Using viruses to treat cancer

Diagram: Nature Vol 256, 2015

The use of viruses as vector for the delivery of pharmaceutical agents or as a direct method to treat disease has been the subject of research for over a decade in various countries around the world. Referred to as oncolytic viruses (OV), they selectively replicate and kill cancer cells and spread within the tumor, but do not harm normal tissue. OVs are also very effective at inducing immune responses to themselves and to the infected tumor cells this assisting with cancer cell identification and apoptosis. OVs encompass a broad diversity of DNA and RNA viruses included such well known ones as measles and herpes simplex. By providing a diverse platform for immunotherapy the OVs can operate as in situ vaccines, or armed with immunomodulatory transgenes or combined with other immunotherapies. 

What makes this form of treatment potentially revolutionary is that many viruses preferentially infect cancer cells as the very nature of a malignancy suppresses normal antiviral response thus providing a perfect target for the virus. In some aspects, mutations which drive tumour growth also make cancer cells vulnerable to infection.

Both the United States and Europe have this year approved the use of a genetically engineered virus, talimogene laherparepvec (T-VEC) to treat advanced melanoma. T-VEC causes herpes however the virus has been genetically engineered to drastically reduce this risk and a gene has also been inserted which encodes a protein to stimulate a person's immune system. Results from a large clinical trial supported by biotechnology giant Amgen, published this year, demonstrated concrete results in tumour reduction and an increased survival period.

In time, some of the best known viruses which have proven to be such a scourge for humans may yet prove to have powerful beneficial uses.