A MODEL OF CORRECTIVE GENE-TRANSFER IN X-LINKED ICHTHYOSIS

Single gene recessive genetic skin disorders offer attractive prototyp es 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 expr ession 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 ster oid sulfatase enzymatic activity in proportion to the number of provir al integrations in XLI cells. Transduced and uncorrected XLI keratinoc ytes, along with normal controls, were then grafted onto immunodeficie nt mice to regenerate full thickness human epidermis, Unmodified XLI k eratinocytes regenerated a hyperkeratotic epidermis lacking STS expres sion with defective skin barrier function, effectively recapitulating the human disease in vivo. Transduced XLI keratinocytes from the same patients, however, regenerated epidermis histologically indistinguisha ble from that formed by keratinocytes from patients with normal skin, Transduced XLI epidermis demonstrated STS expression in vivo by immuno staining as well as a normalization of histologic appearance at 5 week s post-grafting, In addition, transduced XLI epidermis demonstrated a return of barrier function parameters to normal, These findings demons trate corrective gene delivery in human XLI patient skin tissue at bot h molecular and functional levels and provide a model of human cutaneo us gene therapy.