No abstract

Although animal models have been evaluated for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, none have fully recapitulated the lung disease phenotypes seen in humans who have been hospitalized. Here, we evaluate transgenic mice expressing the human angiotensin I-converting enzyme 2 (ACE2) receptor driven by the cytokeratin-18 (K18) gene promoter (K18-hACE2) as a model of SARS-CoV-2 infection. Intranasal inoculation of SARS-CoV-2 in K18-hACE2 mice results in high levels of viral infection in lungs, with spread to other organs. A decline in pulmonary function occurs 4 days after peak viral titer and correlates with infiltration of monocytes, neutrophils and activated T cells. SARS-CoV-2-infected lung tissues show a massively upregulated innate immune response with signatures of nuclear factor-κB-dependent, type I and II interferon signaling, and leukocyte activation pathways. Thus, the K18-hACE2 model of SARS-CoV-2 infection shares many features of severe COVID-19 infection and can be used to define the basis of lung disease and test immune and antiviral-based countermeasures.

evere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the global COVID-19 pandemic infecting more than 111 million people and causing 2.4 million deaths. Clinical disease in humans ranges from asymptomatic infection to pneumonia, severe respiratory compromise, multi-organ failure and systemic inflammatory syndromes. The rapid expansion and prolonged nature of the COVID-19 pandemic and its accompanying morbidity, mortality and destabilizing socioeconomic effects have made the development of SARS-CoV-2 therapeutics and vaccines an urgent global health priority 1. Indeed, the emergency use authorization and rapid deployment of antibody-based countermeasures, including mAbs, immune plasma therapy and messenger RNA, and inactivated and viral-vectored vaccines has provided hope for curtailing disease and ending the pandemic. The spike protein of the SARS-CoV-2 virion binds the cell-surface receptor angiotensin-converting enzyme 2 (ACE2) to promote entry into human cells 2. Because the spike protein is critical for viral entry, it has been targeted for vaccine development and therapeutic antibody interventions. SARS-CoV-2 S proteins are cleaved to yield S1 and S2 fragments. The S1 protein includes the N-terminal (NTD) and receptor-binding (RBD) domains, whereas the S2 protein promotes membrane fusion. The RBD is recognized by many potently neutralizing monoclonal antibodies 3-7 , protein-based inhibitors 8 and serum antibodies 9. The current suite of antibody therapeutics and vaccines was designed with a spike protein based on strains circulating during the early phases of the pandemic in 2020. More recently, variants with enhanced transmissibility have emerged in the United Kingdom (B.1.1.7), South Africa (B.1.351), Brazil (B.1.1.248) and elsewhere with multiple substitutions in the spike protein, including in the NTD and the receptor-binding motif (RBM) of the RBD. Preliminary studies with pseudoviruses suggest that neutralization by some antibodies and immune sera may be diminished against variants expressing mutations in the spike gene 10-13. Given these

Highlights d Adenovirus transduction of human ACE2 enables SARS-CoV-2 infection of BALB/c mice d High levels of viral RNA and infectious SARS-CoV-2 accumulate in lungs d Mice transduced with human ACE2 develop viral pneumonia after SARS-CoV-2 infection d Neutralizing mAbs protect from SARS-CoV-2-induced lung infection and inflammation

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