CORRECTIVE GENE-TRANSFER IN THE HUMAN SKIN DISORDER LAMELLAR ICHTHYOSIS

Lamellar ichthyosis (LI) is a disfiguring skin disease characterized b y abnormal epidermal differentiation and defective cutaneous barrier f unction(1,2). LI has been associated with loss of keratinocyte transgl utaminase 1 (TGase1)(3,4) an enzyme believed necessary for normal form ation of the cornified epidermal barrier. Using LI as a prototype for therapeutic cutaneous gene delivery, we have used the human skin/immun odeficient mouse xenograft model to correct the molecular, histologic and functional abnormalities of LI patient skin in vivo. We have used TGase1-deficient primary keratinocytes from LI patients combined with high-efficiency transfer of functional TGase1 to regenerate engineered human LI epidermis on immunodeficient mice. Engineered LI epidermis d isplayed normal TGase1 expression in vivo, unlike unengineered LI epid ermis where TGase1 was absent. Epidermal architecture was also normali zed by TGase1 restoration, as was expression of the epidermal differen tiation marker filaggrin. Engineered LI skin demonstrated restoration of cutaneous barrier function measures to levels seen in epidermis reg enerated by keratinocytes from patients with normal skin, indicating f unctional correction in vivo of the proposed primary pathophysiologic defect in LI. These results confirm a major role for TGase1 in epiderm al differentiation and demonstrate a potential future approach to ther apeutic gene delivery in human skin.