n addition, these animals are euthymic and immunocompetent, which makes HLGP skin a good alternative for human skin research. A major disadvantage of the HLGP model is the unavailability of antibodies for identification of specific cell types. Our contact electrode is one of the most suitable systems for delivery to the skin epidermis. Skin GET can result in transfected cells in the epidermis, dermis, hypodermis, and even the muscle layer, dependent on the electrodes, injection techniques, animal species and plasmid designs used, for example whether tissue specific promoters are involved. GET with plate AbMole Tuberostemonine electrodes transfects cells to the mouse dermis, the epidermis of xenograft human skin, or both epidermis and dermis of rat. GET with needle electrodes or needle arrays can reach the deep layers of the skin and result in transgenic cells in the dermis, epidermis, hypodermis and subcutaneous muscle layer of the mouse or rat or dermis of the pig. Interestingly, both epidermis and muscle layer were transfected by pulse delivery with plate-and-fork electrode as was shown with a variation of the timecourse of expression. Moreover, transfection in the lower dermis of rabbit was achieved by GET with tweezer electrodes. In this study and in our previous work, we demonstrated that targeted transgenic expression to the epidermis can be obtained in Hartley guinea pig or HLGP skin after GET with the MEA. A similar result was observed in another study performed in Hartley guinea pig skin using a similar, but more invasive electrode. The computer simulation of the skin model for delivery with the meander electrode showed that majority of electric field acted in the epidermal layer of skin within a depth of 125 mm. It is understandable that GET with surface contact electrodes like the MEA results in exclusively transgene expression in the epidermis. Several studies have reported the expression level and duration of gene delivery with skin GET, it is hard to make an accurate comparison among them because different animal species were used and delivery of various transgenes was performed using a variety of pulse parameters and electrodes. Obviously, gene transfection into different cell types can lead to various levels and kinetics of transgenic expression because the cell half-lives are varied. In addition, the variation in half-lives of gene products can contribute to the duration of expression. It is well known that transfection of stable cells such as muscle fibers can result in relatively high and long-term gene expression, while transfection of fast growing cells such as cancer cells produces a very short duration of gene expression. Skin GET with a plate electrode either in mice or rats can produce transgene expression with duration of two weeks, which is similar in time course to our studies with guinea pig or HLGP skin with MEA GET.