In diseases of both the retina – the back of the eye – and the cornea – the front of the eye – stem cells derived from adult or postnatal animals show remarkable ability to replace damaged cells that may be the cause of visual impairment.
"Proof of principle has indicated that stem cells can reconstitute damaged eye tissue," said J. Wayne Streilein, M.D., President and Senior Scientist at The Schepens Eye Research Institute in Boston, the nation’s largest independent eye research institute. "There is every hope that this will lead to restoration of vision in eyes blinded by disease."
The Schepens Eye Research Institute endorses the use of federal funds for research using stem cells derived from donor embryonic tissue in an effort to find new diagnoses, treatments, and cures for blinding diseases. On August 9, President George W. Bush announced that the federal government would allow limited research on human embryonic-derived stem cells that already exist.
Currently, stem cells from human embryonic tissue are not used at The Schepens. Stem cells are progenitor cells - cells that are not yet differentiated that could give rise to any other kind of cell in the body. The National Institutes of Health, a primary funding agency for scientists at The Schepens, has said that stem cells hold "enormous promise" for medicine. The cells are found in embryos and in some adult tissue, and can form almost all the tissue of the body.
Scientists say biomedical research using stem cells extracted from human embryos could lead to cures for a host of diseases, such as Parkinson's disease, diabetes and Alzheimer's, as well as treatments for debilitating brain and spinal injuries. They also could be useful for curing blinding diseases.
Schepens scientists, funded by the National Institutes of Health, currently research stem cells derived from animals. There is no prohibition against animal-derived sources of stem cells, from both embryonic and adult animal tissue, and the statement by President Bush on August 9 does not change that.
In one Schepens laboratory, scientists are using neuronal stem cells of postnatal rodent origin to try to replace damaged photoreceptors in the retina of adult rodents. This is known as retinal transplantation, and it gives hope that damaged retinal cells can be replaced by new, healthy cells, ultimately restoring vision. Such research, which currently involves stem cells derived from the adult rat hippocampal region of the brain and from postnatal brain tissue, could yield new treatments and cures for a variety of eye diseases, such as macular degeneration, retinitis pigmentosa, and glaucoma, but also for diseases of the central nervous system, such as Parkinson's and Alzheimer's.
Among the findings so far -- adult stem cells transplanted into the retina do in fact become retinal cells, and even begin to make connections through the optic nerve to the brain. While it's not yet known if they will actually restore function, it is a major breakthrough to know that these stem cells may take over the functioning for damaged cells in the retina, the thin tissue at the back of the eye on to which light is focused and sent on to the brain.
In another laboratory, scientists are using animal-derived stem cells to try to treat dry eye syndrome. This condition, in which the eyes do not produce proper tears, leads to discomfort for millions of people, primarily postmenopausal women. One of the glands that produces a component of tears is called the lacrimal gland. When that gland malfunctions, it results in a dry eye condition known as "aqueous-deficient" dry eye, and the eye cannot produce enough tears. There is no cure.
Schepens scientists are using stem cells to try to replace damaged cells in the lacrimal gland and restore its function, so that tear production becomes normal. They are isolating stem cells from the lacrimal gland and then, eventually, injecting them back into a nonfunctioning gland to regenerate the gland and restore function. They are using stem cells from the adult mouse and eventually will try using stem cells from the infant mouse.
Similarly, Schepens scientists have isolated cells from the conjunctiva of human and rat eyes that appear to be stem cells. These cells could be used to repair damaged cells in the conjunctiva - the inner surface of the eyelid - that also causes a dry eye condition. Thus, function to the conjunctiva could be restored.
"While our knowledge of stem cells in the eye is derived from animals, it is crucial to learn whether these findings also are applicable to humans. This can only happen if the federal government allows such research," Dr. Streilein said.
Human embryonic-derived stem cells currently are not in use at The Schepens, but may at some point become necessary to help cure blindness. Schepens scientists doing such research are guided by principles of three basic areas of concern: the need for research to cure disease; the regulatory status; and ethical considerations. Schepens scientists comply with all regulations regarding the use of stem cells in research and will continue to do so. Ethical or moral issues constantly are weighed against the scientific principles of the need for such research and the resulting benefits.
Providing hope where there is no cure, doing research that holds promise for millions of people, The Schepens Eye Research Institute sees enormous potential benefit from embryonic- and adult-derived stem cells for finding treatments and cures for blinding diseases.
The Schepens Eye Research Institute, an affiliate of Harvard Medical School, is the largest independent eye research center in the nation, both in size of faculty and support from the National Eye Institute. The Institute, begun in 1950, has a renowned faculty of more than 60 scientists, including immunologists, molecular and cell biologists and physicists who investigate cures for blinding diseases and aids for people with low vision. Many diagnostic techniques and devices, surgical methods and medications related to eye disease were developed by Institute faculty.