Live, attenuated RNA virus vaccines are efficacious but subject to reversion to virulence. Among RNA viruses, replication fidelity is recognized as a key determinant of virulence and escape from antiviral therapy; increased fidelity is attenuating for some viruses. Coronavirus (CoV) replication fidelity is approximately 20-fold greater than that of other RNA viruses and is mediated by a 3'→5' exonuclease (ExoN) activity that probably functions in RNA proofreading. In this study we demonstrate that engineered inactivation of severe acute respiratory syndrome (SARS)-CoV ExoN activity results in a stable mutator phenotype with profoundly decreased fidelity in vivo and attenuation of pathogenesis in young, aged and immunocompromised mice. The ExoN inactivation genotype and mutator phenotype are stable and do not revert to virulence, even after serial passage or long-term persistent infection in vivo. ExoN inactivation has potential for broad applications in the stable attenuation of CoVs and, perhaps, other RNA viruses.

Funding information This work was supported by: NIAID NIH HHS, United States Grant ID: U54 AI057157

NIAID NIH HHS, United States Grant ID: 5F32AI080148

NIAID NIH HHS, United States Grant ID: AI075297

NIAID NIH HHS, United States Grant ID: U54-AI057157

NIAID NIH HHS, United States Grant ID: F32 AI080148

NIAID NIH HHS, United States Grant ID: HHSN272200900007C

PHS HHS, United States Grant ID: HHSN272200900007C

NIAID NIH HHS, United States Grant ID: R01 AI075297 More Less keyboard_arrow_down