Moreover, transgenic mice expressing human angiotensin-converting enzyme 2 (ACE2) and mouse transduced human-ACE2 have been used to investigate SARS-CoV-2 infection; however, owing to the inaccessibility of mouse ACE2 (11, –, 13), laboratory mice are resistant to infection with some clinical SARS-CoV-2 strains. Here, ACE2 is linked to infection.