A Mouse Model for Betacoronavirus Subgroup 2c Using a Bat Coronavirus Strain HKU5 Variant

Agnihothram, Sudhakar; Yount, Boyd L.; Donaldson, Eric F.; Huynh, Jeremy; Menachery, Vineet D.; Gralinski, Lisa E.; Graham, Rachel L.; Becker, Michelle M.; Tomar, Sakshi; Scobey, Trevor D.; Osswald, Heather L.; Whitmore, Alan; Gopal, Robin; Ghosh, Arun K.; Mesecar, Andrew; Zambon, Maria; Heise, Mark; Denison, Mark R.; Baric, Ralph S.

Molecular characterization of BtCoV HKU5-SE. In Vero cells, BtCoV HKU5-SE replicated with kinetics similar to those of MERS-CoV (MERS-CoV SA1, the Saudi Arabian isolate) and SARS-CoV at earlier time points and achieved peak titers at 24 h p.i. (Fig. 1B and C) . Cytopathology was characterized by fusion of cells starting at 18 h p.i., and cell death was noted at~36 h p.i. BtCoV HKU5-SE was stable in cell culture, as indicated by realtime PCR analysis of ORF1 and ORF8 expression through passage six (see Fig. S1D in the supplemental material). BtCoV HKU5-SE replicated with kinetics similar to those of the MERS-CoV England isolate (MERS-CoV Eng 1) (Fig. S2A ). Interestingly, there was a marked difference in virus replication (Fig. S2B ) in highlevel-ACE2-expressing H2B Calu-3 cells (a lung epithelial cell line), where BtCoV HKU5-SE replicated to lower titers than either MERS-CoV isolates or SARS-CoV. Although speculative, this growth difference is supported by low-level expression of N protein ( Fig. S2C ) at later time points and could reflect different sensitivities to interferon in Calu-3 cells.