Therefore, to elucidate the pathogenesis of SARS-CoV-2 and develop vaccines and treatments for COVID-19, appropriate preclinical animal models that not only express human angiotensin-converting enzyme (ACE2), a functional receptor of SARS-CoV-2, but also can recapitulate the symptoms, is immediately required [3, 4]. This evidence concerns the gene ACE2 and COVID-19.