Oncolytic viruses selectively infect and kill cancer cells without harming normal tissue. To create this therapy, existing viruses are modified in the lab so that they can infect cancer cells, multiply, and destroy the cancer cells as well as the tumor mass. The viruses multiply in cancer cells but not in normal cells.
In addition to being able to directly kill cancer cells, oncolytic viruses can trigger an anti-tumor immune response. Tumors have an innate ability to avoid the immune system. If a few cancer cells pop up, the immune system typically recognizes and eliminates them. Any cancer cells that escape elimination change their cell surface so they can hide from the immune system, growing and spreading. Oncolytic viruses awaken the immune system so that it can promote a strong response against cancer.
One oncolytic virus has been approved for treatment of melanoma—the therapy is injected directly into the melanoma. Multiple clinical trials have shown promising results in several types of cancer.