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A virus injected directly into the bloodstream could be used to treat people with aggressive brain tumours, Scientists have found that the naturally occurring virus could act as an effective immunotherapy in patients with brain cancer or other cancers that have spread to the brain. They showed that a type of virus called reovirus could cross the blood-brain barrier to reach tumours, where it replicates and kills the cancer cells.
They also found that the virus was able to ‘switch-on’ the body’s own defense systems to attack the cancer. The study authors, from the University of Leeds and The Institute of Cancer Research in London, believe reovirus therapy could be used in conjunction with other cancer therapies to make them more potent – and a clinical trial is currently underway. Because the virus infects cancer cells and leaves healthy cells alone, patients receiving the treatment reported only mild flu-like side effects.
Scientists thought it was unlikely that the virus would be able to pass from the blood into the brain because of the blood-brain barrier, a protective membrane around the brain. That would have meant that the only way they could get the virus into the brain was to inject it directly into the brain – which is challenging, would not be suitable for all patients, and cannot be regularly repeated. But the research demonstrated that the virus could be administered through a single-dose intravenous drip.
Nine patients took part in the study, they had cancers that had either spread to the brain from other parts of the body or were fast-growing gliomas, a type of brain cancer that is difficult to treat, and has a poor prognosis. All the patients were due to have the tumours removed surgically. But in the days before the surgeons operated, the patients were given the virus drip.
Once the tumours were removed, samples were taken and analysed for signs that the virus had been able to reach the cancer, sometimes deep within the brain. In all nine patients, there was evidence that the virus had reached its target. The researchers also found that the presence of reovirus stimulated the body’s own immune system, with white blood cells or ‘killer’ T-cells being attracted to the tumour site to attack the cancer.
Tissue samples from patients who had surgery but not the virus therapy served as a control. When compared with the control samples, the tissue taken from the people who had received the reovirus had higher levels of interferons, proteins that ‘switch-on’ the body’s immune system. According to Dr Adel Samson, co-lead author and medical oncologist at the Leeds Institute of Cancer and Pathology, at the University of Leeds, “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.
Human immune systems aren’t very good at detecting cancers, because cancer cells look like human 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. In the study, they were able to show that reovirus could infect cancer cells in the brain. And, importantly, brain tumours infected with reovirus became much more visible to the immune system.
Although the earlier trial demonstrated that the reovirus was reaching the cancer cells after just a single dose, doctors have decided to give it repeatedly to patients because of the way it ‘kick starts’ the body’s own defences. 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. 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.
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