Talimogene laherparepvec is a genetically engineered herpes virus (an oncolytic herpes virus). Two genes were removed – one that shuts down an individual cell's defenses, and another that helps the virus evade the immune system – and a gene for human GM-CSF was added. The drug works by replicating in cancer cells, causing them to burst; it was also designed to stimulate an immune response against the patient's cancer, which has been demonstrated by multiple pieces of data, including regression of tumors which have not been injected with talimogene laherparepvec.
