Correction of steroid sulfatase deficiency by gene transfer into basal cells of tissue-cultured epidermis from patients with recessive X-linked ichthyosis

Treatments for Non-Syndromic Inherited Ichthyosis, Including Emergent Pathogenesis-Related Therapy

The term 'inherited ichthyosis' refers to a heterogeneous group of mendelian disorders of cornification that involve the integument with varying degrees of scaling. The management of ichthyosis poses a challenge for most physicians. Treatment options proposed in the literature include moisturizers, topical keratolytics, topical and systemic vitamin D analogues, and topical and systemic retinoids; however, some of these modalities are less reliable than others. Despite the therapeutic impasse imposed by the options above, the emergence of pathogenesis-based treatments along with novel gene therapies appear promising and hold the potential to halt or even revert disorders that arise from single genetic mutations, although research is still quite lacking in this domain. Hence, this review aims to highlight the various treatment modalities available for the management of the cutaneous manifestations of non-syndromic inherited ichthyosis, with an added emphasis on pathogenesis-targeted therapies.

Current Strategies for the Gene Therapy of Autosomal Recessive Congenital Ichthyosis and Other Types of Inherited Ichthyosis

Mutations in genes such as transglutaminase-1 (TGM1), which are responsible for the formation and normal functioning of a lipid barrier, lead to the development of autosomal recessive congenital ichthyosis (ARCI). ARCIs are characterized by varying degrees of hyperkeratosis and the presence of scales on the body surface since birth. The quality of life of patients is often significantly affected, and in order to alleviate the manifestations of the disease, symptomatic therapy with moisturizers, keratolytics, retinoids and other cosmetic substances is often used to improve the condition of the patients' skin. Graft transplantation is commonly used to correct defects of the eye. However, these approaches offer symptomatic treatment that does not restore the lost protein function or provide a long-term skin barrier. Gene and cell therapies are evolving as promising therapy for ARCIs that can correct the functional activity of altered proteins. However, these approaches are still at an early stage of development. This review discusses current studies of gene and cell therapy approaches for various types of ichthyosis and their further prospects for patient treatment.

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

INTRODUCTION

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

SOURCES OF DATA

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

AREAS OF AGREEMENT

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

AREAS OF CONTROVERSY

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

GROWING POINTS

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

AREAS TIMELY FOR DEVELOPING RESEARCH

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

DATA AVAILABILITY STATEMENT

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

CRISPR/Cas9 gene editing for genodermatoses: progress and perspectives

Genodermatoses constitute a clinically heterogeneous group of devastating genetic skin disorders. Currently, therapy options are largely limited to symptomatic treatments and although significant advances have been made in ex vivo gene therapy strategies, various limitations remain. However, the recent technical transformation of the genome editing field promises to overcome the hurdles associated with conventional gene addition approaches. In this review, we discuss the need for developing novel treatments and describe the current status of gene editing for genodermatoses, focusing on a severe blistering disease called epidermolysis bullosa (EB), for which significant progress has been made. Initial research utilized engineered nucleases such as transcription activator-like effector nucleases and meganucleases. However, over the last few years, clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) have upstaged older generation gene editing tools. We examine different strategies for CRISPR/Cas9 application that can be employed depending on the type and position of the mutation as well as the mode of its inheritance. Promising developments in the field of base editing opens new avenues for precise correction of single base substitutions, common in EB and other genodermatoses. We also address the potential limitations and challenges such as safety concerns and delivery efficiency. This review gives an insight into the future of gene editing technologies for genodermatoses.

Gene Therapy: Recent Advances and Applications in Dermatology

Background:

Gene therapy is an innovative and exciting new branch of medicine. Despite the fact that a human disease has yet to be cured using this therapeutic approach, numerous clinical trials are taking place around the world based on encouraging preclinical data.

Objective:

The aim of this review is to bring the reader up to date with this rapidly advancing field and to highlight the technical advances that must occur before gene therapy will become common practice in dermatology.

Methods:

The current level of gene delivery technology restricts the applications. The advantages and disadvantages of viral and nonviral gene delivery systems are discussed.

Results:

Considerable advances are being made in the areas of cancer immunotherapy and vaccines. Of particular importance to the treatment of skin diseases will be the isolation and ex vivo manipulation of epidermal stem cells, the development of skin-specific regulatory sequences for gene expression, and the formulation of gene delivery systems suitable for systemic administration.

Conclusions:

In general, skin and keratinocytes are considered to be good targets for gene transfer applications, and several diseases have been identified as potential candidates for treatment in the near future.

Management of ichthyosis and related conditions gene-based diagnosis and emerging gene-based therapy

Knowledge of the molecular basis of many inherited diseases has grown exponentially during the past decade. Inherited skin diseases, including the ichthyoses and related conditions, benefited from that explosion of information, much of which has relevance for the clinical setting. In this section, the authors review the genes now known to be involved in ichthyosis, the methods for detecting mutations in those genes in the clinical diagnostic laboratory, options for using that information for diagnosis and pregnancy/family planning decisions, and current and future therapies based on the knowledge of the molecular basis of the ichthyosis.

X-linked ichthyosis: an oculocutaneous genodermatosis

X-linked ichthyosis (XLI) is an X-linked recessive disorder of cutaneous keratinization with possible extracutaneous manifestations. It was first described as a distinct type of ichthyosis in 1965. XLI is caused by a deficiency in steroid sulfatase activity, which results in abnormal desquamation and a retention hyperkeratosis. XLI is usually evident during the first few weeks of life as polygonal, loosely adherent translucent scales in a generalized distribution that desquamate widely. These are quickly replaced by large, dark brown, tightly adherent scales occurring primarily symmetrically on the extensor surfaces and the side of the trunk. In addition, extracutaneous manifestations such as corneal opacities, cryptorchidism, and abnormalities related to contiguous gene syndromes may be observed. Diagnosis of XLI is usually made clinically, as the histopathology is nonspecific, but confirmation may be obtained through either biochemical or genetic analysis. Treatment should focus on cutaneous hydration, lubrication, and keratolysis and includes topical moisturizers and topical retinoids.

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.

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.

Ichthyosis: etiology, diagnosis, and management

The ichthyoses are a heterogeneous group of disorders with both inherited and acquired forms. Clinical presentation, pattern of inheritance, and laboratory evaluation may establish a precise diagnosis, which can assist in prognosis and genetic counseling. Congenital autosomal recessive ichthyosis (CARI) usually presents at birth, often as a collodion baby. CARI can progress into any one of a spectrum of disorders. Lamellar ichthyosis is characterized by dark, plate (armor)-like scale. This disease is often caused by mutations in the gene encoding the enzyme transglutaminase 1. Congenital ichthyosiform erythroderma is another phenotype within CARI, marked by generalized redness and fine white scale. Epidermolytic hyperkeratosis is an autosomal dominant disorder characterized by hyperkeratosis and blistering, and at least six clinical phenotypes have been described. It may be due to mutations in the gene encoding the intermediate filament proteins keratin 1 and 10. Ichthyosis vulgaris is the most common ichthyosis, and is inherited in an autosomal dominant pattern. Involvement is generally mild and may vary greatly with climate and humidity. X-linked ichthyosis, due to a defect in the enzyme steroid sulfatase, affects males with generalized scaling that usually begins soon after birth. There may be associated corneal opacities that do not affect vision. Sjögren-Larsson syndrome is an autosomal recessive ichthyosis associated with progressive spastic paralysis and mental retardation. This condition is caused by mutations in the gene for fatty aldehyde dehydrogenase. Refsum's disease, due to accumulation of phytanic acid, results in ichthyosis and progressive neurologic dysfunction. The erythrokeratodermas are characterized by hyperkeratosis and localized erythema. Erythrokeratodermia variabilis is autosomal dominant and characterized by generalized or localized hyperkeratosis and migratory red patches. Mutations in the genes encoding the gap junction proteins, connexins, underlie this disorder. Netherton's syndrome is an autosomal recessive disorder characterized by ichthyosis, a hair shaft abnormality and atopy. The ichthyosis may present at birth with erythroderma or in some cases a collodion presentation. However, a frequent characteristic skin manifestation is ichthyosis linearis circumflexa. Netherton's syndrome has been found to be due to an abnormality in a serum protease inhibitor. Acquired ichthyosis can have a variety of underlying causes including neoplastic, infectious, drugs, endocrine, metabolic, autoimmune, malabsorptive states, and hereditary. Topical, and in more severe cases, systemic, therapy are useful in managing this array of disorders of cornification.

Suppression of the immune response against exogenous desmoglein 3 in desmoglein 3 knockout mice: an implication for gene therapy

Gene therapies for recessive genetic diseases may provoke unwanted immune responses against the introduced gene product because patients, especially those with null mutation of a certain protein, have no tolerance for the protein of interest. This study used desmoglein 3 knockout (Dsg3-/-) mice as a disease model for a genetic defect in DSG3, to investigate whether nonviral gene therapy induces an immune response against Dsg3 and whether the reaction against Dsg3 can be prevented. When mouse Dsg3 cDNA was injected in the skin of Dsg3-/- mice, 50% of treated Dsg3-/- mice developed anti-Dsg3 IgG, which can bind native Dsg3 in vivo. To prevent this response, we used an anti-CD40L monoclonal antibody, MR1, which blocks the costimulatory interaction between CD40 and CD40L. To evaluate the effect of MR1, we grafted Dsg3+/+skin on Dsg3-/- mice, to mimic stable gene transfer of Dsg3. After skin grafting, all the recipient Dsg3-/- mice were treated with either MR1 (n=8) or control hamster IgG (n=8). All of the control IgG-treated mice developed circulating anti-Dsg3 IgG about 2 wk after grafting, and IgG deposition was observed on the surfaces of keratinocytes in the grafted Dsg3+/+skin. Such anti-Dsg3 IgG production was significantly prevented, however, when the recipient mice were treated with MR1. These findings suggested that gene therapies for recessive diseases may provoke an immune response against the transgene product, and that the CD40-CD40L interaction might be a reasonable target for effective prevention of such undesirable immune responses, leading, in turn, to a successful gene therapy.

Tissue-engineered skin substitutes

The last two years have seen new tissue-engineered skin substitutes come onto the market and begin to resolve the various roles to which each is best suited. It is becoming evident that some of the very expensive cell-based products have cost-benefit advantage despite their high price and are valuable within the restricted applications for which they are intended. The use of skin substitutes for testing purposes has extended from epidermal keratinocytes to other integumentary epithelia and into preparations containing multiple cell types in which reactions resulting from paracrine interactions can be examined. Challenges remain in the application of gene therapy techniques to skin substitutes, both the control of transgene expression and in the selection of suitable genes to transfect. A coming challenge is the production of tissue-engineered products without the use of animal products other than human cells. A challenge that may be diminishing is the importance of acute rejection of allogeneic tissue-engineered skin substitutes.

Efficient gene transfer into human keratinocytes with recombinant adeno-associated virus vectors

Gene transfer into the skin is a promising approach to treat inherited or acquired dermatological diseases and systemic monogenic deficiencies. For this purpose, the efficient and sustained gene delivery into keratinocytes is of critical importance. Recombinant adeno-associated virus (rAAV) vectors hold the potential to achieve a long-term gene transfer into various human organs. In order to evaluate this potential for skin gene therapy, human keratinocytes were transduced in vitro with rAAV vectors encoding the reporter genes beta-galactosidase (rAAV/LacZ) or green fluorescent protein (rAAV/GFP). Using rAAV/LacZ at a multiplicity of infection (MOI) of five transducing particles per cell, up to 70% of human keratinocytes were transduced within 48 h. This effect was independent of individual skin donors and different body areas serving as the source for keratinocyte isolation. rAAV had no significant influence on cell viability, but induced a growth arrest in transduced keratinocytes. This growth arrest was overcome by replating cells in fresh media. rAAV/GFP-transduced keratinocytes could be passaged several times, expressed GFP for up to 50 days, and passed the transgene to their daughter cells, suggesting that keratinocyto precursor cells were also transduced. Taken together, the results suggest that rAAV is a promising gene transfer vehicle for skin gene therapy.

Cultivation of human keratinocyte stem cells: current and future clinical applications

Cultured human keratinocytes have a wide spectrum of clinical applications. Clinical results reported by several investigators are, however, contradictory. In this review, the authors discuss the biological and surgical issues which play a key role in the clinical outcome of cultured epidermal autografts used for the treatment of massive full-thickness burns. The importance of cultivation of epidermal stem cells and of their transplantation onto a wound bed prepared with donor dermis is emphasised. The paper also reviews recent data showing that: (i) cultured epidermal autografts bearing melanocytes can be used for the treatment of stable vitiligo; (ii) keratinocytes isolated from other lining epithelia, such as oral, urethral and corneal epithelia, can be cultivated and grafted onto patients suffering from disabling epithelial defects; (iii) keratinocyte stem cells can be stably transduced with retroviral vectors and are therefore attractive targets for the gene therapy of genodermatoses.

In vivo gene transfer to skin and wound by microseeding

BACKGROUND

Gene transfer to skin has many potential applications but lacks a safe, practical delivery method. This report presents a new technique, microseeding, for in vivo gene transfer to skin and wounds and for DNA-mediated vaccination. The plasmid DNA solution was delivered directly to the target cells of the skin by a set of oscillating solid microneedles driven by a modified tattooing device.

MATERIALS AND METHODS

Skin and partial-thickness excisional wounds in pigs were microseeded with either hEGF expression plasmid or beta-galactosidase expression plasmid. Human EGF was also delivered by single injection or particle bombardment. hEGF expression in wound fluid and in target tissue was determined by ELISA with anti-hEGF-specific antibodies. Additionally, weanling pigs were microseeded with a hemagglutinin of swine influenza virus expression plasmid and production of anti-HA-specific antibodies was determined by blocking ELISA.

RESULTS

hEGF expression in microseeded partial thickness wounds (5664 pg/site) and skin sites (969 pg/site) peaked 2 days after transfection being four- to seven-fold higher than gene transfer by a single intradermal injection and two- to three-fold higher than particle-mediated gene transfer. The beta-galactosidase-expressing cells were detected in dermis and epidermis. Pigs microseeded with HA expression plasmid were protected from infection by the Swine influenza virus.

CONCLUSIONS

These results demonstrate that microseeding is a simple and effective method for in vivo gene transfer to skin and wounds and is more efficient than single injection and particle-mediated gene transfer.

The major inherited disorders of cornification. New advances in pathogenesis

This article provides a synopsis of the major (most common) inherited disorders of cornification. It also reviews the recent advances that have been made for each disorder and their practical applications.

Corrective transduction of human epidermal stem cells in laminin-5-dependent junctional epidermolysis bullosa

Laminin-5 is composed of three distinct polypeptides, alpha3, beta3, and gamma2, which are encoded by three different genes, LAMA3, LAMB3, and LAMC2, respectively. We have isolated epidermal keratinocytes from a patient presenting with a lethal form of junctional epidermolysis bullosa characterized by a homozygous mutation of the LAMB3 gene, which led to complete absence of the beta3 polypeptide. In vitro, beta3-null keratinocytes were unable to synthesize laminin-5 and to assemble hemidesmosomes, maintained the impairment of their adhesive properties, and displayed a decrease of their colony-forming ability. A retroviral construct expressing a human beta3 cDNA was used to transduce primary beta3-null keratinocytes. Clonogenic beta3-null keratinocytes were transduced with an efficiency of 100%. Beta3-transduced keratinocytes were able to synthesize and secrete mature heterotrimeric laminin-5. Gene correction fully restored the keratinocyte adhesion machinery, including the capacity of proper hemidesmosomal assembly, and prevented the loss of the colony-forming ability, suggesting a direct link between adhesion to laminin-5 and keratinocyte proliferative capacity. Clonal analysis demonstrated that holoclones expressed the transgene permanently, suggesting stable correction of epidermal stem cells. Because cultured keratinocytes are used routinely to make autologous grafts for patients suffering from large skin or mucosal defects, the full phenotypic reversion of primary human epidermal stem cells defective for a structural protein opens new perspectives in the long-term treatment of genodermatoses.

The sulfatase gene family

During the past few years, molecular analyses have provided important insights into the biochemistry and genetics of the sulfatase family of enzymes, identifying the molecular bases of inherited diseases caused by sulfatase deficiencies. New members of the sulfatase gene family have been identified in man and other species using a genomic approach. These include the gene encoding arylsulfatase E, which is involved in X-linked recessive chondrodysplasia punctata, a disorder of cartilage and bone development. Another important breakthrough has been the discovery of the biochemical basis of multiple sulfatase deficiency, an autosomal recessive disorder characterized by a severe of all sulfatase activities. These discoveries, together with the resolution of the crystallographic structure of sulfatases, have improved our understanding of the function and evolution of this fascinating family of enzymes.

A model of corrective gene transfer in X-linked ichthyosis

Single gene recessive genetic skin disorders offer attractive prototypes for the development of therapeutic cutaneous gene delivery. We have utilized X-linked ichthyosis (XLI), characterized by loss of function of the steroid sulfatase arylsulfatase C (STS), to develop a model of corrective gene delivery to human skin in vivo. A new retroviral expression vector was produced and utilized to effect STS gene transfer to primary keratinocytes from XLI patients. Transduction was associated with restoration of full-length STS protein expression as well as steroid sulfatase enzymatic activity in proportion to the number of proviral integrations in XLI cells. Transduced and uncorrected XLI keratinocytes, along with normal controls, were then grafted onto immunodeficient mice to regenerate full thickness human epidermis. Unmodified XLI keratinocytes regenerated a hyperkeratotic epidermis lacking STS expression with defective skin barrier function, effectively recapitulating the human disease in vivo. Transduced XLI keratinocytes from the same patients, however, regenerated epidermis histologically indistinguishable from that formed by keratinocytes from patients with normal skin. Transduced XLI epidermis demonstrated STS expression in vivo by immunostaining as well as a normalization of histologic appearance at 5 weeks post-grafting. In addition, transduced XLI epidermis demonstrated a return of barrier function parameters to normal. These findings demonstrate corrective gene delivery in human XLI patient skin tissue at both molecular and functional levels and provide a model of human cutaneous gene therapy.

Clonal analysis of stably transduced human epidermal stem cells in culture

We have transduced normal human keratinocytes with retroviral constructs expressing a bacterial beta-galactosidase (beta-gal) gene or a human interleukin-6 (hIL-6) cDNA under control of a long terminal repeat. Efficiency of gene transfer averaged approximately 50% and 95% of clonogenic keratinocytes for beta-gal and hIL-6, respectively. Both genes were stably integrated and expressed for more than 150 generations. Clonal analysis showed that both holoclones and their transient amplifying progeny expressed the transgene permanently. Southern blot analysis on isolated clones showed that many keratinocyte stem cells integrated multiple proviral copies in their genome and that the synthesis of the exogenous gene product in vitro was proportional to the number of proviral integrations. When cohesive epidermal sheets prepared from stem cells transduced with hIL-6 were grafted on athymic animals, the serum levels of hIL-6 were strictly proportional to the rate of secretion in vitro and therefore to the number of proviral integrations. The possibility of specifying the level of transgene expression and its permanence in a homogeneous clone of stem cell origin opens new perspectives in the long-term treatment of genetic disorders.

Puncture-mediated gene transfer to the skin

Simple and efficient gene transfer to the skin would facilitate many local and systemic gene therapy applications. Here we report a novel approach that allows installation and expression of plasmid DNA without a particulate carrier into the skin for the purposes of gene therapy. A device with a constantly high-frequency oscillating bundle of fine metal needles allows puncturing of the skin and leads to DNA transfer to skin-associated cells and expression of reporter genes in mice. Furthermore, puncture-mediated instillation of an expression vector coding for a single T cell epitope induces specific cellular immune responses. If this approach could be optimized, puncture-mediated gene transfer might be useful for the treatment of large body areas with plasmid DNA for the purpose of somatic gene therapy.