The researchers don't yet know if the cells can actually integrate into the complex circuitry of the eye to restore vision, but early results are promising. The transplanted cells do express many of the proteins needed to respond to light, and they make neural connections when grown in a dish with other retinal cells. However, the true test will come with Reh's current experiments: transplanting the cells into blind animals. "We should know within the next year if the cells can restore vision," says Reh.
Other groups are also developing stem cell therapies for the retina. Advanced Cell Technology (ACT), a stem cell biotechnology company based in Alameda, CA, has developed a way to turn embryonic stem cells into pigment epithelial cells, another cell type lost in macular degeneration.
When implanted into the eyes of animal models, the cells protect against further degeneration of the photoreceptors and improve vision, says Robert Lanza, vice president of research and scientific development at ACT. The company plans to file for permission from the Food and Drug Administration to start human trials of the therapy by the end of next year, he says.