MDNews - Minnesota

RDEB: A HISTORY OF TREATMENT ALTHOUGH RESEARCHERS HAVE identified 18 genes in which mutations can cause reces- sive dystrophic epidermolysis bullosa (RDEB), until 2007, there was no treatment other than wound management. Extensive laboratory trials in which researchers performed bone marrow transplantation (BMT) on mice with RDEB extended their lifespans, according to Mark Osborn, PhD, Assistant Professor in the Division of Blood and Marrow Transplantation at the University of Minnesota Medical School and member of the University of Minnesota's Center for Genome Engineering. A clinical trial also has yielded some extraordinary outcomes. For example, when checking on a patient following BMT, a dermatologist found him eating potato chips in his bed. RDEB can cause tenderness in the esophagus, and sharp foods can tear the tissue. This particular patient's disorder had affected the esophagus in a way that made eating nearly impossible, necessitating use of a feeding tube. But the trial's successes are counterbalanced by challenges that demonstrate the need for additional treatment modalities. Chemotherapy and radiation regimens employed to wipe out bone marrow prior to transplant are highly toxic, and not all patients survive the process, Osborn notes. "What we would ultimately like to do is take a patient's own cells, correct whatever mutation they have, and by employing a second set of technology — adult stem cell technology — coax these into becoming blood-forming cells or tissue … and ultimately deliver them in some fashion back to the patient," he says. Making the Cut Osborn and his team are exploring the application of transcription activator-like effector nucleases (TALENs) to correct faulty genes in patients with recessive dystrophic epidermolysis bullosa (RDEB) — a genetic disorder that affects internal organs and causes highly fragile skin that easily blisters and tears, according to the Dystrophic Epidermolysis Bullosa Research Association of America. Osborn and his team performed research on mice, and their study was published in the June 2013 issue of Molecular Therapy. "What we did was analyze the sequence around [this] particular mutation and custom-designed a DNA-binding protein that would go specifically to that site and then actually cut the DNA," Osborn explains. "In tandem, we provide a repair template for the cell. So, we create a small injury to the cell — to the DNA — and ask the cell to repair itself off the normal template we provide." The cut-and-repair proteins essentially act as a molecular scalpel, making a break in the DNA that the cell then repairs. This process of gene editing actually excises the faulty gene base and then sutures it with the constructed normal base. Once researchers deliver the protein and the repair template, they screen cells for the desired changes. In this case, the findings showed a potentially effective, self-propagating therapy. "What we found was a fairly high percentage of the cells we recovered had corrected — and importantly, the correc- tion was permanent," Osborn says. "[That means] once we fix it, it's a permanent correction, so that every time the cell divides and introduces daughter cells, those cells now have the corrected sequence." Further Specificity TALEN-based gene correction is still in laboratory studies. However, just as clinicians worked to develop more precise methods for delivering proteins to DNA bases, Osborn predicts further refinements to the process. Constructing patient-specific treatments will be critical for optimal results, as no two cases of EB are the same. "That's where we hope to go," Osborn says. "To be able to treat each individual patient as individual patients, and be able to maximize efficiency and efficacy to … accomplish that on a larger scale." ■

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