Scientists have succeeded in reversing some of the symptoms of Parkinson's disease in rats by implanting human stem cells in their brains, it was announced yesterday.
The news will bring new hope to those suffering from the degenerative brain disease that currently has no permanent cure. But other experts cautioned that there are reasons to be concerned about the potential side-effects of such treatment.
The research, reported at the European Society on Human Reproduction and Embryology conference in Berlin yesterday, was the first to use human stem cells, rather than those derived from animals.
Stem cells are the body's building blocks which can develop into any part of the body, from limbs to blood to brain tissue. They can be obtained from donated embryos, left over after fertility treatment, or from an embryo deliberately cloned for therapeutic purposes.
The team of scientists, based at Hadassah University hospital in Jerusalem, used stem cells from a cloned embryo. They manipulated them in the laboratory to derive specialist neurons that are missing from patients with Parkinson's disease. Then they inserted the neurons in the brains of rats with the disease, which manifests itself in behavioural symptoms such as continually turning and failing to make side steps when dragged across a surface.
The symptoms were considerably reduced after the transplant, the researchers said. "This study shows for the first time that human embryonic stem cell-developed neural precursors can induce partial functional recovery in an experimental model of Parkinson's disease," Benjamin Reubinoff told the conference.
"We believe these observations are encouraging, and set the stage for future development that may eventually allow the use of embryonic stem cells for the treatment of Parkinson's disease."
Equally importantly, the stem cells did not proliferate by continuously dividing once inside the brain. This happened in a disastrous trial in the US after human volunteers had foetal stem cells transplanted into their brains.
Three years ago, US scientists admitted that the experiment had gone horribly wrong because the cells grew too well in 15% of the volunteers, producing excessive quantities of dopamine - the brain chemical thought to be in short supply in Parkinson's sufferers. The patients began to suffer severe side effects, such as writhing and jerking their limbs. One man was reduced to being fed through a tube.
Azim Surani, professor of developmental biology at Cambridge University, said the Israeli experiment was interesting and suggested that neurons derived through laboratory processes could function in a living creature. But the long-term effect on the rats needed to be studied.
"We really need to know how long these animals were kept," he said. "Do these neurons endure and function over a long period of time? The second thing is the side-effects. Too much dopamine is not good. In a long-term study one would want to know if there is any over-proliferation of donor cells which is potentially a problem."
Scientists at Newcastle University are waiting for permission from the Human Fertilisation and Embryology Authority to start cloning human embryos for research for the first time in Britain, in order to derive stem cells for use in diabetes patients.
Last year a team led by Shin-Yong Moon, from the National University of Seoul, announced the first stem cell line from cloned human embryos. Yesterday he said that work was continuing to improve the technique.
