In 1796, Edward Jenner showed that the cowpox virus could be used to inoculate people against smallpox. Today, the same vaccine is being looked at as a potential treatment against cancer. Vaccinia poxvirus is just one of several viruses that has been hijacked for the purpose of killing cancer tumors (herpesvirus is another high profile enlistee). These viruses, known as oncolytic viruses, are currently in late-stage human testing and have shown remarkable promise.
Through genetic engineering, such oncolytic viruses have been altered slightly to specifically seek out and attack cancer cells. Upon infection, the virus replicates and continues to infect new cancer cells, often killing them. To bolster cell death of the cancer, many engineered viruses also include an immune system protein (GM-CSF) that serves to boost the natural response of the individual’s immune system. The inclusion of this protein attracts white blood cells to mount a two-front attack on the cancer cells.
Cancer patients need not worry about the altered viruses infecting healthy cells. In the case of vaccinia poxvirus, the genetic engineers have removed a gene known as thymidine kinase. This gene is necessary for replication within the body.
The vaccinia virus is showing early promise in its effectiveness against a variety of cancers. In a phase II clinical trial, 18 of 24 patients diagnosed with liver cancer survived for a minimum of 12 months. In comparison, roughly half of liver cancer patients typically survive to the one-year mark. A phase III clinical trial is scheduled to begin later in the year.
An early-stage trial has also tested the engineered virus against colorectal, ovarian, skin and lung cancers.
In these early studies, patients reported flu-like symptoms to the treatment. However, no other major side effects were reported. Individuals who have previously received a smallpox vaccine showed no reduction in benefits.
Beyond the vaccinia virus, an engineered herpesvirus known as OncoVex is showing promise against head and neck cancer. The treatment is currently in phase III clinical trials. A nearly identical virus has already met approval in China and is currently available.
If these new cancer treatments eventually make it to market, they will almost certainly be paired with chemotherapy or radiation. Treatment studies focused wholly on virus treatment have not been nearly as successful as those that incorporate a combination of virus therapy and chemo or radiation.