Oncolytic Viruses in Cancer Treatment: A Review.

Importance: Oncolytic viruses (OVs) are emerging as important agents in cancer treatment. Oncolytic viruses offer the attractive therapeutic combination of tumor-specific cell lysis together with immune stimulation, therefore acting as potential in situ tumor vaccines. Moreover, OVs can be engineered for optimization of tumor selectivity and enhanced immune stimulation and can be readily combined with other agents. The effectiveness of OVs has been demonstrated in many preclinical studies and recently in humans, with US Food and Drug Administration approval of the oncolytic herpesvirus talimogene laherparepvec in advanced melanoma, a major breakthrough for the field. Thus, the OV approach to cancer therapy is becoming more interesting for scientists, clinicians, and the public. The main purpose of this review is to give a basic overview of OVs in clinical development and provide a description of the current status of clinical trials.

Observations: In 2016 approximately 40 clinical trials are recruiting patients, using a range of OVs in multiple cancer types. There are also many more trials in the planning stages. Therefore, we are now in the most active period of clinical OV studies in the history of the field. There are several OVs currently being tested with many additional engineered derivatives. In OV clinical trials, there are a number of specific areas that should be considered, including viral pharmacokinetics and pharmacodynamics, potential toxic effects, and monitoring of the patients' immune status. Clinical development of OVs is increasingly focused on their immune stimulatory properties, which may work synergistically with immune checkpoint inhibitors and other strategies in the treatment of human cancer.

Conclusions and Relevance: Oncolytic viruses are an active area of clinical research. The ability of these agents to harness antitumor immunity appears to be key for their success. Combinatorial studies with immune checkpoint blockade have started and the results are awaited with great interest.