Retinal Cell Transplants May Restore Sight

But scientists are now researching ways to resolve some types of blindness. And the most recent research holds promise for more than just vision problems.

Background
The retina, which sits at the back of the eye, has specialized cells called photoreceptors that absorb light. Sometimes individuals are born with genetic problems that prevent these photoreceptors - the cells that absorb light - from developing properly. Also, conditions like retinitis pigmentosa and macular degeneration, which develop later in life, can cause the receptors to break down and eventually die. If the receptors can't absorb light, the nerves of the eye can't send messages to the brain about what the person is looking at.

There are cases of blindness that can result from damage to the brain or another part of the nervous system. But in the case of genetic problems or degenerative eye conditions, the nerves are still intact; it's the retinal problems that are causing blindness. And it's these cases that cell transplant research has been addressing.

Past research
For several years now scientists have been attempting to
use transplants of retinal cells to either prevent or resolve blindness resulting from damaged photoreceptors. Two years ago, during a study at the University of Toronto, stem cells were taken from the retinas of human cadavers and transplanted into the eyes of newborn mice. These cells developed into photoreceptors.

This research, though, brought up some questions. For one thing, the mice used were all healthy. Would it be possible to use stem cell transplants to help mice who were blind?

Early research was largely unsuccessful; most of the stem cells didn't develop into photoreceptors. Something seemed to be inhibiting the process. The theory was that damaged retinas (in individuals who were already blind) weren't capable of repair; they couldn't give the correct information to the stem cells about how to develop.

Recent breakthroughs
The most recent research was a joint effort of the University of Michigan and University College of London in affiliation with Moorfield's Eye Hospital. This time, scientists decided on a different approach to the problem. They tried transplanting two different types of cells - undifferentiated stem cells from mouse fetuses, and slightly developed cells from newborn mice. The more mature cells developed into many more photoreceptors than did the stem cells. The mice, which had been blind due to genetic problems, began to show signs that they could see: their pupils started to react to light.

This latest research has led to more theories - and more questions. It does seem that slightly mature cells can tolerate the stress of being moved better than younger - or older - ones (which would explain why transplants of mature cells haven't been very successful). The "newborn" cells also attach better to the retina than the mature cells used in previous transplants.

The biggest question seems to concern the implications of this research for other types of cell transplants. Researchers are now considering using cells that have developed slightly instead of completely undifferentiated stem cells. And of course, that means they need to find ways to develop stem cells into the types of cells needed for a particular treatment.

There's still a lot of work to be done, even on cell transplants for blindness. And of course the controversy surrounding the use of stem cells continues. But any research into ways to cure disease and other conditions, even it isn't successful, helps scientists understand more about the way the body functions. And this understanding may be the key to future treatments and cures of all kinds.