Cutaneous gene transfer and therapy: the present and the future

Current standards and pitfalls associated with the transfection of primary fibroblast cells

Cultured fibroblast cells, especially dermal cells, are used for various types of scientific research, particularly within the medical field. Desirable features of the cells include their ease of isolation, rapid cellular growth, and high degree of robustness. Currently, fibroblasts are mainly used to obtain pluripotent cells via a reprogramming process. Dermal fibroblasts, are particularly useful for gene therapies used for promoting wound healing or minimizing skin aging. In recent years, fibroblast transfection efficiencies have significantly improved. In order to introduce molecules (most often DNA or RNA) into cells, viral-based systems (transduction) or non-viral methods (transfection) that include physical/mechanical processes or lipid reagents may be used. In this article, we describe critical points that should be considered when selecting a method for transfecting fibroblasts. The most effective methods used for the transfection of fibroblasts include both viral-based and non-viral nucleofection systems. These methods result in a high level of transgene expression and are superior in terms of transfection efficacy and viability.

Advances in Gene/Cell Therapy in Epidermolysis Bullosa

In the past few years, substantial preclinical and experimental advances have been made in the treatment of the severe monogenic skin blistering disease epidermolysis bullosa (EB). Promising approaches have been developed in the fields of protein and cell therapies, including allogeneic stem cell transplantation; in addition, the application of gene therapy approaches has become reality. The first ex vivo gene therapy for a junctional EB (JEB) patient was performed in Italy more than 8 years ago and was shown to be effective. We have now continued this approach for an Austrian JEB patient. Further, clinical trials for a gene therapy treatment of recessive dystrophic EB are currently under way in the United States and in Europe. In this review, we aim to point out that sustainable correction of autologous keratinocytes by stable genomic integration of a therapeutic gene represents a realistic option for patients with EB.

Topical gene electrotransfer to the epidermis of hairless guinea pig by non-invasive multielectrode array

Topical gene delivery to the epidermis has the potential to be an effective therapy for skin disorders, cutaneous cancers, vaccinations and systemic metabolic diseases. Previously, we reported on a non-invasive multielectrode array (MEA) that efficiently delivered plasmid DNA and enhanced expression to the skin of several animal models by in vivo gene electrotransfer. Here, we characterized plasmid DNA delivery with the MEA in a hairless guinea pig model, which has a similar histology and structure to human skin. Significant elevation of gene expression up to 4 logs was achieved with intradermal DNA administration followed by topical non-invasive skin gene electrotransfer. This delivery produced gene expression in the skin of hairless guinea pig up to 12 to 15 days. Gene expression was observed exclusively in the epidermis. Skin gene electrotransfer with the MEA resulted in only minimal and mild skin changes. A low level of human Factor IX was detected in the plasma of hairless guinea pig after gene electrotransfer with the MEA, although a significant increase of Factor IX was obtained in the skin of animals. These results suggest gene electrotransfer with the MEA can be a safe, efficient, non-invasive skin delivery method for skin disorders, vaccinations and potential systemic diseases where low levels of gene products are sufficient.

Transcutaneous gene gun delivery of hNC16A Induces BPAG2-specific tolerance

Immune recognition and rejection of tissues expressing transfected genes is a major complication of gene replacement therapy for inherited genetic disorders. Owing to the high immunogenicity of human bullous pemphigoid antigen 2 (hBPAG2), the induction and maintenance of tolerance to this neo-antigen is essential to deliver the gene product to patients with epidermolysis bullosa junctionalis. In a skin grafting mouse model, we used gene gun transfection with a construct encoding hNC16A, the immunodominant domain of hBPAG2, to induce antigen-specific immune tolerance. Eighty percent of wild-type mice transfected with hNC16A showed long-term survival of skin grafts expressing hBPAG2. Tolerance was stable and transferable by T cells but not by B cells of tolerant mice to naive hosts. A dense Foxp3(+) regulatory T-cell (T(reg)) infiltrate was noticed in grafts of tolerant mice and depletion of these cells resulted in a loss of tolerance. Taken together, we show that long-lasting hBPAG2-specific tolerance was induced with gene gun delivery of hNC16A through a T(reg)-dependent mechanism. This is of relevance to patients undergoing gene therapy and has broader implications for the treatment of antigen-specific autoimmune diseases.

Nucleofection: a new method for cutaneous gene transfer?

Background. Transfection efficacy after nonviral gene transfer in primary epithelial cells is limited. The aim of this study was to compare transfection efficacy of the recently available method of nucleofection with the established transfection reagent FuGENE6. Methods. Primary human keratinocytes (HKC), primary human fibroblasts (HFB), and a human keratinocyte cell line (HaCaT) were transfected with reporter gene construct by FuGENE6 or Amaxa Nucleofector device. At corresponding time points, β-galactosidase expression, cell proliferation (MTT-Test), transduction efficiency (X-gal staining), cell morphology, and cytotoxicity (CASY) were determined. Results. Transgene expression after nucleofection was significantly higher in HKC and HFB and detected earlier (3 h vs. 24 h) than in FuGENE6. After lipofection 80%–90% of the cells remained proliferative without any influence on cell morphology. In contrast, nucleofection led to a decrease in keratinocyte cell size, with only 20%–42% proliferative cells. Conclusion. Related to the method-dependent increase of cytotoxicity, transgene expression after nucleofection was earlier and higher than after lipofection.

Determination of the depth of excision using a dermatome (Aesculap) to export all hair follicle bulbs from a donor site in the dog

The aim of the study was to determine the depth of excision using a dermatome to excise all hair follicle bulbs from the donor site. Partial-thickness skin samples of different depth, ranging from 0.4 to 1 mm, were excised using a dermatome (Aesculap) from the dorsal aspect of the trunk of the dog. Biopsies, using a 6-mm biopsy punch, were performed in the centre of each donor site and excised sample. They were processed routinely for histological examination and the aspect of the hair follicles was observed. Split-thickness skin grafts of >or=0.7 mm deep performed with a dermatome contain the entire hair follicle.

Safe Selection of Genetically Manipulated Human Primary Keratinocytes with Very High Growth Potential Using CD24

Stable and safe corrective gene transfer in stem keratinocytes is necessary for ensuring success in cutaneous gene therapy. There have been numerous encouraging preclinical approaches to cutaneous gene therapy in the past decade, but it is only recently that a human volunteer suffering from junctional epidermolysis bullosa could be successfully grafted using his own non-selected, genetically corrected epidermal keratinocytes. However, ex vivo correction of cancer-prone genetic disorders necessitates a totally pure population of stably transduced stem keratinocytes for grafting. Antibiotic selection is not compatible with the need for full respect for natural cell fate potential and avoidance of immunogenic response in vivo. In order to surmount these problems, we developed a strategy for selecting genetically modified stem cell keratinocytes. Driving ectopic expression of CD24 (a marker of post-mitotic keratinocytes) at the surface of clonogenic keratinocytes permitted their full selection. Engineered keratinocytes expressing CD24 and the green fluorescent protein (GFP) tracer gene were shown to retain their original growth and differentiation potentials both in vitro and in vivo over 300 generations. Also, they did not exhibit signs of genetic instability. Using ectopic expression of CD24 as a selective marker of genetically modified human epidermal stem cells appears to be the first realistic approach to safe cutaneous gene therapy in cancer-prone disease conditions.

Femtosecond laser: a new intradermal DNA delivery method for efficient, long‐term gene expression and genetic immunization

A femtosecond laser beam gene transduction (SG-LBGT) system is described as a novel and efficient method of intradermal (i.d.) nonviral gene delivery in mice by permeabilizing cells utilizing femtosecond laser pulses. Using this approach, significant gene expression and efficient dermal transduction lasting for >7 months were obtained. The ability of this new DNA gene transfer method to enhance genetic vaccination was tested in BALB/C mice. A single i.d. injection of a plasmid (10 microg) containing the hepatitis B virus (HBV) surface antigen (HBsAg), followed by pulses of laser, induced high titers of HBsAg-specific antibodies lasting for >210 days and increased levels of IgG1, IgG2a, IFNgamma, and IL-4, indicating the activation of both Th1 and Th2 cells. Moreover, mice vaccinated using the SG-LBGT followed by challenge with pHBV showed increased protection against viral challenge, as detected by decreased levels of HBV DNA, suggesting an efficient Th1 effect against HBV-infected replicating cells. Tumor growth retardation was induced in vaccinated mice challenged with an HBsAg-expressing syngeneic tumor. In most of the parameters tested, administration of plasmid followed by laser application was significantly more effective and prolonged than that of plasmid alone. Tissue damage was not detected and integration of the plasmid into the host genomic DNA probably did not occur. We suggest that the LBGT method is an efficient and safe technology for in vivo gene expression and vaccination and emphasizes its potential therapeutic applications for i.d. nonviral gene delivery.

Adenoviral gene delivery to primary human cutaneous cells and burn wounds

The adenoviral transfer of therapeutic genes into epidermal and dermal cells is an interesting approach to treat skin diseases and to promote wound healing. The aim of this study was to assess the in vitro and in vivo transfection efficacy in skin and burn wounds after adenoviral gene delivery. Primary keratinocytes (HKC), fibroblasts (HFB), and HaCaT cells were transfected using different concentrations of an adenoviral construct (eGFP). Transfection efficiency and cytotoxicity was determined up to 30 days. Expression was quantified by FACS analysis and fluorimeter. Cytotoxicity was measured using the trypan blue exclusion method. 45 male Sprague Dawley rats received 2x10(8) pfu of Ad5-CMV-LacZ or carrier control intradermally into either superficial partial thickness scald burn or unburned skin. Animals were euthanized after 48 h, 7 or 14 days posttreatment. Transgene expression was assessed using immunohistochemistry and bioluminescent assays. The highest transfection rate was observed 48 h posttransfection: 79% for HKC, 70% for HFB, and 48% for HaCaT. The eGFP expression was detectable in all groups over 30 days (P>0.05). Cytotoxic effects of the adenoviral vector were observed for HFB after 10 days and HaCaT after 30 days. Reporter gene expression in vivo was significantly higher in burned skin compared with unburned skin (P=0,004). Gene expression decreases from 2 to 7 days with no significant expression after 14 days. This study demonstrates that effective adenoviral-mediated gene transfer of epidermal primary cells and cell-lines is feasible. Ex vivo gene transfer in epithelial cells might have promise for the use in severely burned patients who receive autologous keratinocyte sheets. Transient cutaneous gene delivery in burn wounds using adenoviral vectors causes significant concentrations in the wound tissue for at least 1 week. Based on these findings, we hypothesize that transient cutaneous adenoviral gene delivery of wound healing promoting factors has potential for clinical application.

Topical non-invasive gene delivery using gemini nanoparticles in interferon-γ-deficient mice

Cutaneous gene therapy, although a promising approach for many dermatologic diseases, has not progressed to the stage of clinical trials, mainly due to the lack of an effective gene delivery system. The main objective of this study was to construct and evaluate gemini nanoparticles as a topical formulation for the interferon gamma (IFN-gamma) gene in an IFN-gamma-deficient mouse model. Nanoparticles based on the gemini surfactant 16-3-16 (NP16-DNA) and another cationic lipid cholesteryl 3beta-(-N-[dimethylamino-ethyl] carbamate) [Dc-chol] (NPDc-DNA) were prepared and characterized. Zetasizer measurement indicated a bimodal distribution of 146 and 468 nm average particle sizes for the NP16-DNA (zeta-potential +51 mV) nanoparticles and monomodal distribution of 625 nm (zeta-potential +44 mV) for the NPDc-DNA. Circular dichroism studies showed that the gemini surfactant compacted the plasmid more efficiently compared to the Dc-chol. Small-angle X-ray scattering measurements revealed structural polymorphism in the NP16-DNA nanoparticles, with lamellar and Fd3m cubic phases present, while for the NPDc-DNA two lamellar phases could be distinguished. In vivo, both topically applied nanoparticles induced higher gene expression compared to untreated control and naked DNA (means of 0.480 and 0.398 ng/cm(2) vs 0.067 and 0.167 ng/cm(2)). However, treatment with NPDc-DNA caused skin irritation, and skin damage, whereas NP16-DNA showed no skin toxicity. In this study, we demonstrated that topical cutaneous gene delivery using gemini surfactant-based nanoparticles in IFN-gamma-deficient mice was safe and may provide increased gene expression in the skin due to structural complexity of NP16 nanoparticles (lamellar-cubic phases).

Gene therapy for autosomal dominant disorders of keratin

Dominant mutations that interfere with the assembly of keratin filaments cause painful and disfiguring epidermal diseases like pachyonychia congenita and epidermolysis bullosa simplex. Genetic therapies for such diseases must either suppress the production of the toxic proteins or correct the genetic defect in the chromosome. Because epidermal skin cells may be genetically modified in tissue culture or in situ, gene correction is a legitimate goal for keratin diseases. In addition, recent innovations, such as RNA interference in animals, make an RNA knockdown approach plausible in the near future. Although agents of RNA reduction (small interfering RNA, ribozymes, triplex oligonucleotides, or antisense DNA) can be delivered as nucleotides, the impermeability of the skin to large charged molecules presents a serious impediment. Using viral vectors to deliver genes for selective inhibitors of gene expression presents an attractive alternative for long-term treatment of genetic disease in the skin.

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

Gene transfer represents the unique therapeutic issue for a number of inherited skin disorders including junctional epidermolysis bullosa (JEB), an untreatable genodermatose caused by mutations in the adhesion ligand laminin 5 (alpha3beta3gamma2) that is secreted in the extracellular matrix by the epidermal basal keratinocytes. Because gene therapy protocols require validation in animal models, we have phenotypically reverted by oncoretroviral transfer of the curative gene the keratinocytes isolated from dogs with a spontaneous form of JEB associated with a genetic mutation in the alpha3 chain of laminin 5. We show that the transduced dog JEB keratinocytes: (1) display a sustained secretion of laminin 5 in the extracellular matrix; (2) recover the adhesion, proliferation, and clonogenic capacity of wild-type keratinocytes; (3) generate fully differentiated stratified epithelia that after grafting on immunocompromised mice produce phenotypically normal skin and sustain permanent expression of the transgene. We validate an animal model that appears particularly suitable to demonstrate feasibility, efficacy, and safety of genetic therapeutic strategies for cutaneous disorders before undertaking human clinical trials.

Generation of recombinant skin in vitro by adeno-associated virus type 2 vector transduction

It has long been recognized that skin may be a particularly good target for pharmacologic gene therapy and as a platform for the secretion of systemically distributed molecules. Adeno-associated virus type 2 (AAV) is a useful vector for skin gene therapy because skin is the natural host tissue for AAV, in which it functions as an autonomous parvovirus. We demonstrate here that recombinant (r) AAV vectors carrying the granulocyte-macrophage colony-stimulating factor (GM-CSF), human papillomavirus E6, or green fluorescent protein (GFP) transgene could transduce primary human keratinocytes in ex vivo culture. We further demonstrate that these transduced cells could be used to form a transgene-positive recombinant skin (r-skin), using the organotypic epithelial raft culture system. Transduction of keratinocytes was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) for RNA expression, enzyme-linked immunosorbent assay (ELISA) for product secretion, intracellular staining for protein expression, vector-chromosomal junction PCR and Southern blot analysis of proviral sequences, in situ immunohistochemistry analysis of protein expression, and ultraviolet light fluorescence for GFP expression. AAV/GM-CSF/Neo-infected keratinocyte/raft skins secreted GM-CSF at levels as high as 25 ng/cm(2) of skin and maintained expression to 60 days postinfection. These data support the utility and efficiency of AAV-based gene delivery to produce genetically altered keratinocytes and r-skin.

Molecular genetics of the ichthyoses

The ichthyoses are a large, clinically, genetically, and etiologically heterogeneous group of disorders of cornification due to abnormal differentiation and desquamation of the epidermis. Although they differ in clinical features, inheritance, and structural and biochemical abnormalities of the epidermis, they often pose a diagnostic challenge. For each of the 12 ichthyoses and related disorders described here, the major disease genes have been identified and genotype-phenotype correlation have begun to emerge. The molecular findings reveal the functional importance and interactions of many different epidermal proteins and metabolic pathways, including major structural proteins (keratins, loricrin), enzymes involved in lipid metabolism (transglutaminase 1, lipoxygenases, fatty aldehyde dehydrogenase, steroid sulfatase, glucocerebrosidase, Delta8-Delta7 sterol isomerase, 3beta-hydroxysteroid dehydrogenase), and protein catabolism (LEKTI), peroxisomal transport and processing (Peroxin 7 receptor, Phytanoyl-CoA hydroxylase) and DNA repair (proteins of the transcription repair complex). This review highlights the spectacular advances in the molecular genetics and biology of heritable ichthyoses over the past decade. It illustrates the power of molecular diagnostics for refining disease classification, providing prenatal diagnosis, improving genetic counseling, and clinical management.

Xeroderma pigmentosum: from symptoms and genetics to gene-based skin therapy

Xeroderma pigmentosum (XP) is a rare, recessively inherited genodermatosis prone to ultraviolet (UV)-induced skin neoplasms from keratinocyte origin, i.e. basal and squamous cell carcinoma. Cells from classic XP patients fail to properly eliminate UV-induced DNA lesions by the nucleotide excision repair (NER) mechanism. A variant form of XP, called XP-V suffers from faulty translesion synthesis. We review here recent data on XP gene products whose alterations affect NER and result in one of the 7 complementation groups of XP. Encouraging results of retrovirus-based genetic correction of XP keratinocytes are summarized and support realistic prospects of gene therapy for the XP-C complementation group.

Inherited junctional epidermolysis bullosa in the German Pointer: establishment of a large animal model

Junctional epidermolysis bullosa (JEB) is a genodermatosis suitable for gene therapy because conventional treatments are ineffective. Here, we elucidate the genetic basis of mild JEB in a breed of dogs that display all the clinical traits observed in JEB patients. The condition is associated with reduced expression of laminin 5 caused by a homozygous insertion (4818+207ins6.5 kb) of repetitive satellite DNA within intron 35 of the gene (lama3) for the laminin alpha3 chain. The intronic mutation interferes with maturation of the alpha3 pre-messenger RNA resulting in the coexpression of a transcript with a 227 nucleotide insertion and a wild-type mRNA that encodes scant amounts of the alpha3 polypeptide. Our results show that the amino acid sequence and structure of the canine and human alpha3 chain are highly conserved and that the reduced expression of laminin 5 affects the adhesion and clonogenic potential of the JEB keratinocytes. These JEB dogs provide the opportunity to perform gene delivery in a naturally occurring genodermatosis and to evaluate host tolerance to recombinant laminin 5.

An In Vivo Model of Wound Healing in Genetically Modified Skin-Humanized Mice

Cutaneous wound-healing disorders are a major health problem that requires the development of innovative treatments. Whithin this context, the search for reliable human wound-healing models that allow us to address both mechanistic and therapeutic matters is warranted. In this study, we have developed a novel invivo wound-healing model in a genetically modified human context. Our model is based on the regeneration of human skin on the back of nude mice by transplantation of a cultured bioengineered skin equivalent previously designed in our laboratory. In this setting, human keratinocytes in the epidermal compartment were genetically modified with a retroviral vector encoding the enhanced green fluorescent protein (EGFP). After stable engraftment of the EGFP skin was achieved (9-12 wk after grafting), a small circular full thickness wound was performed on this mature human skin. A wide variety of parameters involved in wound healing were monitored, including tissue architecture, cell proliferation, epidermal differentiation, dermal remodelling, and basement membrane regeneration. Wounded gene-targeted skin-humanized mice re-capitulated native skin wound-healing features. In addition, when keratinocyte growth factor (KGF), a growth factor that has been shown to improve wound healing, was added to wounds during 3 d, the re-epithelialization was significantly accelerated. The present wound-healing model system provides a suitable in vivo tool to test gene transfer strategies for human skin repair. It also serves as a complementary platform for studies in genetically modified mice and as a model to evaluate pharmaceutical therapeutic approaches for impaired wound healing.

A cutaneous gene therapy approach to treat infection through keratinocyte-targeted overexpression of antimicrobial peptides

Infection represents a major associated problem in severely burned patients, as it causes skin graft failure and increases the risk of mortality. Topical and systemic antibiotic treatment is limited by the appearance of resistant bacterial strains. Antimicrobial peptides (AMPs) are gene-encoded "natural antibiotics" that form part of the innate mechanism of defense and may be active against such antibiotic-resistant microorganisms. Several microbicidal peptides are expressed in human skin under inflammatory conditions, and their function is not only limited to microbial killing but also influences tissue repair and adaptive immunity. Protein delivery through cutaneous gene therapy is a promising therapeutic tool for both skin and nonskin diseases. Here we present a gene transfer approach aimed at delivering antimicrobial peptides from keratinocytes. Adenoviral vectors encoding antimicrobial peptide genes were used to infect human keratinocytes growing either on plastic or as part of cultured skin equivalents. Inhibition of bacterial growth occurred both in conditioned media and in direct contact with AMPs gene-transduced keratinocytes. In addition, we showed cooperative effects after transfer of combinations of genes encoding for AMPs with structural differences. Combined cutaneous tissue engineering in conjunction with (microbicidal) gene therapy emerges as a tailored therapeutic approach that is useful for wound coverage and, in this case, concomitantly combating infection.

Current approaches and perspectives in human keratinocyte-based gene therapies

Inherited and acquired disorders are liable to treatment with somatic gene therapy. The skin, and in particular epidermal cells, are particularly suited to genetic manipulation and follow-up of therapeutic effects. Cutaneous gene therapy may be effective for skin defects and systemic abnormalities. The robust basic and preclinical data available today would support the application of keratinocyte-based gene therapy to patients.

Xeroderma pigmentosum: from genetics to hopes and realities of cutaneous gene therapy

Xeroderma pigmentosum (XP) is a rare genodermatosis transmitted as an autosomal and recessive trait. XP patients are highly photosensitive and prone to develop skin tumours in sun-exposed areas. Biochemical and genetic studies have demonstrated that nucleotide excision repair, the most versatile DNA repair mechanism, is deficient in XP cells, leading to ultraviolet-induced hypermutagenesis and a predisposition of XP patients to cancer. Cloning of XP genes responsible for the disease, together with the poor efficacy of classical pharmacological treatments, have motivated approaches towards cutaneous gene therapy of the XP. The author's group have successfully reconstructed XP skin in vitro from XP keratinocytes and fibroblasts. More recently, the possibility to fully revert the phenotype of XP keratinocytes after retrovirus-mediated transfer of the adequate wild-type XP gene in XP keratinocytes was demonstrated. Reconstruction of genetically corrected XP skin in vitro constitutes a new hope toward cutaneous gene therapy of the XP.

Functional improvement of mutant keratin cells on addition of desmin: an alternative approach to gene therapy for dominant diseases

A major challenge to the concept of gene therapy for dominant disorders is the silencing or repairing of the mutant allele. Supplementation therapy is an alternative approach that aims to bypass the defective gene by inducing the expression of another gene, with similar function but not susceptible to the disrupting effect of the mutant one. Epidermolysis bullosa simplex (EBS) is a genetic skin fragility disorder caused by mutations in the genes for keratins K5 or K14, the intermediate filaments present in the basal cells of the epidermis. Keratin diseases are nearly all dominant in their inheritance. In cultured keratinocytes, mutant keratin renders cells more sensitive to a variety of stress stimuli such as osmotic shock, heat shock or scratch wounding. Using a 'severe' disease cell culture model system, we demonstrate reversion towards wild-type responses to stress after transfection with human desmin, an intermediate filament protein normally expressed in muscle cells. Such a supplementation therapy approach could be widely applicable to patients with related individual mutations and would avoid some of the financial obstacles to gene therapy for rare diseases.

Microfabricated silicon microneedles for nonviral cutaneous gene delivery

BACKGROUND

The skin represents an accessible somatic tissue for therapeutic gene transfer. The superficial lipophilic layer of the skin, the stratum corneum, however, constitutes a major obstacle to the cutaneous delivery of charged macromolecules such as DNA.

OBJECTIVES

To determine whether silicon-based microneedles, microfabricated via a novel isotropic etching/BOSCH reaction process, could generate microchannels in the skin of sufficient dimensions to facilitate access of lipid : polycation : pDNA (LPD) nonviral gene therapy vectors.

METHODS

Scanning electron microscopy was used to visualize the microconduits created in heat-separated human epidermal sheets after application of the microneedles. Following confirmation of particle size and particle surface charge by photon correlation spectrocopy and microelectrophoresis, respectively, the diffusion of fluorescent polystyrene nanospheres and LPD complexes through heat-separated human epidermal sheets was determined in vitro using a Franz-type diffusion cell. In-vitro cell culture with quantification by flow cytometry was used to determine gene expression in human keratinocytes (HaCaT cells).

RESULTS

The diffusion of 100 nm diameter fluorescent polystyrene nanospheres, used as a readily quantifiable predictive model for LPD complexes, through epidermal sheets was significantly enhanced following membrane treatment with microneedles. The delivery of LPD complexes either into or through the membrane microchannels was also demonstrated. In both cases considerable interaction between the particles and the epidermal sheet was observed. In-vitro cell culture was used to confirm that LPD complexes mediated efficient reporter gene expression in human keratinocytes in culture when formulated at the appropriate surface charge.

CONCLUSIONS

These studies demonstrate the utility of silicon microneedles in cutaneous gene delivery. Further studies are required to elucidate fully the influence of the physicochemical characteristics of gene therapy vectors, e.g. particle diameter and surface charge, on their diffusion through microchannels and to quantify gene expression in vivo.

Tumeurs cutanées au cours du xeroderma pigmentosum au Maroc

INTRODUCTION

Xeroderma pigmentosum is a rare recessive and autosomically transmitted genodermatosis. Its cutaneous manifestations are dominated by skin cancers. This investigation aims at studying the epidemiologic, clinic, histologic, therapeutic and evolutive aspects of the skin tumors during xeroderma pigmentosum.

PATIENTS AND METHODS

A retrospective monocentric study was carried out in the Dermatology and Veneorology Department of Ibn Rochd University Hospital of Casablanca, Morocco. It included all the xeroderma pigmentosum admitted to hospital or followed-up from 1990 to 2000. All the dossiers were included. The anatomopathologic study was carried out in all the skin tumor cases.

RESULTS

One hundred and twenty xeroderma pigmentosum were admitted in 10 Years. Fifty-four percent of the cases were females and 46 p. 100 were males. The mean apparition of the first tumor was 7.7 Years. One hundred and fifty-three skin tumors were diagnosed in 96 patients (80 p. 100). These tumors were of basocellular carcinoma type in 32.6 p. 100, of squamous cell carcinoma type in 33.9 p. 100 and of melanoma type in 11 p. 100. Ocular tumors were found in 31 cases (25.8 p. 100) and buccal in 8 cases. Therapeutically, the surgical exeresis of one or many tumors was performed in all cases. Electrocoagulation was associated in 42 p. 100 of the cases and skin graft in 52 p. 100. Cutaneous relapses after surgery were noticed in 55 cases (57.2 p. 100). Twenty-five patients died and 31 were lost to follow-up.

DISCUSSION

Our series is characterized by a large frequency of mainly cutaneous tumors (80 p. 100) in comparison with the largest review of literature (45 p. 100). These tumors were mainly represented by basocellular and squamous cell carcinoma with onset at an early age (7.7 Years). Our series is also characterized by a large frequency of cutaneous relapses after surgery (51.6 p. 100). Neglecting advice on photoprotection and the lack of regular control visits lead to the proliferation of large size tumors, making therapeutic strategies difficult or even impossible.

A Comparison of Targeting Performance of Oncoretroviral Versus Lentiviral Vectors on Human Keratinocytes

The epidermis, like other rapidly renewing tissues, relies on a stem cell compartment to undergo constant regeneration. In order to develop realistic and long-lasting therapeutic approaches for some skin disorders, gene transfer to these critical cells must be obtained. While efficient retroviral ex vivo targeting and transgene integration in human keratinocytes is tightly dependent on proliferation, transferring genetic information to quiescent cells in culture also presents advantages, including the possibility of targeting putative dormant epidermal stem cells. In the present study we compared the efficiency of transduction achieved with a third-generation of human immunodeficiency virus (HIV)-based lentiviral vector to that obtained with a Moloney murine leukemia oncoretroviral vector (MLV) on proliferating and quiescent human keratinocytes growing in vitro in standard Rheinwald and Green cultures as well as in confluent organotypic cultures. Each viral vector contained the enhanced green fluorescent protein (EGFP) as a reporter gene. The lentiviral vector, but not the MLV vector, led to EGFP expression both in nondividing and proliferating epidermal cell populations in vitro. This feature was clearly evident when direct targeting of human keratinocytes, forming part of the epidermal component of an organotypic skin culture, was attempted. Keratinocytes modified by both MLV and the lentiviral vector allowed long-term regeneration of genetically engineered human skin on the backs of immunodeficient nonobese diabetic/severe combined immunodeficiency disorders (NOD/SCID) mice. However, EGFP transgene expression in the context of the MLV (long-terminal repeat [LTR]-driven) or lentiviral vector (cytomegalovirus [CMV]-driven) demonstrated clear differences both in quantitative terms and in the in vivo localization pattern.

Genetic correction of canine dystrophic epidermolysis bullosa mediated by retroviral vectors

We have assessed the suitability of retroviral vectors for gene therapy of recessive dystrophic epidermolysis bullosa (RDEB) in dogs expressing a mutated collagen type VII. Isolation and analysis of the 9 kb dog collagen type VII cDNA identified the causative genetic mutation G1906S and disclosed the interspecies conservation of collagen type VII. Highly efficient transfer of the wild-type collagen type VII cDNA to both dog RDEB and human primary RDEB collagen type VII-null keratinocytes using recombinant vectors derived from LZRS-Ires-zeo and MSCV retroviruses achieved sustained and permanent expression of the transgene product. The expression and post-translational modification profile of the recombinant collagen type VII was comparable to that of the wild-type counterpart. The recombinant canine collagen type VII in human RDEB keratinocytes and dog cells corrected the observable defects caused by RDEB keratinocytes in cell cultures and in vitro reconstructed skin. Hypermotility was fully reverted in human RDEB keratinocytes, and strongly reduced in the dog RDEB cells. This observation suggests that not only infection efficiency but also high expression levels are required to ensure therapeutic efficacy in the presence of mutated gene products. Our results set the basis for preclinical gene therapy assays in the first immune-competent large animal model for an inherited skin disease and broaden the spectrum of preclinical and clinical applications of retroviral vectors in the transfer of large recombinant genes in epithelial cells.

Genetic correction of DNA repair-deficient/cancer-prone xeroderma pigmentosum group C keratinocytes

Xeroderma pigmentosum (XP) is a rare photosensitive and cancer-prone syndrome transmitted as an autosomal recessive trait. Most cancers developed by XP patients are basal and squamous cell carcinoma strikingly restricted to sun-exposed parts of the skin. Cells from patients with classic XP are deficient in nucleotide excision repair, a versatile biochemical mechanism for removal of ultraviolet-induced DNA lesions. Among the seven classic XP complementation groups known to date (XP-A to XP-G), XP-C is the most common one in Europe and North Africa and XP-C patients remain free of neurologic problems often seen in other XP complementation groups. This has prompted us to undertake genetic correction of XP-C fibroblasts and particularly keratinocytes, which are the most relevant cells in relation to skin cancer and have proven recently to be capable of reconstructing XP-C skin in vitro. In this study, we demonstrate that DNA repair capacity, cell survival properties, and transition from proliferative to abortive keratinocyte colonies toward UVB irradiation can be fully recovered in keratinocytes from patients with XPC transduced with a retroviral vector stably driving the expression of the wild-type XPC protein. In addition, we show that in the absence of UV, XP-C keratinocytes exhibit intrinsic cell cycle abnormalities, and beta(1)-integrin overexpression, defects that are also both fully reversed after genetic correction. Together with full correction of the defects in XP-C corrected keratinocytes, in vitro reconstruction of skin from these cells open a rational perspective to XP tissue therapy.

Xeroderma Pigmentosum: Mondscheinkinder. Xeroderma Pigmentosum: Children of the Moon

Xeroderma pigmentosum is based on a genetic defect in the DNA repair system, which is diagnosed in early childhood. Xeroderma pigmentosum is a rare disorder, which is transmitted in an autosomal recessive manner. Children with xeroderma pigmentosum display hypersensitivity to ultraviolet (UV) radiation. These patients experience serious sunburns with minimal exposure and then develop poikiloderma in the sun-exposed areas. Squamous cell carcinomas, basal cell carcinomas and malignant melanomas all appear during childhood. The majority of patients do not reach adult, but die from metastatic cutaneous malignancies. Genetically, xeroderma pigmentosum is differentiated into 7 complementation groups (XP-A to XP-G) and the xeroderma pigmentosum variants (XP-V). The assignment to the specific complementation group is made by fusing of xeroderma pigmentosum fibroblasts. Xeroderma pigmentosum must be distinguished from other so-called DNA repair deficiency syndromes, including Cockayne syndrome and trichothiodystrophy. A topical DNA repair enzyme appears to be helpful. A recombinant liposomal encapsulated T4 endonuclease V repairs UV-induced cyclobutane-pyrimidine dimers. Direct curative treatment of xeroderma pigmentosum could be achieved with gene therapy in future. Transfection of an intact repair gene which specifically codes for the missing repair protein could open new possibilities in the therapy of xeroderma pigmentosum.

Genetic reversion of inherited skin disorders

Human epidermis is a squamous stratified epithelium whose integrity relies on balanced processes of cell attachment, proliferation, and differentiation. In monogenic skin dermatoses, such as mecano-bullous diseases, or DNA repair deficiencies such as the xeroderma pigmentosum (XP), alterations of skin integrity may have devastating consequences as illustrated by the extremely high epidermal cancer proneness of XP patients. The lack of efficient pharmacological treatments, the easy accessibility of skin, and the possibility of long term culture and genetic manipulations ex vivo of epidermal keratinocytes, have encouraged approaches toward gene transfer and skin therapy prospects. We review here some of the human genetic disorders that exhibit major traits in skin, as well as requirements and difficulties inherent to approaches aimed at stable phenotypic correction.

Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse

Recent achievements in the genetic correction of keratinocytes isolated from patients with junctional epidermolysis bullosa have paved the way to a gene therapy approach for the disease. Because gene therapy protocols require preclinical validation in animals, we have characterized spontaneous animal models of junctional epidermolysis bullosa. In this study we have elucidated the genetic basis of the hereditary junctional mechanobullous disease in the Belgian horse, a condition characterized by blistering of the skin and mouth epithelia, and exungulation (loss of the hoof). Immunofluorescence analysis associated the condition to the absent expression of the gamma2 chain of laminin 5 and designated Lamc2 as the candidate gene. Comparative analysis of the nucleotide sequence of the full-length gamma2 cDNA isolated by reverse transcription polymerase chain reaction amplification of total RNA purified from the epithelium of a junctional epidermolysis bullosa foal and a healthy control disclosed a homozygous basepair insertion (1368insC) in the affected animal. Mutation 1368insC results in a downstream premature termination codon and is predicted to cause absent expression of the laminin gamma2 polypeptide. Our results also show that: (i) the horse junctional epidermolysis bullosa genetically corresponds to the severe Herlitz form of junctional epidermolysis bullosa in man; (ii) the amino acid sequence and structure of the horse laminin gamma2 chain are virtually identical to the human counterpart; (iii) the moderate eruption of skin blisters in the affected animals with respect to the human Herlitz junctional epidermolysis bullosa patients correlates with the protection provided by hair. Our observations suggest that the affected foals are a convenient source of epithelial cells from tissues that cannot be obtained from human junctional epidermolysis bullosa patients, and imply that hairless strains of animals with recessive skin disorders would be the best models for in vivo gene therapy approaches to skin blistering diseases.

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.

Reduced expression of the epithelial adhesion ligand laminin 5 in the skin causes intradermal tissue separation

Laminin 5, the major keratinocyte adhesion ligand, is found in the lamina lucida subregion of the epidermal basement membrane of the skin, where it colocalizes with the anchoring filaments. Mutations in the genes encoding laminin 5 cause junctional epidermolysis bullosa, an inherited skin blistering disease characterized by abnormal hemidesmosomes and cleavage of the lamina lucida leading to epidermal detachment. In this work we describe the genetic basis of a new subtype of lethal inherited epidermolysis bullosa associated with reduced skin reactivity to laminin 5, presence of mature hemidesmosomes, and intradermal cleavage of the skin. The epidermolysis bullosa patients were heterozygous for a nonsense mutation (Q896X) and a splice site mutation (764-10T-->G) in the gene (LAMC2) for the gamma2 chain of laminin 5. The nonsense mutation causes accelerated decay of the corresponding mRNA, while the splice site mutation results in maturation of a cryptic wild-type gamma2 mRNA leading to reduced expression of wild-type laminin 5. In vitro studies using the probands' keratinocytes showed that secretion of reduced amounts of functional laminin 5 in the patient, although permitting formation of hemidesmosomes, fail to restore efficient cell adhesion. Our results provide the first evidence that laminin 5 contributes to the firm adhesion of the epithelial basement membrane to the underlying stroma. They also show that a low expression level of laminin 5 induces assembly of mature hemidesmosomes in vivo but fails to assure a stable cohesion of the dermal-epidermal junction.

Participation of the melanocortin-1 receptor in the UV control of pigmentation

The cloning of the melanocortin-1 receptor (MC1R) gene from human melanocytes and the demonstration that these cells respond to the melanocortins alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) with increased proliferation and melanogenesis have renewed the interest in investigation the physiological role of these hormones in regulating human pigmentation. Alpha-melanocyte stimulating hormone and ACTH are both synthesized in the human epidermis, and their synthesis is upregulated by exposure to ultraviolet radiation (UVR). Activation of the MC1R by ligand binding results in stimulation of cAMP formation, which is a principal mechanism for inducing melanogenesis. The increase in cAMP is required for the pigmentary response of human melanocytes to UVR, and for allowing them to overcome the UVR-induced G1 arrest. Treatment of human melanocytes with alpha-MSH increases eumelanin synthesis, an effect that is expected to enhance photoprotection of the skin. Population studies have revealed more than 20 allelic variants of the MC1R gene. Some of these variants are overexpressed in individuals with skin type I or II, red hair, and poor tanning ability. Future studies will aim at further exploration of the role of these variants in MC1R function, and in determining constitutive human pigmentation, the response to sun exposure, and possibly the susceptibility to skin cancer.