A trial of a potential new brain cancer treatment has shown that a virus injected directly into the bloodstream can reach tumours deep inside the brain and switch on the body's own defence system to attack them. The trial involved just nine patients, but scientists said that if the results could be replicated in larger studies, the naturally occurring 'reovirus' could be developed into an effective immunotherapy for people with aggressive brain tumours.
"This is the first time it has been shown that a therapeutic virus is able to pass through the brain-blood barrier," said Adel Samson, a medical oncologist at the University of Leeds' Institute of Cancer and Pathology who co-led the work. He said their trial had shown not only that a virus could be delivered to a tumour deep in the brain, but that when it reached its target, "it stimulated the body's own immune defences to attack the cancer".
Published in the journal Science Translational Medicine on Wednesday, the trial involved nine patients with tumours that had either spread to the brain from other areas or were fast-growing gliomas, an aggressive type of brain cancer. All the patients were due to have their tumours removed surgically, but in the days beforehand they were each given a single dose of the reovirus administered via intravenous drip into the bloodstream.
Once the tumours were removed, the scientists analysed samples to see if the virus had been able to reach the cancer, which in some cases was deep within the brain. In all nine patients, there was evidence that the virus had reached its target, they said. There were also signs that the replicating virus had stimulated the immune system, with white blood cells or so-called "killer" T-cells being drawn to the tumour to attack it.
Because the virus only infects cancer cells and leaves healthy cells alone, patients who received the experimental treatment reported only mild side-effects such as slight flu-like symptoms. Until these positive results, scientists had been doubtful about whether the virus would be able to pass into the brain because of the protective blood-brain barrier membrane. However, injecting the virus directly into the brain would be difficult and potentially dangerous.