ACE2 and COVID-19: The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the current outbreak of coronavirus disease 2019 (COVID-19) shares many similarities with the SARS coronavirus in 2002–2003 (SARS-CoV), including 76% sequence identity in the spike protein (S) (1, –3), a common receptor of the angiotensin converting enzyme 2 (ACE2) (4, –6), and the fusion mechanism that involves cleavages of spike at the S1–S2 and S2ʹ sites (7).