Epidermal keratinocytes can secrete polypeptides into the bloodstream, and
they can be easily expanded in culture and genetically modified. It is thus
possible to use epidermal keratinocytes for the systemic delivery of trans
gene products. Here we review the development of epidermal secretory system
s, from cultured keratinocytes to skin grafts and transgenic mouse models.
We also discuss a gene-switch approach for regulated cutaneous gene deliver
y.