Overcoming Obstacles for Gene Therapy for Recessive Dystrophic Epidermolysis Bullosa

Abstract

Recessive dystrophic epidermolysis bullosa (RDEB, OMIM ID #226600) is a severe blistering disease that affects quality of life and is associated with increased mortality, often from squamous cell carcinoma (Fine et al., 1999). Mutations in COL7A1, the gene that encodes type VII collagen, lead to blistering with resultant wounds and scarring. Treatment approaches have included tissue-, cell-, and gene-based therapies, including recent efforts at bone marrow ablation and allogeneic stem cell transplantation (Wagner et al., 2010). Because a single gene defect is responsible for the disease manifestations, researchers have focused on the development of gene therapy approaches. Unfortunately, several problems have hampered clinical development of vector-based gene therapy for this disease, including low transfer efficacy and the large size of the COL7A1 cDNA (Goto et al., 2006). In a previous study, a COL7A1 “minigene” that encoded a truncated type VII collagen was developed. This minigene was compatible size-wise with retroviral vectors and reversed the DEB phenotype to normal in transduced keratinocytes (Chen et al., 2000). An alternative to retroviral gene therapy is trans-splicing, an approach that employs the cell spliceosome to recombine an endogenous target pre-mRNA and an exogenously delivered RNA molecule called the pre-transsplicing molecule (PTM). A partial, wild-type coding sequence from the PTM is inserted to replace disease-causing sequences in order to generate a new, reprogrammed wild-type mRNA to correct the disease phenotype (Wally et al., 2008). In this issue, Murauer et al. report on their efforts with trans-splicing techniques to create a potential therapy for RDEB. These investigators introduced a partial, wild-type COL7A1 PTM via retroviral transduction of RDEB keratinocytes and achieved full-length type VII collagen expression. Transduced cells displayed functional correction of the RDEB phenotype, including normal morphology, reduced invasive capacity, normal localization of type VII collagen at the basement membrane, and assembly of collagen into anchoring fibril-like structures. Through the following questions, we examine this paper in greater detail. For brief answers, please refer to the supplementary information online