Cells from human embryos could be used to help some people with spinal injuries to walk again, successful work involving rats has indicated.
Scientists from the University of California at Irvine college of medicine said that paralysed rats walked again after being injected with stem cells from "early-stage" human embryos. They hope that the breakthrough will prove to American policy makers that the use of human embryonic stem cells and therapeutic cloning - presently banned in the US - are justified.
The team, led by Hans Keirstead, took stem cells from early-stage human embryos, and altered them in the laboratory into oligodendrocytes. These are the primal cells that form myelin, the vital fatty sheath that surrounds nerve fibres. These cells were transplanted into paralysed rats with bruised spines. After nine weeks, the rats regained the ability to walk, New Scientist magazine reports today.
Analysis of the rats' spinal cords showed that the oligodendrocytes had wrapped themselves around neurons and formed new myelin sheaths. They also secreted growth substances that appeared to have stimulated the formation of new nerves.
Dr Keirstead said last week that he planned to use the same technique to treat human patients who had suffered recent spinal cord injuries and localised damage.
Treating people who have been paralysed for years or suffer from degenerative nerve diseases would be far more difficult. Stem cells can develop into every form of tissue in the body; early embryos consist of stem cells, which then specialise as the embryo matures. If removed from the embryo early enough, they retain that ability to metamorphose into any sort of tissue. That realisation opened up the possibility of many new treatments.
But in Britain and America, the use of stem cells is strictly regulated, and the European Union may ban any such experiments. In the US, federal money cannot be used for stem-cell research.
The latest work was funded by the US biotechnology company Geron, whose president, Thomas Okarma, said only embryonic stem cells could really succeed in new therapies. Embryonic cells could be mass-produced, unlike adult stem cells. Mr Okarma said that one cell bank derived from a single embryo could yield enough neurons to treat 10 million Parkinson's disease patients. He added that adult stem cells might not be as versatile as embryonic ones.
He said: "At this moment, there is very little hard evidence that a bone marrow stem cell can turn into anything but blood or that a skin stem cell can become anything but skin."
The method does not hold any immediate promise for accident victims such as the actor Christopher Reeve, who was paralysed from the neck down in a riding accident in May 1995. His spine was badly crushed by the bones of his neck, cutting many nerves to the rest of his body. In the rat research, the repaired nerves were only "bruised".
Mr Reeve has been among those lobbying to reverse the US government's opposition to stem-cell research. Dozens of scientists are working on spinal cord repair methodologies. But despite numerous successes in rats, hardly any have moved forward to human trials.