Recessive dystrophic epidermolysis bullosa (RDEB) is a debilitating blistering skin disorder caused by loss-of-function mutations in COL7A1 encoding type VII collagen (C7), the main component of anchoring fibrils (AFs) at the dermal-epidermal junction (DEJ). Although conventional gene therapy approaches through viral vectors have been tested in pre-clinical and clinical trials, they are limited by transgene size constraints and only support unregulated gene expression. Genome editing could potentially overcome some of these limitations, and CRISPR/Cas9 has already been applied in research studies to restore COL7A1 expression. Delivery of suitable repair templates for repair of DNA cleaved by Cas9 is still major challenge, and alternative base editing strategies may offer corrective solutions for certain mutations.
We demonstrate highly targeted and efficient cytidine deamination and molecular correction of a defined RDEB mutation (c.425A>G) leading to restoration of full-length C7 protein expression in primary human fibroblasts and iPSCs. C7 basement membrane expression and skin architecture were restored with de novo AFs identified by electron microscopy in base edited human RDEB grafts recovered from immunodeficient mice. The results demonstrate the potential and promise of emerging base editing technologies in tackling inherited disorders with well-defined single nucleotide mutations
