As most neutralizing monoclonal antibodies (mAbs) isolated from convalescent COVID-19 patients target the RBD (4–8), by which the S protein binds to receptor angiotensin-converting enzyme 2 (ACE2) and promotes the exposure of the fusion peptides within the S2 component to contribute to viral membrane fusion with host cells, this domain is the main target for the design of therapeutics and vaccines (9, 10). Here, ACE2 is linked to COVID-19.