Targeting genes: delivery and persistent expression of a foreign gene driven by mammalian regulatory elements in vivo.

We present evidence that a foreign gene driven by natural mammalian regulatory elements can be targeted to hepatocytes and the resultant gene expression made to persist. This was accomplished using a soluble DNA carrier system consisting of two covalently linked components: 1) a polycation, poly-L-lysine, that can bind DNA in a strong but non-damaging interaction, and 2) an asialoglycoprotein which can be targeted specifically to hepatocytes by cell surface asialoglycoprotein receptors unique to this cell type. A plasmid, palb-CAT, containing the gene for chloramphenicol acetyltransferase (CAT) driven by mouse albumin regulatory sequences was complexed to the carrier system. Intravenous injection of palb-CAT DNA in the form of a complex resulted in the presence of CAT enzyme activity in liver homogenates 24 h after injection. The targeted gene expression, however, was transient, reaching a maximum of 10 units/g liver at 24 h but was not detectable by 96 h. However, partial hepatectomy 30 min after injection resulted in persistent high levels of hepatic CAT activity (11.3 units/g) through 11 weeks post-injection. Southern analysis of livers 11 weeks after partial hepatectomy demonstrated that some of the targeted DNA had been integrated into the host genome. We conclude that a foreign gene driven by natural mammalian regulatory elements can be delivered to hepatocytes by intravenous injection in vivo using a soluble DNA carrier system. Foreign gene expression targeted in this manner can be made to persist by stimulation of hepatocyte replication.