Lipidic vector systems for gene transfer.

Clinical application of gene therapy depends on the development of suitable gene transfer vehicles (vectors). Although generally not as efficient as viral vectors, nonviral systems such as lipidic vectors have the potential advantages of being less toxic, nonrestrictive in cargo DNA size, potentially targetable, and easy to produce in relatively large amounts. More important, lipidic vectors generally lack immunogenicity, allowing repeated in vivo transfection using the same vector. In this paper, we will attempt to summarize some of the recent advances in lipidic gene delivery vectors. Three types of lipidic gene transfer vectors are described: 1) DNA/cationic liposome complexes, 2) DNA encapsulated in neutral or anionic liposomes, and 3) liposome-entrapped, polycation-condensed DNA (LPDI and LPDII). We review the various factors affecting vector structure and gene delivery efficiency, and we discuss the possible mechanisms of gene transfer and their implications in vector design.