Characterization of factors that determine lentiviral vector tropism in skin tissue using an ex vivo model

Lentiviral tropism to a solid tissue may be determined by receptor availability, the differentiation state of cells and the three-dimensional architecture of the tissue.

Using skin organ cultures, lentiviral vector tropism was compared with that of keratinocytes in cell culture. Furthermore, the tropism of lentiviral vector to mouse and human tissues was compared ex vivo, in attempt to validate the mouse skin as an experimental system for human gene therapy of skin diseases.

The results obtained indicated that although early progenitor keratinocytes (keratin 15+ and p63+), when grown in culture are permissive to lentiviral vector, they are resistant to transduction in their native 'niche' in the skin tissue. Transiently amplifying keratinocytes (keratin 14+) on the other hand, are permissive to lentiviral vector transduction, in cell culture and in the skin, after separation of the epidermis from the dermis layer. Keratinocytes (keratin 14+) in the hair follicle of human skin are resistant to lentiviral transduction, even after partial digestion of the extracellular matrix collagen. By contrast, collagenase pretreatment of mouse tissue facilitated transduction of keratinocytes within the hair follicle. Because lentivirus pseudotyped by two envelopes (amphotropic murine leukemia virus and vesicular stomatitis virus G glycoprotein) display the same tropism, we suggest that receptor availability is not the critical factor in the pattern of skin tissue transduction.

Taken together, the results obtained in the present study indicate that lentiviral vector tropism in the three-dimensional skin tissue is distinct from the tropism to keratinocytes in culture and is dependent on a complex interplay of extracellular restrictions.