Normal and Gene-Corrected Dystrophic Epidermolysis Bullosa Fibroblasts Alone Can Produce Type VII Collagen at the Basement Membrane Zone

Management of Skin Lesions in Patients with Epidermolysis Bullosa by Topical Treatment: Systematic Review and Meta-Analysis

Epidermolysis bullosa (EB) is the overarching term for a set of rare inherited skin fragility disorders that result from mutations in at least 20 different genes. Currently, there is no cure for any of the EB subtypes associated with various mutations. Existing therapies primarily focus on alleviating pain and promoting early wound healing to prevent potential complications. Consequently, there is an urgent need for innovative therapeutic approaches. The objective of this research was to assess the efficacy of various topical treatments in patients with EB with the goal of achieving wound healing. A secondary objective was to analyse the efficacy of topical treatments for symptom reduction. A literature search was conducted using scientific databases, including The Cochrane Library, Medline (Pubmed), Web of Science, CINHAL, Embase, and Scopus. The protocol review was registered in PROSPERO (ID: 418790), and inclusion and exclusion criteria were applied, resulting in the selection of 23 articles. Enhanced healing times were observed compared with the control group. No conclusive data have been observed on pain management, infection, pruritus episodes, and cure rates over time. Additionally, evidence indicates significant progress in gene therapies (B-VEC), as well as cell and protein therapies. The dressing group, Oleogel S-10, allantoin and diacerein 1%, were the most represented, followed by fibroblast utilisation. In addition, emerging treatments that improve the patient's innate immunity, such as calcipotriol, are gaining attention. However, more trials are needed to reduce the prevalence of blistering and improve the quality of life of individuals with epidermolysis bullosa.

Innovations in the Treatment of Dystrophic Epidermolysis Bullosa (DEB): Current Landscape and Prospects

Dystrophic epidermolysis bullosa (DEB) is one of the major types of EB, a rare hereditary group of trauma-induced blistering skin disorders. DEB is caused by inherited pathogenic variants in the COL7A1 gene, which encodes type VII collagen, the major component of anchoring fibrils which maintain adhesion between the outer epidermis and underlying dermis. DEB can be subclassified into dominant (DDEB) and recessive (RDEB) forms. Generally, DDEB has a milder phenotype, while RDEB patients often have more extensive blistering, chronic inflammation, skin fibrosis, and a propensity for squamous cell carcinoma development, collectively impacting on daily activities and life expectancy. At present, best practice treatments are mostly supportive, and thus there is a considerable burden of disease with unmet therapeutic need. Over the last 20 years, considerable translational research efforts have focused on either trying to cure DEB by direct correction of the COL7A1 gene pathology, or by modifying secondary inflammation to lessen phenotypic severity and improve patient symptoms such as poor wound healing, itch, and pain. In this review, we provide an overview and update on various therapeutic innovations for DEB, including gene therapy, cell-based therapy, protein therapy, and disease-modifying and symptomatic control agents. We outline the progress and challenges for each treatment modality and identify likely prospects for future clinical impact.

The potential of gene therapy for recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa (EB) encompasses a heterogeneous group of inherited skin fragility disorders with mutations in genes encoding the basement membrane zone (BMZ) proteins that normally ensure dermal-epidermal integrity. Of the four main EB types, recessive dystrophic EB (RDEB), especially the severe variant, represents one of the most debilitating clinical entities with recurrent mucocutaneous blistering and ulceration leading to chronic wounds, infections, inflammation, scarring and ultimately cutaneous squamous cell carcinoma, which leads to premature death. Improved understanding of the molecular genetics of EB over the past three decades and advances in biotechnology has led to rapid progress in developing gene and cell-based regenerative therapies for EB. In particular, RDEB is at the vanguard of advances in human clinical trials of advanced therapeutics. Furthermore, the past decade has witnessed the emergence of a real collective, global effort involving academia and industry, supported by international EB patient organisations such as the Dystrophic Epidermolysis Bullosa Research Association (DEBRA), amongst others, to develop clinically relevant and marketable targeted therapeutics for EB. Thus, there is an increasing need for the practising dermatologist to become familiar with the concept of gene therapy, fundamental differences between various approaches and their human applications. This review explains the principles of different approaches of gene therapy; summarises its journey and discusses its current and future impact in RDEB.

Development of Minicircle Vectors Encoding COL7A1 Gene with Human Promoters for Non-Viral Gene Therapy for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare autosomal inherited skin disorder caused by mutations in the COL7A1 gene that encodes type VII collagen (C7). The development of an efficient gene replacement strategy for RDEB is mainly hindered by the lack of vectors able to encapsulate and transfect the large cDNA size of this gene. To address this problem, our group has opted to use polymeric-based non-viral delivery systems and minicircle DNA. With this approach, safety is improved by avoiding the usage of viruses, the absence of bacterial backbone, and the replacement of the control viral cytomegalovirus (CMV) promoter of the gene with human promoters. All the promoters showed impressive C7 expression in RDEB skin cells, with eukaryotic translation elongation factor 1 α (EF1α) promoter producing higher C7 expression levels than CMV following minicircle induction, and COL7A1 tissue-specific promoter (C7P) generating C7 levels similar to normal human epidermal keratinocytes. The improved system developed here has a high potential for use as a non-viral topical treatment to restore C7 in RDEB patients efficiently and safely, and to be adapted to other genetic conditions.

Highly branched poly(β-amino ester)s for gene delivery in hereditary skin diseases

Non-viral gene therapy for hereditary skin diseases is an attractive prospect. However, research efforts dedicated to this area are rare. Taking advantage of the branched structural possibilities of polymeric vectors, we have developed a gene delivery platform for the treatment of an incurable monogenic skin disease - recessive dystrophic epidermolysis bullosa (RDEB) - based on highly branched poly(β-amino ester)s (HPAEs). The screening of HPAEs and optimization of therapeutic gene constructs, together with evaluation of the combined system for gene transfection, were comprehensively reviewed. The successful restoration of type VII collagen (C7) expression both in vitro and in vivo highlights HPAEs as a promising generation of polymeric vectors for RDEB gene therapy into the clinic. Considering that the treatment of patients with genetic cutaneous disorders, such as other subtypes of epidermolysis bullosa, pachyonychia congenita, ichthyosis and Netherton syndrome, remains challenging, the success of HPAEs in RDEB treatment indicates that the development of viable polymeric gene delivery vectors could potentially expedite the translation of gene therapy for these diseases from bench to bedside.

Clinical Perspectives of Gene-Targeted Therapies for Epidermolysis Bullosa

New insights into molecular genetics and pathomechanisms in epidermolysis bullosa (EB), methodological and technological advances in molecular biology as well as designated funding initiatives and facilitated approval procedures for orphan drugs have boosted translational research perspectives for this devastating disease. This is echoed by the increasing number of clinical trials assessing innovative molecular therapies in the field of EB. Despite remarkable progress, gene-corrective modalities, aimed at sustained or permanent restoration of functional protein expression, still await broad clinical availability. This also reflects the methodological and technological shortcomings of current strategies, including the translatability of certain methodologies beyond preclinical models as well as the safe, specific, efficient, feasible, sustained and cost-effective delivery of therapeutic/corrective information to target cells. This review gives an updated overview on status, prospects, challenges and limitations of current gene-targeted therapies.

The utility of dermal fibroblasts in treatment of skin disorders: A paradigm of recessive dystrophic epidermolysis bullosa

Dermal fibroblasts are the most accessible cells in the skin that have gained significant attention in cell therapy. Applying dermal fibroblasts' regenerative capacity can introduce new patterns to develop cell-based therapies to treat skin disorders. Dermal fibroblasts originate from mesenchymal cells and are located within the dermis. These cells are mainly responsible for synthesizing glycosaminoglycans, collagens, and components of extracellular matrix supporting skin's structural integrity. Preclinical studies suggested that allogeneic and autologous dermal fibroblasts provide widespread and beneficial applications for wound healing, burn ulcers, and inherited skin disorders. In this regard, generating induced pluripotent stem cells (iPSCs) from fibroblasts and gene-edited fibroblasts are promising approaches for treating skin disorders. Here, we aimed to review literature about ongoing and completed clinical trials that applied fibroblasts and bioengineered fibroblasts as therapeutic agents for various skin disorders. This review explores cell therapy protocols from the earliest phase of allogeneic and autologous fibroblasts development in different benches to translating them into bedside-level treatment for skin disorders, particularly recessive dystrophic epidermolysis bullosa.

Gene Therapy and its Application in Dermatology

Gene therapy is an experimental technique to treat genetic diseases. It is based on the introduction of nucleic acid with the help of a vector, into a diseased cell or tissue, to correct the gene expression and thus prevent, halt, or reverse a pathological process. It is a promising treatment approach for genetic diseases, inherited diseases, vaccination, cancer, immunomodulation, as well as healing of some refractory ulcers. Both viral and nonviral vectors can be used to deliver the correct gene. An ideal vector should have the ability for sustained gene expression, acceptable coding capacity, high transduction efficiency, and devoid of mutagenicity. There are different techniques of vector delivery, but these techniques are still under research for assessment of their safety and effectiveness. The major challenges of gene therapy are immunogenicity, mutagenicity, and lack of sustainable therapeutic benefit. Despite these constraints, therapeutic success was obtained in a few genetic and inherited skin diseases. Skin being the largest, superficial, easily accessible and assessable organ of the body, may be a promising target for gene therapy research in the recent future.

Molecular mechanism of extracellular matrix disorder in pelvic organ prolapses

Pelvic organ prolapses (POP) notably reduces the quality of life in elderly populations due to bladder and bowel dysfunction, incontinence, and coital problems. Extracellular matrix (ECM) disorder is a pivotal event in the progression of POP, but to date, its specific underlying mechanism remains unclear. The ligaments of patients with POP and healthy controls were collected to compare the expression of Homeobox11 (HOXA11) and transforming growth factor β (TGF-β1) via immunohistochemical analysis. HOXA11 and TGF-β1 were overexpressed or knocked down in fibroblast cells to explore their effects on the expression of collagen and matrix metalloproteinases (MMPs). HOXA11 and TGF-β1 were greatly reduced in the ligaments of patients with POP. The overexpression and downregulation of HOXA11 and TGF-β1 can mediate ECM disorder via regulating expression of collagen (Col) and MMPs. In addition, HOXA11 and TGF-β1 exerted synergistic effect on the expression of Col and MMPs. The present study identified that HOXA11 and TGF-β1 serve critical roles in mediating ECM disorders, which may be of clinical significance for the diagnosis and treatment of patients with POP.

Toward Combined Cell and Gene Therapy for Genodermatoses

To date, more than 200 monogenic, often devastating, skin diseases have been described. Because of unmet medical needs, development of long-lasting and curative therapies has been consistently attempted, with the aim of correcting the underlying molecular defect. In this review, we will specifically address the few combined cell and gene therapy strategies that made it to the clinics. Based on these studies, what can be envisioned for the future is a patient-oriented strategy, built on the specific features of the individual in need. Most likely, a combination of different strategies, approaches, and advanced therapies will be required to reach the finish line at the end of the long and winding road hampering the achievement of definitive treatments for genodermatoses.

Footprint-free gene mutation correction in induced pluripotent stem cell (iPSC) derived from recessive dystrophic epidermolysis bullosa (RDEB) using the CRISPR/Cas9 and piggyBac transposon system

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a monogenic skin blistering disorder caused by mutations in the type VII collagen gene. A combination of biological technologies, including induced pluripotent stem cells (iPSCs) and several gene-editing tools, allows us to develop gene and cell therapies for such inherited diseases. However, the methodologies for gene and cell therapies must be continuously innovated for safe clinical use.

OBJECTIVE

In this study, we used the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology to correct the pathogenic mutation in RDEB-specific iPSCs, and the piggyBac transposon system so that no residual gene fragments remained in the genome of iPSCs after correcting the mutation.

METHODS

For homologous recombination (HR)-based gene editing using CRISPR/Cas9, we designed guide RNA and template DNA including homologous sequences with drug-mediated selection cassette flanked by inverted repeat sequences of the transposon. HR reaction using CRISPR/Cas9 was induced in RDEB-specific iPSCs, and mutation-corrected iPSCs (MC-iPSCs) was obtained. Consequently, the selection cassette in the genome of MC-iPSCs was removed by transposase expression.

RESULTS

After CRISPR/Cas9-induced gene editing, we confirmed that the pathogenic mutation in RDEB-specific iPSCs was properly corrected. In addition, MC-iPSCs had no genetic footprint after removing the selection cassette by transposon system, and maintained their "stemness". When differentiating MC-iPSCs into keratinocytes, the expression of type VII collagen was restored.

CONCLUSIONS

Our study demonstrated one of the safer approaches to establish gene and cell therapies for skin hereditary disorders for future clinical use.

Revertant mosaic fibroblasts in recessive dystrophic epidermolysis bullosa

BACKGROUND

Revertant mosaicism has been described previously in recessive dystrophic epidermolysis bullosa (RDEB), manifesting as regions of skin with normal mechanical and biological characteristics. Here we report the discovery of revertant dermal fibroblasts, unique in that all other documented cases of revertant mosaicism occur in epidermal keratinocytes.

OBJECTIVES

To determine the cause of revertant mosaicism found in a patient with RDEB from isolated epidermal keratinocytes and dermal fibroblasts in blister and mosaic skin regions.

METHODS

Skin biopsies were taken from blister and mosaic skin regions of a patient with RDEB. Allele identification was confirmed and the type VII collagen (C7) content and COL7A1 expression profile of isolated keratinocytes and fibroblasts was determined.

RESULTS

Keratinocytes isolated from the mosaic area had a slight increase in C7, although overall expression of COL7A1 was unchanged between blister and mosaic fibroblasts. Differential allele expression was identified in blister and mosaic fibroblasts using targeted RNA sequencing (TREx), where the allele harbouring a point mutation was preferentially expressed over that containing a frameshift mutation. A crossing over event was identified in mosaic fibroblasts that was not present in blister fibroblasts, yielding a functional COL7A1 allele in a subset of cells.

CONCLUSIONS

In documenting a novel case of revertant mosaicism in RDEB, we have identified dermal fibroblasts as having the capacity to correct blistering functionally. We have also pioneered the use of TREx in quantifying allele-specific expression. Using fibroblasts instead of keratinocytes for RDEB therapies offers advantages in the local and systemic therapy of RDEB. What's already known about this topic? Revertant mosaicism has been previously documented in patients with recessive dystrophic epidermolysis bullosa (RDEB), however, it has only been found in epidermal keratinocytes. What does this study add? We have demonstrated that COL7A1 gene reversion in dermal fibroblasts occurs and is able to form functional skin in a patient with RDEB. Additionally, we have pioneered a new application for targeted RNA sequencing in quantifying allele-specific expression in fibroblasts and keratinocytes. What is the translational message? This opens up possibilities for using fibroblasts as local and systemic therapy for patients with RDEB.

Safety and early efficacy outcomes for lentiviral fibroblast gene therapy in recessive dystrophic epidermolysis bullosa

BACKGROUNDRecessive dystrophic epidermolysis bullosa (RDEB) is a severe form of skin fragility disorder due to mutations in COL7A1 encoding basement membrane type VII collagen (C7), the main constituent of anchoring fibrils (AFs) in skin. We developed a self-inactivating lentiviral platform encoding a codon-optimized COL7A1 cDNA under the control of a human phosphoglycerate kinase promoter for phase I evaluation.METHODSIn this single-center, open-label phase I trial, 4 adults with RDEB each received 3 intradermal injections (~1 × 106 cells/cm2 of intact skin) of COL7A1-modified autologous fibroblasts and were followed up for 12 months. The primary outcome was safety, including autoimmune reactions against recombinant C7. Secondary outcomes included C7 expression, AF morphology, and presence of transgene in the injected skin.RESULTSGene-modified fibroblasts were well tolerated, without serious adverse reactions or autoimmune reactions against recombinant C7. Regarding efficacy, there was a significant (P < 0.05) 1.26-fold to 26.10-fold increase in C7 mean fluorescence intensity in the injected skin compared with noninjected skin in 3 of 4 subjects, with a sustained increase up to 12 months in 2 of 4 subjects. The presence of transgene (codon-optimized COL7A1 cDNA) was demonstrated in the injected skin at month 12 in 1 subject, but no new mature AFs were detected.CONCLUSIONTo our knowledge, this is the first human study demonstrating safety and potential efficacy of lentiviral fibroblast gene therapy with the presence of COL7A1 transgene and subsequent C7 restoration in vivo in treated skin at 1 year after gene therapy. These data provide a rationale for phase II studies for further clinical evaluation.TRIAL REGISTRATIONClincalTrials.gov NCT02493816.FUNDINGCure EB, Dystrophic Epidermolysis Bullosa Research Association (UK), UK NIHR Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London, and Fondation René Touraine Short-Exchange Award.

Functional therapies for cutaneous wound repair in epidermolysis bullosa

Chronic wounding as a result of recurrent skin blistering in the painful genetic skin disease epidermolysis bullosa, may lead to life-threatening infections, increased risk of tumor formation, and other serious medical complications. Therefore, epidermolysis bullosa patients have an urgent need for optimal wound care and tissue regeneration. Therapeutic strategies using gene-, protein-, and cell-therapies are being developed to improve clinical symptoms, and some of them have already been investigated in early clinical trials. The most favorable options of functional therapies include gene replacement, gene editing, RNA targeting, and harnessing natural gene therapy. This review describes the current progress of the different approaches targeting autologous skin cells, and will discuss the benefits and challenges of their application.

CRISPR/Cas9-Based Cellular Engineering for Targeted Gene Overexpression

Gene and cellular therapies hold tremendous promise as agents for treating genetic disorders. However, the effective delivery of genes, particularly large ones, and expression at therapeutic levels can be challenging in cells of clinical relevance. To address this engineering hurdle, we sought to employ the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system to insert powerful regulatory elements upstream of an endogenous gene. We achieved robust activation of the COL7A1 gene in primary human umbilical cord blood CD34⁺ hematopoietic stem cells and peripheral blood T-cells. CD34⁺ cells retained their colony forming potential and, in a second engineering step, we disrupted the T-cell receptor complex in T-cells. These cellular populations are of high translational impact due to their engraftment potential, broad circulatory properties, and favorable immune profile that supports delivery to multiple recipients. This study demonstrates the feasibility of targeted knock in of a ubiquitous chromatin opening element, promoter, and marker gene that doubles as a suicide gene for precision gene activation. This system merges the specificity of gene editing with the high level, sustained gene expression achieved with gene therapy vectors. We predict that this design concept will be highly transferrable to most genes in multiple model systems representing a facile cellular engineering platform for promoting gene expression.

Bullosis Diabeticorum: A Rare Presentation with Immunoglobulin G (IgG) Deposition Related Vasculopathy. Case Report and Focused Review

BACKGROUND Bullosis diabeticorum (BD) is a condition characterized by recurrent, spontaneous, and non-inflammatory blistering in patients with poorly controlled diabetes mellitus. While etiopathogenesis remains unclear, roles of neuropathy, vasculopathy and UV light are hypothesized. Most literature reports negative direct and indirect immunofluorescence findings in diabetics with bullous eruptions. Porphyria cutanea tarda, bullous pemphigoid, epidermolysis bullosa, and pseudoporphyria are other differential diagnoses of bullous lesions, and they must be excluded. CASE REPORT We present a 42-year-old African American male with long standing poorly controlled insulin dependent diabetes mellitus with blisters on his left hand and feet. The blisters were noticed three weeks prior to presentation and, thereafter, rapidly increased in size and spontaneously ruptured. Physical examination revealed a multitude of both roofed and unroofed bullous painless skin lesions. Hematoxylin and eosin (H&E) staining dramatized the dermal-epidermal blistering and re-epithelization process. Direct Immunofluorescence (DIF) was positive for 2 + IgG deposition in the already thickened basement membrane of the capillaries of the superficial vascular plexus. After debridement, his wounds greatly improved with over three months of aggressive wound care. CONCLUSIONS Primary immunologic abnormality likely plays no role in the onset of BD. To date, only one article has reported nonspecific capillary-associated immunoglobulin M and C3. This is the first case of BD with IgG deposition in the superficial capillary basement membrane. Positive findings on DIF suggest vasculopathy. Dermal microangiopathy, secondary to immunologic abnormality, is a possible underlying pathogenesis to bullae formation. Punch biopsy with DIF can be an additional diagnostic modality in the management of such cases.

Gentamicin induces functional type VII collagen in recessive dystrophic epidermolysis bullosa patients

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is an incurable disease caused by mutations in the gene encoding type VII collagen, the major component of anchoring fibrils (AF). We previously demonstrated that gentamicin produced functional type VII collagen in RDEB cells harboring nonsense mutations. Herein, we determined whether topical or intradermal gentamicin administration induces type VII collagen and AFs in RDEB patients.

METHODS

A double-blind, placebo-controlled pilot trial assessed safety and efficacy of topical and intradermal gentamicin in 5 RDEB patients with nonsense mutations. The topical arm tested 0.1% gentamicin ointment or placebo application 3 times daily at 2 open erosion sites for 2 weeks. The intradermal arm tested daily intradermal injection of gentamicin solution (8 mg) or placebo into 2 intact skin sites for 2 days in 4 of 5 patients. Primary outcomes were induction of type VII collagen and AFs at the test sites and safety assessment. A secondary outcome assessed wound closure of topically treated erosions.

RESULTS

Both topical and intradermal gentamicin administration induced type VII collagen and AFs at the dermal-epidermal junction of treatment sites. Newly created type VII collagen varied from 20% to 165% of that expressed in normal human skin and persisted for 3 months. Topical gentamicin corrected dermal-epidermal separation, improved wound closure, and reduced blister formation. There were no untoward side effects from gentamicin treatments. Type VII collagen induction did not generate anti-type VII collagen autoantibodies in patients' blood or skin.

CONCLUSION

Topical and intradermal gentamicin suppresses nonsense mutations and induces type VII collagen and AFs in RDEB patients. Gentamicin therapy may provide a readily available treatment for RDEB patients with nonsense mutations.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02698735.

FUNDING

Epidermolysis Bullosa Research Partnership, Epidermolysis Bullosa Medical Research Foundation, NIH, and VA Merit Award.

Next generation human skin constructs as advanced tools for drug development

Many diseases, as well as side effects of drugs, manifest themselves through skin symptoms. Skin is a complex tissue that hosts various specialized cell types and performs many roles including physical barrier, immune and sensory functions. Therefore, modeling skin in vitro presents technical challenges for tissue engineering. Since the first attempts at engineering human epidermis in 1970s, there has been a growing interest in generating full-thickness skin constructs mimicking physiological functions by incorporating various skin components, such as vasculature and melanocytes for pigmentation. Development of biomimetic in vitro human skin models with these physiological functions provides a new tool for drug discovery, disease modeling, regenerative medicine and basic research for skin biology. This goal, however, has long been delayed by the limited availability of different cell types, the challenges in establishing co-culture conditions, and the ability to recapitulate the 3D anatomy of the skin. Recent breakthroughs in induced pluripotent stem cell (iPSC) technology and microfabrication techniques such as 3D-printing have allowed for building more reliable and complex in vitro skin models for pharmaceutical screening. In this review, we focus on the current developments and prevailing challenges in generating skin constructs with vasculature, skin appendages such as hair follicles, pigmentation, immune response, innervation, and hypodermis. Furthermore, we discuss the promising advances that iPSC technology offers in order to generate in vitro models of genetic skin diseases, such as epidermolysis bullosa and psoriasis. We also discuss how future integration of the next generation human skin constructs onto microfluidic platforms along with other tissues could revolutionize the early stages of drug development by creating reliable evaluation of patient-specific effects of pharmaceutical agents. Impact statement Skin is a complex tissue that hosts various specialized cell types and performs many roles including barrier, immune, and sensory functions. For human-relevant drug testing, there has been a growing interest in building more physiological skin constructs by incorporating different skin components, such as vasculature, appendages, pigment, innervation, and adipose tissue. This paper provides an overview of the strategies to build complex human skin constructs that can faithfully recapitulate human skin and thus can be used in drug development targeting skin diseases. In particular, we discuss recent developments and remaining challenges in incorporating various skin components, availability of iPSC-derived skin cell types and in vitro skin disease models. In addition, we provide insights on the future integration of these complex skin models with other organs on microfluidic platforms as well as potential readout technologies for high-throughput drug screening.

Novel and emerging therapies in the treatment of recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous group of inherited blistering diseases that affects ∼ 500,000 people worldwide. Clinically, individuals with EB have fragile skin and are susceptible to blistering following minimal trauma, with mucous membrane and other organ involvement in some subtypes. Within the spectrum of EB, ∼ 5% of affected individuals have the clinically more severe recessive dystrophic (RDEB) variant with a prevalence of 8 per one million of the population. RDEB is caused by loss-of-function mutations in the type VII collagen gene, COL7A1, which leads to reduced or absent type VII collagen (C7) and a paucity of structurally effective anchoring fibrils at the dermal-epidermal junction (DEJ). Currently, there is no cure for RDEB, although considerable progress has been made in testing novel treatments including gene therapy (lentiviral and gamma retroviral vectors for COL7A1 supplementation in keratinocytes and fibroblasts), as well as cell therapy (use of allogeneic fibroblasts, mesenchymal stromal cells (MSCs), and bone marrow transplantation (BMT)). Here, we review current treatment modalities available as well as novel and emerging therapies in the treatment of RDEB. Clinical trials of new translational therapies in RDEB offer hope for improved clinical management of patients as well as generating broader lessons for regenerative medicine that could be applicable to other inherited or acquired abnormalities of wound healing or scarring.

Efficient in vivo gene editing using ribonucleoproteins in skin stem cells of recessive dystrophic epidermolysis bullosa mouse model

The prokaryotic CRISPR/Cas9 system has recently emerged as a powerful tool for genome editing in mammalian cells with the potential to bring curative therapies to patients with genetic diseases. However, efficient in vivo delivery of this genome editing machinery and indeed the very feasibility of using these techniques in vivo remain challenging for most tissue types. Here, we show that nonreplicable Cas9/sgRNA ribonucleoproteins can be used to correct genetic defects in skin stem cells of postnatal recessive dystrophic epidermolysis bullosa (RDEB) mice. We developed a method to locally deliver Cas9/sgRNA ribonucleoproteins into the skin of postnatal mice. This method results in rapid gene editing in epidermal stem cells. Using this method, we show that Cas9/sgRNA ribonucleoproteins efficiently excise exon80, which covers the point mutation in our RDEB mouse model, and thus restores the correct localization of the collagen VII protein in vivo. The skin blistering phenotype is also significantly ameliorated after treatment. This study provides an in vivo gene correction strategy using ribonucleoproteins as curative treatment for genetic diseases in skin and potentially in other somatic tissues.

Cell therapy for basement membrane-linked diseases

For most disorders caused by mutations in genes encoding basement membrane (BM) proteins, there are at present only limited treatment options available. Genetic BM-linked disorders can be viewed as especially suited for treatment with cell-based therapy approaches because the proteins that need to be restored are located in the extracellular space. In consequence, complete and permanent engraftment of cells does not necessarily have to occur to achieve substantial causal therapeutic effects. For these disorders cells can be used as transient vehicles for protein replacement. In addition, it is becoming evident that BM-linked genetic disorders are modified by secondary diseases mechanisms. Cell-based therapies have also the ability to target such disease modifying mechanisms. Thus, cell therapies can simultaneously provide causal treatment and symptomatic relief, and accordingly hold great potential for treatment of BM-linked disorders. However, this potential has for most applications and diseases so far not been realized. Here, we will present the state of cell therapies for BM-linked diseases. We will discuss use of both pluripotent and differentiated cells, the limitation of the approaches, their challenges, and the way forward to potential wider implementation of cell therapies in the clinics.

Lentiviral Engineered Fibroblasts Expressing Codon-Optimized COL7A1 Restore Anchoring Fibrils in RDEB

Cells therapies, engineered to secrete replacement proteins, are being developed to ameliorate otherwise debilitating diseases. Recessive dystrophic epidermolysis bullosa (RDEB) is caused by defects of type VII collagen, a protein essential for anchoring fibril formation at the dermal-epidermal junction. Whereas allogeneic fibroblasts injected directly into the dermis can mediate transient disease modulation, autologous gene-modified fibroblasts should evade immunological rejection and support sustained delivery of type VII collagen at the dermal-epidermal junction. We demonstrate the feasibility of such an approach using a therapeutic grade, self-inactivating-lentiviral vector, encoding codon-optimized COL7A1, to transduce RDEB fibroblasts under conditions suitable for clinical application. Expression and secretion of type VII collagen was confirmed with transduced cells exhibiting supranormal levels of protein expression, and ex vivo migration of fibroblasts was restored in functional assays. Gene-modified RDEB fibroblasts also deposited type VII collagen at the dermal-epidermal junction of human RDEB skin xenografts placed on NOD-scid IL2Rgamma(null) recipients, with reconstruction of human epidermal structure and regeneration of anchoring fibrils at the dermal-epidermal junction. Fibroblast-mediated restoration of protein and structural defects in this RDEB model strongly supports proposed therapeutic applications in man.

Gene editing toward the use of autologous therapies in recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a disease caused by mutations in the COL7A1 gene that result in absent or dysfunctional type VII collagen protein production. Clinically, RDEB manifests as early and severe chronic cutaneous blistering, damage to internal epithelium, an increased risk for squamous cell carcinoma, and an overall reduced life expectancy. Recent localized and systemic treatments have shown promise for lessening the disease severity in RDEB, but the concept of ex vivo therapy would allow a patient's own cells to be engineered to express functional type VII collagen. Here, we review gene delivery and editing platforms and their application toward the development of next-generation treatments designed to correct the causative genetic defects of RDEB.

Intravenously Administered Recombinant Human Type VII Collagen Derived from Chinese Hamster Ovary Cells Reverses the Disease Phenotype in Recessive Dystrophic Epidermolysis Bullosa Mice

Recessive dystrophic epidermolysis bullosa (RDEB) is an inherited disorder characterized by skin fragility, blistering, and multiple skin wounds with no currently approved or consistently effective treatment. It is due to mutations in the gene encoding type VII collagen (C7). Using recombinant human C7 (rhC7) purified from human dermal fibroblasts (FB-rhC7), we showed previously that intravenously injected rhC7 distributed to engrafted RDEB skin, incorporated into its dermal-epidermal junction (DEJ), and reversed the RDEB disease phenotype. Human dermal fibroblasts, however, are not used for commercial production of therapeutic proteins. Therefore, we generated rhC7 from Chinese hamster ovary (CHO) cells. The CHO-derived recombinant type VII collagen (CHO-rhC7), similar to FB-rhC7, was secreted as a correctly folded, disulfide-bonded, helical trimer resistant to protease degradation. CHO-rhC7 bound to fibronectin and promoted human keratinocyte migration in vitro. A single dose of CHO-rhC7, administered intravenously into new-born C7-null RDEB mice, incorporated into the DEJ of multiple skin sites, tongue and esophagus, restored anchoring fibrils, improved dermal-epidermal adherence, and increased the animals' life span. Furthermore, no circulating or tissue-bound anti-C7 antibodies were observed in the mice. These data demonstrate the efficacy of CHO-rhC7 in a preclinical murine model of RDEB.

Medical cell technologies for treatment of patients suffering from recessive dystrophic epidermolysis bullosa. Method of intracutaneous administration of fibroblasts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited disease developing due to genetic abnormalities in the synthesis of Type VII collagen by fibroblasts. A low production rate of Type VII collagen and abnormalities related to the formation of anchoring fibrils weaken the epidermis and derma adhesion strength, which results in the formation of blisters or erosions in case of any mechanical injury. Fibroblasts and keratinocytes belong to the key sources of Type VII collagen in the skin. Application of allogeneic fibroblasts is a promising cell technique for treating RDEB patients. The therapeutic effect of fibroblasts intradermal administration is stipulated by high stability of newly synthesized Type VII collagen and its ability to form anchoring fibrils in the area of the dermoepidermal junction. According to experimental and clinical studies, it is possible to boost the content of Type VII collagen in the dermoepidermal junction area and heal long-term skin defects in RDEB patients by means of intradermal administration of allogeneic fibroblasts.

Gene therapy: pursuing restoration of dermal adhesion in recessive dystrophic epidermolysis bullosa

The replacement of a defective gene with a fully functional copy is the goal of the most basic gene therapy. Recessive dystrophic epidermolysis bullosa (RDEB) is characterised by a lack of adhesion of the epidermis to the dermis. It is an ideal target for gene therapy as all variants of hereditary RDEB are caused by mutations in a single gene, COL7A1, coding for type VII collagen, a key component of anchoring fibrils that secure attachment of the epidermis to the dermis. RDEB is one of the most severe variants in the epidermolysis bullosa (EB) group of heritable skin diseases. Epidermolysis bullosa is defined by chronic fragility and blistering of the skin and mucous membranes due to mutations in the genes responsible for production of the basement membrane proteins. This condition has a high personal, medical and socio-economic impact. People with RDEB require a broad spectrum of medications and specialised care. Due to this being a systemic condition, most research focus is in the area of gene therapy. Recently, preclinical works have begun to show promise. They focus on the virally mediated ex vivo correction of autologous epithelium. These corrected cells are then to be expanded and grafted onto the patient following the lead of the first successful gene therapy in dermatology being a grafting of corrected tissue for junctional EB treatment. Current progress, outstanding challenges and future directions in translating these approaches in clinics are reviewed in this article.

Aminoglycosides restore full-length type VII collagen by overcoming premature termination codons: therapeutic implications for dystrophic epidermolysis bullosa

Patients with recessive dystrophic epidermolysis bullosa (RDEB) have severe, incurable skin fragility, blistering, and multiple skin wounds due to mutations in the gene encoding type VII collagen (C7), the major component of anchoring fibrils mediating epidermal-dermal adherence. Nearly 10-25% of RDEB patients carry nonsense mutations leading to premature stop codons (PTCs) that result in truncated C7. In this study, we evaluated the feasibility of using aminoglycosides to suppress PTCs and induce C7 expression in two RDEB keratinocyte cell lines (Q251X/Q251X and R578X/R906) and two primary RDEB fibroblasts (R578X/R578X and R163X/R1683X). Incubation of these cells with aminoglycosides (geneticin, gentamicin, and paromomycin) resulted in the synthesis and secretion of a full-length C7 in a dose-dependent and sustained manner. Importantly, aminoglycoside-induced C7 reversed the abnormal RDEB cell phenotype and incorporated into the dermal-epidermal junction of skin equivalents. We further demonstrated the general utility of aminoglycoside-mediated readthrough in 293 cells transiently transfected with expression vectors encoding 22 different RDEB nonsense mutations. This is the first study demonstrating that aminoglycosides can induce PTC readthrough and restore functional C7 in RDEB caused by nonsense mutations. Therefore, aminoglycosides may have therapeutic potential for RDEB patients and other inherited skin diseases caused by nonsense mutations.

Cell therapy in dermatology

Harnessing the regenerative capacity of keratinocytes and fibroblasts from human skin has created new opportunities to develop cell-based therapies for patients. Cultured cells and bioengineered skin products are being used to treat patients with inherited and acquired skin disorders associated with defective skin, and further clinical trials of new products are in progress. The capacity of extracutaneous sources of cells such as bone marrow is also being investigated for its plasticity in regenerating skin, and new strategies, such as the derivation of inducible pluripotent stem cells, also hold great promise for future cell therapies in dermatology. This article reviews some of the preclinical and clinical studies and future directions relating to cell therapy in dermatology, particularly for inherited skin diseases associated with fragile skin and poor wound healing.

The genetics of skin fragility

Genetic skin fragility manifests with diminished resistance of the skin and mucous membranes to external mechanical forces and with skin blistering, erosions, and painful wounds as clinical features. Skin fragility disorders, collectively called epidermolysis bullosa, are caused by mutations in 18 distinct genes that encode proteins involved in epidermal integrity and dermal-epidermal adhesion. The genetic spectrum, along with environmental and genetic modifiers, creates a large number of clinical phenotypes, spanning from minor localized lesions to severe generalized blistering, secondary skin cancer, or early demise resulting from extensive loss of the epidermis. Laboratory investigations of skin fragility have greatly augmented our understanding of genotype-phenotype correlations in epidermolysis bullosa and have also advanced skin biology in general. Current translational research concentrates on the development of biologically valid treatments with therapeutic genes, cells, proteins, or small-molecule compounds in preclinical settings or human pilot trials.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

Generation of 3D skin equivalents fully reconstituted from human induced pluripotent stem cells (iPSCs)

Recent generation of patient-specific induced pluripotent stem cells (PS-iPSCs) provides significant advantages for cell- and gene-based therapy. Establishment of iPSC-based therapy for skin diseases requires efficient methodology for differentiating iPSCs into both keratinocytes and fibroblasts, the major cellular components of the skin, as well as the reconstruction of skin structures using these iPSC-derived skin components. We previously reported generation of keratinocytes from human iPSCs for use in the treatment of recessive dystrophic epidermolysis bullosa (RDEB) caused by mutations in the COL7A1 gene. Here, we developed a protocol for differentiating iPSCs into dermal fibroblasts, which also produce type VII collagen and therefore also have the potential to treat RDEB. Moreover, we generated in vitro 3D skin equivalents composed exclusively human iPSC-derived keratinocytes and fibroblasts for disease models and regenerative therapies for skin diseases, first demonstrating that iPSCs can provide the basis for modeling a human organ derived entirely from two different types of iPSC-derived cells.

One goal, different strategies--molecular and cellular approaches for the treatment of inherited skin fragility disorders

Epidermolysis bullosa (EB) is a heterogeneous group of inherited diseases characterized by the formation of blisters in the skin and mucosa. There is no cure or effective treatment for these potentially severe and fatal diseases. Over the past few years, several reports have proposed different molecular strategies as new therapeutic options for the management of EB. From classical vector-based gene therapy to cell-based strategies such as systemic application of bone marrow stem cells or local application of fibroblasts, a broad range of molecular approaches have been explored. This array also includes novel methods, such as protein replacement therapy, gene silencing and the use of induced pluripotent stem cells (iPCs). In this review, we summarize current concepts of how inherited blistering diseases might be treated in the future and discuss the opportunities, promises, concerns and risks of these innovative approaches.

Cell-based therapies for epidermolysis bullosa - from bench to bedside

Significant progress has been made over the past two decades in molecular genetics of epidermolysis bullosa (EB), a group of heritable blistering disorders, with diagnostic and prognostic implications. More recently, novel molecular approaches have been developed towards potential treatment of EB, with emphasis on gene-, protein-, and cell-based strategies. This overview highlights cell-based approaches that have recently been tested in pilot clinical trials, attesting to the potential of regenerative medicine for blistering skin diseases.

Topical application of recombinant type VII collagen incorporates into the dermal-epidermal junction and promotes wound closure

Patients with recessive dystrophic epidermolysis bullosa (RDEB) have incurable skin fragility, blistering, and skin wounds due to mutations in the gene that codes for type VII collagen (C7) that mediates dermal-epidermal adherence in human skin. In this study, we evaluated if topically applied human recombinant C7 (rC7) could restore C7 at the dermal-epidermal junction (DEJ) and enhance wound healing. We found that rC7 applied topically onto murine skin wounds stably incorporated into the newly formed DEJ of healed wounds and accelerated wound closure by increasing re-epithelialization. Topical rC7 decreased the expression of fibrogenic transforming growth factor-β2 (TGF-β2) and increased the expression of anti-fibrogenic TGF-β3. These were accompanied by the reduced expression of connective tissue growth factor, fewer α smooth muscle actin (α-SMA)-positive myofibroblasts, and less deposition of collagen in the healed neodermis, consistent with less scar formation. In addition, using a mouse model in which skin from C7 knock out mice was grafted onto immunodeficient mice, we showed that applying rC7 onto RDEB grafts with wounds restored C7 and anchoring fibrils (AFs) at the DEJ of the grafts and corrected the dermal-epidermal separation. The topical application of rC7 may be useful for treating patients with RDEB and patients who have chronic skin wounds.

Cell- and protein-based therapy approaches for epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a clinically heterogeneous heritable skin fragility disorder characterized by mechanically induced mucocutaneous blistering. On the molecular level DEB is caused by mutations leading to deficiency in collagen VII (CVII), a large extracellular protein building anchoring fibrils that attach the epidermis to the dermis. Severely affected patients suffer from wounds, which heal with excessive scarring causing mutilating deformities of hands and feet. The patients are also predisposed to development of aggressive squamous cell carcinomas at sites of chronic wounds. Currently no available therapies exist for this extremely disabling and stigmatizing disorder. We are developing and evaluating cell- and protein-based therapies for the management of DEB. Dermal fibroblasts are easy to propagate in vitro, they produce CVII, and they have immunomodulating capacities, which makes it possible to use allogeneic fibroblasts for therapy without risking major adverse effects from the host's immune system. Hence, fibroblasts, and fibroblast-like cells such as mesenchymal stromal cells, are prime candidates for cell-based DEB therapies. An alternative for management of disorders caused by defects in proteins with relatively low turnover rate is to introduce the protein de novo to the tissue by direct application of the protein. CVII is long-lived and expressed in moderate amounts in the skin; this makes injection of collagen VII protein a realistic approach for the treatment of DEB. Here we present methods and protocols that we are using for fibroblast- and recombinant CVII-based therapies of DEB in our model of this disease, the CVII hypomorphic mouse. These protocols are directed towards management of DEB but they can be easily adapted for the treatment of other skin fragility disorders.