Wednesday, November 4, 1998 Published at 13:07 GMT
Cancer immunity - at a price
Immune patients suffered a brain disease
Humans may be capable of naturally defeating cancer - although if you have such immunity you are likely to have a rare brain disease.
Scientists have seen for the first time how the body can naturally fight off the disease, just as it does the common cold.
In a study published in the Nature Medicine journal, Dr Robert Darnell found T-cells - immune cells that attack invaders - can kill cancer cells.
Normally T-cells would not attack cancer cells because they do not recognise them as a threat to the body.
The finding means that many people could develop cancers, fight them off, and remain unaware that they ever had them, Dr Darnell said.
He added that the research may make it possible to "boost" a cancer patient's immune response to the disease, which could mean an end to surgery and unpleasant courses of chemotherapy or radiotherapy.
However, the immune response has only been seen in patients suffering from a rare form of brain disorder.
Doctors had suspected such a response existed but had not been able to find solid evidence of them.
Dr Darnell, of Rockefeller University in the US, said: "We have discovered something that had been hypothesised for a long time - which is that the body is able to make an immune response that can kill its own cancer cells."
Dr Darnell's team studied patients with a condition known as paraneoplastic cerebellar disorder (PCD), which causes brain damage.
When such patients come to doctors, 90% of them are found to have cancerous tumours of which they had not previously been aware.
However, these tumours are usually small, and it seemed as if something was preventing them from progressing.
Dr Darnell set out to see if whatever was causing the brain damage was also holding those tumours in check.
His team studied four PCD patients. One was in the early stage of the condition and the other three had suffered chronic PCD for six months or more.
They found that the patients' tumour cells were producing a protein - cdr2 - that is normally found only in the brain.
It is this protein that attracts the destructive attention of the T-cells - they killed the cells with cdr2 on them.
However, in some cases they also killed cdr2-marked cells in their natural habitat - the brain.
This is not normally supposed to happen as the brain is kept separate from the body's other systems, and doctors are continuing to investigate how the immune system attacks the brain.
The protein was not found in people other than PCD patients, but Dr Darnell suggested that there might be a similar protein that elicits the same response in others.
The reason the response was only found in PCD patients could be because they visited their doctor with it - a patient with immunity to cancer who did not have PCD would have no reason to seek medical advice, he said.
"To illustrate," he said, "if you were to develop a small tumour that was recognised and eradicated by your immune system, that success would not come to the attention of physicians."
The team was able to reproduce their results in laboratory conditions, meaning that it could be possible to boost a cancer patient's immune response and kill the tumour naturally.
They manipulated some cells so that they would produce cdr2, and put them in a lab dish with immune cells from the patients.
"This is really the first observation of cells that can kill tumours in people. We'd like to find out how normal this is," Dr Darnell said.
"What we believe is going on is that cancer cells are sometimes expressing (producing) proteins normally made only in the brain by neurones.
"When these are taken out and expressed in tumour cells it's a lot like the body seeing a foreign protein produced by virus."