Genetic Polymorphisms and Molecular Mechanisms Mediating Oncolytic Potency of Reovirus Strains

The Dearing strain of Mammalian orthoreovirus (T3D) is undergoing clinical trials as an oncolytic virotherapeutic agent. In this study, a comprehensive phenotypic and genetic comparison of T3D virus stocks from various laboratories and commercial sources revealed that T3D laboratory strains differ substantially in their oncolytic activities in vitro and in vivo. Superior replication of the most-oncolytic T3D lab strain was attributed to several mechanistic advantages: virus-cell binding, viral RNA transcriptase activity, viral inclusion morphology, and differential activation of RIG-I versus NFκB-dependent signalling pathways. Viral S4, M1 and L3 gene segments were each independently associated with a distinct mechanistic advantage. Furthermore, the specific missense polymorphisms that governed replication potency were identified, and utilized to generate a hybrid of T3D laboratory strains with further-augmented replication in tumor cells. Together, the results depict an elaborate balance between reovirus replication and host-cell signaling to achieve optimal oncolytic reovirus efficacy.