Emerging Therapies Treatment of Epidermolysis Bullosa

Epidermolysis bullosa (EB) comprises a phenotypically diverse group of inherited blistering diseases that affect the skin and, in some subtypes, mucous membranes and other organs. Clinically, individuals with EB have fragile skin and are susceptible to blistering following minimal trauma. Depending on the level of blistering within the dermal-epidermal basement membrane zone, EB is classified into four main categories; simplex, junctional, dystrophic and Kindler syndrome. The sub-classification of EB extends to over 30 clinical subtypes with pathogenic mutations in at least 18 distinct genes. Within the spectrum of EB, ∼ 5% of affected individuals have the clinically more severe recessive dystrophic (RDEB) variant. Dystrophic EB is caused by mutations in the COL7A1 gene encoding type VII collagen (C7) the major component of anchoring fibril adhesion structures that link the epidermal basement membrane to the subjacent dermis . Inheritance of DEB can be autosomal dominant (DDEB) or autosomal recessive (RDEB) and all cases result from COL7A1 mutations; more than 1,500 mutations have been reported globally, most of which are specific to individual families. In RDEB, the COL7A1 pathology usually involves bi-allelic loss-of-function mutations with point mutations or small insertions/deletions leading to nonsense, splice site, frameshift, or occasionally missense mutations disrupting C7 synthesis, secretion and polymerisation and thereby causing structurally defective anchoring fibrils leading to skin fragility. The most severe forms of RDEB are associated with a complete absence of expression of C7 in skin basement membrane leading to no discernible anchoring fibrils.

The management of RDEB remains complex with no curative therapy currently available. The main principle of care is to manage blisters and erosions, control infection and prevent complications. Symptom relief is very important as both pain and itch have severely deleterious impacts on quality of life. In RDEB, blisters form following minor trauma and/or friction. These blisters need to be lanced to prevent extension of the blister and further skin damage. Pain is a common and constant feature seen in patients with RDEB and arises from four major sources: skin, pain associated with procedures, bone and gastrointestinal . For skin care, semi-occlusive dressings that are non-adhesive such as silicone and foam dressings are preferable for treating erosions and reducing skin pain as they absorb exudate and offer some physical protection, thereby providing a moist, clean barrier against bacteria. Opioids in the form of morphine, oxycodone, codeine and fentanyl given by a variety of routes including oral, subcutaneous and sublingual are an effective method of relieving most types of pain in RDEB. For oesophageal pain, H2 blockers and proton pump inhibitors for gastro-oesophageal reflux can be used and systemic steroids can be utilised during episodes of acute oesophageal blistering. Tricyclic antidepressants such as amitriptyline and doxepin taken orally have anecdotally been shown to be beneficial to manage pain in junctional EB (11). Pruritus is a common problem and often correlates with the severity of EB, with RDEB individuals often experiencing significant skin itching . The primary cause of pruritus in RDEB remains unclear but has been postulated that wound healing and inflammation may contribute to an itch-scratch-blister cycle leading to further skin damage. Menthol containing, oil-based products may be partially helpful in relieving itch.

Oral care is difficult in RDEB due to microstomia, ankyloglossia and vestibule obliteration and so there is a tendency to develop dental abscesses and periodontal disease, both of which can cause pain. Caries in RDEB can be reduced through regular dental follow up to optimise oral hygiene and professional cleaning with fluoride therapy. Extraction of teeth was previously considered the mainstay of treatment but today prevention of dental disease is the main aim with dentists working closely as part of a multidisciplinary approach. Oral pain can be minimised by rinsing the mouth with coating products such as sucralfate or with the use of topical anaesthetics.

Insensible losses and thermal dysregulation from chronic wounds leads to a hypercatabolic inflammatory state requiring an increased calorie intake. As a result, the severity of EB often correlates with malnutrition and so RDEB patients often have an inadequate nutrition with growth retardation commonly seen in at least half of all children with RDEB . One consequence of inadequate nutrition is pubertal delay and short stature. In most patients with RDEB, bone mineral density is reduced due to poor nutritional status, low 25-[OH] vitamin D levels and reduced mobility. In RDEB, bone mineral density and serum bone profile should be monitored and managed with the use of calcium and vitamin D supplements and bisphosphonates to reduce the risk of fractures . If pubertal delay is present in RDEB, it is important to attain age appropriate secondary sexual characteristics for psychological reasons and to optimise growth and acquiring peak bone mineral content, therefore, hormonal induction of puberty is often recommended.

New Therapies

Allogeneic fibroblasts
Fibroblasts have the capacity to synthesise C7 as well as modulating wound healing. On this basis, a number of RDEB murine and human studies have been conducted injecting allogeneic normal human fibroblasts intradermally with the aim of potentially increasing C7 expression and also improving wound healing (80).

A proof-of-concept study in 5 RDEB individuals demonstrated that a single intradermal injection of allogeneic fibroblasts (5 × 106 cells injected into the superficial dermis over ∼ 1 cm2) increased COL7A1 expression for at least 3 months in most subjects (80). The study also demonstrated the low immunogenicity of allogeneic fibroblasts and lack of host response at an immunological and histological level. The injected cells were not detectable at 2 weeks post-injection, the time-point at which an increase in C7 protein at the DEJ was seen. In murine studies, it has been suggested that this increase in C7 protein at the DEJ may be secondary to donor fibroblasts releasing wild-type full length C7 that can be incorporated into the DEJ for the short time that these donor fibroblasts are present (81). Of note, in the human studies, the increase in C7 was most apparent in RDEB individuals who had some baseline expression of C7 compared to those who had a complete absence of the protein. The source of the new C7 is likely to reflect upregulation of the RDEB subjects’ own mutant, but partially functional C7, a mechanism supported by a lack of new normal-appearing anchoring fibrils. A further study showed that a single injection of allogeneic fibroblasts could increase COL7A1 expression for 3–6 months and C7 protein for 9–12 months. The expression of heparin binding-EGF-like growth factor (HB-EGF) was thought to mediate this increase in endogenous C7 expression.

With regard to wound healing, a phase II double-blinded, randomised, controlled trial in RDEB patients comparing injections of allogeneic cultured fibroblasts in suspension solution versus suspension solution alone, with the injections given across eroded areas found that in both arms there was a reduction in erosion size, suggesting that perhaps the trauma of either injection might, at least in part, be responsible for the clinical responses. On the other hand, a further prospective, randomised, double-blind, within-patient, vehicle-controlled trial of subjects with RDEB was conducted in 11 patients. Twenty-six erosions were treated; 14 with a single treatment of 5 × 106 allogeneic fibroblasts per linear cm of erosion margin and 12 with vehicle. Fibroblast injections produced a greater reduction in erosion area than did vehicle alone during the first 28 days. After 28 days, there was no significant difference between fibroblasts and vehicle although further injections were not administered.

Mesenchymal stromal cells
Multipotent mesenchymal cells are found in several tissues, including the bone marrow and have the ability to migrate to injured tissue and stimulate tissue regeneration, thus making this therapy potentially relevant to RDEB wounds. The clinical use of MSCs in RDEB was first reported in a 13-year-old and 25-year-old patient from Chile in 2010. The MSCs were derived from the bone marrow of healthy, unrelated individuals and injected intradermally. Both subjects had clinically severe blistering with a complete absence of C7 expression. Either 0.5 × 106 MSCs or vehicle were injected into both intact and chronically ulcerated sites. At week 12, wounds treated with MSCs had almost healed compared to sites treated with placebo with benefits lasting for 4 months post injection. Thereafter, skin fragility resembled baseline with ulceration. New C7 was seen in a linear pattern at the junction between the epidermis and dermis, suggesting that intradermal administration of allogeneic MSCs may lead to de novo C7 expression in the skin as well as prevention of blistering and improvements in wound healing in patients with RDEB.

Subsequently, El Darouti et al. conducted a double-blind study, randomising 14 patients with clinically severe RDEB into two equal groups. Both groups received intravenous MSCs derived from healthy bone marrow aspiration from one healthy parent but group one was also given 5 mg/kg/day of ciclosporin to reduce inflammation or protect against rejection with the patients in group two receiving a placebo suspension. Both groups were seen fortnightly for 12 weeks and were reported to have fewer new blisters, to have an increased rate of wound healing, and to demonstrate new anchoring fibrils on skin biopsies. Two individuals demonstrated clinical benefit at 12 months, whereas the improvements in the remainder peaked 3 months after infusion and waned thereafter.

Petrof et al. enrolled 10 children aged 1–11 years in the U.K. with RDEB who had partial or complete absence of C7 protein, in an open-label, phase I/II clinical trial. Each child received three IV infusions of either 20 × 106 cells per infusion (weight ≤ 20 kg) or 40 × 106 cells per infusion (weight > 20 kg) (equivalent to 1–3 × 106 cells per kg) of BM-MSCs on days 0, 7 and 28. No severe adverse events occurred (other than the transient noxious smell associated with the preservative dimethyl sulphoxide). Skin biopsies revealed no increase in C7 and no new anchoring fibrils at day 60 post infusion. One subject showed no clinical benefit, whereas two had sustained improvement at one year, and in the others there were transient improvements such as less skin redness, less skin pain and itching, and better wound healing that lasted for 4–6 months after the third infusion of MSCs. The optimal dosing, route of administration and consequences of multiple repeat dosing of allogeneic MSCs in RDEB has yet to be fully evaluated. However, murine studies have shown the impact and superiority of high density intradermal injections of MSCs compared to fibroblasts, suggesting that further human clinical trials are needed if the maximal benefits of MSC cell therapy in RDEB are to be realised.

The mechanism by which MSCs lead to a clinical improvement in wound healing in RDEB has not yet been established but seems to be indirect and trophic through the release of various growth factors and cytokines , i.e. without the need for the MSCs to engraft. MSCs express tumour necrosis factor alpha (TNFα)-stimulated protein 6 (TSG-6), which in other studies has been associated with an improvement in wound healing and downregulation of B-cell proliferation, monocyte maturation, secretion of IFN-γ and TNF-α at wounded tissue sites, while also promoting increased secretion of anti-inflammatory IL-10 from macrophages. In addition to TSG-6, MSCs also mediate immunosuppression through the secretion of nitric oxide, transforming growth factor-beta (TGF-β) and indoleamine 2,3-dioxygenase.

Regarding other cells, potentially with stem rather than stromal functionality, human umbilical cord blood derived unrestricted somatic stem cells (USSCs) have shown potential to regenerate RDEB skin in animal models. In murine models, it has been shown that USSCs express C7 and accelerate wound healing when injected intradermally in mice that have full-thickness excisional wounds. An intradermal injection of USSCs modified with a luciferase reporter gene, injected at a distant site to the wound revealed specific migration to the wound. These data suggest that CB-derived USSCs may contribute to wound repair and may be worth exploring as cell therapy for patients with RDEB. In terms of optimizing MSCs for clinical use, preconditioning of MSCs with TGF-β, TNF-α, and SDF-1α, induces a simultaneous upregulation in COL7A1, TSG-6, and CXCR4 which results in a six to eight-fold increase in COL7A1 expression by MSCs (97). This pre-conditioning increased C7 levels towards the 30% of the amount of wild-type C7 believed to ameliorate the blistering seen in RDEB. Such pre-conditioning effects, however, have yet to be assessed therapeutically in humans.

Bone marrow transplantation
Following the effectiveness of bone marrow (BM) stem cells in murine RDEB, a clinical trial of whole bone marrow transplantation (BMT) was performed in children with RDEB.

In 2010, Wagner et al. (100) reported use of high dose chemotherapy to immunoablate individuals with RDEB to permit more reliable lymphohaematopoietic engraftment, followed by unfiltered whole bone marrow transplantation, usually from a tissue-matched sibling donor. Seven patients entered the trial and 6 underwent BMT. One patient died before the BMT because of heart failure, possibly related to cyclophosphamide toxicity and pre-existing renal failure. All RDEB subjects had more than 50% body surface area coverage with blisters and erosions. Following BMT, 3 subjects showed clinical improvement with only 10% BSA involvement and 3 showed an improvement with 25% BSA involvement. A further patient died 6 months post-transplant from infection secondary to graft failure. Of note, donor cells homed to injured skin with increased C7 expression seen at the DEJ in 5 of the 6 subjects. The subject that did not show evidence of increased C7 expression post-BMT was still reported to show an improvement in their clinical status, similar to that seen in the other 5 subjects that did show an increase in C7 expression. Clinical response seems to have been sustained; none of the treated subjects has been cured of their RDEB but several have had markedly fewer blisters in follow up to 8 years post-BMT. Donor-skin chimerism was seen in the skin of BMT recipients. A substantial number of cells of donor origin were found in BMT recipient skin, confirming that donor cells home to injured skin in patients with severe RDEB. Donor cells of both haematopoietic (CD45+), and non-haematopoietic, non-endothelial cells (CD45-, CD31-) were found in the epidermis and dermis of BMT recipients, although donor non-haematopoietic cells were considered to be the most likely source of new C7. Despite the increase in C7 expression, there was a lack of mature anchoring fibrils on transmission electron microscopy (TEM), although later evaluation will be needed given the several years anchoring fibril maturation may take.

Regarding the interconnectivity between BM cells and skin repair, the release of HMGB-1 from hypoxic keratinocytes and the mobilisation of Lin-/PDGFRα+ epithelial progenitor cells from bone marrow to the circulation and differentiating into keratinocytes capable of generating new C7 in the skin, supports the potential mechanism of action of BMT (78). However, the homing of these cells to injured skin post-BMT has not yet been fully established. Reports suggest that the C-X-C type chemokine ligand 12 (CXCL12), known as stromal cell-derived factor 1α (SDF-1α), and its receptor, CXCR4 may direct the migration of progenitor cells to various tissues. The transcription factor hypoxia inducible factor-1 alpha, HIF-1α, in endothelial cells in ischaemic tissue regulates the expression of SDF-1α, enabling CXCR4+ progenitor cells to home from the circulation to target ischaemic tissue. Overall, despite the clinical data, the precise mechanism by which BMT leads to clinical improvement has not yet been fully elucidated. Of clinical significance, however, immunoablative conditioning in RDEB pre-BMT has been associated with mortality rates in excess of 25%. To lessen mortality, several refined stem cell transplantation protocols have been developed that focus on reduced intensity conditioning (RIC). Combination conditioning has been reduced from using busulfan, fludarabine, and cyclophosphamide to combination therapy with fludarabine and low doses of cyclophosphamide and radiation, although further refinements continue to be applied. Thus far, it appears that RIC is associated with less toxicity and relatively good disease amelioration, but published data are currently lacking.

Grafting revertant mosaicism skin/keratinocytes
In patients with various inherited cutaneous diseases, patches of spontaneously appearing normal skin can be seen where the inherited mutation has genetically corrected itself in those sites. This phenomenon is referred to as revertant mosaicism or “natural gene therapy” and a key goal has been to try to exploit these natural events in the treatment of RDEB. Thus far, revertant mosaicism has not been explored therapeutically in RDEB although in some forms of junctional EB, grafting of cultured revertant keratinocytes or punch grafting of revertant skin has been undertaken, with sustained improvement in recipient mutant skin sites being demonstrated for the latter.

The opportunity to expand keratinocytes derived from a patch of revertant mosaicism offers a personalised and patient specific form of therapy. As these cells have naturally corrected part of the deleterious mutation, there is no need for further genetic manipulation. Gostynski et al. isolated revertant keratinocytes from an individual with generalised intermediate junctional EB and expanded these into epidermal sheets to graft on to areas of mutant skin lacking an epidermis. The surgical approach led to successful grafting although functional benefits were not apparent. Of note, despite cultured keratinocytes displaying 30% reversion, when grafted, less than 3% of keratinocytes remained reverted in the graft; the reasons for this relative loss of reverted cells is not known. More successful was punch graft transplantation of revertant skin in an individual with junctional EB that resulted in successful transfer of the donor cell genotype and phenotype with enhanced expression of laminin-332 and better skin integrity maintained for at least 18 months. Nevertheless a key challenge is to find methods for higher in vitro expansion of revertant keratinocytes as well as being able to more readily identify the revertant skin patches. One new approach has been to generate inducible pluripotent stem cells (iPSCs) from revertant keratinocytes, which potentially then offers copious functional cells that can be differentiated into multiple tissue lineages.

Gene therapy
Gene therapy strategies in RDEB aim to provide therapeutic benefit through manipulation of DNA or RNA. Typically, viral mediated ex vivo gene transfer approaches have been used whereby the patient’s skin cells are cultured, transduced with a viral vector encoding the transgene expressing the wild-type protein and then these gene modified cells can then either be transplanted back via grafting of epithelial sheets or skin equivalents (epidermis/dermis), or by intradermal injections (e.g. of genetically supplemented fibroblasts). Viral mediated gene transfer has been the preferred gene delivery method, firstly, due to the ability to deliver a transgene and integrate it into the host genomic DNA, and secondly because viral vector approaches achieve higher transduction efficiencies for longer-term gene expression. Gamma retroviral (RV) and lentiviral (LV) vectors have been the main delivery methods for RDEB gene therapy studies, despite the large size of the COL7A1 cDNA (> 9 kb). Regarding specific pre-clinical work for RDEB, one study used an LV-mediated system to make intradermal injections of corrected patient-derived RDEB fibroblasts to restore C7 at the dermal-epidermal junction for 4 months in an RDEB skin model. Moreover, it was subsequently shown that direct intradermal injections of an LV vector containing COL7A1 cDNA could produce stable expression of human C7 in fibroblasts and endothelial cells for at least 3 months in a murine model. To compensate for the large size of COL7A1, an RV vector with a truncated COL7A1 “mini-gene” was first assessed. Immortalised RDEB keratinocytes could be transduced to express a mini-C7 protein product that improved cell motility, adhesion, and proliferation, although mini-gene therapy approaches have not been pursued to clinical trials.

The first clinical study of ex vivo gene therapy for EB was in an individual with junctional EB, with restoration of laminin-332 expression following RV-mediated transfection of epidermal stem cells with the LAMB3 gene, leading to phenotypic correction in the grafted skin. Of note, follow up for more than 8 years has shown sustained synthesis of laminin-332 protein with no evidence of blistering, inflammation, tumourigenesis or immune response in the grafted area. In a second case, the same RV gene therapy protocol was used in an Austrian junctional EB patient in whom ex vivo skin gene therapy targeting autologous epidermal stem cells was used to produce five skin sheets each measuring 5 × 7 cm that were grafted onto wounded areas on the patient’s thighs; clinical responses in this patient are still being evaluated.

The first gene therapy trial in RDEB involved grafting of ex vivo autologous COL7A1 gene supplemented epidermal sheets in 4 adults in a phase I clinical trial. In this study, autologous keratinocytes were transduced with GMP grade gamma-RV containing full-length COL7A1. Autologous epidermal sheets measuring ∼35 cm2 (approximately the size of a playing card) were grafted onto 6 wounds in each of the patients. No serious adverse events were reported and there was C7 expression at the dermal-epidermal junction on graft sites in 90% of biopsies at 3 months, 66% of biopsies at 6 months and 42% at 12 months. Wound healing was variable and generally waned over one year. Longer term follow-up will be required to ascertain long-term efficacy and safety.

The risk of insertional mutagenesis arising from use of certain classical viral vectors has led to a new generation of self-inactivating (SIN) viral vectors which incorporate deletion of the U3 region of the 3′-long terminal repeat that renders them unable to activate cellular genes in the host’s genome. A SIN-LV-based vector was used to deliver full-length COL7A1 cDNA sequence into patient-derived RDEB keratinocytes and fibroblasts (110). This approach gave close to 95% transduction efficiency and demonstrated persistent synthesis and secretion of normal C7 over a 5 month observation period in vitro. These corrected cells were also able to produce normal anchoring fibrils when grafted onto immunodeficient mice. Other investigators are currently carrying out a clinical trial of SIN-LV vector COL7A1 addition to autologous fibroblasts for intradermal injection (ClinicalTrials.gov identifier: NCT02493816), and others are developing a SIN-RV vector containing full length COL7A1 with the aim being to transplant bioengineered skin containing genetically supplemented keratinocytes and fibroblasts (www.genegraft.eu).

As an alternative to viral-mediated transduction, a phage-mediated platform has been used to deliver COL7A1 cDNA into patient-derived RDEB primary epidermal progenitor cells. The authors used a phiC31 phage integrase, which can integrate large (up to 10 kb) DNA sequences. The experimental data revealed relatively lower transfection efficiency rates (∼ 45% at 2 days) compared to viral transduction methods, but through culture expansion and selection of C7-producing cells, a ∼ 99% success rate after a 10-day selection period was noted. Moreover, C7 production by epidermal progenitor cells was suggested by persistent expression for 14 weeks, i.e. spanning multiple turnover cycles of keratinocytes. The same phiC31 phage integrase platform was subsequently used to correct patient-derived RDEB fibroblasts. Corrected fibroblasts were then injected into an RDEB skin model and were shown to restore C7 expression in the skin. Nevertheless, the requirement to include the phiC31 integrase gene, the lack of responsiveness to endogenous gene regulation, and the potential for random insertional mutagenesis may be limiting factors for phage therapy.

Cationic polymers such as linear poly (β-amino ester)s (LPAEs) have also emerged as an effective gene delivery vector. Branched poly (β-amino ester) s (HPAEs) have a three-dimensional spatial structure and are thought to improve the interaction of polymers with DNA, prevent DNA degradation by enzymes and increase cellular uptake of polyplexes. HPAEs have not been developed for gene delivery as yet, as synthesising these highly branched polymers remains a technical challenge. A novel design of the HPAEs has been derived from the functional LPAE components to see whether this may provide an effective gene delivery vector. This has been assessed in vivo in various cell types including RDEB keratinocytes to deliver therapeutic COL7A1 cDNA.

Gene silencing technologies such as RNA interference (RNAi) are useful in dominant forms of DEB, if designed to knockdown the mutant allele without silencing the wild-type allele, with pre-clinical data to support therapeutic use of such an approach. Another methodology, pertinent mainly to RDEB but possibly also dominant disease, is to try to modulate splicing of pre-messenger RNA to induce skipping of the mutated exon. Using 2′-O-methyl antisense oligoribonucleotides (AONs) in an RDEB skin equivalent xenograft model, one or two subcutaneous injections of AONs at doses ranging from 400 µg up to 1 mg was able to induce skipping of exons containing loss-of-function mutations (in exons 73 and 80) and thereby restore C7 expression and anchoring fibril formation (125). A further method is to apply spliceosome-mediated RNA trans-splicing (SMaRT) to address target mutations at a post transcriptional level. Splicing is induced in trans between the exogenous RNA and target endogenous pre-mRNA via an engineered RNA trans-splicing molecule (RTM). Specifically, RV transduction of RDEB keratinocytes with a 3′ pre-trans-splicing molecule resulted in correction of full-length C7 expression. Transduced cells showed normal localisation of C7 at the basement membrane zone in skin equivalents with assembly into anchoring fibril-like structures, i.e. demonstrating correction of an RDEB phenotype in vitro (126). In further work, a 5′ RTM capable of replacing COL7A1 exons 1 to 15 in murine keratinocytes was injected into the skin of wild-type mice using a gene gun with vector delivery and expression in the skin.

Approximately 15% of all pathogenic mutations in COL7A1 involve premature termination codons (PTCs) that lead to truncated proteins and/or nonsense-mediated mRNA decay. Both in vitro and in vivo studies have revealed that aminoglycoside antibiotics can suppress primary PTCs and produce some degree of full length functional protein in genetic disorders such as cystic fibrosis (CF) and Duchenne’s muscular dystrophy (DMD). In RDEB, preclinical analysis has been performed using two RDEB keratinocyte cell lines harbouring nonsense mutations and primary fibroblast cultures from two RDEB patients with nonsense mutations. Aminoglycosides (G418, gentamicin, and paramomycin) were able to induce PTC read-through and restore functional full-length C7. Aminoglycoside therapy may provide a non-invasive option in treating RDEB patients that carry nonsense mutations but has not yet been trialled. Potential toxicity and the extent of the readthrough necessary to generate functional correction, however, remain important considerations that may limit immediate clinical translation.

Genomic editing techniques including zinc-finger nucleases (ZFNs), meganucleases (MN), transcription activator-like effector nucleases (TALENs) and the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 nuclease system are being developed, some or all of which may have relevance to RDEB therapeutics.

Moreover, the advent reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) that can differentiate into any cell type, is an exciting new development in RDEB therapy. It is possible to correct RDEB fibroblasts through homologous recombination using transcription activator-like effector nucleases (TALENs) and then reprogram these into iPSCs, which then differentiate into keratinocytes. Murine studies have also successfully generated iPSCs in culture from multipotent keratinocyte lineages capable of forming a fully developed epidermis. Subsequently, others have reported successful generation of iPSCs from healthy human skin fibroblasts and individuals with RDEB. Another study took a different approach using direct injections and teratoma formation which allows spontaneous differentiation of iPS cells into an epidermis. Regarding new therapeutic opportunities, an approach in which iPSCs generated from naturally corrected revertant RDEB cells could be used to enable the production of autologous epithelial and mesenchymal cells, perhaps paving the way for personalised therapy in EB.

Protein therapy
Given that the essential skin pathology in RDEB is a lack of C7 in epidermal basement membrane, C7 protein replacement therapy has been evaluated using animal models for preclinical studies. Initial studies successfully demonstrated that intradermal injections of recombinant human C7 can lead to incorporation of the new protein specifically into basement membrane of Col7a1 null mice, resulting in an improvement in the blistering phenotype for up to 2 months. Furthermore, topical application of human recombinant C7 accelerated wound healing in mice, and intravenously administered rC7 homed to engrafted RDEB mouse skin and restored C7, anchoring fibrils, and epidermal-dermal adherence.