Issue link: https://viewer.e-digitaledition.com/i/320514
On the Fulfi lling the Promise of Genetic Surgery Treatment Frontier: A RAPIDLY DEVELOPING APPROACH MAY REWRITE THE BOOK ON HOW TO TREAT GENETIC DISORDERS. RDEB: A HISTORY OF TREATMENT ALTHOUGH RESEARCHERS HAVE identifi ed 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. By Michael Ferguson a n error-free repair pathway ca lled homologous recombination." Researchers must custom-build these proteins, a nd in the past 20 yea rs, signifi cant progress has been made to refi ne delivery systems and the speed with which they can be designed. Since he entered the field, Osborn notes, the protein-building process has been reduced from one year to less than one week. " T h e r e's b e e n a c h a n g e i n t h e plat form, but rea lly t he speed a nd ava ilabilit y of t hese rea gent s have opened the door to many people who otherwise wouldn't be able to employ [them]," Osborn says. "They've certainly become more user-friendly." Making the Cut Osborn and his team are exploring the application of transcription activa- tor-like effector nucleases (TALENs) to correct faulty genes in patients with recessive dyst roph ic epider molysis bullosa (RDEB) — a genetic disorder that affects internal organs and causes highly fragile skin that easily blisters and tears, according to the Dystrophic E p i d e r m o l y s i s B u l l o s a R e s e a r c h Association of America. Osborn and his team performed research on mice, and their study was published in the June 2013 issue of Molecular Therapy. " W h a t w e d id w a s a n a l y z e t he sequence around [this] particular muta- tion and custom-designed a DNA-binding protein that would go specifi cally 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 essen- t i a l l y a c t a s a mole c u l a r s c a lp e l , making a break in the DNA that the cell then repairs. This process of gene ed it ing ac t ua l ly excises t he fau lt y 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 correction 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 laborator y studies. However, just as clinicians worked to develop more precise methods for delivering proteins to DNA bases, Osborn predicts further refi nements to the process. Constructing patient-specifi c treatments will be criti- cal 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 a s indiv idua l patients, a nd be able to ma ximize efficiency and efficacy to … accomplish that on a larger scale." ■ T HE HUMAN GENOME is composed of more than 3 billion base pairs of DNA, and alterations to a single base can cause a broad range of catastrophic diseases, such as Down syndrome and sickle cell anemia, as well as more obscure but similarly devastating conditions, such as epidermolysis bullosa (EB). Seeking curative treatments for such disorders, researchers have developed several methods for editing faulty genes using genetic surgery. Genetic surgery allows physicians t o re s e c t f a u lt y p or t ion s of DN A ba ses a nd repla ce t hem w it h cor- rected f unctiona l copies. However, d i r e c t i n g c o r r e c t e d g e n e s t o t h e precise DNA proved an early challenge for resea rchers, according to Ma rk Osborn, PhD, Assistant Professor in the Div ision of Blood a nd Ma rrow Transplantation at the University of Minnesota Medical School. "Those genes have to go somewhere in the genome, a nd where they go is semi-random," says Osborn, who is a lso a member of the Universit y of Minnesota's Center for Genome Engineering. "They can disrupt other important sequences, and some gene therapy trials have actually led to more severe disease from the treatment itself because t he genetic la ndscape ha s been disrupted." Those experiences drove researchers to develop more precise methods for delivering proteins to targeted DNA. "People started to generate these proteins that could be designed for par- ticular spots in the genome, [and then] co-localize in that spot and cut the DNA," Osborn explains. "In response to that, the cell actually up-regulates CORE CORE 2 4 | Long Island MD NEWS ■ M D N E W S . CO M