Somatic mosaicism in skin fragility disorders: mechanisms and therapeutic perspectives

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Revertant mosaicism is a phenomenon occurring in an individual with a disease-causing germline mutation, wherein a subpopulation of cells re-acquires the wild-type phenotype through a naturally occurring recombination, back or second-site mutation. This so called natural gene therapy has been reported in several inherited disorders, including single cases of epidermolysis bullosa (EB). EB comprises a heterogeneous group of skin fragility disorders, characterized by blistering of the skin after minor trauma and caused by mutations in components of the dermal-epidermal adhesion complexes. In our large cohort of more than 700 patients with molecularly confirmed EB, we have so far identified revertant mosaicism in 15 patients with severe and mild forms of junctional EB, dystrophic EB and Kindler syndrome. The objective of this proposal is to generate new knowledge on the molecular mechanisms that underlie revertant mosaicism in skin fragility disorders and on therapeutic potential of the reverted cells. We will identify more patients with revertant mosaicism and different EB forms and disclose the underlying molecular mechanisms. With careful clinical investigation and quantitative documentation, the shape and different patterns of the reverted skin patches and the natural history of revertant mosaicism in EB will be defined. As a prerequisite for application of the reverted cells in cell-based therapy approaches, these cells will be functionally characterized with migration, proliferation and apoptosis assays. Isolation and growth conditions for reverted keratinocytes will be optimized, with the goal of establishing cell therapy with the patients' own naturally corrected cells. Organotypic co-cultures closely resemble the three-dimensional structure and cellular composition of the skin; they will be used to assess the behaviour of the reverted keratinocytes and the competition between reverted and mutant cells. This research will help improve our understanding on the role of the proteins that are important for skin integrity and on the significance of the reverted cells as disease modifying factors and therapeutic agents.