Expression of naked DNA in human, pig, and mouse skin

Direct cutaneous gene delivery in a human genetic skin disease

The skin is an accessible somatic tissue for therapeutic gene transfer and, depending on therapeutic goals, a variety of cutaneous gene delivery approaches are currently available. Recent advances in direct injection of naked DNA into intact skin have shown promise and are less labor-intensive than approaches involving grafting of genetically modified cells. We have regenerated skin from transglutaminase 1 (TGase1)-deficient patients with the genetic skin disease lamellar ichthyosis (LI) on nude mice to examine the corrective impact of direct naked plasmid injection. Regenerated LI patient skin receiving repeated in vivo injections with a TGase1 expression plasmid displayed restoration of TGase1 expression in the correct tissue location in the suprabasal epidermis. Unlike LI skin regenerated from keratinocytes, first transduced in vitro with a retroviral expression vector for TGase1 prior to grafting, however, directly injected LI skin displayed a nonuniform TGase1 gene expression pattern. In further contrast, direct injection failed to correct the central histologic and functional abnormalities of the disease. These data demonstrate that partial restoration of gene expression can be achieved via direct injection of naked DNA in human genetic skin disease tissue but underscore the need for new advances to achieve efficient and sustained plasmid-based gene delivery to the skin.

A model of corrective gene transfer in X-linked ichthyosis

Single gene recessive genetic skin disorders offer attractive prototypes 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 expression 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 steroid sulfatase enzymatic activity in proportion to the number of proviral integrations in XLI cells. Transduced and uncorrected XLI keratinocytes, along with normal controls, were then grafted onto immunodeficient mice to regenerate full thickness human epidermis. Unmodified XLI keratinocytes regenerated a hyperkeratotic epidermis lacking STS expression with defective skin barrier function, effectively recapitulating the human disease in vivo. Transduced XLI keratinocytes from the same patients, however, regenerated epidermis histologically indistinguishable from that formed by keratinocytes from patients with normal skin. Transduced XLI epidermis demonstrated STS expression in vivo by immunostaining as well as a normalization of histologic appearance at 5 weeks post-grafting. In addition, transduced XLI epidermis demonstrated a return of barrier function parameters to normal. These findings demonstrate corrective gene delivery in human XLI patient skin tissue at both molecular and functional levels and provide a model of human cutaneous gene therapy.