Five men all over the age of 60 have received treatment as part of a phase I trial, which began in 2010 at the Southern General Hospital in Glasgow. They all received an injection of brain cells close to areas of the brain damaged by stroke. These cells were derived from stem cells taken from a fetus. Three months after treatment they showed signs of increased mobility and in one case, improved sight. A sixth patient received the treatment less than three months ago, and a further six are due to be treated as part of the trial.
Professor Keith Muir, chair of clinical imaging at the University of Glasgow and who is leading the trial, urged caution. He told the BBC that while the changes were 'nothing very dramatic', the doctors were nonetheless surprised to see any improvement in the patients.
'So far we've seen no evidence of any harmful effects. We're dealing with a group of people a long time after a stroke with significant disability and we don't really expect these patients to show any change over time', said Professor Muir.
He added: 'It's interesting to see that in all the patients so far they have improved slightly over the course of their involvement in the study'. Further trials will be required to establish if the stem cells can help repair damaged tissue.
Chris Mason, professor of regenerative medicine bioprocessing at University College London, said even the slightest improvements could be extremely valuable to patients in improving their quality of life. 'Being able to feed yourself or drink a cup of tea is a massive gain for a patient', he said.
The trial, which is believed to be the first to treat stroke patients using brain cells, is around halfway to completion. 'We hope to tease out over the next 18 months whether the improvement is due to the treatment', Professor Muir told BBC News.
Some critics have questioned the use of fetal stem cells, citing ethical considerations. 'For many it will be ethically troubling that this treatment involves injecting several million cells from an aborted fetus', said Philippa Taylor, head of public policy at the Christian Medical Fellowship.
However, Michael Hunt, chief executive officer of ReNeuron - the company that produced the stem cells used in the trial - said no more cells would need to be extracted.
'We originally derived this material nine years ago from fetal tissue', he said. 'But what we've been able to do with the technology is to grow cells from the original sample such that we don't have to source any further tissue'.
The findings were presented at the International Society for Stem Cell Research's annual meeting in Yokohama, Japan.