ACE2 and infection: Experimental COVID-19 models have made use of either transgenic mice overexpressing human ACE2 like the K18-hACE2 mice, mouse-adapted strains of the SARS-CoV-2 virus, or more recently, mice with humanized immune systems that require adenoviral-induced overexpression of human ACE2 to induce infection susceptibility (58, 70–72).