A naturally occurring virus, which can be injected directly into the bloodstream, has the potential to boost the immune system and enable it fight aggressive brain tumours, scientists have found.

The findings showed that a type of virus called reovirus, when injected directly into the bloodstream, can cross the blood-brain barrier to reach tumours deep inside the brain.Here, it replicates cancer cells and "switches on" the body's own defence system to attack and kills them.It could act as an effective immunotherapy in patients with brain cancer or other cancers that have spread to the brain, the researchers said."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," said Adel Samson, medical oncologist at the University of Leeds.

"This study was about showing that a virus could be delivered to a tumour in the brain. Not only was it able to reach its target, but there were signs it stimulated the body's own immune defences to attack the cancer," Samson added, in the paper published in the journal Science Translational Medicine.Based on the results, a new trial has started where patients will be given reovirus in combination with the standard treatment of radiotherapy and chemotherapy which follows surgery.

"The presence of cancer in the brain dampens the body's own immune system. The presence of the reovirus counteracts this and stimulates the defence system into action," Susan Short, Professor at the varsity, who is leading the trial."The additional effect of the virus on enhancing the body's immune response to the tumour will increase the amount of tumour cells that are killed by the standard treatment, radiotherapy and chemotherapy," Short said.