Inactivating three interferon antagonists attenuates pathogenesis of an enteric coronavirus

Authors: DENG, XUFANG - Loyola University - Illinois; Buckley, Alexandra; PILLATZKI, ANGELA - South Dakota State University; Lager, Kelly; Faaberg, Kay; BAKER, SUSAN - Loyola University - Illinois

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2020
Publication Date: 8/17/2020
Citation: Deng, X., Buckley, A.C., Pillatzki, A., Lager, K.M., Faaberg, K.S., Baker, S.C. 2020. Inactivating three interferon antagonists attenuates pathogenesis of an enteric coronavirus. Journal of Virology. 94(17). https://doi.org/10.1128/JVI.00565-20.
DOI: https://doi.org/10.1128/JVI.00565-20

Interpretive Summary: Porcine epidemic diarrhea virus (PEDV), a coronavirus, appeared suddenly in the US in 1993 and led to dramatic losses to the swine herd and economic losses to producers. There is no modified live vaccine (MLV) available, and the current killed or subunit vaccines have proven insuffient in controlling what is still a problematic disease in the field. Previous work by multiple investigators have shown that coronaviruses are capable of suppressing the host immune response by incorporating several domains capable of inhibiting interferons, called interferon antagonists. Using an infectious clone of CoV porcine epidemic diarrhea virus (icPEDV), we generated viruses with inactive versions of three interferon antagonist regions individually, or combined in one virus designated icPEDV-mut4. Cells were infected with these mutant viruses and showed higher levels of interferon mRNA as compared to icPEDV infection, consistent with inactivation of interferon antagonists. icPEDV-mut4 elicited the most robust interferon responses, which severely limited virus replication. To evaluate clinical disease and virus shedding, we infected piglets with either wild-type icPEDV or icPEDV-mut4. We report that icPEDV-mut4 infection of piglets did not induce diarrhea, although we detected virus replication in gut epithelial cells, and low levels of virus shedding. Importantly, icPEDV-mut4 infection elicited IgG and neutralizing antibody responses to PEDV. Inactivating these three CoV interferon antagonists is an approach for generating candidate vaccines to limit the replication and disease caused by enteric CoVs.

Technical Abstract: Coronaviruses (CoV) have repeatedly emerged from wildlife hosts into humans and livestock animals to cause epidemics with significant morbidity and mortality. CoV outbreaks in swine are mostly associated with enteric infections, which cause diarrhea and fatal disease in young animals. The constellation of viral factors that contribute to developing severe enteric disease is not known. Here, we investigated CoV interferon antagonists, proteins that block host interferon responses, for their contribution to CoV enteric disease and virus shedding. Using an infectious clone of CoV porcine epidemic diarrhea virus (icPEDV), we generated viruses with inactive versions of interferon antagonist nonstructural proteins 1, 15 and 16 individually, or combined in one virus designated icPEDV-mut4. We infected interferon responsive PK1 cells with these mutant viruses and detected higher levels of interferon gene expression as compared to wild-type PEDV infection, consistent with inactivation of an antagonist. icPEDV-mut4 elicited the most robust interferon responses, which severely limited virus replication. To evaluate clinical disease and virus shedding, we infected piglets with either wild-type icPEDV or icPEDV-mut4. We report that icPEDV-mut4 infection of piglets did not induce diarrhea, although we detected virus replication in gut epithelial cells, and low levels of virus shedding. Importantly, icPEDV-mut4 infection elicited IgG and neutralizing antibody responses to PEDV. These results identify nsp1, nsp15 and nsp16 as virulence factors that contribute to the development of PEDV-induced diarrhea in swine. Inactivating these three CoV interferon antagonists is an approach for generating candidate vaccines to limit the replication and disease caused by enteric CoVs.