Issue 116 Item 5 Stem Cells Rescue Retina

Bone marrow saves eyesight. Bone marrow stem cells might one day deliver drugs to the eye, halting age- and diabetes-related blindness. The cells can treat a genetic condition that causes mouse retinas to degenerate.

When the stem cells – that usually make blood vessels – were injected into the fluid-filled space of the eye they became part of developing blood vessels in the retina.

Faulty capillary formation is central to both the leading causes of adult blindness in the US: diabetic retinopathy and age-related macular degeneration.

"It just blew me away that we could use these cells as magic bullets," says one of the research team Martin Friedlander, ophthalmologist at the Scripps Research Institute in La Jolla, California.

His team worked on mice carrying a genetic mutation for retina development. Normally, these animals start to lose retina blood vessels around two weeks after birth and become completely blind by one month. Bone marrow stem cells stabilized capillaries for up to a month after the injection.

Whether the mice can see, remains to be tested, but the retinas appear normal.

"What’s so interesting about these cells is that they go directly to where they are needed, incorporate into the normal developing [blood vessels] and just sort of join the party," says ophthalmologist Lois Smith of Harvard Medical School in Cambridge, Massachusetts, who studies blindness in premature babies.

Excess capillaries can also cause blindness. So Friedlander’s group next exploited

the cells’ targeting ability to deliver a protein to the retina that stopped blood

vessels growing. Before being injected the cells were genetically modified to produce

the protein.

More than a million people a year loose vision due to diabetic retinopathy and macular degeneration. Friedlander hopes that "in the not-too-distant future" doctors will be able to treat these diseases using stem cells from patients’ own bone marrow.

Before then, much more work must be done in animal models to rule out dangerous side-effects. "You would have to be very careful that the modified cells don’t get out into other areas of body and kill blood vessels in the heart, brain, and limbs," cautions Karl Csaky, who studies macular degeneration at the National Eye Institute in Bethesda, Maryland.

Nonetheless, Csaky feels the work holds great promise because the cells can replace degenerating blood vessels in a system that biologists believed up to now was irreplaceable. Nature Medicine, Published online doi: 10.1038/nm744,