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Casey scientists tackle challenges of stem cell therapy for AMD
When it comes to experimental treatments for age-related macular degeneration (AMD), stem cell transplantation continues to generate great interest. Patients are especially curious about its potential to restore vision lost to the advanced dry form of the disease, which currently is untreatable.
Although Casey Eye Institute researchers are not yet testing stem cell therapy in humans, they are collaborating with scientists at the National Eye Institute, biotechnology companies and other academic institutions to transform laboratory discoveries into new treatments. On the way, however, they must overcome a number of hurdles, such as determining the best methods to increase the cells’ survival and to determine if they've survived after transplantation.
Stem cell research for AMD is still in the early phase and primarily evaluating its safety, says Casey director David Wilson, M.D. “Although there are relatively effective treatments for wet AMD, we have not addressed vision loss from the advanced dry type. Stem cell therapy offers a promising approach,” Dr. Wilson says.
At Casey, researchers are focusing on the transplantation of retinal pigment epithelium (RPE) cells, one of the cell layers lining the back of the eye. The RPE performs crucial housekeeping duties, supporting and nourishing the retina’s light-sensing photoreceptors. In early AMD, RPE cells begin to deteriorate and become less able to keep visual cells healthy. By repopulating the retina with healthy RPE cells, the hope is to forestall the disease's progression.
Scientists are testing RPE cells produced through a cutting-edge technique called induced pluripotent stem (iPS) cell technology. With this method, cells from blood or skin are converted into undifferentiated cells and then reprogrammed to become specialized RPE cells.
Keeping cells alive
One of the major challenges in stem cell transplantation is ensuring their survival in the eye, says Trevor McGill, Ph.D., research assistant professor at Casey, and a leading expert in cell-based investigations for retinal disease. For more than a decade, Dr. McGill and his laboratory have been studying the immune response of cell transplantation in animal models. To prevent rejection, they use high doses of steroids and other immunosuppressants, which can cause unpleasant side effects. “The question becomes, ‘how do you minimize rejection without high doses of these drugs?’” says Dr. McGill.
One possible solution may involve using the patient’s own cells, called autologous transplantation. “With the advent of new technologies, we can reprogram a patient’s blood cells to become stem cells and then coax them into becoming RPE cells for transplantation back into the patient,” he says. “Because the cells are derived from the same individual, theoretically, they should not be rejected,” he adds. So far, Dr. McGill and his team are seeing some improvement in cell survival with autologous transplantation. However, producing these tailor-made cell products on a commercial basis may also pose challenges, he says.
Casey researchers are also studying how best to deliver the cell therapies to the retina. Earlier this year, a team led by Dr. Wilson published a study in the medical journal Retina describing a new surgical approach that was highly successful in increasing cell survival.
An ID for cells?
Another challenge, says Dr. McGill, is that "we don’t have the ability to mark these cells and know if they are surviving in the eye, even with today’s sophisticated imaging technology." What may look like RPE cells in imaging tests may actually be immune cells, he adds. Dr. McGill’s group is collaborating with the laboratory of Casey ophthalmic imaging
pioneer David Huang, M.D., Ph.D., to develop a contrast agent using gold nanoparticles that label the cells. “By incubating cells with this reflective substance, we hope to visualize them with optical coherence tomography,” he says. The project, supported by a grant from Research to Prevent Blindness, will also develop new ways to interpret the light that radiates from the transplanted cells.