This article is more than 12 years old

This article is more than 12 years old

British scientists have discovered cells that are the source of the most common form of childhood leukaemia after studying twin sisters from Kent, one of whom fell ill with the disease.

The achievement, a world first, came after doctors treating four-year-old Olivia Murphy, from Bromley, learned that her identical twin, Isabella, had not developed the illness.

Their parents, Sarah and Justin, agreed to take part in the research, in the hope that it would help reduce the number of children needing chemotherapy.

Less aggressive therapies

The work was hailed as a big step forward by cancer experts, who said it would lead to less aggressive therapies for sick children and new drugs.

It is the first time scientists have discovered the tiny but crucial group of cells that are the root cause of human cancer. Only a fraction of a percent of cancer cells drive the disease.

Cancer specialists now aim to develop drugs that target the cells with precision, effectively destroying the engine at the heart of the disease. The discovery is expected to boost the search for similar cells that drive other types of cancer.

Olivia was two when she was diagnosed with acute lymphoblastic leukaemia, which strikes one in 2,000 people before their early teens. She has since received chemotherapy for the disease, which has a success rate of more than 80%.

During treatment, she contracted a chickenpox virus that overwhelmed her immune system and left her blind in one eye.

Vital clues

Doctors at Great Ormond Street Hospital and the Institute of Cancer Research in London joined forces with the scientists at Oxford University to study the sisters in the hope that they would reveal vital clues about the cause of the disease.

"The twins gave us this unprecedented opportunity to look at the very earliest stages of this disease ... there is no other way we could have got at this," Professor Tariq Enver, of the John Radcliffe hospital, in Oxford, said.

The doctors compared blood samples from the two girls and found that both had genetically abnormal cells in their blood. The defect was caused by two genes, called MEL and AML, fusing together inside stem cells that make blood in bone marrow.

However, this alone was not enough to cause leukaemia. Further tests revealed that Olivia's blood stem cells carried a second defect, a missing gene, which switched the cells from a "pre-leukaemia" state into full-blown leukaemia.

Although Olivia has now been treated for her illness, her sister still has a 10% chance of developing the disease.

Helping other families

"What we have always said is that anything that would improve the treatment, we would be very, very happy to contribute to," the twins' mother said.

"We have seen the families who have gone through all the chemotherapy. Anything which leads to a lessening of the intensity of the chemotherapy which can help other families is a good thing.

"Without the research we wouldn't have had the treatment available to us."

Writing in the US journal Science, the team described how they confirmed their discovery by injecting blood cells with the genetic defects into mice. The animals developed a leukaemia-like disease.

Doctors said pre-leukaemia cells developed in one of the twins some time after the first month of pregnancy and spread to the other while in the womb.

Shortly after birth, a chance infection, perhaps from a common cold virus, was enough to trigger the second, dangerous mutation in Olivia.

"What we've never been able to see before is where this disease begins. The surprising thing is that it's a very small population, only 1% of leukaemia cells, that turn out to be the ring leaders," Enver said.

Tailor-made therapy

The cells may also be to blame for cancer returning after treatment. If chemotherapy does not wipe them all out, they can slowly begin to produce new cancer cells years later. The discovery gives doctors the first chance to tailor chemotherapy to suit individual children.

"This is undoubtedly a major step," Professor Andy Pearson, a paediatric oncologist at the Institute of Cancer Research at the Royal Marsden hospital, in London, said.

"We'll be able to monitor children for these cells throughout their treatment and stop when they have been killed off. It will also help us develop new treatments aimed at these cells that drive leukaemia."

In the future, it might be possible to screen children for pre-leukaemia cells and give them preventative treatment.

"We don't know what causes the initial genetic abnormality," a spokesman for Leukaemia Research said.

"It's possible this is one of many, many genetic mishaps that occur in the womb as a matter of course, but are not usually so unlucky."