Development of an in vitro model for animal species susceptibility to SARS-CoV-2 replication based on expression of ACE2 and TMPRSS2 in avian cells

The SARS-CoV-2 (SC2) virus has caused a worldwide pandemic because of the viruss ability to transmit efficiently human-to-human. A key determinant of infection is the attachment of the viral spike protein to the host receptor angiotensin-converting enzyme 2 (ACE2). Because of the presumed zoonotic origin of SC2, there is no practical way to assess every species susceptibility to SC2 by direct challenge studies. In an effort to have a better predictive model of animal host susceptibility to SC2, we expressed the ACE2 and/or transmembrane serine protease 2 (TMPRSS2) genes from humans and other animal species in the avian fibroblast cell line, DF1, that is not permissive to infection. We demonstrated that expression of both human ACE2 and TMPRSS2 genes is necessary to support SC2 infection and replication in DF1 and a non-permissive sub-lineage of MDCK cells. Titers of SC2 in these cell lines were comparable to those observed in control Vero cells. To further test the model, we developed seven additional transgenic cell lines expressing the ACE2 and TMPRSS2 derived from Felis (cat), Equus (horse), Sus (pig), Capra (goat), Mesocricetus (Golden hamster), Myotis lucifugus (Little Brown bat) and Hipposideros armiger (Great Roundleaf bat) in DF1 cells. Results demonstrate permissive replication of SC2 in cat, Golden hamster, and goat species, but not pig or horse, which correlated with the results of reported challenge studies. The development of this cell culture model allows for more efficient testing of the potential susceptibility of many different animal species for SC2 and emerging variant viruses. IMPORTANCESARS-CoV-2 (SC2) is believed to have originated in animal species and jumped into humans where it has produced the greatest viral pandemic of our time. Identification of animal species susceptible to SC2 infection would provide information on potential zoonotic reservoirs, and transmission potential at the human-animal interface. Our work provides a model system to test the ability of the virus to replicate in an otherwise non-permissive cell line by transgenic insertion of the ACE2 and TMPRSS2 genes from human and other animal species. The results from our in vitro model positively correlate with animal infection studies enhancing the predicative capability of the model. Importantly, we demonstrate that both proteins are required for successful virus replication. These findings establish a framework to test other animal species for susceptibility to infection that may be critical zoonotic reservoirs for transmission, as well as to test variant viruses that arise over time.