Remarkable new research from scientists in the UK has shown how a naturally occurring, and mostly harmless, virus is being recruited into attacking brain cancer and enhancing the tumor-targeting abilities of the body's own immune system.

Harnessing a virus to help instead of harm is a technique that has shown great promise over recent years. Specific cancer-killing viruses are dubbed oncolytic viruses, and everything from Zika to poliovirus are being tapped to attack deadly forms of cancer.

The latest study highlights a type of virus called reovirus, which has previously been shown to effectively home in on cancer cells, while often leaving healthy cells alone. For the first time researchers have shown that the reovirus has a remarkable ability to cross the protective membrane that surrounds the brain, called the blood-brain barrier.

A small cohort of human subjects, all with aggressive forms of brain cancer, were administered an intravenous infusion of the reovirus several days before their tumors were removed surgically. After surgery, samples were then taken of the removed tumors and the virus was found in all removed samples.

"This is the first time it has been shown that a therapeutic virus is able to pass through the brain-blood barrier, and that opens up the possibility this type of immunotherapy could be used to treat more people with aggressive brain cancers," says Adel Samson, co-lead author on the study.

As well as showing the reovirus had effectively infected the cancer cells, the study excitingly found evidence that the virus stimulated the body's natural immune system activity as well. By homing in on the tumor cells, the virus in effect made the tumor more visible to the immune system.

"Our immune systems aren't very good at 'seeing' cancers – partly because cancer cells look like our body's own cells, and partly because cancers are good at telling immune cells to turn a blind eye. But the immune system is very good at seeing viruses," explains co-lead author Alan Melcher.

A new human trial inspired by this research is already underway in the UK. The plan is administer the reovirus to patients as an adjunct to traditional radiotherapy and chemotherapy. The hope is the virus helps flag the cancer cells to the body's own defenses. The new trial will deliver multiple doses of the virus to single patients over several months.

"The presence of cancer in the brain dampens the body's own immune system. The presence of the reovirus counteracts this and stimulates the defense system into action," explains Susan Short, who is leading this new trial at the University of Leeds. "Our hope is that the additional effect of the virus on enhancing the body's immune response to the tumor will increase the amount of tumor cells that are killed by the standard treatment, radiotherapy and chemotherapy."

The study was published recently in the journal Science Translational Medicine.