Fueling immune checkpoint blockade with oncolytic viruses: Current paradigms and challenges ahead

An emerging challenge in improving response rates to immune checkpoint inhibitors (ICIs) is to convert an immune cold tumour into a hot tumour. Oncolytic viruses (OVs) are seen as a promising therapeutic platform because they can replicate in cancer cells and lyse them. Currently, the key tenet for OVs has changed from killing cancer cells by viral lysis to efficiently and coordinately activating the host immune system. Virus vectors have inherent immunostimulatory functions, which can be further improved by cotreatment with other cancer immunotherapies or adding transgenes to viral platforms. OV usage also faces limitations, such as host antiviral immune responses, tumour-associated resistance, and replication in nonmalignant cells. In this review, we introduced major OV candidates and discussed how they help turn cold tumours into hot ones. Then, recent preclinical and clinical studies combining OVs and ICIs or testing ICI-armed OVs were discussed. Finally, we highlighted key challenges ahead to promote coordination and stimulate collaboration within the research community.