Fibroblasts show more potential as target cells than keratinocytes in COL7A1 gene therapy of dystrophic epidermolysis bullosa

Histological and molecular restoration of type VII collagen in Recessive dystrophic epidermolysis bullosa mouse skin by topical injection of keratinocyte-like cells differentiated from human adipose-derived mesenchymal stromal cells

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin fragility disorder caused by mutations in the COL7A1 gene, which encodes type VII collagen (COL7), the main constituent of anchoring fibrils for attaching the epidermis to the dermis. Persistent skin erosions frequently result in intractable ulcers in RDEB patients. Adipose-derived mesenchymal stromal cells (AD-MSCs) are easily harvested in large quantities and have low immunogenicity. Therefore, they are suitable for clinical use, including applications involving allogeneic cell transplantation. Keratinocyte-like cells transdifferentiated from AD-MSCs (KC-AD-MSCs) express more COL7 than undifferentiated AD-MSCs and facilitate skin wound healing with less contracture. Therefore, these cells can be used for skin ulcer treatment in RDEB patients.

OBJECTIVE

We investigated whether KC-AD-MSCs transplantation ameliorated the RDEB phenotype severity in the grafted skin of a RDEB mouse model (col7a1-null) on the back of the immunodeficient mouse.

METHODS

KC-AD-MSCs were intradermally injected into the region surrounding the skin grafts, and this procedure was repeated after 7 days. After a further 7-day interval, the skin grafts were harvested.

RESULTS

Neodeposition of COL7 and generation of anchoring fibrils at the dermal-epidermal junction were observed, although experiments were based on qualitative.

CONCLUSION

KC-AD-MSCs may correct the COL7 insufficiency, repair defective/reduced anchoring fibrils, and improve skin integrity in RDEB patients.

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.

Current topics in Epidermolysis bullosa: Pathophysiology and therapeutic challenges

Epidermolysis bullosa (EB) is a group of inherited skin and mucosal fragility disorders resulting from mutations in genes encoding basement membrane zone (BMZ) components or proteins that maintain the integrity of BMZ and adjacent keratinocytes. More than 30 years have passed since the first causative gene for EB was identified, and over 40 genes are now known to be responsible for the protean collection of mechanobullous diseases included under the umbrella term of EB. Through the elucidation of disease mechanisms using human skin samples, animal models, and cultured cells, we have now reached the stage of developing more effective therapeutics for EB. This review will initially focus on what is known about blister wound healing in EB, since recent and emerging basic science data are very relevant to clinical translation and therapeutic strategies for patients. We then place these studies in the context of the latest information on gene therapy, read-through therapy, and cell therapy that provide optimism for improved clinical management of people living with EB.

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.

Ex vivo gene modification therapy for genetic skin diseases-recent advances in gene modification technologies and delivery

Genetic skin diseases, also known as genodermatoses, are inherited disorders affecting skin and constitute a large and heterogeneous group of diseases. While genodermatoses are rare with the prevalence rate of less than 1 in 50,000 - 200,000, they frequently occur at birth or early in life and are generally chronic, severe, and could be life-threatening. The quality of life of patients and their families are severely compromised by the negative psychosocial impact of disease, physical manifestations, and the lack or loss of autonomy. Currently, there are no curative treatments for these conditions. Ex vivo gene modification therapy that involves modification or correction of mutant genes in patients' cells in vitro and then transplanted back to patients to restore functional gene expression has being developed for genodermatoses. In this review, the ex vivo gene modification therapy strategies for genodermatoses are reviewed, focusing on current advances in gene modification and correction in patients' cells and delivery of genetically modified cells to patients with discussions on gene therapy trials which have been performed in this area.

hTERT-Driven Immortalization of RDEB Fibroblast and Keratinocyte Cell Lines Followed by Cre-Mediated Transgene Elimination

The recessive form of dystrophic epidermolysis bullosa (RDEB) is a crippling disease caused by impairments in the junctions of the dermis and the basement membrane of the epidermis. Using ectopic expression of hTERT/hTERT + BMI-1 in primary cells, we developed expansible cultures of RDEB fibroblasts and keratinocytes. We showed that they display the properties of their founders, including morphology, contraction ability and expression of the respective specific markers including reduced secretion of type VII collagen (C7). The immortalized keratinocytes retained normal stratification in 3D skin equivalents. The comparison of secreted protein patterns from immortalized RDEB and healthy keratinocytes revealed the differences in the contents of the extracellular matrix that were earlier observed specifically for RDEB. We demonstrated the possibility to reverse the genotype of immortalized cells to the state closer to the progenitors by the Cre-dependent hTERT switch off. Increased β-galactosidase activity and reduced proliferation of fibroblasts were shown after splitting out of transgenes. We anticipate our cell lines to be tractable models for studying RDEB from the level of single-cell changes to the evaluation of 3D skin equivalents. Our approach permits the creation of standardized and expandable models of RDEB that can be compared with the models based on primary cell cultures.

Cellular therapy options for genetic skin disorders with a focus on recessive dystrophic epidermolysis bullosa

INTRODUCTION

Combinatorial cell and gene therapies for life-threatening inherited skin disorders have shown tremendous potential for preclinical and clinical implementation with significant progress made for recessive dystrophic epidermolysis bullosa (RDEB). To date, various cell lineages including resident skin cells and adult stem cells have been investigated for gene and cell therapy for RDEB reaching the clinical trial stage.

SOURCES OF DATA

Sources of data are key recent literature, ClinicalTrials.gov, Clinicaltrialsregister.eu and pharma press releases.

AREAS OF AGREEMENT

Cell-based gene transfer using autologous patients' cells has demonstrated positive outcomes in preclinical and clinical trials and highlighted the importance of targeting resident skin stem cells to achieve a meaningful long-term effect. Additionally, adult stem cells, such as mesenchymal stromal cells, have the potential to ameliorate systemic manifestations of the disease.

AREAS OF CONTROVERSY

While proven safe, the clinical trials of localized treatment have reported only modest and transient improvements. On the other hand, the risks associated with systemic therapies remain high and should be carefully weighed against the potential benefits. It is unclear to what extent adult stem cells can contribute to skin regeneration/wound healing.

GROWING POINTS

Further research is warranted in order to fulfil the potential of cellular therapies for RDEB. The development of combinatorial gene and cell-based approaches is required to achieve long-term clinical benefits.

AREAS TIMELY FOR DEVELOPING RESEARCH

Induced pluripotent stem cells can potentially provide a valuable source of autologous patient material for cellular therapies. In addition, recent advances in the field of gene editing can overcome hurdles associated with conventional gene addition approaches.

DATA AVAILABILITY STATEMENT

No new data were generated or analysed in support of this review.

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.

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.

Manipulation of Transgene Expression in Fibroblast Cells by a Multifunctional Linear-Branched Hybrid Poly(β-Amino Ester) Synthesized through an Oligomer Combination Approach

Delivery of functional genetic materials into fibroblast cells to manipulate the transgene expression is of great significance in skin gene therapy. Despite numerous polymeric gene delivery systems having been developed, highly safe and efficient fibroblast gene transfection has not yet been achieved. Here, through a new linear oligomer combination strategy, linear poly(β-amino ester) oligomers are connected by the branching units, forming a new type of poly(β-amino ester). This new multifunctional linear-branched hybrid poly(β-amino ester) (LBPAE) shows high-performance fibroblast gene transfection. In human primary dermal fibroblasts (HPDFs) and mouse embryo fibroblasts (3T3s), ultrahigh transgene expression is achieved by LBPAE: up to 3292-fold enhancement in Gaussia luciferase (Gluc) expression and nearly 100% of green fluorescence protein expression are detected. Concurrently, LBPAE is of high in vitro biocompatibility. In depth mechanistic studies reveal that versatile LBPAE can navigate multiple extra- and intracellular barriers involved in the fibroblast gene transfection. More importantly, LBPAE can effectively deliver minicircle DNA encoding  COL7A1 gene (a large and functional gene construct) to substantially upregulate the expression of type VII collagen (C7) in HPDFs, demonstrating its great potential in the treatment of C7-deficiency related genodermatoses such as recessive dystrophic epidermolysis bullosa.

Amlexanox Enhances Premature Termination Codon Read-Through in COL7A1 and Expression of Full Length Type VII Collagen: Potential Therapy for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare monogenic blistering disorder caused by the lack of functional type VII collagen, leading to skin fragility and subsequent trauma-induced separation of the epidermis from the underlying dermis. A total of 46% of patients with RDEB harbor at least one premature termination codon (PTC) mutation in COL7A1, and previous studies have shown that aminoglycosides are able to overcome RDEB PTC mutations by inducing "read-through" and incorporation of an amino acid at the PTC site. However, aminoglycoside toxicity will likely prevent widespread clinical application. Here the FDA-approved drug amlexanox was tested for its ability to read-through PTC mutations in cells derived from patients with RDEB. Eight of 12 different PTC alleles responded to treatment and produced full length protein, in some cases more than 50% relative to normal controls. Read-through type VII collagen was readily detectable in cell culture media and also localized to the dermal-epidermal junction in organotypic skin culture. Amlexanox increased COL7A1 transcript and the phosphorylation of UPF-1, an RNA helicase associated with nonsense-mediated mRNA decay, suggesting that amlexanox inhibits nonsense-mediated mRNA decay in cells from patients with RDEB that respond to read-through treatment. This preclinical study demonstrates the potential of repurposing amlexanox for the treatment of patients with RDEB harboring PTC mutation in COL7A1.

CRISPR/Cas9-based genetic correction for recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe disorder caused by mutations to the COL7A1 gene that deactivate production of a structural protein essential for skin integrity. Haematopoietic cell transplantation can ameliorate some of the symptoms; however, significant side effects from the allogeneic transplant procedure can occur and unresponsive areas of blistering persist. Therefore, we employed genome editing in patient-derived cells to create an autologous platform for multilineage engineering of therapeutic cell types. The clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 system facilitated correction of an RDEB-causing COL7A1 mutation in primary fibroblasts that were then used to derive induced pluripotent stem cells (iPSCs). The resulting iPSCs were subsequently re-differentiated into keratinocytes, mesenchymal stem cells (MSCs) and haematopoietic progenitor cells using defined differentiation strategies. Gene-corrected keratinocytes exhibited characteristic epithelial morphology and expressed keratinocyte-specific genes and transcription factors. iPSC-derived MSCs exhibited a spindle morphology and expression of CD73, CD90 and CD105 with the ability to undergo adipogenic, chondrogenic and osteogenic differentiation in vitro in a manner indistinguishable from bone marrow-derived MSCs. Finally, we used a vascular induction strategy to generate potent definitive haematopoietic progenitors capable of multilineage differentiation in methylcellulose-based assays. In totality, we have shown that CRISPR/Cas9 is an adaptable gene-editing strategy that can be coupled with iPSC technology to produce multiple gene-corrected autologous cell types with therapeutic potential for RDEB.

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.

Analysis of the functional consequences of targeted exon deletion in COL7A1 reveals prospects for dystrophic epidermolysis bullosa therapy

Genetically evoked deficiency of collagen VII causes dystrophic epidermolysis bullosa (DEB)-a debilitating disease characterized by chronic skin fragility and progressive fibrosis. Removal of exons carrying frame-disrupting mutations can reinstate protein expression in genetic diseases. The therapeutic potential of this approach is critically dependent on gene, protein, and disease intrinsic factors. Naturally occurring exon skipping in COL7A1, translating collagen VII, suggests that skipping of exons containing disease-causing mutations may be feasible for the treatment of DEB. However, despite a primarily in-frame arrangement of exons in the COL7A1 gene, no general conclusion of the aptitude of exon skipping for DEB can be drawn, since regulation of collagen VII functionality is complex involving folding, intra- and intermolecular interactions. To directly address this, we deleted two conceptually important exons located at both ends of COL7A1, exon 13, containing recurrent mutations, and exon 105, predicted to impact folding. The resulting recombinantly expressed proteins showed conserved functionality in biochemical and in vitro assays. Injected into DEB mice, the proteins promoted skin stability. By demonstrating functionality of internally deleted collagen VII variants, our study provides support of targeted exon deletion or skipping as a potential therapy to treat a large number of individuals with DEB.

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.

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.

Dystrophic epidermolysis bullosa: a review

Dystrophic epidermolysis bullosa is a rare inherited blistering disorder caused by mutations in the COL7A1 gene encoding type VII collagen. The deficiency and/or dysfunction of type VII collagen leads to subepidermal blistering immediately below the lamina densa, resulting in mucocutaneous fragility and disease complications such as intractable ulcers, extensive scarring, malnutrition, and malignancy. The disease is usually diagnosed by immunofluorescence mapping and/or transmission electron microscopy and subsequently subclassified into one of 14 subtypes. This review provides practical knowledge on the disease, including new therapeutic strategies.

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.

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.

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.

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.

TALEN-based gene correction for epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is characterized by a functional deficit of type VII collagen protein due to gene defects in the type VII collagen gene (COL7A1). Gene augmentation therapies are promising, but run the risk of insertional mutagenesis. To abrogate this risk, we explored the possibility of using engineered transcription activator-like effector nucleases (TALEN) for precise genome editing. We report the ability of TALEN to induce site-specific double-stranded DNA breaks (DSBs) leading to homology-directed repair (HDR) from an exogenous donor template. This process resulted in COL7A1 gene mutation correction in primary fibroblasts that were subsequently reprogrammed into inducible pluripotent stem cells and showed normal protein expression and deposition in a teratoma-based skin model in vivo. Deep sequencing-based genome-wide screening established a safety profile showing on-target activity and three off-target (OT) loci that, importantly, were at least 10 kb from a coding sequence. This study provides proof-of-concept for TALEN-mediated in situ correction of an endogenous patient-specific gene mutation and used an unbiased screen for comprehensive TALEN target mapping that will cooperatively facilitate translational application.

Management of severe epidermolysis bullosa by haematopoietic transplant: principles, perspectives and pitfalls

People with severe forms of epidermolysis bullosa (EB) develop widespread blistering and progressively debilitating multisystem complications that may result in a shortened lifespan. As some wounds in EB individuals are difficult or impossible to access with topical therapy, we examined the potential of systemic therapy with normal haematopoietic stem cells. In both animal models and children with EB, healthy donor cells from the haematopoietic graft migrated to the injured skin; simultaneously, there was an increase in the production of skin-specific structural proteins deficient in EB, increased skin integrity and reduced tendency to blister formation. Even though the majority of evaluable individuals have had a positive response in skin healing, frequently changing their quality of life, the improvement in lifestyle has been varied and the overall clinical response incomplete. To change the current amelioration of disease into a full cure, we propose to (i) increase safety as well as efficacy of haematopoietic cell transplant (HCT) using co-infusion of mesenchymal stromal/stem cells with haematopoietic stem cells and non-myeloablative conditioning for transplant; (ii) optimize homing of donor cells into the skin erosions in animal models of EB; and (iii) discover and test new drugs for EB therapy using patient-specific induced pluripotent stem cells. We conclude that although HCT has always been a risky treatment restricted to those with serious life-threatening or debilitating diseases, by most benchmarks, the results of HCT in EB have shown that HCT has the potential of being a durable, systemic therapy for people with severe forms of EB.

Remodeling of the dermal-epidermal junction in bilayered skin constructs after silencing the expression of the p.R2622Q and p.G2623C collagen VII mutants

The integrity of skin depends on a complex system of extracellular matrix molecules that form a biological scaffold. One of its elements is the dermal basement membrane that provides a link between the epidermis and the dermis. Mutations in collagen VII, a key component of the dermal membrane zone, are associated with dystrophic epidermolysis bullosa. Although it has been proposed that silencing the mutated COL7A1 allele is a promising approach to restore the dermal basement membrane zone formed in the presence of collagen VII mutants, limitations exist to testing this proposal. Here, we employed a model that utilized skin-like constructs in which engineered collagen VII mutant chains harboring the R2622Q or G2623C substitution were expressed conditionally, but the wild-type chains were expressed unconditionally. We demonstrated that switching off the production of the mutant collagen VII chains in skin constructs restores the organization of collagen VII and laminin 332 deposits in the dermal-epidermal junction to the level of control. We also demonstrated that remodeling of collagen IV deposits was not fully effective after silencing the expression of collagen VII mutants. Thus, our study suggests that while silencing mutant alleles of COL7A1 may repair critical elements of the affected dermal basement membrane, it may not be sufficient to fully remodel its entire architecture initially formed in the presence of the mutant collagen VII chains.

Correction of dog dystrophic epidermolysis bullosa by transplantation of genetically modified epidermal autografts

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin blistering condition caused by mutations in the gene coding for collagen type VII. Genetically engineered RDEB dog keratinocytes were used to generate autologous epidermal sheets subsequently grafted on two RDEB dogs carrying a homozygous missense mutation in the col7a1 gene and expressing baseline amounts of the aberrant protein. Transplanted cells regenerated a differentiated and vascularized auto-renewing epidermis progressively repopulated by dendritic cells and melanocytes. No adverse immune reaction was detected in either dog. In dog 1, the grafted epidermis firmly adhered to the dermis throughout the 24-month follow-up, which correlated with efficient transduction (100%) of highly clonogenic epithelial cells and sustained transgene expression. In dog 2, less efficient (65%) transduction of primary keratinocytes resulted in a loss of the transplanted epidermis and graft blistering 5 months after transplantation. These data provide the proof of principle for ex vivo gene therapy of RDEB patients with missense mutations in collagen type VII by engraftment of the reconstructed epidermis, and demonstrate that highly efficient transduction of epidermal stem cells is crucial for successful gene therapy of inherited skin diseases in which correction of the genetic defect confers no major selective advantage in cell culture.

Epidermal and dermal integration into sphere-templated porous poly(2-hydroxyethyl methacrylate) implants in mice

Percutaneous medical devices remain susceptible to infection and failure. We hypothesize that healing of the skin into the percutaneous device will provide a seal, preventing bacterial attachment, biofilm formation, and subsequent device failure. Porous poly(2-hydroxyethyl methacrylate) [poly(HEMA)] with sphere-templated pores (40 microm) and interconnecting throats (16 microm) were implanted in normal C57BL/6 mice for 7, 14, and 28 days. Poly(HEMA) was either untreated, keeping the surface nonadhesive for cells and proteins, or modified with carbonyldiimidazole (CDI) or CDI reacted with laminin 332 to enhance adhesion. No clinical signs of infection were observed. Epidermal and dermal response within the poly(HEMA) pores was evaluated using light and transmission electron microscopy. Cells (keratinocytes, fibroblasts, endothelial cells, inflammatory cells) and basement membrane proteins (laminin 332, beta4 integrin, type VII collagen) could be demonstrated within the poly(HEMA) pores of all implants. Blood vessels and dermal collagen bundles were evident in all of the 14- and 28-day implants. Fibrous capsule formation and permigration were not observed. Sphere-templated polymers with 40 microm pores demonstrate an ability to recapitulate key elements of both the dermal and the epidermal layers of skin. Our morphological findings indicate that the implant model can be used to study the effects of biomaterial pore size, pore interconnect (throat) size, and surface treatments on cutaneous biointegration. Further, this model may be used for bacterial challenge studies.

Overview of epidermolysis bullosa

Epidermolysis bullosa (EB) is classified into major types - EB simplex (EBS), junctional EB (JEB) and dystrophic EB (DEB) - on the basis of the level of tissue separation within the cutaneous basement membrane zone. Recent advances in research on EB have led to the identification of 10 genes responsible for EB. The Japanese Ministry of Health, Labor and Welfare has designated JEB and DEB, but not EBS, as specified diseases. However, EBS has a lethal variant and should also be registered as a specified disease. In the Third Consensus Meeting on the Diagnosis and Classification of EB held in Vienna in 2007, it was recommended that Kindler syndrome should be classified as a subtype of EB. Corrective gene therapy is the most ideal therapy for EB, but much more research is required before it can be developed and used in clinical practice. Cell-based therapies using fibroblasts and bone marrow cells have recently attracted considerable attention.

Gene therapy for recessive dystrophic epidermolysis bullosa

Among the severe genetic disorders of the skin that are suitable for gene and cell therapy, most efforts have been made in the treatment of blistering diseases including dystrophic epidermolysis bullosa. This condition can be recessively or dominantly inherited, depending on the nature and position of the mutation or mutations in the gene encoding type VII collagen. At present, there is no specific treatment for recessive dystrophic epidermolysis bullosa, and gene and cell therapy approaches hold great promise. This article discusses the different gene therapy approaches that have been used for the treatment of this disease and the new perspectives that they open.

Keratinocyte-/fibroblast-targeted rescue of Col7a1-disrupted mice and generation of an exact dystrophic epidermolysis bullosa model using a human COL7A1 mutation

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe hereditary bullous disease caused by mutations in COL7A1, which encodes type VII collagen (COL7). Col7a1 knockout mice (COL7(m-/-)) exhibit a severe RDEB phenotype and die within a few days after birth. Toward developing novel approaches for treating patients with RDEB, we attempted to rescue COL7(m-/-) mice by introducing human COL7A1 cDNA. We first generated transgenic mice that express human COL7A1 cDNA specifically in either epidermal keratinocytes or dermal fibroblasts. We then performed transgenic rescue experiments by crossing these transgenic mice with COL7(m+/-) heterozygous mice. Surprisingly, human COL7 expressed by keratinocytes or by fibroblasts was able to rescue all of the abnormal phenotypic manifestations of the COL7(m-/-) mice, indicating that fibroblasts as well as keratinocytes are potential targets for RDEB gene therapy. Furthermore, we generated transgenic mice with a premature termination codon expressing truncated COL7 protein and performed the same rescue experiments. Notably, the COL7(m-/-) mice rescued with the human COL7A1 allele were able to survive despite demonstrating clinical manifestations very similar to those of human RDEB, indicating that we were able to generate surviving animal models of RDEB with a mutated human COL7A1 gene. This model has great potential for future research into the pathomechanisms of dystrophic epidermolysis bullosa and the development of gene therapies for patients with dystrophic epidermolysis bullosa.

Progress in heritable skin diseases: translational implications of mutation analysis and prospects of molecular therapies*

Epidermolysis bullosa, a group of blistering disorders, serves as the paradigm of the tremendous progress made in understanding the molecular genetics of heritable skin diseases. Mutations in 10 distinct genes have been disclosed in the classic forms of epidermolysis bullosa, and the level of expression of the mutated genes within the cutaneous basement membrane zone, the types and combinations of mutations and their consequences at the mRNA and protein levels, when placed in the context of the individual's genetic background and exposure to environmental trauma, all determine the subtype and the phenotypic severity in each case. The translational implications of mutation analysis include improved diagnosis and subclassification, refined genetic counseling of families at risk, and development of DNA-based pre natal and preimplantation genetic diagnosis. The prospects of molecular therapies for epidermolysis bullosa include further development of strategies for gene therapy, protein replacement therapy and cell-based therapies, including stem cell therapy and bone marrow transfer. Collectively, advances in the molecular genetics of heritable skin diseases clearly emphasize the value of basic research for improved diagnostics and patient care for genetic skin diseases.

Mechanisms of fibroblast cell therapy for dystrophic epidermolysis bullosa: high stability of collagen VII favors long-term skin integrity

Here, we report on the first systematic long-term study of fibroblast therapy in a mouse model for recessive dystrophic epidermolysis bullosa (RDEB), a severe skin-blistering disorder caused by loss-of-function of collagen VII. Intradermal injection of wild-type (WT) fibroblasts in >50 mice increased the collagen VII content at the dermal-epidermal junction 3.5- to 4.7-fold. Although the active biosynthesis lasted <28 days, collagen VII remained stable and dramatically improved skin integrity and resistance to mechanical forces for at least 100 days, as measured with a digital 3D-skin sensor for shear forces. Experiments using species-specific antibodies, collagen VII-deficient fibroblasts, gene expression analyses, and cytokine arrays demonstrated that the injected fibroblasts are the major source of newly deposited collagen VII. Apart from transitory mild inflammation, no adverse effects were observed. The cells remained within an area Collapse

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MESH Headings

• Animals
• Animals, Newborn
• Blotting, Western
• Cell- and Tissue-Based Therapy/methods
• Cells, Cultured
• Collagen Type VII/metabolism
• Epidermolysis Bullosa Dystrophica/metabolism
• Epidermolysis Bullosa Dystrophica/pathology
• Epidermolysis Bullosa Dystrophica/therapy
• Fibroblasts/metabolism
• Fibroblasts/physiology
• Fibroblasts/ultrastructure
• Flow Cytometry
• Humans
• In Situ Nick-End Labeling
• Mice
• Mice, Transgenic
• Microscopy, Electron, Transmission
• Reverse Transcriptase Polymerase Chain Reaction
• Skin/metabolism
• Skin/pathology

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Affiliation(s)

Johannes S Kern Deparment of Dermatology, University Medical Center Freiburg, Freiburg, Germany
Stefan Loeckermann
Anja Fritsch
Ingrid Hausser
Wera Roth
Thomas M Magin
Claudia Mack
Marcel L Müller
Oliver Paul
Patrick Ruther
Leena Bruckner-Tuderman

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Transgene-specific host responses in cutaneous gene therapy: the role of cells expressing the transgene

A major issue in long-term gene therapy is host immune responses to therapeutic cells when transgene encodes a potential antigen. The nature of these responses depends on several factors including the type of cell and tissue expressing the transgene. Keratinocytes and fibroblasts, which are known to display distinct immunogenic profiles, are both potential targets for transgene expression in cutaneous gene therapy. However, whether there is an immunological advantage in targeting one cell type over the other is not known. To study the effect of cell type on transgene-specific host responses independent of antigen levels or methods of gene transfer and transplantation, we used a skin transplantation model in which transgene expression can be targeted transgene to either keratinocytes or fibroblasts. Although targeting an antigen to either cell type resulted in the induction of immune responses, these responses differed significantly. Transgenic keratinocytes were rejected acutely by a dominant Th2 response, while in the majority of grafted animals transgenic fibroblasts failed to induce acute rejection despite the induction of Th1 type inflammation in the graft. In a small number of mice, transgenic fibroblasts persisted for at least 20 weeks despite elicitation of antigen-specific responses. Therefore, fibroblasts may be an immunologically preferred target over keratinocytes for cutaneous gene therapy.

Epidermolysis bullosa: prospects for cell-based therapies

Heritable forms of epidermolysis bullosa (EB) are characterized by chronic, lifelong blistering and erosions due to mutations in 10 distinct genes expressed at the cutaneous basement membrane zone. No specific treatment for this group of intractable diseases is currently available. Recent progress in molecular therapies has indicated that cell-based approaches may potentially offer amelioration--and perhaps even cure--for afflicted individuals. In this issue, Wong et al. (2008) demonstrate the feasibility of direct intradermal injection of allogeneic fibroblasts to the lesional skin of patients with recessive dystrophic EB, with improvement in skin fragility.

Bone marrow cell transfer into fetal circulation can ameliorate genetic skin diseases by providing fibroblasts to the skin and inducing immune tolerance

Recent studies have shown that skin injury recruits bone marrow-derived fibroblasts (BMDFs) to the site of injury to accelerate tissue repair. However, whether uninjured skin can recruit BMDFs to maintain skin homeostasis remains uncertain. Here, we investigated the appearance of BMDFs in normal mouse skin after embryonic bone marrow cell transplantation (E-BMT) with green fluorescent protein-transgenic bone marrow cells (GFP-BMCs) via the vitelline vein, which traverses the uterine wall and is connected to the fetal circulation. At 12 weeks of age, mice treated with E-BMT were observed to have successful engraftment of GFP-BMCs in hematopoietic tissues accompanied by induction of immune tolerance against GFP. We then investigated BMDFs in the skin of the same mice without prior injury and found that a significant number of BMDFs, which generate matrix proteins both in vitro and in vivo, were recruited and maintained after birth. Next, we performed E-BMT in a dystrophic epidermolysis bullosa mouse model (col7a1(-/-)) lacking type VII collagen in the cutaneous basement membrane zone. E-BMT significantly ameliorated the severity of the dystrophic epidermolysis bullosa phenotype in neonatal mice. Type VII collagen was deposited primarily in the follicular basement membrane zone in the vicinity of the BMDFs. Thus, gene therapy using E-BMT into the fetal circulation may offer a potential treatment option to ameliorate genetic skin diseases that are characterized by fibroblast dysfunction through the introduction of immune-tolerated BMDFs.

An approach to achieve long-term expression in skin gene therapy

For gene therapy purposes, the skin is an attractive organ to target for systemic delivery of therapeutic proteins to treat systemic diseases, skin diseases, or skin cancer. To achieve long-term stable expression of a therapeutic gene in keratinocytes (KC), we have developed an approach using a bicistronic retroviral vector expressing the desired therapeutic gene linked to a selectable marker (multidrug resistant gene, MDR) that is then introduced into KC and fibroblasts (FB) to create genetically modified human skin equivalent (HSE). After grafting the HSE onto immunocompromised mice, topical colchicine treatment is used to select and enrich for genetically modified keratinocyte stem cells (KSC) that express MDR and are resistant to colchicine's antimitotic effects. Both the apparatus for topical colchicine delivery and the colchicine doses have been optimized for application to human skin. This approach can be validated by systemic delivery of therapeutic factors such as erythropoietin and the antihypertensive atrial natriuretic peptide.

Potential of fibroblast cell therapy for recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited skin-blistering disorder caused by mutations in the COL7A1 gene that lead to reduced type-VII collagen and defective anchoring fibrils at the dermal-epidermal junction (DEJ). Presently there are no effective treatments for this disorder. Recent mouse studies have shown that intradermal injections of normal human fibroblasts can generate new human type-VII collagen and anchoring fibrils at the DEJ. To assess potential clinical benefits in humans, we gave single intradermal injections of allogeneic fibroblasts to five subjects with RDEB. We noted increased type-VII collagen at the DEJ at 2 weeks and at 3 months following injection and increased anchoring fibrils, although none of these had normal morphology. No adverse effects, clinical or immunopathologic, were noted. We believe the major effect of allogeneic fibroblasts is to increase the recipients' own COL7A1 mRNA levels with greater deposition of mutant type-VII collagen at the DEJ and formation of additional rudimentary anchoring fibrils. Nevertheless, this mutant protein may be partially functional and capable of increasing adhesion at the DEJ. This is the first study demonstrating that intradermal injections of allogeneic fibroblasts have therapeutic potential in human subjects with RDEB.