Expression of interferon gamma by recombinant rabies virus strongly attenuates virus pathogenicity and enhances safety and efficacy of post-exposure treatment vectors
Animal model experiments have shown interferon gamma (IFNγ) expression correlates with survival from infection with attenuated rabies virus and reduction of neurological sequelae. Therefore, we hypothesized that rapid production of IFNγ by the rabies virus itself would induce a more robust antiviral response than would occur naturally, thereby attenuating the virus and enhancing its safety and efficacy as pre- and post-exposure treatment for rabies. We reverse-engineered IFNγ-expressing recombinant RABV: SPBNγ, GASγ and GASγGAS. Morbidity and mortality were monitored in mice infected intranasally with SPBNγ or control virus to determine the degree of attenuation attributable to viral IFNγ. Incorporation of IFNγ into the rabies genome highly attenuated the virus. SPBNγ has an LD50 more than 100 fold greater than SPBN(-). Subsequent experiments were designed to assess how viral IFNγ expression could attenuate SPBNγ, and determine the ability of virus-expressed IFNγ to improve the safety and immunogenicity of existing vaccine vectors for use as pre- and post-exposure treatment (PET). In vitro and in vivo mouse experiments show that SPBNγ infection enhances type I IFN expression, in the absence of increased viral replication. Furthermore, knockout mice lacking the type I interferon receptor (IFNAR-/-) rapidly die from SPBNγ infection. Since SPBNγ retains residual pathogenicity in adult mice, we used GASγ and GASγGAS, constructed on attenuated backbones, for subsequent studies. Mortality and morbidity were monitored in suckling mice and models of pre- and post-exposure treatment. Behavioral testing was also used to measure neurological deficits in mice surviving PET. We demonstrate that GASγ and GASγGAS are significantly attenuated in suckling mice compared to the highly attenuated GASGAS vaccine. GASγ better protects mice from lethal DRV4 RABV infection in both pre- and post-exposure models compared to GASGAS. Finally, GASγGAS significantly reduces post-infection neurological sequelae, compared to its control vector, during PET of DRV4 infection. We conclude that expression of IFNγ by a vaccine vector can further enhance its safety profile while increasing its efficacy as a traditional vaccine and PET. Furthermore, the mechanism of attenuation is due, at least in part, to increased induction of type I IFN.
Barkhouse, Darryll, "Expression of interferon gamma by recombinant rabies virus strongly attenuates virus pathogenicity and enhances safety and efficacy of post-exposure treatment vectors" (2014). ETD Collection for Thomas Jefferson University. AAI3705004.