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.

A recent study by Anthony et al. estimates the presence of approximately 320,000 different viruses circulating in mammalian zoonotic reservoirs that have the potential to cross the species barrier and to emerge as new human pathogens (13, 31) . Among coronaviruses, high RNA recombination frequencies coupled with the existence of interchangeable S domains suggest that some zoonotic strains are likely poised for cross-species transmission events into human populations (3). This study articulates a strategy that would enable rapid development of therapeutics and targeted evaluation of vaccines against future emerging zoonotic CoVs. A biopreparedness platform that includes panels of recombinant alpha-, beta-, and gammacoronaviruses for targeted therapeutic and vaccine evaluations can provide a strategy for rapidly identifying drugs with therapeutic potential against future emerging zoonotic CoVs. Previous studies have shown that the feline and murine S ectodomains and/or the S RBDs of the group 2b CoV S glycoproteins are interchangeable (16, 19) . As preemergent SARSlike CoV group 2b strains with broad ACE2 receptor specificities have recently been isolated from bats (11), it seems likely that similar group 2c strains exist that have broad host range phenotypes as well. In addition, the antigenic distances and minimal cross-neutralization phenotypes seen across and within group 2b and 2c strains (21) demonstrate an inherent vulnerability in current vaccine and therapeutic design strategies, which focus on single emerging isolates for control purposes. Rather, the synthetic resurrection of the group 2b HKU3 strain Bat-SRBD (which has the spike RBD from SARS-CoV) (16) and, here, the MERS-CoV-like group 2c BtCoV HKU5-SE isolate provide crucial reagents for identifying broad-spectrum antivirals while addressing targeted issues in vaccine design. BtCoV HKU5 and MERS-CoV share high sequence identity across important replicase protein targets (7, 14, 32) . As most zoonotic viruses are difficult to culture and usually exist as sequence signatures in repository databases, the advent of synthetic biology has provided an approach for resurrecting representative strains from these highly heterogeneous pools (16, 33, 34) . Consequently, the potential risks versus benefits of these experiments and the plans for containment of the recombinant viruses were discussed in detail with the University of North Carolina Institutional Biosafety Committee in advance of these experiments.