Gene-Corrected Fibroblast Therapy for Recessive Dystrophic Epidermolysis Bullosa using a Self-Inactivating COL7A1 Retroviral Vector

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.

Twin prime editing mediated exon skipping/reinsertion for restored collagen VII expression in recessive dystrophic epidermolysis bullosa

Gene editing nucleases, base editors, and prime editors are potential locus specific genetic treatment strategies for recessive dystrophic epidermolysis bullosa (RDEB); however, many RDEB COL7A1 mutations are unique, making the development of personalized editing reagents challenging. 270 of the ∼320 COL7A1 EB mutations reside in exons that can be skipped, and antisense oligonucleotides (ASO) and gene editing nucleases have been used to create in-frame deletions. ASOs are transient and nucleases generate deleterious double stranded DNA breaks (DSB) and uncontrolled mixtures of allele products. We developed a twin prime editing (twinPE) strategy using the PEmax and recently evolved PE6 prime editors and dual prime editing guide RNAs flanking COL7A1 exon five. Prime editing-mediated deletion of exon 5 with a homozygous premature stop codon was achieved in RDEB fibroblasts, keratinocytes, and iPSC with minimal DSBs, and collagen type VII (C7) protein was restored. TwinPE can replace the target exon with recombinase attachment sequences, and we exploited this to re-insert a normal copy of exon 5 using the Bxb1 recombinase. These findings demonstrate that twinPE can facilitate locus-specific, predictable, in-frame deletions and sequence replacement with few DSBs as a strategy that may enable a single therapeutic agent to treat multiple RDEB patient cohorts.

Emerging Gene Therapeutics for Epidermolysis Bullosa under Development

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

Advances in Genetic Reprogramming: Prospects from Developmental Biology to Regenerative Medicine

The foundations of cell reprogramming were laid by Yamanaka and co-workers, who showed that somatic cells can be reprogrammed into pluripotent cells (induced pluripotency). Since this discovery, the field of regenerative medicine has seen advancements. For example, because they can differentiate into multiple cell types, pluripotent stem cells are considered vital components in regenerative medicine aimed at the functional restoration of damaged tissue. Despite years of research, both replacement and restoration of failed organs/ tissues have remained elusive scientific feats. However, with the inception of cell engineering and nuclear reprogramming, useful solutions have been identified to counter the need for compatible and sustainable organs. By combining the science underlying genetic engineering and nuclear reprogramming with regenerative medicine, scientists have engineered cells to make gene and stem cell therapies applicable and effective. These approaches have enabled the targeting of various pathways to reprogramme cells, i.e., make them behave in beneficial ways in a patient-specific manner. Technological advancements have clearly supported the concept and realization of regenerative medicine. Genetic engineering is used for tissue engineering and nuclear reprogramming and has led to advances in regenerative medicine. Targeted therapies and replacement of traumatized , damaged, or aged organs can be realized through genetic engineering. Furthermore, the success of these therapies has been validated through thousands of clinical trials. Scientists are currently evaluating induced tissue-specific stem cells (iTSCs), which may lead to tumour-free applications of pluripotency induction. In this review, we present state-of-the-art genetic engineering that has been used in regenerative medicine. We also focus on ways that genetic engineering and nuclear reprogramming have transformed regenerative medicine and have become unique therapeutic niches.

Skin Allograft after Bone Marrow Transplantation of Patient with Recessive Dystrophic Epidermolysis Bullosa

In this study, we present a 26-year-old woman with case presentation of recessive dystrophic epidermolysis bullosa who had developed squamous cell carcinoma. The patient underwent bone marrow transplant and skin grafting with the same bone marrow donor. After excision of squamous cell carcinoma and skin grafting, no tumor was observed; thus, chemotherapy and radiation were no longer needed.

Therapeutic base editing and prime editing of COL7A1 mutations in recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin fragility disorder caused by loss-of-function mutations in the COL7A1 gene, which encodes type VII collagen (C7), a protein that functions in skin adherence. From 36 Korean RDEB patients, we identified a total of 69 pathogenic mutations (40 variants without recurrence), including point mutations (72.5%) and insertion/deletion mutations (27.5%). For fibroblasts from two patients (Pat1 and Pat2), we applied adenine base editors (ABEs) to correct the pathogenic mutation of COL7A1 or to bypass a premature stop codon in Pat1-derived primary fibroblasts. To expand the targeting scope, we also utilized prime editors (PEs) to correct the COL7A1 mutations in Pat1- and Pat2-derived fibroblasts. Ultimately, we found that transfer of edited patient-derived skin equivalents (i.e., RDEB keratinocytes and PE-corrected RDEB fibroblasts from the RDEB patient) into the skin of immunodeficient mice led to C7 deposition and anchoring fibril formation within the dermal-epidermal junction, suggesting that base editing and prime editing could be feasible strategies for ex vivo gene editing to treat RDEB.

Current developments in gene therapy for epidermolysis bullosa

INTRODUCTION

The genodermatosis epidermolysis bullosa (EB) is a monogenetic disease, characterized by severe blister formation on the skin and mucous membranes upon minimal mechanical trauma. Causes for the disease are mutations in genes encoding proteins that are essential for skin integrity. In EB, one of these proteins is either functionally impaired or completely absent. Therefore, the development and improvement of DNA and RNA-based therapeutic approaches for this severe blistering skin disease is mandatory to achieve a treatment option for the patients.

AREAS COVERED

Currently, there are several forms of DNA/RNA therapies potentially feasible for EB. Whereas some of them are still at the preclinical stage, others are clinically advanced and have already been applied to patients. In particular, this is the case for a cDNA replacement approach successfully applied for a small number of patients with junctional EB.

EXPERT OPINION

The heterogeneity of EB justifies the development of therapeutic options with distinct modes of action at a DNA or RNA level. Besides, splicing-modulating therapies, based on RNA trans-splicing or short antisense oligonucleotides, especially designer nucleases, have steadily improved in efficiency and safety and thus likely represent the most promising gene therapy tool in the near future.

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.

Review of the Latest Methods of Epidermolysis Bullosa and Other Chronic Wounds Treatment Including BIOOPA Dressing

Epidermolysis bullosa (EB) is a hereditary genetic skin disorder, classified as a type of genodermatosis, which causes severe, chronic skin blisters associated with painful and potentially life-threatening complications. Currently, there is no effective therapy or cure for EB. However, over the past decade, there have been several important advances in treatment methods, which are now approaching clinical application, including gene therapy, protein replacement therapy, cell therapy (allogeneic fibroblasts, mesenchymal stromal cells), bone marrow stem cell transplant, culture/vaccination of revertant mosaic keratinocytes, gene editing/engineering, and the clinical application of inducible pluripotent stem cells. Tissue engineering scientists are developing materials that mimic the structure and natural healing process to promote skin reconstruction in the event of an incurable injury. Although a cure for EB remains elusive, recent data from animal models and preliminary human clinical trials have raised the expectations of patients, clinicians, and researchers, where modifying the disease and improving patients’ quality of life are now considered attainable goals. In addition, the lessons learned from the treatment of EB may improve the treatment of other genetic diseases.

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.

Advances in gene therapy and their application to skin diseases: A review

With recent advances in genetic engineering technology, gene therapy is now being considered as a treatment not only for congenital diseases but also acquired diseases, such as cancer. Gene therapeutic agents for hereditary immune disorders, haemophilia, retinal diseases, neurodegenerative diseases, and lymphoma have been approved in the United States and Europe. In the field of dermatology, clinical trials of gene therapy have been conducted, because the skin is an easily accessible organ that represents an attractive tissue for gene therapy. In recent years, gene therapy has been attempted for a variety of skin diseases, such as genodermatoses (including epidermolysis bullosa and Netherton syndrome), cutaneous lymphoma, and malignant melanoma. As a result, it is difficult to grasp the current status of gene therapy in dermatology. This review focuses on each of the gene-transfer techniques currently in use and describes the current status of gene therapy for skin diseases using each technology.

Gene Replacement Therapies for Genodermatoses: A Status Quo

Epidermolysis bullosa (EB) is a genodermatosis, characterized by the formation of extended blisters and lesions on the skin and mucous membranes upon minimal mechanical trauma. The disease is caused by mutations in genes encoding proteins that are essential for skin stability. Functional impairment, reduction, or absence of one of these proteins results in skin fragility due to reduced connectivity between dermis and epidermis. Currently, gene therapy represents the only treatment option with the potential to cure this severe blistering skin disease. Two promising forms of gene therapy are potentially feasible for EB: gene replacement and genome editing. While genome editing for genodermatoses remains at the preclinical stage, gene replacement approaches are clinically advanced and have been applied already to a small number of patients with junctional and dystrophic forms of EB. Here, the viral transduction of the “wild-type” transgene into skin stem cells, followed by autologous grafting of corrected epidermal sheets, led to the regeneration of stable skin. Recent developments regarding designer nuclease-based gene editing strategies enable the establishment of alternative options to restore the gene function in genodermatoses. This is particularly true in cases wherein genetic constellation hinders gene therapy-based gene replacement.

Exploring the potential of the recombinant human collagens for biomedical and clinical applications: a short review

Natural animal collagen and its recombinant collagen are favourable replacements in human tissue engineering due to their remarkable biomedical property. However, this exploitation is largely restricted due to the potential of immunogenicity and virus contamination. Exploring new ways to produce human collagen is fundamental to its biomedical and clinical application. All human fibrillar collagen molecules have three polypeptide chains constructed from a repeating Gly-Xaa-Yaa triplet, where Xaa and Yaa represent one random amino acid. Using cDNA techniques to modify several repeat sequences of the cDNA fragment, a novel human collagen, named recombinant human-like collagen (rHLC), with low immunogenicity and little risk from hidden virus can be engineered and notably tailored to specific applications. Human-like collagen (HLC) was initially used as a coating to modify the tissue engineering scaffold, and then used as the scaffold after cross-link agents were added to increase its mechanical strength. Due to its good biocompatibility, low immunogenicity, stabilised property, and the ability of mass production, HLC has been widely used in skin injury treatments, vascular scaffolds engineering, cartilage, bone defect repair, skincare, haemostatic sponge, and drug delivery, including coating with medical nanoparticles. In this review, we symmetrically reviewed the development, recent advances in design and application of HLC, and other recombinant human collagen-based biomedicine potentials. At the end, future improvements are also discussed.

Epidermolysis bullosa

Epidermolysis bullosa (EB) is an inherited, heterogeneous group of rare genetic dermatoses characterized by mucocutaneous fragility and blister formation, inducible by often minimal trauma. A broad phenotypic spectrum has been described, with potentially severe extracutaneous manifestations, morbidity and mortality. Over 30 subtypes are recognized, grouped into four major categories, based predominantly on the plane of cleavage within the skin and reflecting the underlying molecular abnormality: EB simplex, junctional EB, dystrophic EB and Kindler EB. The study of EB has led to seminal advances in our understanding of cutaneous biology. To date, pathogenetic mutations in 16 distinct genes have been implicated in EB, encoding proteins influencing cellular integrity and adhesion. Precise diagnosis is reliant on correlating clinical, electron microscopic and immunohistological features with mutational analyses. In the absence of curative treatment, multidisciplinary care is targeted towards minimizing the risk of blister formation, wound care, symptom relief and specific complications, the most feared of which - and also the leading cause of mortality - is squamous cell carcinoma. Preclinical advances in cell-based, protein replacement and gene therapies are paving the way for clinical successes with gene correction, raising hopes amongst patients and clinicians worldwide.

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.

CRISPR/Cas9-based targeted genome editing for correction of recessive dystrophic epidermolysis bullosa using iPS cells

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited skin disorder caused by mutations in the COL7A1 gene encoding type VII collagen (C7). The spectrum of severity depends on the type of mutation in the COL7A1 gene. C7 is the major constituent of anchoring fibrils (AFs) at the basement membrane zone (BMZ). Patients with RDEB lack functional C7 and have severely impaired dermal-epidermal stability, resulting in extensive blistering and open wounds on the skin that greatly affect the patient's quality of life. There are currently no therapies approved for the treatment of RDEB. Here, we demonstrated the correction of mutations in exon 19 (c.2470insG) and exon 32 (c.3948insT) in the COL7A1 gene through homology-directed repair (HDR). We used the clustered regulatory interspaced short palindromic repeats (CRISPR) Cas9-gRNAs system to modify induced pluripotent stem cells (iPSCs) derived from patients with RDEB in both the heterozygous and homozygous states. Three-dimensional human skin equivalents (HSEs) were generated from gene-corrected iPSCs, differentiated into keratinocytes (KCs) and fibroblasts (FBs), and grafted onto immunodeficient mice, which showed normal expression of C7 at the BMZ as well as restored AFs 2 mo postgrafting. Safety assessment for potential off-target Cas9 cleavage activity did not reveal any unintended nuclease activity. Our findings represent a crucial advance for clinical applications of innovative autologous stem cell-based therapies for RDEB.

Base Editor Correction of COL7A1 in Recessive Dystrophic Epidermolysis Bullosa Patient-Derived Fibroblasts and iPSCs

Genome editing represents a promising strategy for the therapeutic correction of COL7A1 mutations that cause recessive dystrophic epidermolysis bullosa (RDEB). DNA cleavage followed by homology-directed repair (HDR) using an exogenous template has previously been used to correct COL7A1 mutations. HDR rates can be modest, and the double-strand DNA breaks that initiate HDR commonly result in accompanying undesired insertions and deletions (indels). To overcome these limitations, we applied an A•T→G•C adenine base editor (ABE) to correct two different COL7A1 mutations in primary fibroblasts derived from RDEB patients. ABE enabled higher COL7A1 correction efficiencies than previously reported HDR efforts. Moreover, ABE obviated the need for a repair template, and minimal indels or editing at off-target sites was detected. Base editing restored the endogenous type VII collagen expression and function in vitro. We also treated induced pluripotent stem cells (iPSCs) derived from RDEB fibroblasts with ABE. The edited iPSCs were differentiated into mesenchymal stromal cells, a cell population with therapeutic potential for RDEB. In a mouse teratoma model, the skin derived from ABE-treated iPSCs showed the proper deposition of C7 at the dermal-epidermal junction in vivo. These demonstrate that base editing provides an efficient and precise genome editing method for autologous cell engineering for RDEB.

Base Editor Correction of COL7A1 in Recessive Dystrophic Epidermolysis Bullosa Patient-Derived Fibroblasts and iPSCs

Genome editing represents a promising strategy for the therapeutic correction of COL7A1 mutations that cause recessive dystrophic epidermolysis bullosa (RDEB). DNA cleavage followed by homology-directed repair (HDR) using an exogenous template has previously been used to correct COL7A1 mutations. HDR rates can be modest, and the double-strand DNA breaks that initiate HDR commonly result in accompanying undesired insertions and deletions (indels). To overcome these limitations, we applied an A•T→G•C adenine base editor (ABE) to correct two different COL7A1 mutations in primary fibroblasts derived from RDEB patients. ABE enabled higher COL7A1 correction efficiencies than previously reported HDR efforts. Moreover, ABE obviated the need for a repair template, and minimal indels or editing at off-target sites was detected. Base editing restored the endogenous type VII collagen expression and function in vitro. We also treated induced pluripotent stem cells (iPSCs) derived from RDEB fibroblasts with ABE. The edited iPSCs were differentiated into mesenchymal stromal cells, a cell population with therapeutic potential for RDEB. In a mouse teratoma model, the skin derived from ABE-treated iPSCs showed the proper deposition of C7 at the dermal-epidermal junction in vivo. These demonstrate that base editing provides an efficient and precise genome editing method for autologous cell engineering for RDEB.

Epidermolysis bullosa: Advances in research and treatment

Epidermolysis bullosa (EB) is the umbrella term for a group of rare inherited skin fragility disorders caused by mutations in at least 20 different genes. There is no cure for any of the subtypes of EB resulting from different mutations, and current therapy only focuses on the management of wounds and pain. Novel effective therapeutic approaches are therefore urgently required. Strategies include gene‐, protein‐ and cell‐based therapies. This review discusses molecular procedures currently under investigation at the EB House Austria, a designated Centre of Expertise implemented in the European Reference Network for Rare and Undiagnosed Skin Diseases. Current clinical research activities at the EB House Austria include newly developed candidate substances that have emerged out of our translational research initiatives as well as already commercially available medications that are applied in off‐licensed indications. Squamous cell carcinoma is the major cause of death in severe forms of EB. We are evaluating immunotherapy using an anti‐PD1 monoclonal antibody as a palliative treatment option for locally advanced or metastatic squamous cell carcinoma of the skin unresponsive to previous systemic therapy. In addition, we are evaluating topical calcipotriol and topical diacerein as potential agents to improve the healing of skin wounds in EBS patients. Finally, the review will highlight the recent advancements of gene therapy development for EB.

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.

Gene Therapy for Epidermolysis Bullosa

Epidermolysis bullosa is a family of diseases characterized by blistering and fragility of the skin in response to mechanical trauma. Advances in our understanding of epidermolysis bullosa pathophysiology have provided the necessary foundation for the first clinical trials of gene therapy for junctional and dystrophic epidermolysis bullosa. These therapies show that gene therapy is both safe and effective, with the potential to correct the molecular and clinical phenotype of patients with epidermolysis bullosa. Improvements in gene delivery and in preventing immune reactions will be among the challenges that lie ahead during further therapeutic development.

The Clinical Trials of Mesenchymal Stem Cell Therapy in Skin Diseases: An Update and Concise Review

The skin is one of the crucial body organs with anatomy and physiology linked to various disorders including congenital and acquired diseases. Nowadays, mesenchymal stem cell (MSCs)- based therapy has appeared as a promising therapeutic field, in which many see opportunities to cure the costliest and incurable diseases. However, one question to be asked is that if the use of MSCs in clinical trials studies and diseases treatment has improved. In this study, the clinical trials using MSCs in skin diseases were reviewed. A remarkable number of clinical trial studies are in progress in this field; however, only a few of them have led to tangible benefits for patients. The relevant papers and ongoing clinical trials that address MSC's therapeutic goals for various skin disorders were examined. This review can be very useful for both the dermatologists and basic skin researchers interested in contributing to stem cell-based therapeutic researches in the area of skin disorders.

RNA Viruses as Tools in Gene Therapy and Vaccine Development

RNA viruses have been subjected to substantial engineering efforts to support gene therapy applications and vaccine development. Typically, retroviruses, lentiviruses, alphaviruses, flaviviruses rhabdoviruses, measles viruses, Newcastle disease viruses, and picornaviruses have been employed as expression vectors for treatment of various diseases including different types of cancers, hemophilia, and infectious diseases. Moreover, vaccination with viral vectors has evaluated immunogenicity against infectious agents and protection against challenges with pathogenic organisms. Several preclinical studies in animal models have confirmed both immune responses and protection against lethal challenges. Similarly, administration of RNA viral vectors in animals implanted with tumor xenografts resulted in tumor regression and prolonged survival, and in some cases complete tumor clearance. Based on preclinical results, clinical trials have been conducted to establish the safety of RNA virus delivery. Moreover, stem cell-based lentiviral therapy provided life-long production of factor VIII potentially generating a cure for hemophilia A. Several clinical trials on cancer patients have generated anti-tumor activity, prolonged survival, and even progression-free survival.

Ex Vivo COL7A1 Correction for Recessive Dystrophic Epidermolysis Bullosa Using CRISPR/Cas9 and Homology-Directed Repair

Recessive dystrophic epidermolysis bullosa is a rare and severe genetic skin disease resulting in blistering of the skin and mucosa. Recessive dystrophic epidermolysis bullosa (RDEB) is caused by a wide variety of mutations in COL7A1-encoding type VII collagen, which is essential for dermal-epidermal adhesion. Here we demonstrate the feasibility of ex vivo COL7A1 editing in primary RDEB cells and in grafted 3D skin equivalents through CRISPR/Cas9-mediated homology-directed repair. We designed five guide RNAs to correct a RDEB causative null mutation in exon 2 (c.189delG; p.Leu64Trpfs*40). Among the site-specific guide RNAs tested, one showed significant cleavage activity in primary RDEB keratinocytes and in fibroblasts when delivered as integration-deficient lentivirus. Genetic correction was detected in transduced keratinocytes and fibroblasts by allele-specific highly sensitive TaqMan-droplet digital PCR (ddPCR), resulting in 11% and 15.7% of corrected COL7A1 mRNA expression, respectively, without antibiotic selection. Grafting of genetically corrected 3D skin equivalents onto nude mice showed up to 26% re-expression and normal localization of type VII collagen as well as anchoring fibril formation at the dermal-epidermal junction. Our study provides evidence that precise genome editing in primary RDEB cells is a relevant strategy to genetically correct COL7A1 mutations for the development of future ex vivo clinical applications.

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.

Inside out: regenerative medicine for recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa is classified as a genodermatosis, an inherited genetic skin disorder that results in severe, chronic skin blistering with painful and life-threatening complications. Although there is currently no cure for epidermolysis bullosa, concurrent advances in gene and stem cell therapies are converging toward combinatorial therapies that hold the promise of clinically meaningful and lifelong improvement. Recent studies using hematopoietic stem cells and mesenchymal stromal/stem cells to treat epidermolysis bullosa have demonstrated the potential for sustained, effective management of the most severe cases. Furthermore, advances in the use of gene therapy and gene-editing techniques, coupled with the development of induced pluripotent stem cells from patients with epidermolysis bullosa, allow for autologous therapies derived from a renewable population of cells that are patient-specific. Here we describe emerging treatments for epidermolysis bullosa and other genodermatoses, along with a discussion of their benefits and limitations as effective therapies.

Therapies for genetic extracellular matrix diseases of the skin

A specialized, highly developed dermal extracellular matrix (ECM) provides the skin with its unique mechano-resilient properties and is vital for organ function. Accordingly, genetically acquired deficiency of dermal ECM proteins or proteins essential for the post-translational modification and homeostasis of the dermal ECM, results in diseases affecting the skin. Some of these diseases are lethal or lead to severe complications for the affected individuals. At present limited efficient and evidence-based treatment options exist for genetic ECM diseases of the skin. There is thus a high unmet medical need, creating an urgent demand to develop improved care for these diseases. Here, by drawing examples from the wealth of research on epidermolysis bullosa, we present the current status of biological and small molecule therapies for genetic ECM diseases with skin manifestations. We discuss challenges, and using existing data to propose strategies and future directions allowing development of more efficacious therapies and advancement of them into clinical practice.

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.

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.

The Molecular Revolution in Cutaneous Biology: Emerging Landscape in Genomic Dermatology: New Mechanistic Ideas, Gene Editing, and Therapeutic Breakthroughs

Stunning technological advances in genomics have led to spectacular breakthroughs in the understanding of the underlying defects, biological pathways and therapeutic targets of skin diseases leading to new therapeutic interventions. Next-generation sequencing has revolutionized the identification of disease-causing genes and has a profound impact in deciphering gene and protein signatures in rare and frequent skin diseases. Gene addition strategies have shown efficacy in junctional EB and in recessive dystrophic EB (RDEB). TALENs and Cripsr/Cas9 have emerged as highly efficient new tools to edit genomic sequences to creat new models and to correct or disrupt mutated genes to treat human diseases. Therapeutic approaches have not been limited to DNA modification and strategies at the mRNA, protein and cellular levels have also emerged, some of which have already proven clinical efficacy in RDEB. Improved understanding of the pathogenesis of skin disorders has led to the development of specific drugs or repurposing of existing medicines as in basal cell nevus syndrome, alopecia areata, melanoma and EB simplex. These discoveries pave the way for improved targeted personalized medicine for rare and frequent diseases. It is likely that a growing number of orphan skin diseases will benefit from combinatory new therapies in a near future.

Correction of Recessive Dystrophic Epidermolysis Bullosa by Transposon-Mediated Integration of COL7A1 in Transplantable Patient-Derived Primary Keratinocytes

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by defects in type-VII collagen (C7), a protein encoded by the COL7A1 gene and essential for anchoring fibril formation at the dermal-epidermal junction. Gene therapy of RDEB is based on transplantation of autologous epidermal grafts generated from gene-corrected keratinocytes sustaining C7 deposition at the dermal-epidermal junction. Transfer of the COL7A1 gene is complicated by its very large size and repetitive sequence. This article reports a gene delivery approach based on the Sleeping beauty transposon, which allows integration of a full-length COL7A1 cDNA and secretion of C7 at physiological levels in RDEB keratinocytes without rearrangements or detrimental effects on their clonogenic potential. Skin equivalents derived from gene-corrected RDEB keratinocytes were tested in a validated preclinical model of xenotransplantation on immunodeficient mice, where they showed normal deposition of C7 at the dermal-epidermal junction and restoration of skin adhesion properties. These results indicate the feasibility and efficacy of a transposon-based gene therapy approach to RDEB.

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.