Stem cells show potential for treating vision loss

Stem cells are moving closer to clinical application and, in ophthalmology, one day could be part of a new therapeutic paradigm centered on stabilizing retinal tissue damaged by diseases such as retinopathy of prematurity, said Martin Friedlander, MD, PhD, professor of ophthalmology, Scripps Research Institute, La Jolla, CA.

In a symposium on innovations in restoring vision, Dr. Friedlander described efforts in his lab and elsewhere in a relatively new field known as regenerative medicine. Regenerative medicine describes the evolution of stem cell biology research toward applications in animals and humans. Although there are ethical issues surrounding the use of embryonic stem cells, the use of adult stem cells may circumvent many of them and remove some of the barriers that have held up stem cell research, Dr. Friedlander said.

Progress also depends on obtaining adequate funding, whether from federal, state, or private resources.

"There is tremendous interest in the potential regenerative capacity of these cells at multiple levels," Dr. Friedlander said. He noted that the Department of Defense recently earmarked millions of dollars for stem cell research, primarily in efforts aimed at helping injured soldiers. In addition, more than 1,000 biotechnology companies are involved in regenerative medicine or stem cell projects, up from 100 or so just a few years ago, another indication that this approach is moving closer to an array of clinical applications.

He discussed potential applications of residual stem cells, which are cells that reside in various locations in adults, maintaining pluripotency. Under the appropriate stimulus, they can differentiate into a variety of tissues and contribute to regeneration. In ophthalmology, corneal limbal stem cells already are being studied in this fashion to facilitate healing following corneal transplants or to address the damage caused by corneal destructive diseases.

Retinal applications also are moving forward. Several papers have been published in the past year or two demonstrating that embryonic stem cells can be stimulated down a pathway that results in development of photoreceptors or ganglion cells that then can be transplanted into mice and will develop into photoreceptors.

Many labs, including Dr. Friedlander's, are also working with adult hematopoietic stem cells. One therapeutic paradigm being studied is that of vascular reconstruction rather than destruction with antiangiogenic drugs and procedures in the treatment of ischemic and degenerative retinopathies. Autologous bone marrow or cord blood derived from hematopoietic stem cells is used to target sites of neovascularization and gliosis through paracrine function and differentiation into endothelial and microgial elements. The result is stabilization of damaged retinal tissue.