Patients who had human embryonic stem cells implanted into their eyes to correct vision loss have experienced no long-term ill-effects, a study has confirmed.
Up to three years after treatment, the procedure still appears to be safe, scientists reported. There had been concerns about tumours being triggered by hyperactive stem cells and immune system rejection.
“Embryonic stem cells have the potential to become any cell type in the body”
In more than half the patients, the treatment also restored some sight.
All 18 patients given the experimental therapy had different forms of macular degeneration, a common cause of blindness and impaired vision.
Professor Robert Lanza, chief scientific officer at the US company Advanced Cell Technology, which funded the research, said: “Embryonic stem cells have the potential to become any cell type in the body, but transplantation has been complicated by problems including the risk of teratoma (tumour) formation and immune rejection.
“As a result, immunoprivileged sites that do not produce a strong immune response, such as the eye, have become the first parts of the human body to benefit from this technology,” he said.
Human embryonic stem cells (hESCs) are blank-slate “mother cells” taken from early-stage embryos that have the ability to develop into any type of body tissue.
In two trials hESCs were first coaxed under the influence of chemical signals to “differentiate” into immature retinal cells.
They were then transplanted into the eyes of nine patients with Stargardt’s macular dystrophy and nine with dry atrophic age-related macular degeneration.
No effective treatments exist for either condition, both of which can result in complete blindness caused by the loss of light-receiving photoreceptor cells in the retina.
All study participants had one of three different doses of the cells injected under the retina of the eye with the worst vision.
Writing in The Lancet medical journal, the researchers said the hESC-derived cells were well tolerated for up to 37 months after transplantation.
“Much work remains to be done before… stem cell therapies go beyond regulatory trials, but the path is now set in motion”
No evidence of hyper-proliferation or rejection were detected during a typical follow-up period of 22 months.
Tests showed substantial improvement in 10 of 18 treated eyes. Eight patients were able to read more than 15 additional letters on a sight chart in their first year after treatment. Untreated eyes did not show the same visual improvements.
Professor Steven Schwartz, one of the study leaders from the Jules Stein Eye Institute in Los Angeles, said: “Our results suggest the safety and promise of hESCs to alter progressive vision loss in people with degenerative diseases and mark an exciting step towards using hESC-derived stem cells as a safe source of cells for the treatment of various medical disorders requiring tissue repair or replacement.”
In a linked comment in the journal, Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine in the US, said: “Since the discovery of hESC in 1998, much has transpired, including political, ethical and scientific debates, with an overall push to achieve the promise of human therapies.
“Now, we have follow-up that extends to longer than three years in patients treated with hESC-derived stem cells, showing both safety and apparent efficacy,” he said.
“Much work remains to be done before… stem cell therapies go beyond regulatory trials, but the path is now set in motion,” he added.