Immune conversion of tumor microenvironment by oncolytic viruses: the protoparvovirus H-1PV case study

Cancer cells utilize multiple mechanisms to evade and suppress anticancer immune responses creating a "cold" immunosuppressive tumor microenvironment. Oncolytic virotherapy is emerging as a promising approach to revert tumor immunosuppression and enhance the efficacy of other forms of immunotherapy. Growing evidence indicates that oncolytic viruses (OVs) act in a multimodal fashion, inducing immunogenic cell death and thereby eliciting robust anticancer immune responses. In this review, we summarize information about OV-mediated immune conversion of the tumormicroenvironment. As a case study we focus on the rodent protoparvovirus H-1PV and its dual role as an oncolytic and immunemodulatory agent. Potential strategies to improve H-1PV anticancer efficacy are also discussed.