Base editing, the introduction of a single base correction in genomic DNA, has the potential to treat genetic skin diseases such as recessive dystrophic epidermolysis bullosa (RDEB), which is characterized by mutations in the COL7A1 gene and type VII collagen (C7) deficiency. Hitherto, base editing has been harnessed to correct disease-causing mutations but a reproducible platform for efficient gene correction and a safe approach for clinical translation remain elusive. Adenine base editors (ABEs) convert A-T base pairs to G-C base pairs without requiring double-stranded DNA breaks or donor DNA templates. Here we employ ABE8e, a new variant of ABE, for gene correction in primary RDEB fibroblasts harbouring the recurrent RDEB nonsense mutation c.5047 C>T (p.Arg1683*) in exon 54 of COL7A1 and use a next generation sequencing workflow to interrogate post-treatment outcomes. Electroporation of ABE8e mRNA to a bulk population of RDEB patient fibroblasts resulted in 94.6% correction of the pathogenic allele, restoring COL7A1 mRNA and expression of C7 protein in western blots and in 3D skin constructs. Unbiased off-target DNA and RNA editing analysis did not detect off-target editing in treated patient-derived fibroblasts. A silent ‘bystander’ mutation was installed by ABE8e proximal to the on-target site but we diminished this by altering the concentrations of the ABE8e and sgRNA treatment, demonstratinga dose-dependent relationship with the efficiency of bystander editing. Taken together, we have established a highly efficient pipeline for gene correction in primary fibroblasts with a favourable safety profile. This work lays a foundation for therapies for RDEB patients using ex vivo or in vivo base editing strategies.

ESDR268 - ABE8e adenine base editor corrects COL7A1 nonsense mutation efficiently and safely

The scientific meeting of the European Society for Dermatological Research (ESDR) is held yearly, usually in September. With an international attendance of more than 1000 skin scientists from around the globe, the four-day event includes short oral presentations from peer-reviewed abstracts, keynote lectures from international experts, sponsored symposia, satellite programs, educational events as well as an important focus on posters, networking and building collaborations amongst scientists. For more information about this year’s meeting visit our website.