Uptake of exogenous DNA via the skin

Easy accessibility makes the skin extremely attractive for therapeutic gene transfer, but this feature may be equally responsible for inadvertent DNA uptake. Therefore we studied lacZ reporter gene expression after epicutaneous and intracutaneous administration of naked DNA, lipofection and transferrinfection to intact, tape-stripped, and wound-healing skin of hairless mice. Gold particles coated with 1 microg pCMVnlslacZ were inoculated with a gene gun as a positive control. Beta-galactosidase expression by skin cells, i.e., keratinocytes of the upper epithelial layers and single cells in the upper dermis, determined by X-Gal histochemistry was not observed except after ballistic gene transfer. By polymerase chain reaction we detected lacZ DNA after skin bombardment up to 4 weeks. After intracutaneous and epicutaneous application to normal and tape-stripped skin of the various delivery systems lacZ DNA was detectable up to 1 week. Epicutaneous application of the delivery systems to wounded skin resulted in lacZ DNA detectability up to 48 h only. Reverse-transcriptase polymerase chain reaction indicated transcription of the reporter gene after particle bombardment and intracutaneous injection, up to 48 h, but not after epicutaneous application of either delivery system. The possibility of inadvertent uptake of exogeneous DNA by intact and tape-stripped skin is evidenced by the detection of reporter gene DNA after epicutaneous application of naked DNA and DNA complexed to cationic lipids or transferrin-polylysine (transferrinfection). However, the effects of the presence and persistence of foreign genes in the target cells are not clear yet.