Medicine: Breakthrough in the Blink of the Eye
Less than an inch across and barely 0.02 inches thick, the retina is where the future of medicine is being shaped. This plate-shaped layer of nerve tissue on the inner surface of the eye is the testing ground for gene and cell therapies that are expected to change the face of medicine.
“Until a decade ago, degenerative retinal and macular diseases were incurable,” says ophthalmologist Eyal Banin, director of the Center for Retinal and Macular Degeneration (CRMD) at the Hadassah–Hebrew University Medical Center. “Since then, they have been targeted by breakthrough medical technologies—innovations we anticipate will apply to the entire central nervous system. This is a seminal time to be working in this field.”
Dr. Banin and his colleagues at the CRMD are not only working in the field, they are helping develop it. They have implemented gene therapy in patients suffering a form of hereditary childhood blindness (Leber congenital amaurosis, or LCA) and they have developed a treatment for age-related macular degeneration, which will be among the world’s first human embryonic stem cell-based products.
Much of the credit for this, says Dr. Banin, is due to the vision (“no pun intended,” he says, smiling) of the Hadassah Medical Organization in establishing the CRMD in 2002. “It rapidly became a major player in the field,” he says. “It not only gave patients with retinal disease a ‘home,’ it allowed us to focus on disorders that were neglected because there was so little treatment to offer.”
Important to that focus was gaining better understanding of the diseases that afflict the retina. “Many of them are genetically determined. One of our long-term goals is to map the phenotype [how the condition manifests] and genotype [which genes are involved] in affected Israeli patients,” says molecular geneticist Dror Sharon, who joined the CRMD team in 2002. “We recruit families with hereditary retinal degeneration, characterize their disease by quantifying retinal function and structure and then search their DNA to find the genes and mutations that cause their disease.”
The CRMD’s DNA bank currently has 1,200 families, comprising several thousand individuals—large by any standard. Sharon has tracked down the culprit genes in one in three, among them several previously unreported, and learned which mutations are more common in different subpopulations.
Among his first findings was a novel founder-mutation in the RPE65 gene, which causes LCA and is relatively prevalent among Jews of North African descent. The disease triggers early, with severe loss of vision that often progresses to total blindness.
Researchers at the University of Pennsylvania were working in this same area at the same time. Soon after the RPE65 mutation had been identified in Israeli patients, the American team received Food and Drug Administration approval to perform a clinical gene therapy trial based on their own groundbreaking work—following a decade in which gene therapy had stood at a virtual standstill, after complications in systemic gene therapy for other diseases.
The American researchers showed that the healthy RPE65 gene could be packaged in a viral vector and injected under the retina. Once in place, the virus successfully transferred the normal gene to retinal cells and began expressing it—allowing production of the normal, functional RPE65 protein. “In 2008, the RPE65 LCA treatment was reported to be both safe and effective, and that helped open the way for our own trials here in Israel,” says Dr. Banin.
The path was clear, but the trial needed funding. “Translational research like this requires a large financial outlay,” says Dr. Banin. “Our tremendous good fortune was that the Macula Vision Research Foundation stepped forward with a generous grant. Without their support, there would have been no clinical trial.”
Founded in 1997 by karen and Herb Lotman, founder and chairman of Keystone Foods Corporation, the nonprofit Macula Vision Research Foundation, based in Pennsylvania, has given grants totaling $17.2 million to research in retinal diseases. They increased those grants by 25 percent this year. The Lotmans are proud “that studies conducted by leading vision scientists and funded by the foundation have led to some of the greatest breakthroughs of the past decade.”
With funding in place, the team could bring the novel gene therapy to Israel. Working closely with ophthalmologist Samuel G. Jacobson of the University of Pennsylvania’s Scheie Eye Institute and molecular biologist and viral vector expert William Hauswirth of the University of Florida at Gainesville, who pioneered this treatment in the United States, they initiated a phase 1 clinical trial early in 2010, making Hadassah fourth in the world to apply such gene therapy to the eye.
“We delivered a viral vector carrying the intact RPE65 gene by subretinal injection to three patients, all of whom had been legally blind since birth,” explains Dr. Banin. “Because it was experimental, we had to have Health Ministry authorization to give only a low dose to a small part of the retina in one eye in patients older than 18. In the first three patients, the therapy proved both safe and effective: In the treated regions, retinal sensitivity to light increased significantly, often [a] hundredfold above the pretreatment thresholds—and this in a disease whose usual course is continuous deterioration of vision. This was a source of tremendous excitement for us, and for our patients, who are now asking us to treat the second eye.”
The science that underpins this first trial is being used by the CRMD team to develop gene therapy for another inherited retinal disease, in research whose starting point is lambs that failed to gambol. The disease is achromatopsia, in which the retinal cones (the photoreceptors that drive high-resolution and color viewing) are dysfunctional, and the world appears in blurry shades of gray. When lambs born to Kibbutz Ein Harod’s prize flock stood motionless during daylight, playing and grazing only after dark, the experts were anxiously called in.
Electroretinography was among tests performed on the lambs by veterinary ophthalmologist Ron Ofri of the Hebrew University of Jerusalem’s Koret School of Veterinary Medicine, leading to diagnosis of achromatopsia. Molecular geneticist Elisha Gootwine of Israel’s Institute of Animal Science then tracked the malfunction to a spontaneous mutation in the lambs’ CNGA3 gene.
It was on this same gene that mutations had been identified in the CRMD’s phenotype-genotype project as a major cause of achromatopsia in Israeli patients, one of these mutations shared by Jewish and Arab patients. “The very fortunate occurrence of a large animal model with a mutation in the CNGA3 gene here in Israel allowed us to start developing gene therapy for this disease,” explains Dr. Banin.
William Hauswirth helped the team engineer viral vectors carrying normal copies of the CNGA3 gene; Dr. Edward Averbukh of Hadassah’s ophthalmology department developed a new field of ovine ophthalmic surgery—again the Macula Vision Research Foundation helped fund the work. “With improvement of vision in the lambs, we are on the way to developing a treatment for our 130-plus achromatopsia patients,” says Dr. Banin.
Gene therapy is one groundbreaking modality now being tested and applied in retinal diseases. A second is cell therapy—the use of healthy cells to support, repair and regenerate damaged tissue. Here again, the tiny retina is key, with the only human embryonic stem cell-based clinical trial running worldwide being applied in the eye. Since 2002, the CRMD and Hadassah’s Human Embryonic Stem-Cell Center, which is headed by Dr. Benjamin Reubinoff, have been developing a stem cell-based treatment for the dry form of age-related macular degeneration (AMD).
The macula is the small area of special light-sensitive cells in the retina that allows us to see fine detail, to read, drive and recognize faces,” says Dr. Banin. “In AMD, the macula’s retinal pigment epithelium cells fail, leading to dysfunction and, ultimately, degeneration of the photoreceptors overlaying them, with loss of central vision.”
AMD is the leading cause of vision loss in the aging population worldwide, and it is also the major cause of blindness in the Western world. In the United States, it affects more than 10 million people, with predictions that the number will double by 2020, as the baby-boomer population ages. There is no effective treatment for the dry form of AMD, and it has been a major emphasis of the CRMD since it opened.
Its decade of research has led to the development of a technology that allows derivation of RPE cells from human embryonic stem cells. “Stem cells from human embryos are pluripotent, able to differentiate into any of the body’s cell types,” says stem cell pioneer Dr. Reubinoff. “They can also multiply endlessly, thus providing an unlimited source for deriving the cells of interest. We managed to create conditions in which they form the type of RPE cells that fail in AMD.”
The cells were created in culture, but would they work? “We transplanted them into an animal model with retinal degeneration caused by RPE dysfunction and saw that they could indeed provide a rescue effect, slowing the course of degeneration,” says Dr. Banin. “We published this work in the journal Cell Stem Cell in 2009, and it is the basis for the cell-based treatment we now want to apply in patients.”
In the years since publication, the team has been conducting safety studies in preparation for clinical trials. Safety was considerably enhanced by a scientific triumph: Hadassah’s development of therapeutic stem cell lines without using animal components, announced in June 2012.
“Human embryonic stem cell lines have always been produced and maintained using mouse-feeder cells and cow albumin,” says Dr. Reubinoff. “We worked very hard to free our cell lines from any contamination from animal-derived components, and were the first in the world to succeed.”
RPE cells derived from human embryonic stem cells will be only the first stem cell-based therapy. Drs. Banin and Reubinoff and their teams believe it will be followed by additional cell types derived to treat other retinal diseases as well as nervous system disorders.
“The retina is an extension of the brain,” says Dr. Banin. “It’s comprised of neural tissue, and is part of the central nervous system. As such, it’s now the testing ground that will hopefully lead to application of this technology for other neuronal degenerative diseases, such as Parkinson’s and multiple sclerosis. Ben Reubinoff is working on this with Dr. Tamir Ben-Hur, chair of neurology at Hadassah.”
Stem cell therapy and gene therapy are largely limited to the eye, but they are, believes Dr. Banin, the way of the future—a future, he says, he wants “to see begin at Hadassah, by providing vision, light and hope to patients suffering blinding diseases.”