Therapy with oncolytic viruses: progress and challenges

Oncolytic viruses (OVs) are an emerging class of cancer therapeutics that offer the benefits of selective replication in tumour cells, delivery of multiple eukaryotic transgene payloads, induction of immunogenic cell death and promotion of antitumour immunity, and a tolerable safety profile that largely does not overlap with that of other cancer therapeutics. To date, four OVs and one non-oncolytic virus have been approved for the treatment of cancer globally although talimogene laherparepvec (T-VEC) remains the only widely approved therapy. T-VEC is indicated for the treatment of patients with recurrent melanoma after initial surgery and was initially approved in 2015. An expanding body of data on the clinical experience of patients receiving T-VEC is now becoming available as are data from clinical trials of various other OVs in a range of other cancers. Despite increasing research interest, a better understanding of the underlying biology and pharmacology of OVs is needed to enable the full therapeutic potential of these agents in patients with cancer. In this Review, we summarize the available data and provide guidance on optimizing the use of OVs in clinical practice, with a focus on the clinical experience with T-VEC. We describe data on selected novel OVs that are currently in clinical development, either as monotherapies or as part of combination regimens. We also discuss some of the preclinical, clinical and regulatory hurdles that have thus far limited the development of OVs. Oncolytic viruses (OVs) provide a novel cancer treatment strategy, with a mechanism of action and toxicity profiles that are distinctly different to those of more traditional therapies. Thus far, four OVs have entered clinical use globally, yet only talimogene laherparepvec (T-VEC) has entered widespread clinical use. In this Review, the authors describe the clinical and regulatory experience with T-VEC thus far, and how this can guide the development of novel OVs. Discussions of a range of novel OVs with the potential for clinical implementation in the near future are also provided. Key points Talimogene laherparepvec (T-VEC) for patients with melanoma is the first widely approved oncolytic virus, and real-world data from the past 7 years have optimized the role of T-VEC, including identifying patients who are most likely to derive benefit. Research involving T-VEC has since been expanded to clinical trials involving patients with other cancers, earlier administration inclu