Researchers have taken several steps toward using stem cells to treat a rare genetic disease that leaves people with skin so fragile it blisters at the slightest touch. A trio of lab and animal studies reported today could help pave the way for a clinical trial for the disorder, called epidermolysis bullosa (EB).
Although EB is quite rare, occurring in one in 20,000 births, about 500,000 people around the world suffer from some form of the disease. It is caused by defects in any of several genes that code for proteins, such as collagen, that link the top and bottom layers of skin. The gene defect creates fragile skin that easily tears, resulting in painful blisters and sores. There is no cure; physicians usually treat symptoms only by dressing wounds and treating infections. Those with severe forms of EB who survive childhood are also prone to skin cancer and often die from that by their mid-40s.
A few years ago, researchers tried gene therapy in a single EB patient, using a virus to add a corrective gene to skin cells cultured from that person and then grafting sheets of them onto his legs. Although the repaired cells took hold, the risks of the virus used in the trial and challenges of growing enough cells to cover a large surface area led researchers to look for other options.
Several groups have now turned to induced pluripotent stem (iPS) cells, a type of cell created by reprogramming adult cells back into an embryonic state. These iPS cells can be coaxed to grow into large quantities of various adult tissues that are genetically matched to a person and therefore less likely to be rejected by the immune system than cells from a donor.
A Columbia University team pursuing the iPS cell approach recently took advantage of the fact that some EB patients have skin cells that somehow lose the disease-causing mutations and turn back into healthy cells. The scientists transformed some of these “revertant” cells into iPS cells, then from them grew skin cells called keratinocytes that expressed the type of collagen missing in the patients. When grafted onto the back of a strain of mice with a weak immune system that would not reject the cells from a different species, the keratinocytes grew into human skin and produced the correct form of collagen. Using revertant cells in this manner for EB could avoid the risks of gene therapy and “be a little more straightforward,” says study leader Angela Christiano.
But only about 20% to 30% of people with EB have revertant skin cells, so other groups have taken a more traditional approach. In a second study, researchers at Stanford University in Palo Alto, California, created iPS cells from skin cells taken from three EB patients lacking a collagen different from the type studied by the Columbia team. They then fixed the genetic defect in the stem cells before turning them back into keratinocytes. These steps can potentially introduce harmful mutations, and the original cells from EB patients can also carry cancer-causing mutations. But the team reduced this risk by genetically screening and banking only iPS cells free of harmful mutations. The cells grew as skin grafts on mice for up to a month before the cells died.
Neither of these studies showed that cells could help treat the disease in an animal with EB. But in the third study, researchers in Josef Penninger’s lab at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences in Vienna did just that by deriving iPS cells from the skin cells of mice with the same defect as the EB patients studied by the Stanford group. They then repaired the collagen gene; turned the cells into fibroblasts, another type of skin cell; and injected them under the sick mice’s skin. These cells formed skin layers that expressed the correct form of collagen for 18 weeks.
Together, the three papers, published today in Science Translational Medicine, “should provide a lot of optimism that this approach has a lot of legs,” says Anthony Oro, who co-led the Stanford study with Marius Wernig. Both his group and the Columbia team have applied for funding to launch trials of the iPS cell treatment in EB patients.
Although the reports are promising, they also show the challenges of using such cells for the skin disorder, says stem cell scientist Lorenz Studer of Memorial Sloan Kettering Cancer Center in New York City. He points out that the researchers haven’t yet found the right recipe for producing human skin cells that live longer than a few weeks. “This therapy is still kind of on hold until the field can achieve long-term engraftment,” Studer says.
Jakub Tolar of the University of Minnesota, Twin Cities, who also studies iPS and gene therapy for EB, highlights another issue. The skin graft approach won’t treat internal problems that many EB patients suffer from due to the disease’s effects on the lining of the gut and esophagus. Tolar is working on a riskier, but more comprehensive solution: giving EB patients bone marrow transplants of gene-corrected cells made using iPS cells. Still, he’s impressed by the current trio of papers. “It’s gratifying to see they have taken it this far,” Tolar says.