Abstract

Oncolytic viruses (OV) are considered as promising tools in cancer treatment. In addition to direct cytolysis, the stimulation of both innate and adaptive immune responses is the most important mechanism in oncolytic virotherapy that finally leads to the long-standing tumor retardations in the advanced melanoma clinical trials. The OVs have become a worthy method in cancer treatment, due to their several biological advantages including (1) the selective replication in cancer cells without affecting normal cells; (2) the lack of resistance to the treatment; (3) cancer stem cell targeting; (4) the ability to be spread; and (5) the immune response induction against the tumors. Numerous types of viruses; for example, Herpes simplex viruses, Adenoviruses, Reoviruses, Poliovirus, and Newcastle disease virus have been studied as a possible cancer treatment strategy. Although some viruses have a natural orientation or tropism to cancer cells, several others need attenuation and genetic manipulation to increase the safety and tumor-specific replication activity. Two important mechanisms are involved in OV antitumor responses, which include the tumor cell death due to virus replication, and also induction of immunogenic cell death as a result of the immune system responses against the tumor cells. Furthermore, the high efficiency of OV on antitumor immune response stimulation can finally lead to a significant tumor shrinkage.