Stem cells could hold the key to stopping and even reversing the blinding effects of aging, according to recent research.

Many scientists have long felt that embryonic stem cells could halt the progression of or even cure a number of degenerative diseases. Their hope has been that researchers could coax stem cells to grow into healthy cells of any type - cells that doctors could then use to replace damaged cells in patients affected by disease. Eye research is one of the first areas where a real application for using stem cells in this way may just be within reach.

Age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of vision loss for people over 55. The disease does not cause total blindness. Instead, people with AMD develop fuzziness or - in more severe cases - a dark spot in the center of their vision, which does not go away.

AMD destroys central vision by damaging cells in the macula. The macula is part of the retina, a thin layer of nerve cells that detect light and send signals to the brain. You use the macula for seeing clearly as well as seeing what is directly in front of you. Once the macular cells are damaged, there is no way to restore them and in turn restore sight.

In a normal healthy eye, a layer of cells underneath the retina, called retinal pigment epithelium (RPE) cells, perform housekeeping chores for the retina. They clean up cellular debris and supply the retinal cells with nutrition. AMD damages these cells as well. Scientists are researching whether using stem cells to grow new, healthy retinal and RPE cells could halt vision loss or even restore vision.

In a recent study at Harvard Medical School’s Schepens Eye Research Institute, researchers transplanted retinal stem cells into the eyes of mice with retinal disease. The stem cells changed into what appeared to be normal retinal cells, and the mice demonstrated better vision.

“These are the first steps toward the use of stem cells for saving existing vision and then - down the road - restoring vision that has already been lost,” said Dr. Michael Young, an assistant scientist at Schepens Eye Research Institute and the lead author of the study.

An unlimited supply of genetically matched cells

The Harvard study fills in a crucial step by showing that transplanted stem cells can grow into the correct cells and can actually improve vision. But a future reliance on retinal stem cells poses a couple of problems, according to Dr. Robert Lanza, medical director at Advanced Cell Technology, a biotechnology firm in Worcester, Mass.

“It’s believed that one of the main problems for failure in clinical studies is immune rejection,” Lanza said. “Transplanted cells are prone to rejection, particularly adult cells.”

That’s where the hope for embryonic stem cells comes in. Scientists have the technology to transfer genetic material to the embryonic cells to generate new cells that are genetically the same as the patient’s, eliminating the problem of immune rejection.

The second issue is the fact that few cells may be available for transplant. Again, embryonic stem cells come to the rescue by having the potential to create an unlimited supply.

To test stem cells’ real-world ability to fulfill this promise, researchers at ACT attempted first to grow RPE cells from embryonic stem cells. They were successful. The new cells appeared to be RPE cells, and were able to perform the same functions and behaved in the same way.

The team then took the idea a step further and compared the genes of the new RPE cells, derived from embryonic cells, to those of “real” RPE tissue. They also compared the two groups of cells to a third group of retinal cells such as the ones the Harvard researchers used to restore vision loss in the mice.

“We actually found that ours had a closer fingerprint or gene expression profile than the retinal line to the real tissue,” Lanza said. Being able to make such a genetic comparison will help scientists identify which cells in the lab are most likely to behave like real eye tissue.

The next step for researchers is testing on animals to see whether the new RPE cells can actually replace damaged tissue and restore eyesight. If those experiments are successful, scientists are on their way to human trials - and a possible cure for a devastating disease.