ACE2 and infection: The current SARS-CoV-2 mouse model may be critical in line with considering the use of MHV to study its biological mechanisms [127], using gene editing technology to understand mouse genes (ACE2 and TMPRSS2) related to viral binding and entry [128, 129], or transfer of human ACE2 for direct infection [130], and using wild SARS-CoV-2 virus to establish a mouse model for significant clinical phenotype [131].