Interleukin-12-expressing oncolytic virus: A promising strategy for cancer immunotherapy

Oncolytic viruses (OVs) are an emerging class of novel anti-cancer therapeutic agents that selectively infect and destroy cancerous tissues without damaging normal cells. With the recent US Food and Drug Administration (FDA) approval of Herpes Virus (T-VEC) for the treatment of advanced melanoma, oncolytic virotherapy has gained more attention for further development as a novel form of immunotherapy. A viable approach to maximize the efficacy of OVs involves arming them with immune-enhancing cytokines that are capable of boosting the host's immune response to effectively attack tumour cells. Interleukin-12 (IL-12) is a powerful cytokine with potent antitumour activities that activates both innate and adaptive anti-tumour responses. Several studies have demonstrated that IL-12-expressing OVs improve the therapeutic index in pre-clinical tumour models by activating and recruiting dendritic cells (DCs), cytotoxic natural killer (NK) cells and cytotoxic T cells, which subsequently improve tumour clearance. In this review, the immunological mechanisms of IL-12–expressing viruses are discussed.