Human cell adaptation of the swine acute diarrhea syndrome coronavirus spike protein

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a recently identified highly pathogenic swine coronavirus. In vitro, SADS-CoV can infect cell lines from many different species, including humans, highlighting its high zoonotic potential. Coronavirus spike glycoproteins play a critical role in viral entry and are involved in determining viral host range and cellular tropism. Here, we used experimental evolution to investigate how the SADS-CoV spike protein adapts to human cells and to identify potential variants with increased infectivity. We evolved a recombinant vesicular stomatitis virus expressing the SADS-CoV spike (rVSV-SADS) in three human cell lines. After ten passages, increased viral replication was observed, and spike mutations were identified by sequencing. Mutations were functionally characterized in terms of viral fitness, spike processing and fusogenicity. Our results thus identify potential human-adaptive mutations in the SADS-CoV spike that may further enhance its zoonotic potential. Importance Coronavirus transmission from animals represents a serious threat to humans. Pigs are of particular concern because of their proximity to humans and the several coronaviruses they harbor. In particular, the swine acute diarrhea syndrome coronavirus (SADS-CoV) is a recently identified highly pathogenic porcine coronavirus that has a very broad tropism in vitro, highlighting its high zoonotic risk. The coronavirus spike protein is a strong determinant of species tropism, and spike mutations may facilitate cross-species transmission. Here, to identify potential variants with increased ability to enter human cells, we used an experimental evolution approach to study how the SADS-CoV spike adapts to different human cell lines. These mutations, should they occur in nature, could potentially increase the zoonotic potential of SADS-CoV.