These are images of normal (above) and diseased retinas. Patients with MFRP mutations, a cause of retinitis pigmentosa, lose the function of most retinal cells, particularly at the periphery of the retina, leaving them with drastically reduced vision. Personalized gene therapy, using iPS cells, may offer a way to correct this genetic disorder.

Vision loss patients own cells transformed into model for studying disease and developing potential treatment

Columbia University Medical Center (CUMC) researchers have created a way to develop personalized gene therapies for patients with retinitis pigmentosa (RP), a leading cause of vision loss. The approach, the first of its kind, takes advantage of induced pluripotent stem (iPS) cell technology to transform skin cells into retinal cells, which are then used as a patient-specific model for disease study and preclinical testing.

Using this approach, researchers led by Stephen H. Tsang, MD, PhD, showed that a form of RP caused by mutations to the gene MFRP (membrane frizzled-related protein) disrupts the protein that gives retinal cells their structural integrity. They also showed that the effects of these mutations can be reversed with gene therapy. The approach could potentially be used to create personalized therapies for other forms of RP, as well as other genetic diseases. The paper was published recently in the online edition of Molecular Therapy, the official journal of the American Society for Gene & Cell Therapy.

In normal, or wild-type, retinal cells (left), the protein actin forms the cells cytoskeleton, creating an internal support structure that looks like a series of connected hexagons. In cells with MFRP mutations (center), this structure fails to form, compromising cellular function. When diseased retinal cells are treated with gene therapy to insert normal copies of MFRP (right), the cells cytoskeleton and function are restored. (Image credit: Lab of Stephen H. Tsang, MD, PhD/Columbia University Medical Center.)

The use of patient-specific cell lines for testing the efficacy of gene therapy to precisely correct a patients genetic deficiency provides yet another tool for advancing the field of personalized medicine, said Dr. Tsang, the Laszlo Z. Bito Associate Professor of Ophthalmology and associate professor of pathology and cell biology.

While RP can begin during infancy, the first symptoms typically emerge in early adulthood, starting with night blindness. As the disease progresses, affected individuals lose peripheral vision. In later stages, RP destroys photoreceptors in the macula, which is responsible for fine central vision. RP is estimated to affect at least 75,000 people in the United States and 1.5 million worldwide.

More than 60 different genes have been linked to RP, making it difficult to develop models to study the disease. Animal models, though useful, have significant limitations because of interspecies differences. Researchers also use human retinal cells from eye banks to study RP. As these cells reflect the end stage of the disease process, however, they reveal little about how the disease develops. There are no human tissue culture models of RP, as it would dangerous to harvest retinal cells from patients. Finally, human embryonic stem cells could be useful in RP research, but they are fraught with ethical, legal, and technical issues.

The use of iPS technology offers a way around these limitations and concerns. Researchers can induce the patients own skin cells to revert to a more basic, embryonic stem celllike state. Such cells are pluripotent, meaning that they can be transformed into specialized cells of various types.

In the current study, the CUMC team used iPS technology to transform skin cells taken from two RP patientseach with a different MFRP mutationinto retinal cells, creating patient-specific models for studying the disease and testing potential therapies.

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Patient-specific stem cells and personalized gene therapy ...

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