Stem cells will be grafted into the brains of patients during the new trial. Credit: ALAMY

UK researchers have been given the go-ahead for a clinical trial to assess the use of stem-cell transplants for stroke. Twelve people will take part in the preliminary safety study, the first time that brain-derived stem cells have been used to treat stroke patients.

The trial, due to start later this year, will see different doses of cultured human neural stem cells grafted into the brains of patients who have had a stroke — often caused by a blood clot blocking one of the vessels leading to the brain. The study will assess how safe the procedure is, but will also monitor changes in mobility and brain function.

"I'm cautious but hopeful," says neurologist Keith Muir of the University of Glasgow, UK, who will coordinate the trial. "We've tried a lot of things in stroke over the years, most of which haven't been helpful."

Stroke is the leading cause of death and the single biggest cause of adult disability in the developed world. Around half of all stroke survivors are left with permanent disabilities. Although clot-busting treatments can help restore blood flow if given soon after the stroke, most treatment focuses on rehabilitation such as physiotherapy.

So researchers are searching for other therapies. Stem-cell transplants are an attractive option because the primitive cells have the potential to form many other cell types, and may be able to repair or replace damaged brain cells.

Human stem cells have been grafted into the brains of stroke patients before, but the results were inconclusive. Because those cells came from an embryonic tumour, scientists were concerned that they might become cancerous in the patients' brains.

Chemical switch

The cells in this study, developed by UK biotechnology firm ReNeuron, have been tailor-made for transplantation. Originally isolated from a human fetus, the cells have been modified by the addition of a gene that promotes cell growth. This helps them to divide in culture in the lab so they can be grown up into the vast numbers required for the trial.

Crucially, the gene's activity can be switched on and off by adding or removing a chemical in the culture dish. When the chemical is removed, the cells stop dividing and are ready for transplantation without the risk of tumour formation. The UK Medicines and Healthcare products Regulatory Agency has given the green light for the use of these cells in the study.

"It's exciting to see things that we've worked on for many years coming to trial," says Steve Dunnett from Cardiff University, UK, who studies cell transplantation.

ReNeuron researchers have already tested the therapy in stroke-damaged rat brains, in which the cells prompted new blood vessels and neurons to form. The animals also regained control of movement in their front paws.

The cells will be transplanted into patients around six months after their stroke, by which time any remaining brain damage is thought to be permanent. "But it's hard to imagine that once you've got an area of dead tissue, transplanting cells into it will make much difference," says Roger Barker from the University of Cambridge, UK, who studies transplantation therapies for neurodegenerative diseases. It may be that the cells will work better if transplanted earlier, he adds.