New research published in the Clinical Cancer Research has found that modified versions of the vaccinia virus have boosted immunotherapy in sarcoma tumours; a hard-to-treat cancer.

The cancer-killing virus with immunotherapy could effectively treat the advanced cancers, which affect the limbs.

The virus, which is a viral component of the smallpox vaccine, was able to switch on the immune system against cancer in rats with sarcoma tumours, leading scientists at The Institute of Cancer Research (ICR), London, to believe that infecting tumours with vaccinia could make immunotherapies work in many more patients – since the immune system is hard-wired to recognise viruses.

The ICR studied sarcomas using tumours in rats and human cells to see whether infection with a vaccinia virus modified to selectively attack cancer cells could uncloak the disease to the immune system, and found that all six animals who received the combination therapy followed by surgery for their sarcoma were cured.

The virus and immunotherapy were given alongside chemotherapy using a procedure known as isolated limb perfusion, which delivers drugs into the bloodstream after cutting off the blood supply in the limb from the rest of the body.

Study co-leader and professor of biological cancer therapies, Kevin Harrington said that the study has “used the fact that viruses are the ancient enemy of the immune system to infect tumours and spark a strong immune reaction against them.

“We showed that infecting cancer cells with a modified vaccinia virus could kill them directly, but most importantly made tumours much easier for the immune system to spot. It’s a powerful demonstration of the potential both of viruses, and scientifically selected combination treatments, to eradicate tumours.

“The different approaches in our combination therapy are already routinely used to treat sarcoma, or available on the NHS for different cancer types – so I am hopeful that we should soon be able to test them all out together in a clinical trial.”

When sarcoma affects the limbs it is normally treated with surgery and radiotherapy – but in around 30% of cases, the disease comes back and spreads.

Immunotherapy has shown great promise in many forms of cancer, but can’t yet be used to treat ‘immune cold’ tumours such as sarcoma, which contain relatively few immune cells.