Posted on behalf of Corie Lok.

Two clinical trials testing retinal cells derived from human embryonic stem cells report positive preliminary results today. A paper published today in The Lancet says that the cells appear to be safe four months after being injected into the eyes of two blind patients and describes visual improvements in the patients.

This isn’t the first trial of therapies based on human embryonic stem cells, nor does it provide the first data on these therapies in humans. It does, however, provide the first — albeit early — data from the only ongoing clinical trial of such a treatment. One trial involves patients with ‘dry’ age-related macular degeneration (AMD), the leading cause of blindness in the developed world, whereas the other is focused a juvenile form of degenerative blindness called Stargardt’s macular dystrophy. Neither condition is treatable.

The results reported today are from the first patient from each of the two trials, both of which will eventually enrol a dozen patients. Final results are expected in 2013. The early-stage safety trials are sponsored by Advanced Cell Technology (ACT), a stem-cell firm in Marlborough, Massachusetts (see ‘Never say die’, a recent News Feature about ACT).

Each of the patients had one of their eyes implanted with cells called retinal pigment epithelial (RPE) cells, which were derived from human embryonic stem cells. The implanted RPE cells are meant to engraft in the retina and replace native RPE cells that have died off as a result of the disease. RPEs provide support to the light-sensing photoreceptors in the retina, so the ultimate goal is for the new RPE cells to rescue dying photoreceptors and slow or even stop further vision loss. The researchers conducting the trials, led by Steven Schwartz at the University of California, Los Angeles, report finding no safety problems with the cell implants in the two patients. They did not see signs of, for example, tumour or other abnormal growths, retinal detachments, or immune rejection of the cells.

“Although at three months it is still very early to tell whether the cells will remain stable, it is good news that there are no signs of problems at this early time point,” says Thomas Reh, a neurobiologist at University of Washington, Seattle, who was not involved with the trials.

For the patient with Stargardt’s, who is a woman in her 50s, the transplanted cells seem to have engrafted in her eye. She reported seeing more colour and better contrast with that eye, and went from merely seeing hand motion before the procedure to counting fingers two weeks afterwards. The patient with dry AMD, who is a woman in her 70s, also said her vision improved, but Schwartz says that he attributes those changes to a placebo effect.

Schwartz cautioned that these are only preliminary results. “This should not be portrayed as necessarily working,” he says. But he says he felt compelled to release data so early on in a safety trial in part to give the patients in the trial a voice. “It’s an important first step,” he says.