Most of the herpesviruses we’ve talked about cause apparent skin pathologies. But in a recent study, Virotherapy, the selective use of genetically engineered viruses to treat disease, successfully treated aggressive melanoma. The virus that the study employed was a modified version of herpes simplex virus type 1. The therapeutic strain, named T-VEC, was developed back in 2006 through the deletion of 2 nonessential viral genes. The first is herpes virus neurovirulence factor gene (ICP34.5); this deletion attenuates the virus, and causes it to infect tumor cells more easily. The second is ICP47, a gene that suppresses host cell antigen presentation (i.e. so the patient’s immune system can better target the cancer cells). T-VEC also has a human gene called granulocyte macrophage colony-stimulating factor. In other words, this gene’s product recruits and stimulates macrophages, which are antigen-presenting cells.
The study injected the mutant into stage III and IV melanoma patients as part of a stage 3 clinical trial. The average survival time of the patients who received the virotherapy was 41 months, as compared to 21.5 months for the control group. These findings could be key in the development of an effective anti-melanoma therapy. In 2011, 65,647 people were diagnosed with melanoma in the United States, of which 9,128 died (13% case fatality!). Melanoma deaths cause about $3.5 billion of lost productivity in the United States alone every year. These results are exciting, but of course, an actual drug may still be a ways off. However, virotherapy is expandable to other types of cancers too, so it could be a useful addition to the current arsenal of cancer therapies.