In Stem-Cell Transplants, Timing Is Everything Stem cells are a promising part of advances in therapy, because they can turn into a variety of cell types. But stem cells may only be useful after they've begun to change into the cell type they're destined to become.
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In Stem-Cell Transplants, Timing Is Everything

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In Stem-Cell Transplants, Timing Is Everything

In Stem-Cell Transplants, Timing Is Everything

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MELISSA BLOCK, host:

A research study published earlier this week was not exactly a headline writer's dream come true. Cell transplant surgery enabled blind mice to show rudimentary responses to light, a modest step toward sight. Blind mice see again was actually how many news outlets described the research, but even if that was overblown, the study may turn out to be extremely important not just for helping blind mice, but for the entire field of cell-based therapies, including stem cells.

NPR's Joe Palca reports.

JOE PALCA: To understand the importance of the vision study, it helps to think about that question nearly every child is asked at some point - what do you want to be when you grow up? At first, all things are possible, firefighter, movie star, radio reporter. But over time, specialization sets in, and the path forward becomes clear. And so it is with stem cells. In their most immature stage, they can become anything - muscle, skin, nerve.

But over time, their role in life becomes clear, and if you ask Rachel Pierson she'll tell you that how mature a cell is determines whether it will make a successful cell transplant. Pierson is a neuroscientist at University College London. She and her colleagues wanted to see if they could repair damage to a critical part of the eye called the retina.

Dr. RACHEL PIERSON (University College London): We were trying to see whether or not transplantation is feasible just as a concept and whether it's possible to get cells to integrate into the retina.

PALCA: Pierson says others have tried cell transplants.

Dr. PIERSON: But what a lot of people have done so far is to use stem cells, which are very immature cells, and they found that they don't turn into retinal cells. So what we wanted to look at was just to see whether or not any type of cell was likely to develop to have this ability to migrate into the retina.

PALCA: And not just migrate to the retina, but actually take up residence there and do what they're supposed to do, translate light coming into a mouse's eye into nerve signals to a mouse's brain.

Since stem cells can't do that, Pierson and her colleagues took more mature cells, cells that were already destined to become a particular kind of retinal cell called a rod. And as they report in the current issue of the journal Nature, that approach worked. The transplants took up residence, and when the researchers shined a light into the mouse's eye, the animal's pupil constricted, meaning it was seeing the light.

Ms. PIERSON: So it seems that if you get cells of the right developmental stage, they can have this ability to integrate and wire up.

PALCA: It's not likely this kind of transplant will ever become a useful therapy in humans - it would mean taking the cells determined to become rods from a developing human eyeball - but when they were younger, those cells were once stem cells, and that gives molecular biologist Anand Swaroop confidence that stem cells will be useful some day in treating eye disease. Swaroop is at the University of Michigan and a participant in the mouse research. He says it may be possible to mature stem cells in the lab.

Dr. ANAND SWAROOP (University of Michigan): Instead of stem cells, if we can use the cells that are going to become rods, then we would have a potential therapy.

PALCA: Given the hype about them, the idea that stem cells themselves might not be useful in therapies takes a bit of getting used to. Clive Stensen is a stem cell biologist at the University of Wisconsin. He says many scientists have been assuming that stem cells will know what to do if they're ever put into a damaged eye or heart or brain. Stensen says stem cells may only know what to do when an animal is still growing and developing.

Dr. CLIVE STENSEN (University of Wisconsin): Putting the same stem cell into an adult animal that's undergone development, the stem cell just sits there and it's slightly confused. It's not in a developing environment and it doesn't receive the correct signals to make the appropriate type of cell.

PALCA: So scientists will have to help stem cells along if they want them to work as therapies.

Joe Palca, NPR News, Washington.

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