ACE2 and COVID-19: In the meanwhile, partial but important information might be obtained by circumscribed experimental and clinical investigations focused some on crucial issues, namely: fate of SARS-CoV-2 infection in human cells manipulated in order to modify ACE2 density; correlation of ACE2 density (in different cell types) and clinical course in human patients; potential role of additional proteins interacting with ACE2, such as the membrane transporter SIT1, which appears to be associated with COVID-19 prognosis and is also affected by anti-hypertensive therapy.