Early circulating strain of SARS-CoV-2 causes severe pneumonia distinct from that caused by variants of concern in mice transduced with an adenoviral vector expressing human ACE2

Abstract To analyze the molecular pathogenesis of SARS-CoV-2, a small animal model such as mice is needed: human ACE2, the receptor of SARS-CoV-2, needs to be expressed in the respiratory tract of mice. We conferred SARS-CoV-2 susceptibility in mice by using an adenoviral vector expressing hACE2 driven by an EF1α promoter with a leftward orientation. In this model, severe pneumonia like human COVID-19 was observed in SARS-CoV-2-infected mice, which was confirmed by dramatic infiltration of inflammatory cells in the lung with efficient viral replication. An early circulating strain of SARS-CoV-2 caused the most severe weight loss when compared to SARS-CoV-2 variants of concern, although histopathological findings, viral replication, and cytokine expression characteristics were comparable. We found that a distinct proteome of an early circulating strain infected lung characterized by elevated complement activation and blood coagulation, which were mild in other variants, can contribute to disease severity. Unraveling the specificity of early circulating SARS-CoV-2 strains is important in elucidating the origin of the pandemic.