For the first time, scientists have successfully transplanted light-detecting cells in the retina, grown from embryonic stem cells, into mice--a feat that could advance similar therapies using the artificial cells to treat degenerative eye diseases toward human trials.

The animal transplant is a huge step for embryonic stem cell-based therapies, which have moved slowly to the clinic despite their promise.

A team of scientists from University College London's Institute of Ophthalmology and Moorfields Eye Hospital in London grew a synthetic retina from embryonic stem cells in the lab, extracted the light-sensitive photoreceptor cells that line the back of the eyes, and transplanted the cells into night-blind mice. Researchers observed that the cells seemed to develop normally, integrating into the existing retina and forming the nerve connections needed to transmit visual information to the brain.

In degenerative eye diseases such as age-related macular degeneration, retinitis pigmentosa and diabetes-related blindness, the loss of photoreceptors causes vision to deteriorate and can lead to blindness.

"This study is an important milestone on the road to developing a widely available cell therapy for blindness as it proves unequivocally that embryonic stem cells can provide a renewable source of photoreceptors that could be used in treatments," said Dr. Rob Buckle, head of Regenerative Medicine at the U.K.'s Medical Research Council, which funded the study.

Previous research by the UCL and Moorfields Eye team found that transplanting immature rod cells--essential for seeing in the dark--from the retinas of healthy mice into blind mice can restore their sight. Since this approach would not be practical in humans, the investigators sought to grow retinas containing the various nerve cells needed for sight.

Using a new technique developed in Japan that involves 3D culture and differentiation of mouse embryonic stem cells, the researchers grew retinal precursor cells that closely resembled cells that developed normally. They then injected about 200,000 artificially grown cells into the retinas of the night-blind mice. Three weeks after the transplant, the artificial cells integrated into the mouse retinas and showed signs of looking like normal mature rod cells. After 6 weeks, the cells were still present, and researchers observed synapse formation, suggesting that the new cells were able to connect with the existing retinal circuitry. The study appears in Nature Biotechnology.

Human embryonic stem cells, or hESCs, are thought to have greater potential for treating disease because of their ability to turn, or differentiate, into more types of human cells than adult stem cells can, yet there are no FDA-approved treatments that use them. The major concern with transplanting hESCs into patients is the potential for hESCs to grow tumors, including teratoma--tumorlike formations containing tissues belonging to all three germ layers.

- here's the Nature Biotechnology abstract

- read the press release