Correction of Dog Dystrophic Epidermolysis Bullosa by Transplantation of Genetically Modified Epidermal Autografts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin blistering condition caused by mutations in the gene coding for collagen type VII. Genetically engineered RDEB dog keratinocytes were used to generate autologous epidermal sheets subsequently grafted on two RDEB dogs carrying a homozygous missense mutation in the col7a1 gene and expressing baseline amounts of the aberrant protein. Transplanted cells regenerated a differentiated and vascularized auto-renewing epidermis progressively repopulated by dendritic cells and melanocytes. No adverse immune reaction was detected in either dog. In dog 1, the grafted epidermis firmly adhered to the dermis throughout the 24-month follow-up, which correlated with efficient transduction (100%) of highly clonogenic epithelial cells and sustained transgene expression. In dog 2, less efficient (65%) transduction of primary keratinocytes resulted in a loss of the transplanted epidermis and graft blistering 5 months after transplantation. These data provide the proof of principle for ex vivo gene therapy of RDEB patients with missense mutations in collagen type VII by engraftment of the reconstructed epidermis, and demonstrate that highly efficient transduction of epidermal stem cells is crucial for successful gene therapy of inherited skin diseases in which correction of the genetic defect confers no major selective advantage in cell culture