies in this regard—e.g., aimed at evaluating PDL-1/PD-1 modulation in COVID-19 patients—might be desirable in order to clarify this important issue and to gain insight into why in COVID-19 patients with an altered immune response the occurrence of hypoxia and inflammation (also present in other diseases such as severe influenza) leads to an undesirable outcome.