In their studies, Dyer and his colleagues analyzed the sphere-forming cells in detail to determine whether they were really retinal stem cells. Painstaking microscopy studies of each cell in the spheres revealed all were pigmented and had features of ciliary epithelial cells. The researchers also compared the structure of the sphere-forming cells with those of confirmed stem cells and other immature cells in the developing retina called progenitor cells. That comparison revealed fundamental differences between the sphere-forming cells and established stem or progenitor cells.
The researchers also found that simply culturing the sphere-forming cells in the same growth medium as is used for stem cells caused them to activate genes characteristic of stem cells, yet remain adult ciliary epithelial cells.
Dyer said that a particularly promising alternative is the possibility of taking samples of adult cellssuch as fibroblasts that form connective tissuefrom a patient with retinal degeneration and exposing them to genetic cues that induce them to revert to stem cells. Those induced pluripotent stem cells could then be manipulated to develop into light-sensing photoreceptor cells that could then be transplanted into the patient's eyes to restore vision.
"This approach would solve many problems of developing cell-based therapy for blindness," Dyer said. "First, these cells are immortal, so they can be grown indefinitely to produce large amounts of cells for treatment. And secondly, they would be immunologically matched to the patient, so there would be no danger of rejection. And thanks to some excellent research during the past 15 years, we know a lot about how to reprogram such
|Contact: Summer Freeman|
St. Jude Children's Research Hospital