Turning killer into cure -- the story of oncolytic herpes simplex viruses.

Viruses have the intrinsic capability to kill host cells. Even when the initial infection consists of only a few viruses, they can reproduce themselves in large quantities within a short time and quickly spread to nearby cells, causing substantial tissue damage. These same infectious properties become desirable if they can be converted into killer agents with specificity for malignant cells. Cancer virotherapy is doing exactly that by modifying viruses in ways that allow them to replicate in malignant cells but not in normal cells. Although relatively young, the field has seen significant progress in recent years. For example, the most recent phase III trial data on a herpes simplex virus (HSV)-based oncolytic virus (T-VEC) show substantial improvement in objective and durable responses over the control arm in melanoma patients, prompting speculation that a virotherapy may receive FDA approval for clinical use in the very near future. This review focuses on HSV-based oncolytic viruses, from their early history to their most recent development, with discussion of promising directions for further improvement.