Transfer and expression of foreign genes in mammalian cells

The transfer of foreign genes into eukaryotic cells, in particular mammalia n cells, has been essential to our understanding of the functional signific ance of genes and regulatory sequences as well as the development of gene t herapy strategies. To this end, different mammalian expression vector syste ms have been designed. The choice of a particular expression system depends on the nature and purpose of the study and will involve selecting particul ar parameters of expression systems such as the type of promoter/enhancer s equences, the type of expression (transient versus stable) and the level of desired expression. In addition, the success of the study depends on effic ient gene transfer. The purification of the expression vectors, as well as the transfer method, affects transfection efficiency. Numerous approaches h ave been developed to facilitate the transfer of genes into cells via physi cal, chemical or viral strategies. While these systems have all been effect ive in vitro they need to be optimized for individual cell types and, in pa rticular, for in vivo transfection.