ReNeuron, a British company developing stem-cell therapies, suffered a setback yesterday when the US regulator put the group's first clinical trial on hold.
The company had filed an application at the beginning of December seeking approval to begin testing its stem-cell therapy for strokes in humans. But it said the food and drug administration (FDA) had put the study on hold without giving further explanation. The company expects more information when it talks to US officials this week.
Michael Hunt, the chief executive, said he had no idea why the study had been delayed. "This is a novel treatment in a brain condition that is completely unserved and the FDA is arguably the world's toughest regulator," he said. "It's perhaps unrealistic to expect it not to look at this very closely. We hope the issues are not going to be fundamental."
The company uses adult stem cells, found in adult tissues, that have the potential to replenish dying cells or regenerate damaged tissues. Its ReN001 stem-cell therapy, for which it submitted the application, is designed to help those left disabled after a stroke.
Shares in the company fell 5.5p to 39p amid speculation there were political undertones to the FDA's decision. The issue of stem cells has raised huge controversy in the US, and last July President George Bush vetoed a bill that would have expanded embryonic stem-cell research.
Mr Hunt admitted there were political issues surrounding stem cells. But he said: "We believe our application is one that does its best to minimise these ethical considerations."
The company has developed a technology with which it can grow numerous cell lines from a single tissue sample, meaning it never again needs to use another original sample.
Analysts also suggested the FDA decision may have arisen from safety concerns, as stem-cell research is still at a very early stage. Experts say that stem cell therapies could prove extremely powerful.
Sam Fazeli, a senior research analyst at investment bank Piper Jaffray, said: "The problem with stem cells is that most of the side effects are completely novel. The FDA is going to have to think very hard before putting this into patients."