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.

Because BtCoV HKU5-SE harbors the SARS-CoV S ectodomain, we evaluated whether a SARS-CoV S-expressing VRP-based vaccine would provide protection from virus-induced disease. Young and aged mice were mock vaccinated (with VEE virus adjuvanted particles [VAP]) or vaccinated with VRP expressing SARS-CoV S glycoprotein and then challenged with 10 5 PFU of BtCoV HKU5-SE. Vaccinated aged animals were completely protected from virusinduced weight loss (Fig. 5A) , and viral replication in the lungs was significantly diminished (~4 log) by day 2 and cleared by 4 days p.i. (Fig. 5B ). In contrast, viral replication was not detected in young mice vaccinated with SARS-CoV S-expressing VRP (see Fig. S3A in the supplemental material), demonstrating complete protection. Consistent with this observation, the 50% plaque reduction neutralization test (PRNT 50 ) titers (against BtCoV HKU5-SE) in vaccinated young and aged animals were 1:1,600 and 1:800, respectively (Fig. 5C) . Furthermore, polyclonal sera against HKU5 N and S proteins did not neutralize BtCoV HKU5-SE (Fig. 5C ). These results are consistent with the idea that CoV S but not N proteins represent the principal determinants of protective humoral immunity after high-titer challenge (15) .