ACE2-independent SARS-CoV-2 infection and mouse adaption emerge after passage in cells expressing human and mouse ACE2

Abstract

Human ACE2 (hACE2) is required for cell attachment and entry of SARS-CoV-2. Mouse ACE2 (mACE2) does not support infection of early SARS-CoV-2 isolates. Herein we describe a new system for generating mouse-adapted SARS-CoV-2 in vitro by serial passaging virus in co-cultures of cell lines expressing hACE2 and mACE2. Mouse-adapted viruses emerged with a series of spike protein amino acid changes, all of which have been reported in human isolates. Mouse-adapted viruses replicated to high titers in C57BL/6J mouse lungs and nasal turbinates, and caused severe lung histopathology. Remarkably, one mouse-adapted virus was able to replicate efficiently in ACE2-negative cell lines, a characteristic not described for any SARS-CoV-2 variants. ACE2-independent entry by SARS-CoV-2 represents a new biology for SARS-CoV-2 with potential widespread implications for disease and intervention development.