An oncolytic virus is a virus that preferentially infects and kills cancer cells. As the infected cancer cells are destroyed by oncolysis, they release new infectious virus particles or virions to help destroy the remaining tumour. Oncolytic viruses are thought not only to cause direct destruction of the tumour cells, but also to stimulate host anti-tumour immune system responses.The potential of viruses as anti-cancer agents was first realised in the early twentieth century, although coordinated research efforts did not begin until the 1960s.
A number of viruses including adenovirus, reovirus, measles, herpes simplex, Newcastle disease virus, and vaccinia have been clinically tested as oncolytic agents.
Most current oncolytic viruses are engineered for tumour selectivity, although there are naturally occurring examples such as reovirus and the senecavirus, resulting in clinical trials.The first oncolytic virus to be approved by a national regulatory agency was genetically unmodified ECHO-7 strain enterovirus RIGVIR, which was approved in Latvia in 2004 for the treatment of skin melanoma; the approval was withdrawn in 2019. An oncolytic adenovirus, a genetically modified adenovirus named H101, was approved in China in 2005 for the treatment of head and neck cancer. In 2015, talimogene laherparepvec (OncoVex, T-VEC), an oncolytic herpes virus which is a modified herpes simplex virus, became the first oncolytic virus to be approved for use in the U.S. and European Union, for the treatment of advanced inoperable melanoma.