Viruses carried by white blood cells have the potential to wipe out spreading cancer, research suggests.
Scientists in Britain have demonstrated that the technique works, using a virus normally found in horses and cattle, to eradicate cancer in mice.
Clinical trials are now being planned which could see similar treatments tested on cancer patients within a year.
If the results are successful, it could lead to many thousands of lives being saved.
Most common cancers, such as those arising in the breast, prostate, colon, and skin, kill by spreading or "metastasising" to the liver, brain and other vital organs.
Once a cancer becomes systemic, travelling through the body via lymph ducts and blood vessels, it becomes much more difficult to treat.
Harmful
Viruses have been suggested in the past as a weapon against cancer, but usually they are neutralised by immune system antibodies too rapidly to be effective. Some viruses can also be harmful to the patients.
The new technique, pioneered by Prof Alan Melcher, a Cancer Research UK scientist based at the University of Leeds, employs white blood cells to smuggle viruses into sites where spreading cancer cells accumulate.
In the mouse study, Prof Melcher’s team loaded T cells — a type of immune system white blood cell — with vesicular stomatitis virus (VSV), which usually infects horses and cattle.
Lethal
The virus is lethal to cancer cells but resisted by healthy cells.
Carried by the T cells, the virus was ferried through the lymph system to the lymph nodes, liver and spleen. There, the viral particles replicated inside cancer cells, eventually bursting out of the cells and killing them.
As the cancer cells were destroyed, they released molecules which triggered a powerful immune system response. This effectively finished the job and wiped out the cancer.
"What you have is a double whammy," said Prof Melcher. "It’s not just that the virus kills the cancer cells. When you get this virus-mediated killing, the immune system sits up and takes notice. That’s important, because one of the big problems with cancer is that often the immune system ignores it."
Metastasising skin, lung and colon cancers were all destroyed in the experiments.
The research, conducted with the help of US scientists from the Mayo Clinic in Maryland, was published online yesterday in the journal ‘Nature Medicine’