A model of corrective gene transfer in X-linked ichthyosis

Single gene recessive genetic skin disorders offer attractive prototypesfor the development of therapeutic cutaneous gene delivery. We haveutilized X-linked ichthyosis (XLI), characterized by loss of function ofthe steroid sulfatase arylsulfatase C (STS), to develop a model ofcorrective gene delivery to human skin in vivo. A new retroviral expressionvector was produced and utilized to effect STS gene transfer to primarykeratinocytes from XLI patients. Transduction was associated withrestoration of full-length STS protein expression as well as steroidsulfatase enzymatic activity in proportion to the number of proviralintegrations in XLI cells. Transduced and uncorrected XLI keratinocytes,along with normal controls, were then grafted onto immunodeficient mice toregenerate full thickness human epidermis. Unmodified XLI keratinocytesregenerated a hyperkeratotic epidermis lacking STS expression withdefective skin barrier function, effectively recapitulating the humandisease in vivo. Transduced XLI keratinocytes from the same patients,however, regenerated epidermis histologically indistinguishable from thatformed by keratinocytes from patients with normal skin. Transduced XLIepidermis demonstrated STS expression in vivo by immunostaining as well asa normalization of histologic appearance at 5 weeks post-grafting. Inaddition, transduced XLI epidermis demonstrated a return of barrierfunction parameters to normal. These findings demonstrate corrective genedelivery in human XLI patient skin tissue at both molecular and functionallevels and provide a model of human cutaneous gene therapy.