Cloned embryonic stem cells have been used to treat animals with Parkinson’s disease for the first time, in an important step towards developing the therapy for human patients.

The successful experiment marks the first time that cloned stem cells have been used to reverse disease in the same animals from which they were derived, and suggests that it should be possible to use therapeutic cloning in medicine.

It points to the medical promise of embryonic stem cell research, as the House of Commons prepares to debate legislation that will regulate the field.

Embryonic stem cells are master cells that can grow into any form of tissue. They thus have the potential to create replacements for cells that are lost or damaged in conditions such as Parkinson’s, diabetes and spinal paralysis.

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• Matter of Conscience

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Scientists also hope that it will be possible eventually to make these cells with embryos cloned from the patients they will be used to treat. As these replacement cells would carry the patient’s genetic code, they could be transplanted without fear of rejection by the immune system.

The research, from a team led by Lorenz Studer, of the Sloan-Kettering Institute in New York, takes science a step closer to such therapeutic cloning, by proving that it can work in an animal model of Parkinson’s disease.

The disorder is caused by the loss of neurons that make dopamine, an important brain signalling chemical, leading to a characteristic tremor and loss of motor skills, and often to depression and dementia.

The scientists first created 187 lines of cloned embryonic stem cells from 24 mice bred to develop the equivalent of Parkinson’s, using a process called somatic cell nuclear transfer.

These cloned cells were then cultured in the laboratory to grow into dopamine neurons. These were then transplanted into the brains of the Parkinsonian mice that provided the DNA with which they were originally created.

When mice received neurons grown from their own cloned stem cells, their neurological symptoms improved and they showed no signs of rejecting the transplanted tissue.

When the neurons were grafted into different mice that were not a genetic match, however, the mice failed to recover.

The findings, which are published in the journal Nature Medicine, suggest that it could be possible to use this cloning approach to treat Parkinson’s in humans.

“Although technically complex . . . these data demonstrate the feasibility of treating individual Parkinsonian mice via therapeutic cloning, and suggest considerable therapeutic potential for the future,” the scientists said. Several important hurdles remain, however, before similar techniques can be tried on humans. First, only two groups, one in Britain and one in the US, have succeeded in cloning human embryos, and none has yet produced stem cells from a cloned embryo.

The inefficiency of cloning, which requires hundreds of eggs to produce a single viable clone, is also expected to limit therapeutic applications.

Many scientists think that the main use of cloning will be to make laboratory models of disease for medical research, rather than treatments to be given to patients. This can be done by inserting human DNA into animal eggs, which will be allowed under the Human Fertilisation and Embryology Bill.

The results also suggest that a different approach to producing patient-matched stem cells — by reprogramming adult cells into an embryonic state — is likely to be useful in therapy. These “induced pluripotent” stem cells also carry the genetic material of patients, but as they are not produced from embryos they may be simpler to create, and raise fewer ethical objections from those who oppose embryo research.

Experts on stem cells and Parkinson’s disease said the results were exciting.

Professor Robin Lovell-Badge, of the National Institute for Medical Research in London, said: “This is a very well conducted study that provides further proof-of-principle of the idea of ‘therapeutic cloning’ using a mouse model.

“Ideally one of the next steps will be to repeat the whole procedure with a monkey model, in which all the individual steps have now been established. This will allow much better tests of functional recovery and safety.”

Kieran Breen, director of research at the Parkinson’s Disease Society, said: “Stem cell therapy offers great hope for repairing the brain in people with Parkinson’s. It may ultimately offer a cure, allowing people to lead a life that is free from the symptoms of Parkinson’s.

“Researchers in this area now need to carry out more studies to satisfy safety concerns and to make the process more efficient before these studies are carried out on people living with Parkinson’s.”

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