May 29th 2008
From The Economist print edition
It may become possible to vaccinate against brain tumours
CERVICAL cancer is caused by a virus. That has been known for some time and it has led to a vaccine that seems to prevent it. Since then, researchers have been looking for other cancers that may be caused by viruses, to see if they too can be prevented. And they seem to have found one—one of the most feared of all. A piece of research expected to be unveiled on June 1st by Duane Mitchell of Duke University in North Carolina, at a meeting of the American Society of Clinical Oncology, hints that glioblastomas, the most lethal form of brain tumour, may also be susceptible to vaccination.
The story began a few years ago when Charles Cobbs of the California Pacific Medical Centre Research Institute in San Francisco found something odd about glioblastomas. He noticed they usually have a form of herpes, called cytomegalovirus, active within them. It is not that catching cytomegalovirus automatically causes a brain tumour—the virus is found, inactive, in about 80% of the population. Nevertheless, there is clearly some connection between virus and tumour, a connection reinforced by Dr Cobbs's discovery that the virus appears to dwell inside the tumour but not in the healthy tissue surrounding it. This led him to speculate that the virus may be creating the tumour as a safe haven to support its own existence.
After learning about Dr Cobbs's work, Dr Mitchell and his colleagues first confirmed the basic findings. They discovered cytomegalovirus in the tumours of more than 90% of those people with glioblastoma whom they examined, but not in healthy brain tissue, nor in non-malignant brain tumours. They then began an experiment on 21 patients who had been diagnosed with glioblastoma.
Their intention was to encourage those patient's immune systems to attack the tumours by training them to recognise the signs of active cytomegalovirus infection. To do that, they drew blood from their patients and exposed the immune-system cells within each sample to bits and pieces of cytomegalovirus, in order to encourage those cells to develop the power to identify the pathogen. The cells were then injected back into the patients they had come from, in the hope that those patients' immune systems would react to cytomegalovirus as if they had encountered it naturally within the body.
The results are encouraging. The normal prognosis for glioblastoma is death within two years, even if a patient is treated with chemotherapy and radiation. Such treatment by itself is reckoned to slow the tumour's growth by between six and eight months. When Dr Mitchell added his crude vaccine to the traditional treatment, this figure rose to more than a year—and in some people the tumours have stopped growing for more than two years, an observation that opens the door to work on a proper vaccine.
Just why active cytomegalovirus is associated with glioblastoma is still unclear. The virus may cause the tumour, as Dr Cobbs suspects, or the tumour may simply provide the virus with a congenial home. From the vaccine-maker's point of view it hardly matters. If a vaccine causes the immune system to destroy infected cells, the cancer will be killed anyway. And that would be very good news indeed.