Improved oncolytic and immunostimulatory activity of the spontaneous jin-3 reovirus mutant in preclinical bladder cancer models

Abstract

Immunotherapy has emerged as a promising strategy for treatment of urothelial carcinoma of the bladder (UCB) but not all patients show clinically desirable responses upon treatment with immune-checkpoint inhibition. Oncolytic viruses may unleash the full potential of immunotherapy. Besides tumor-lysing properties, oncolytic viruses can induce durable and systemic anti-viral and anti-tumor immune responses. Here, we evaluated and compared oncolytic and immunostimulatory properties of wild-type reovirus (R124) and the junction-adhesion molecule-independent mutant reovirus (jin-3) in preclinical models of human UCB. Both reovirus variants effectively infected and replicated in human UCB cells and induced cell lysis in flatbottom or 3D cultures and in ex vivo cultured human tumor tissue slices. However, jin-3 reovirus demonstrated greater efficacy in a dose-dependent manner, effectively inducing expression of immunogenic cell death markers, interferon (IFN)-stimulated genes, and inflammatory cytokines. To study interactions between tumor and immune cells, we established a co-culture system. In this context, co-culturing reovirus-infected bladder tumoroids with peripheral blood mononuclear cells was found to significantly enhance cancer death dose-dependently, alongside induction of key immune mediators such as CXCL10 and immunostimulatory responses, highlighting their potential as candidate agents for clinical translation in UCB.