Sustained phenotypic reversion of junctional epidermolysis bullosa dog keratinocytes: Establishment of an immunocompetent animal model for cutaneous gene therapy

Genetic diagnosis of epidermolysis bullosa: recommendations from an expert Spanish research group

Epidermolysis bullosa (EB) is a rare genetic disease that causes mucocutaneous fragility. It comprises a clinically and genetically heterogeneous group of disorder characterized by spontaneous or contact/friction-induced blistering. EB is classified into 4 types-simplex, junctional, dystrophic, and Kindler syndrome-and 30 subtypes. The disease is caused by defects in proteins implicated in dermal-epidermal adhesion. At least 19 genes have been characterized and more than 1000 mutations identified, thus rendering diagnosis complex. Molecular diagnosis of EB is the last stage of a laborious process that starts with a detailed clinical history compilation and careful procurement of a skin fresh biopsy that includes an area where the epidermis detaches from the dermis. The detachment area makes it possible to establish the cleavage plane by antigen mapping and, in the best scenario, to identify a single candidate gene to search for pathogenic mutations. The results of the molecular diagnosis enable the physician to provide appropriate genetic counseling (inheritance pattern, risk of recurrence, and options for prenatal and preimplantation diagnosis) and implement subsequent preventive programs, as well as to establish a reasonable clinical prognosis facilitating access to specific therapy and rehabilitation. Lastly, molecular diagnosis is essential for the participation of patients in clinical trials, a critical issue given the current incurable status of EB. The present guidelines aim to disseminate the procedure for diagnosing EB in our laboratory and thus avoid suboptimal or incomplete clinical diagnoses. The recommendations we provide are the result of more than 10 years' experience in the molecular diagnosis of EB in Spain.

Epidermolysis bullosa in animals: a review

Epidermolysis bullosa (EB) is a hereditary mechanobullous disease of animals and humans, characterized by an extreme fragility of the skin and mucous membranes. The main feature of EB in humans and animals is the formation of blisters and erosions in response to minor mechanical trauma. Epidermolysis bullosa is caused by mutations in the genes that code for structural proteins of the cytoskeleton of the basal keratinocytes or of the basement membrane zone. Based on the ultrastructural levels of tissue separation, EB is divided into the following three broad categories: epidermolysis bullosa simplex, junctional epidermolysis bullosa and dystrophic epidermolysis bullosa. Human types of EB are divided into several subtypes based on their ultrastructural changes and the mode of inheritance; subtypes are not fully established in animals. In humans, it is estimated that EB affects one in 17,000 live births; the frequency of EB in different animals species is not known. In all animal species, except in buffalo with epidermolysis bullosa simplex, multifocal ulcers are observed on the gums, hard and soft palates, mucosa of the lips, cheek mucosa and dorsum of the tongue. Dystrophic or absent nails, a frequent sign seen in human patients with EB, corresponds to the deformities and sloughing of the hooves in ungulates and to dystrophy or atrophy of the claws in dogs and cats. This review covers aspects of the molecular biology, diagnosis, classification, clinical signs and pathology of EB reported in animals.

Bioengineered skin humanized model of psoriasis

This protocol describes the generation of a skin humanized mouse model for psoriasis using bioengineering approaches. This method is relatively simple, highly reproducible and ensures the obtention of a large and homogenous number of engrafted animals bearing a portion of human skin with psoriatic phenotype. The technique can employ cells from skin biopsies and blood samples from non-related healthy human donors (allogeneic version), as well as skin and blood cells from psoriatic patients (autologous version). In both cases, the psoriatic phenotype was developed after intradermal administration of in vitro derived T1 lymphocytes along with Th17 recombinant cytokines, in conjunction with mild barrier disruption by tape-stripping. This skin-humanized model for psoriasis emerges as a powerful tool to study the mechanisms underlying the pathogenesis of the disease. More importantly, the feasibility of the system may allow the evaluation of different therapeutic compounds in an in vivo system, employing local and/or systemic administration.

Progress towards genetic and pharmacological therapies for keratin genodermatoses: current perspective and future promise

Hereditary keratin disorders of the skin and its appendages comprise a large group of clinically heterogeneous disfiguring blistering and ichthyotic diseases, primarily characterized by the loss of tissue integrity, blistering and hyperkeratosis in severely affected tissues. Pathogenic mutations in keratins cause these afflictions. Typically, these mutations in concert with characteristic features have formed the basis for improved disease diagnosis, prognosis and most recently therapy development. Examples include epidermolysis bullosa simplex, keratinopathic ichthyosis, pachyonychia congenita and several other tissue-specific hereditary keratinopathies. Understanding the molecular and genetic events underlying skin dysfunction has initiated alternative treatment approaches that may provide novel therapeutic opportunities for affected patients. Animal and in vitro disease modelling studies have shed more light on molecular pathogenesis, further defining the role of keratins in disease processes and promoting the translational development of new gene and pharmacological therapeutic strategies. Given that the molecular basis for these monogenic disorders is well established, gene therapy and drug discovery targeting pharmacological compounds with the ability to reinforce the compromised cytoskeleton may lead to promising new therapeutic strategies for treating hereditary keratinopathies. In this review, we will summarize and discuss recent advances in the preclinical and clinical modelling and development of gene, natural product, pharmacological and protein-based therapies for these disorders, highlighting the feasibility of new approaches for translational clinical therapy.

Inherited junctional epidermolysis bullosa (Herlitz type) in German black-headed mutton sheep

This report describes the microscopical, immunohistochemical and ultrastructural findings in the first ovine cases of the Herlitz type of inherited junctional epidermolysis bullosa. Sixteen German black-headed mutton lambs and one crossbred lamb had blisters and ulceration of the skin and mucous membranes in addition to alterations of the horn of the hooves. Microscopically, there was separation of the dermoepidermal junction, which was confirmed to be located in the lamina lucida of the basement membrane by electron microscopy. In areas of subepidermal splitting the hemidesmosomes were missing and in adjacent areas they appeared to be rudimentary and reduced in number. Immunohistochemistry for laminin 5 revealed a markedly reduced expression of this molecule on the dermal side of the blisters, while expression of collagen VII was normal.

Skin bioengineering: preclinical and clinical applications

Regenerative Medicine is an emerging field that combines basic research and clinical observations in order to identify the elements required to replace damaged tissues and organs in vivo and to stimulate the body's intrinsic regenerative capacity. Great benefits are expected in this field as researchers take advantage of the potential regenerative properties of both embryonic and adult stem cells, and more recently, of induced pluripotent stem cells. Bioengineered skin emerged mainly in response to a critical need for early permanent coverage of extensive burns. Later this technology was also applied to the treatment of chronic ulcers. Our group has established a humanized mouse model of skin grafting that involves the use of bioengineered human skin in immunodeficient mice. This model is suitable for the study of physiologic and pathologic cutaneous processes and the evaluation of treatment strategies for skin diseases, including protocols for gene and cell therapy and tissue engineering.

Molecular organization of the basement membrane zone

The dermal-epidermal basement membrane is a complex assembly of proteins that provide adhesion and regulate many important processes such as development, wound healing, and cancer progression. This contribution focuses on the structure and function of individual components of the basement membrane, how they assemble together, and how they participate in human tissues and diseases, with an emphasis on skin involvement. Understanding the composition and structure of the basement membrane provides insight into the pathophysiology of inherited blistering disorders, such as epidermolysis bullosa, and acquired bullous diseases, such as the pemphigoid group of autoimmune diseases and epidermolysis bullosa acquisita.

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.

Role of dermal-epidermal basement membrane zone in skin, cancer, and developmental disorders

The dermal-epidermal basement membrane zone is an important epithelial and stromal interface, consisting of an intricately organized collection of intracellular, transmembrane, and extracellular matrix proteins. The basement membrane zone has several main functions including acting as a permeability barrier, forming an adhesive interface between epithelial cells and the underlying matrix, and controlling cellular organization and differentiation. This article identifies key molecular players of the dermal-epidermal membrane zone, and highlights recent research studies that have identified structural and functional roles of these components in the context of various blistering, neoplastic, and developmental syndromes.

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.

Biological function of laminin-5 and pathogenic impact of its deficiency

The basement membrane glycoprotein laminin-5 is a key component of the anchoring complex connecting keratinocytes to the underlying dermis. It is secreted by keratinocytes as a cross-shaped heterotrimer of alpha3, beta3 and gamma2 chains and serves as a ligand of various transmembrane receptors, thereby regulating keratinocyte adhesion, motility and proliferation. In intact skin, laminin-5 provides essential links to both the hemidesmosomal alpha6beta4 integrin and the collagen type VII molecules which form the anchoring fibrils inserting into the dermis. If the basement membrane is injured, laminin-5 production increases rapidly. It then serves as a scaffold for cell migration, initiates the formation of hemidesmosomes and accelerates basement membrane restoration at the dermal-epidermal junction. Mutations of the laminin-5 genes or auto-antibodies against one of the subunits of laminin-5 may lead to a significant lack of this molecule in the epidermal basement membrane zone. The major contributions of laminin-5 to the resistance of the epidermis against frictional stress but also for basement membrane regeneration and repair of damaged skin are reflected by the phenotype of Herlitz junctional epidermolysis bullosa, which is caused by an inherited absence of functional laminin-5. This lethal disease becomes manifest in widespread blistering of skin and mucous membranes, impaired wound healing and chronic erosions containing exuberant granulation tissue. Here, we discuss current understanding of the biological functions of laminin-5, the pathogenic impact of its deficiency and implications on molecular approaches towards a therapy of junctional epidermolysis bullosa.

Modeling normal and pathological processes through skin tissue engineering

Skin tissue engineering emerged as an experimental regenerative therapy motivated primarily by the critical need for early permanent coverage of extensive burn injuries in patients with insufficient sources of autologous skin for grafting. With time, the approach evolved toward a wider range of applications including disease modeling. We have established a skin-humanized mouse model system consisting in bioengineered human-skin-engrafted immunodeficient mice. This new model allows to performing regenerative medicine, gene therapy, genomics, and pathology studies in a human context on homogeneous samples. Starting from skin cells (keratinocytes and fibroblasts) isolated from normal donor skin or patient's biopsies, we have been able to deconstruct-reconstruct several inherited skin disorders including genodermatoses and cancer-prone diseases in a large number of skin humanized mice. In addition, the model allows conducting studies in normal human skin to gain further insight into physiological processes such as wound healing or UV-responses.

Long-term Engraftment of Single Genetically Modified Human Epidermal Holoclones Enables Safety Pre-assessment of Cutaneous Gene Therapy

Predicting the risks of permanent gene therapy approaches involving the use of integrative gene-targeting vectors has become a critical issue after the unfortunate episode of a clinical trial in children with X-linked severe combined immunodeficiency (X-SCID). Safety pre-assessment of single isolated gene-targeted stem cells or their derivative clones able to regenerate their tissue of origin would be a major asset in addressing untoward gene therapy effects in advance. Human epidermal stem cells, which have extensive proliferative potential in vitro, theoretically offer such a possibility as a method of assessment. By means of optimized organotypic culture and grafting methods, we demonstrate the long-term in vivo regenerative capacity of single gene-targeted human epidermal stem cell clones (holoclones). Both histopathological analysis of holoclone-derived grafts in immunodeficient mice and retroviral insertion site mapping performed in the holoclone in vitro and after grafting provide proof of the feasibility of pre-assessing genotoxicity risks in isolated stem cells before transplantation into patients. Our results provide an experimental basis for previously untested assumptions about the in vivo behavior of epidermal stem cells prospectively isolated in vitro and pave the way for a safer approach to cutaneous gene therapy.

Cutaneous gene delivery

Over the past decade, many approaches to transferring genes into the skin have been investigated. However, most such approaches have been specifically aimed against genodermatosis, and have not produced sufficient results. The goal of such research is to develop a method in which genes are transferred easily, efficiently and stably into keratinocytes, especially into keratinocyte stem cells, and in which the transgene expression persists without a reaction from the host immune response. Although accidental development of cancer has occurred in trials of gene therapy for X-linked severe combined immunodeficiency (X-SCID), resulting in slowing of the progress of this research, the lessons of these setbacks have been applied to further research. Moreover, combined with the techniques acquired from tissue engineering, recent developments in our knowledge about stem cells will lead to new treatments for genodermatoses. The present review summarizes the methods by which therapeutic genes can be transferred into keratinocytes, with discussion of how gene transfer efficiency can be improved, with particular emphasis on disruption of the skin barrier function. It concludes with discussion of the challenges and prospects of keratinocyte gene therapy, in terms of achieving efficient and long-lasting therapeutic effects.

Evaluation of prenatal intra-amniotic LAMB3 gene delivery in a mouse model of Herlitz disease

Prenatal gene therapy has been considered for Herlitz junctional epidermolysis bullosa (H-JEB), a lethal genodermatosis caused by the absence of any of the three subunits of laminin-5, resulting from birth in widespread blistering and erosions of skin and mucosae. To investigate this strategy in an animal model, adenovirus type 5- and adeno-associated virus (AAV) type 2-derived vectors carrying a beta-galactosidase reporter gene or LAMB3 cDNA encoding the beta3 chain of laminin-5 were generated, tested for stability in amniotic fluid and evaluated in vitro on murine H-JEB keratinocytes, and in vivo by prenatal injection into the amniotic cavities of laminin-5 beta3-deficient mice. The different vectors were administered individually or combined at maximum doses on day 14 post coitum. Adenoviral vectors infected preferentially the foetal epidermis, whereas AAV delivered the transgene mainly to mucous membranes of the airways and the upper digestive tract. The LAMB3 transgene was expressed in target epithelia of newborn laminin-5 beta3-deficient mice, and the transgenic beta3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-5 in the basement membranes of skin and mucosae and in a lower extent of tissue separation in the skin. However, only combined delivery of the two vector types led to a minor increase of the life span of H-JEB mice. Failure to rescue diseased animals was, at least in part, due to abandonment of any conspicuous pup by the heterozygous mother. This is the first study of a prenatal gene therapy approach to a heritable blistering disorder. Although our findings indicate that prenatal combined administration of adenoviral and adeno-associated LAMB3 vectors provides therapeutic benefit to H-JEB mice, this animal model appears unsuitable for long-term investigations of the therapeutic concept.