was seen, these responses were neither complete nor durable. The field of virotherapy was nearly abandoned for a time, as the technology required to modify viruses didn't exist whereas chemotherapy and radiotherapy technology enjoyed early success. However, now that these technologies have been thoroughly developed and cancer remains a major cause of mortality, there is still a need for novel cancer therapies, garnering this once-sidelined therapy renewed interest. Herpes simplex virus Herpes simplex virus (HSV) was one of the first viruses to be adapted to attack cancer cells selectively, because it was well understood, easy to manipulate and relatively harmless in its natural state (merely causing cold sores) so likely to pose fewer risks. The herpes simplex virus type 1 (HSV-1) mutant 1716 lacks both copies of the ICP34.5 gene, and as a result is no longer able to replicate in terminally differentiated and non-dividing cells but will infect and cause lysis very efficiently in cancer cells, and this has proved to be an effective tumour-targeting strategy. In a wide range of in vivo cancer models, the HSV1716 virus has induced tumour regression and increased survival times. In 1996, the first approval was given in Europe for a clinical trial using the oncolytic virus HSV1716. From 1997 to 2003, strain HSV1716 was injected into tumours of patients with glioblastoma multiforme, a highly malignant brain tumour, with no evidence of toxicity or side effects, and some long-term survivors. Other safety trials have used HSV1716 to treat patients with melanoma and squamous-cell carcinoma of head and neck. Since then other studies have shown that the outer coating of HSV1716 variants can be targeted to specific types of cancer cells, and can be used to deliver a variety of additional genes into cancer cells, such as genes to split a harmless prodrug inside cancer cells to release toxic chemotherapy, or genes which command infected cancer cells to concentrate protein tagged with radioactive iodine, so that individual cancer cells are killed by micro-dose radiation as well as by virus-induced cell lysis. Other oncolytic viruses based on HSV have also been developed and are in clinical trials. One that has been approved by the FDA for advanced melanoma is Amgen's talimogene laherparepvec. Oncorine (H101) The first oncolytic virus to be approved by a regulatory agency was a genetically modified adenovirus named H101 by Shanghai Sunway Biotech. It gained regulatory approval in 2005 from China's State