Cutaneous gene transfer for skin and systemic diseases

Solid tissues can be manipulated ex vivo and used as vehicles for gene therapy

BACKGROUND

Organ fragments can be cultured for weeks in vitro if they are prepared of microscopic thickness and if the basic organ structure is preserved. Such organ fragments, which we termed micro-organs (MOs), express in culture endogenous tissue-specific gene products. We have exploited this methodology to engineer MOs ex vivo by gene transfer.

METHODS

MOs prepared from spleen, lung, colon and skin were infected using: herpes simplex type-1, adeno virus, vaccinia virus and murine leukemia virus (MuLV), carrying the reporter gene beta-galactosidase.

RESULTS

All four viral vectors infected MOs in culture, with adeno infection giving significantly higher values. After optimization, high levels of expression (> 15% positive cells), comparable to those obtained with the adeno construct, were also obtained using the MuLV construct both in vitro and after implantation into syngeneic hosts. After implantation, the engineered tissue was found to remain localized, become vascularized, and to express the transduced gene for several months.

CONCLUSIONS

The system can be used to study interactions between viruses and tissues both ex vivo and in vivo. Furthermore, the approach proposes a novel platform for ex vivo gene therapy. Such engineered structures could be used as autologous biological pumps for continuous secretion in vivo of gene products of clinical importance.

Recombinant adenovirus-p21 attenuates proliferative responses associated with excessive scarring

Excessive cutaneous scarring is an important clinical disorder resulting in adverse tissue growth and function as well as undesirable cosmetic appearance. p21WAF-1/Cip-1 is a cyclin-dependent kinase inhibitor that blocks cell cycle progression and inhibits cell proliferation. We used a recombinant adenovirus containing the human p21WAF-1/Cip-1 cDNA (rAd-p21) to evaluate proliferative responses in skin models. In vitro dose-response studies using primary human dermal fibroblasts resulted in a dose-dependent expression of p21WAF-1/Cip-1 protein and a 3- to 80-fold reduction in cell proliferation as measured by 5-bromodeoxyuridine incorporation. Further, rAd-p21 reduced type I procollagen production when compared to control virus. A rat polyvinyl alcohol sponge model was used to determine rAd-p21 effects on granulation tissue formation in vivo. Sponges pretreated with a granulation tissue stimulator, rAd-PDGF-B and subsequently rAd-p21 on a second injection, showed a p21WAF-1/Cip-1 specific dose-dependent decrease in percent granulation fill as the rAd-p21 dose increased (p < 0.001). Immunohistochemistry identified human p21WAF-1/Cip-1 expression in sponges treated with rAd-p21 5 days postinjection. Additionally, 5-bromodeoxyuridine and Ki67 staining in sponges treated with rAd-p21 showed a significant decrease in proliferation when compared to rAd-platelet-derived growth factor-B alone or vehicle control groups (p < 0.01). These data support the utility of p21WAF-1/Cip-1 in targeting hyperproliferative disorders of the skin.

Recombinant adeno-associated virus type 2-mediated gene transfer into human keratinocytes is influenced by both the ubiquitin/proteasome pathway and epidermal growth factor receptor tyrosine kinase

Efficient gene delivery into keratinocytes is a prerequisite for successful skin gene therapy. Vectors based on recombinant adeno-associated virus type 2 (rAAV-2) offer several promising features that make them attractive for cutaneous applications. However, highly efficient gene delivery may be hampered by different cellular factors, including lack of viral receptors, impairment of cytoplasmic trafficking or limitations in viral second-strand synthesis. This study was undertaken to find factors that influence rAAV-2-mediated in vitro gene transfer into human keratinocytes and, consequently, ways to optimize gene delivery. Transduction experiments using rAAV-2 vectors expressing green fluorescent protein (GFP) demonstrated that impaired cellular trafficking of vector particles and high levels of autophosphorylation at epidermal growth factor receptor tyrosine kinase (EGF-R TK) have a negative influence on gene transfer into keratinocytes. Treatment of keratinocytes with proteasome inhibitor MG132 resulted in a transient augmentation of GFP expression in up to 37% of cells. Treatment with EGF-R TK inhibitors (quinazoline type) enhanced transgene expression in 10-14.5% of the cells. Gene expression was stable for more than 10 weeks and persisted until proliferative senescence occurred. This stable gene expression allows speculation that keratinocyte stem cells have initially been transduced. These findings might have relevance for the use of rAAV-2 vectors in skin gene therapy: transient enhancement of rAAV-2 transduction with proteasome inhibitors might be useful for genetic promotion of wound healing or skin-directed vaccination. Treatment with quinazolines may increase rAAV-2 transduction of keratinocyte stem cells, which is important for gene therapy approaches to inherited diseases.

Genetic hair and nail disorders

Hair and nails are skin appendages that share with other ectodermal tissues a common developmental pathway. Inherited disorders affecting these two structures therefore very often involve other epithelial components and present with multiple anomalies, generating both physical and psychological distress among patients and their families. The present review briefly describes major recent advances in our understanding of hair and nail genodermatoses.

Assessment of optimal transduction of primary human skin keratinocytes by viral vectors

BACKGROUND

Genetically modified keratinocytes generate transplantable self-renewing epithelia suitable for delivery of therapeutic polypeptides. However, the variety of viral vectors and experimental conditions currently used make fragmented or contradictory the information on the transduction efficiency of the human primary keratinocytes. To compare the suitability of the most currently used viral vectors for efficient gene transfer to human keratinocytes, we have performed a comparative study using a panel of recombinant constructs.

METHODS

For each vector, the transduction efficiency and the persistence of the transgene expression were quantified by fluorescence microscopy and flow cytometry analysis of the infected cells.

RESULTS

We show that: (1) canine and human adenoviral vectors achieve a highly efficient but transient transduction of both primary and immortalized keratinocytes; (2) the adenovirus-associated virus (AAV) vectors transduce immortalized keratinocytes, albeit with a short-lived gene expression (<4 days), but fail to infect primary keratinocytes; and (3) under appropriate conditions, the oncoretroviral and lentiviral vectors can permanently transduce up to 100% of primary keratinocytes, but the highly clonogenic keratinocytes are more efficiently targeted by lentiviral vectors.

CONCLUSIONS

Therefore, AAV vectors are unsuitable to transduce primary keratinocytes, while human and canine adenoviral vectors appears to be appropriate to achieve short-term delivery of therapeutic products. Recombinant retroviruses provide sustained expression of the transgene, but the lentiviral vectors are the most suitable for ex vivo gene therapy because of their ability to transduce clonogenic primary keratinocytes.

Ultrasound and transdermal drug delivery

Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Application of ultrasound to the skin increases its permeability (sonophoresis) and enables the delivery of various substances into and through the skin. This review presents the main findings in the field of sonophoresis, namely transdermal drug delivery and transdermal monitoring. Particular attention is paid to proposed enhancement mechanisms and future trends in the field of cutaneous vaccination and gene delivery.

Translational benefits from research on rare genodermatoses

Significant new discoveries about many of the genodermatoses have been made recently through an improved knowledge of the human genome, advances in molecular screening strategies and also through more comprehensive Internet DNA databases. By 2003, over 350 single gene skin disorders had been characterized at a molecular level. These new data provide more detailed information for patients, allow for more accurate diagnoses, and help improve genetic counselling. Other benefits include the feasibility of carrier screening and DNA-based prenatal testing, as well as a platform for devising new treatments, including somatic gene therapy. Research on rare single gene disorders also provides new insight into more common skin conditions. For example, new ideas about photosensitivity are emerging from discoveries of mutations in a novel component of the actin cytoskeleton (kindlin-1) in the rare inherited poikiloderma disorder, Kindler syndrome. Likewise, new clues to understanding disease pathology in lichen sclerosus have been gleaned from the discovery of pathogenic mutations in the skin protein, extracellular matrix protein 1, in the rare sclerosing inherited skin disorder, lipoid proteinosis. Finally, new insight into what can cause exuberant granulation tissue in chronic wounds has been provided by the discovery of specific mutations in the basement membrane protein, laminin 5, in the rare inherited condition, laryngo-onychocutaneous syndrome. It is clear that a precise research focus on the rare genodermatoses is providing practical benefits for sufferers of these disorders, as well as new lessons and ideas about more common acquired skin conditions.

Thyroid hormones and gamma interferon specifically increase K15 keratin gene transcription

Basal layers of stratified epithelia express keratins K5, K14, and K15, which assemble into intermediate filament networks. Mutations in K5 or K14 genes cause epidermolysis bullosa simplex (EBS), a disorder with blistering in the basal layer due to cell fragility. Nonkeratinizing stratified epithelia, e.g., in the esophagus, produce more keratin K15 than epidermis, which alleviates the esophageal symptoms in patients with K14 mutations. Hypothesizing that increasing the cellular content of K15 could compensate for the mutant K14 and thus ease skin blistering in K14 EBS patients, we cloned the promoter of the K15 gene and examined its transcriptional regulation. Using cotransfection, gel mobility shifts, and DNase I footprinting, we have identified the regulators of K15 promoter activity and their binding sites. We focused on those that can be manipulated with extracellular agents, transcription factors C/EBP, AP-1, and NF-kappaB, nuclear receptors for thyroid hormone, retinoic acid, and glucocorticoids, and the cytokine gamma interferon (IFN-gamma). We found that C/EBP-beta and AP-1 induced, while retinoic acid, glucocorticoid receptors, and NF-kappaB suppressed, the K15 promoter, along with other keratin gene promoters. However, the thyroid hormone and IFN-gamma uniquely and potently activated the K15 promoter. Using these agents, we could boost the amounts of K15 in human epidermis. Our findings suggest that treatments based on thyroid hormone and IFN-gamma could become effective agents in therapy for patients with EBS.

Targets for molecular therapy of skin cancer

Cancers of the skin encompass the first and second most common neoplasms in the United States, epidermal basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), respectively, as well as the melanocytic malignancy, malignant melanoma (MM). Recently identified alterations in the function of specific genes in these cancers provide new potential therapeutic targets. These alterations affect conserved regulators of cellular proliferation and viability, including the Sonic Hedgehog, Ras/Raf, ARF/p53, p16(INK4A)/CDK4/Rb and NF-kappaB pathways. New modalities designed to target these specific proteins may represent promising approaches to therapy of human skin cancers.

Immune-mediated loss of transgene expression in skin: implications for cutaneous gene therapy

A clearer understanding of the immune-mediated loss of transgene from cutaneous epithelium is necessary for development of effective clinical gene therapy protocols for patients who carry null mutations in the target gene. We have used retrovirus-mediated transfer of lacZ to mouse skin as a model to investigate the mechanism of immune-mediated transgene loss in skin. Transduction of C57Bl/6 mouse skin resulted in elicitation of both humoral and cellular immune responses. Antibody responses did not play a major role in the loss of transgene. Infiltration of the transduced skin with CD4(+) and CD8(+) cells and induction of transgene-specific cytotoxic T lymphocytes implied a role for T-cell-mediated responses. Transduction of mice deficient in either major histocompatibility complex (MHC) class I or class II molecules resulted in transient transgene expression. Only in MHC(-/-) mice lacking expression of both class I and class II MHC molecules was persistent transgene expression seen. These data indicate a primary role for T-cell-mediated responses in the immune-mediated loss of transgene expression. Furthermore, CD4 and CD8 T cells have overlapping roles and either population can effectively eliminate transduced cells. Therefore, long-term cutaneous gene therapy may require development of strategies to interfere with activation or function of both T cell populations.

Injection of genetically engineered fibroblasts corrects regenerated human epidermolysis bullosa skin tissue

Current therapeutic strategies for genetic skin disorders rely on the complex process of grafting genetically engineered tissue to recipient wound beds. Because fibroblasts synthesize and secrete extracellular matrix, we explored their utility in recessive dystrophic epidermolysis bullosa (RDEB), a blistering disease due to defective extracellular type VII collagen. Intradermal injection of RDEB fibroblasts overexpressing type VII collagen into intact RDEB skin stably restored correctly localized type VII collagen expression in vivo and normalized hallmark RDEB disease features, including subepidermal blistering and anchoring fibril defects. This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.