Durable and stratum-specific gene expression in epidermis

A number of genetic disorders are manifested in cutaneous epithelium and gene therapy approaches for treatment of such diseases are being considered. A successful gene therapy protocol requires durable and correctly targeted gene expression within the tissue. The continuous renewal and high levels of compartmentalization in epidermis are two challenges for a successful gene therapy of skin disorders. For those disorders which affect the upper layers of epidermis, vectors must be available that target stem cells, but remain silent until the progeny of these cells undergo differentiation. To explore the potential of long-term and targeted vector expression in epidermis, a hybrid retroviral vector encoding the reporter enhanced green fluorescent protein (EGFP) was constructed. The viral enhancer in the long terminal repeat of the vector was replaced with a 510-bp enhancer element of the human involucrin promoter. Keratinocyte-specific expression directed by the hybrid vector was demonstrated in culture and suprabasal-specific expression was observed in organotypic human epidermal cultures. In vivo transduction of mouse skin with this hybrid vector indicated long-term and stratum-specific expression of the transgene in mouse epidermis. The design of similar vectors for various gene therapy applications constitutes an important step toward clinically effective gene therapy.