Current developments in gene therapy for epidermolysis bullosa

Banana fruit (Musa sp.) DNA-magnetite nanoparticles: Synthesis, characterization, and biocompatibility assays on normal and cancerous cells

Magnet-mediated gene therapy has gained considerable interest from researchers as a novel alternative for treating genetic disorders, particularly through the use of superparamagnetic iron oxide nanoparticles (NPs)-such as magnetite NPs (Fe3O4NPs)-as non-viral genetic vectors. Despite their commercial availability for specific genetic transfection, such as in microglia cell lines, many potential uses remain unexplored. Still, ethical concerns surrounding the use of human DNA often impede genetic research. Hence, this study examined DNA-coated Fe3O4NPs (DNA-Fe₃O₄NPs) as potential transfection vectors for human foreskin fibroblasts (HFFs) and A549 (lung cancer) cell lines, using banana (Musa sp.) as a low-cost, and bioethically unproblematic DNA source. Following coprecipitation synthesis, DNA-Fe₃O₄NP characterization revealed a ζ-potential of 40.65 ± 4.10 mV, indicating good colloidal stability in aqueous media, as well as a superparamagnetic regime, evidenced by the absence of hysteresis in their magnetization curves. Successful DNA coating on the NPs was confirmed through infrared spectra and surface analysis results, while magnetite content was verified via characteristic X-ray diffraction peaks. Transmission electron microscopy (TEM) determined the average size of the DNA-Fe3O4NPs to be 14.69 ± 5.22 nm. TEM micrographs also showed no morphological changes in the DNA-Fe3O4NPs over a 30-day period. Confocal microscopy of HFF and A549 lung cancer cell lines incubated with fluoresceinamine-labeled DNA-Fe3O4NPs demonstrated their internalization into both the cytoplasm and nucleus. Neither uncoated Fe3O4NPs nor DNA-Fe3O4NPs showed cytotoxicity to A549 lung cancer cells at 1-50 μg/mL and 25-100 μg/mL, respectively, after 24 h. HFFs also maintained viability at 1-10 μg/mL for both NP types. In conclusion, DNA-Fe3O4NPs were successfully internalized into cells and exhibited no cytotoxicity in both healthy and cancerous cells across a range of concentrations. These NPs, capable of binding to various types of DNA and RNA, hold promise for applications in gene therapy.

A scalable and cGMP-compatible autologous organotypic cell therapy for Dystrophic Epidermolysis Bullosa

We present Dystrophic Epidermolysis Bullosa Cell Therapy (DEBCT), a scalable platform producing autologous organotypic iPS cell-derived induced skin composite (iSC) grafts for definitive treatment. Clinical-grade manufacturing integrates CRISPR-mediated genetic correction with reprogramming into one step, accelerating derivation of COL7A1-edited iPS cells from patients. Differentiation into epidermal, dermal and melanocyte progenitors is followed by CD49f-enrichment, minimizing maturation heterogeneity. Mouse xenografting of iSCs from four patients with different mutations demonstrates disease modifying activity at 1 month. Next-generation sequencing, biodistribution and tumorigenicity assays establish a favorable safety profile at 1-9 months. Single cell transcriptomics reveals that iSCs are composed of the major skin cell lineages and include prominent holoclone stem cell-like signatures of keratinocytes, and the recently described Gibbin-dependent signature of fibroblasts. The latter correlates with enhanced graftability of iSCs. In conclusion, DEBCT overcomes manufacturing and safety roadblocks and establishes a reproducible, safe, and cGMP-compatible therapeutic approach to heal lesions of DEB patients.

Highly efficient CRISPR/Cas9-mediated exon skipping for recessive dystrophic epidermolysis bullosa

Gene therapy based on the CRISPR/Cas9 system has emerged as a promising strategy for treating the monogenic fragile skin disorder recessive dystrophic epidermolysis bullosa (RDEB). With this approach problematic wounds could be grafted with gene edited, patient-specific skin equivalents. Precise gene editing using homology-directed repair (HDR) is the ultimate goal, however low efficiencies have hindered progress. Reframing strategies based on highly efficient non-homologous end joining (NHEJ) repair aimed at excising dispensable, mutation-harboring exons offer a promising alternative approach for restoring the COL7A1 open reading frame. To this end, we employed an exon skipping strategy using dual single guide RNA (sgRNA)/Cas9 ribonucleoproteins (RNPs) targeted at three novel COL7A1 exons (31, 68, and 109) containing pathogenic heterozygous mutations, and achieved exon deletion rates of up to 95%. Deletion of exon 31 in both primary human RDEB keratinocytes and fibroblasts resulted in the restoration of type VII collagen (C7), leading to increased cellular adhesion in vitro and accurate C7 deposition at the dermal-epidermal junction in a 3D skin model. Taken together, we extend the list of COL7A1 exons amenable to therapeutic deletion. As an incidental finding, we find that long-read Nanopore sequencing detected large on-target structural variants comprised of deletions up to >5 kb at a frequency of ~10%. Although this frequency may be acceptable given the high rates of intended editing outcomes, our data demonstrate that standard short-read sequencing may underestimate the full range of unexpected Cas9-mediated editing events.

Current Treatment Landscape for Dystrophic Epidermolysis Bullosa: From Surgical Management to Emerging Gene Therapies and Novel Skin Grafts

Epidermolysis bullosa is a genetic skin disorder characterized by blister formation from mechanical trauma. Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the COL7A1 gene presenting as generalized blisters from birth, which can result in extensive scarring, alopecia, esophageal stenosis, corneal erosions, and nail dystrophy. This disease also often leads to pseudosyndactyly of the digits from the closure of webspaces, progressing to a "mitten hand" deformity. Although traditional and current treatment for DEB is largely supportive with wound care and iterative surgical pseudosyndactyly release, emerging gene therapies and novel skin grafts may offer promising treatment. Studies published in the early 2020s have used HSV-1 vectors expressing missing COL7A1 genes to restore collagen function. One of these treatments, B-VEC, is an HSV-1-based topical gene therapy designed to restore collagen 7 by delivering the COL7A1 gene, leveraging a differentiated HSV-1 vector platform that evades the patient's immune system response. Other work has been performed to retrovirally modify autologous keratinocytes, but limitations of this process include increased labor in harvesting and engineering autologous cells. This article provides an overview of DEB treatment with an emphasis on emerging gene therapies and novel skin grafts, especially as they pertain to pseudosyndactyly treatment.

Emerging Gene Therapeutics for Epidermolysis Bullosa under Development

The monogenetic disease epidermolysis bullosa (EB) is characterised by the formation of extended blisters and lesions on the patient's skin upon minimal mechanical stress. Causal for this severe condition are genetic mutations in genes, leading to the functional impairment, reduction, or absence of the encoded protein within the skin's basement membrane zone connecting the epidermis to the underlying dermis. The major burden of affected families justifies the development of long-lasting and curative therapies operating at the genomic level. The landscape of causal therapies for EB is steadily expanding due to recent breakthroughs in the gene therapy field, providing promising outcomes for patients suffering from this severe disease. Currently, two gene therapeutic approaches show promise for EB. The clinically more advanced gene replacement strategy was successfully applied in severe EB forms, leading to a ground-breaking in vivo gene therapy product named beremagene geperpavec (B-VEC) recently approved from the US Food and Drug Administration (FDA). In addition, the continuous innovations in both designer nucleases and gene editing technologies enable the efficient and potentially safe repair of mutations in EB in a potentially permanent manner, inspiring researchers in the field to define and reach new milestones in the therapy of EB.

Heterogeneity of reported outcomes in epidermolysis bullosa clinical research: a scoping review as a first step towards outcome harmonization

BACKGROUND

Epidermolysis bullosa (EB) is a rare, genetically and clinically heterogeneous group of skin fragility disorders. No cure is currently available, but many novel and repurposed treatments are upcoming. For adequate evaluation and comparison of clinical studies in EB, well-defined and consistent consensus-endorsed outcomes and outcome measurement instruments are necessary.

OBJECTIVES

To identify previously reported outcomes in EB clinical research, group these outcomes by outcome domains and areas and summarize respective outcome measurement instruments.

METHODS

A systematic literature search was performed in the databases MEDLINE, Embase, Scopus, Cochrane CENTRAL, CINAHL, PsycINFO and trial registries covering the period between January 1991 and September 2021. Studies were included if they evaluated a treatment in a minimum of three patients with EB. Two reviewers independently performed the study selection and data extraction. All identified outcomes and their respective instruments were mapped onto overarching outcome domains. The outcome domains were stratified according to subgroups of EB type, age group, intervention, decade and phase of clinical trial.

RESULTS

The included studies (n = 207) covered a range of study designs and geographical settings. A total of 1280 outcomes were extracted verbatim and inductively mapped onto 80 outcome domains and 14 outcome areas. We found a steady increase in the number of published clinical trials and outcomes reported over the past 30 years. The included studies mainly focused on recessive dystrophic EB (43%). Wound healing was reported most frequently across all studies and referred to as a primary outcome in 31% of trials. Great heterogeneity of reported outcomes was observed within all stratified subgroups. Moreover, a diverse range of outcome measurement instruments (n = 200) was identified.

CONCLUSIONS

We show substantial heterogeneity in reported outcomes and outcome measurement instruments in EB clinical research over the past 30 years. This review is the first step towards harmonization of outcomes in EB, which is necessary to expedite the clinical translation of novel treatments for patients with EB.

A Novel Fluorescence-Based Screen of Gene Editing Molecules for Junctional Epidermolysis Bullosa

Junctional epidermolysis bullosa (JEB) is a severe blistering skin disease caused by mutations in genes encoding structural proteins essential for skin integrity. In this study, we developed a cell line suitable for gene expression studies of the JEB-associated COL17A1 encoding type XVII collagen (C17), a transmembrane protein involved in connecting basal keratinocytes to the underlying dermis of the skin. Using the CRISPR/Cas9 system of Streptococcus pyogenes we fused the coding sequence of GFP to COL17A1 leading to the constitutive expression of GFP-C17 fusion proteins under the control of the endogenous promoter in human wild-type and JEB keratinocytes. We confirmed the accurate full-length expression and localization of GFP-C17 to the plasma membrane via fluorescence microscopy and Western blot analysis. As expected, the expression of GFP-C17mut fusion proteins in JEB keratinocytes generated no specific GFP signal. However, the CRISPR/Cas9-mediated repair of a JEB-associated frameshift mutation in GFP-COL17A1mut-expressing JEB cells led to the restoration of GFP-C17, apparent in the full-length expression of the fusion protein, its accurate localization within the plasma membrane of keratinocyte monolayers as well as within the basement membrane zone of 3D-skin equivalents. Thus, this fluorescence-based JEB cell line provides the potential to serve as a platform to screen for personalized gene editing molecules and applications in vitro and in appropriate animal models in vivo.

A scalable, GMP-compatible, autologous organotypic cell therapy for Dystrophic Epidermolysis Bullosa

Background

Gene editing in induced pluripotent stem (iPS) cells has been hailed to enable new cell therapies for various monogenetic diseases including dystrophic epidermolysis bullosa (DEB). However, manufacturing, efficacy and safety roadblocks have limited the development of genetically corrected, autologous iPS cell-based therapies.

Methods

We developed Dystrophic Epidermolysis Bullosa Cell Therapy (DEBCT), a new generation GMP-compatible (cGMP), reproducible, and scalable platform to produce autologous clinical-grade iPS cell-derived organotypic induced skin composite (iSC) grafts to treat incurable wounds of patients lacking type VII collagen (C7). DEBCT uses a combined high-efficiency reprogramming and CRISPR-based genetic correction single step to generate genome scar-free, COL7A1 corrected clonal iPS cells from primary patient fibroblasts. Validated iPS cells are converted into epidermal, dermal and melanocyte progenitors with a novel 2D organoid differentiation protocol, followed by CD49f enrichment and expansion to minimize maturation heterogeneity. iSC product characterization by single cell transcriptomics was followed by mouse xenografting for disease correcting activity at 1 month and toxicology analysis at 1-6 months. Culture-acquired mutations, potential CRISPR-off targets, and cancer-driver variants were evaluated by targeted and whole genome sequencing.

Findings

iPS cell-derived iSC grafts were reproducibly generated from four recessive DEB patients with different pathogenic mutations. Organotypic iSC grafts onto immune-compromised mice developed into stable stratified skin with functional C7 restoration. Single cell transcriptomic characterization of iSCs revealed prominent holoclone stem cell signatures in keratinocytes and the recently described Gibbin-dependent signature in dermal fibroblasts. The latter correlated with enhanced graftability. Multiple orthogonal sequencing and subsequent computational approaches identified random and non-oncogenic mutations introduced by the manufacturing process. Toxicology revealed no detectable tumors after 3-6 months in DEBCT-treated mice.

Interpretation

DEBCT successfully overcomes previous roadblocks and represents a robust, scalable, and safe cGMP manufacturing platform for production of a CRISPR-corrected autologous organotypic skin graft to heal DEB patient wounds.

Paired nicking-mediated COL17A1 reframing for junctional epidermolysis bullosa

Junctional epidermolysis bullosa (JEB) is a debilitating hereditary skin disorder caused by mutations in genes encoding laminin-332, type XVII collagen (C17), and integrin-α6β4, which maintain stability between the dermis and epidermis. We designed patient-specific Cas9-nuclease- and -nickase-based targeting strategies for reframing a common homozygous deletion in exon 52 of COL17A1 associated with a lack of full-length C17 expression. Subsequent characterization of protein restoration, indel composition, and divergence of DNA and mRNA outcomes after treatment revealed auspicious efficiency, safety, and precision profiles for paired nicking-based COL17A1 editing. Almost 46% of treated primary JEB keratinocytes expressed reframed C17. Reframed COL17A1 transcripts predominantly featured 25- and 37-nt deletions, accounting for >42% of all edits and encoding C17 protein variants that localized accurately to the cell membrane. Furthermore, corrected cells showed accurate shedding of the extracellular 120-kDa C17 domain and improved adhesion capabilities to laminin-332 compared with untreated JEB cells. Three-dimensional (3D) skin equivalents demonstrated accurate and continuous deposition of C17 within the basal membrane zone between epidermis and dermis. Our findings constitute, for the first time, gene-editing-based correction of a COL17A1 mutation and demonstrate the superiority of proximal paired nicking strategies based on Cas9 D10A nickase over wild-type Cas9-based strategies for gene reframing in a clinical context.