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INJECTING stem cells from bone marrow into the eye might help prevent many kinds of blindness.

A team at the Scripps Research Institute in La Jolla, California, have shown that a type of stem cells known as endothelial precursor cells can be used both to prevent the degeneration of blood vessels in the eyes of mice and, if genetically modified, to discourage excessive growth. 鈥淲e were beside ourselves with excitement,鈥� says Martin Friedlander, who led the research.

Many eye diseases are triggered by vascular problems. The inherited disease retinitis pigmentosa involves degeneration of the retinal blood vessels. And the leading causes of vision loss in developed countries 鈥� age-related macular degeneration and diabetic retinopathy 鈥� are both caused by a proliferation of vessels in the eye.

Endothelial precursor cells, which reside in mouse bone marrow, are known to encourage the formation of blood vessels during development. So Friedlander鈥檚 team tried injecting EPCs into the eyes of mice.

They found that the cells migrated to the blood vessels in the retina. In healthy eyes, the cells had no effect. But in mice with a genetic defect in which retinal blood vessels deteriorate with age, the cells incorporated themselves into the vessels and prevented any degeneration. These mice had normal retinas 33 days after birth, whereas in mice that were injected with another type of bone marrow cell, the deep blood vessels were nearly all gone by this stage.

Friedlander鈥檚 team also showed that EPCs modified to produce a protein that inhibits the growth of blood vessels could stop new retinal blood vessels forming when injected into the eye. This suggests the cells could help treat proliferative as well as degenerative vascular eye diseases (Nature Medicine, DOI: 10.1038/nm744).

However, it鈥檚 still not clear whether similar EPCs can be purified from human bone marrow. And Friedlander cautions that eye diseases often involve nerve damage as well as abnormal blood vessels.