GENE-TRANSFER IN-VIVO - SUSTAINED EXPRESSION AND REGULATION OF GENES INTRODUCED INTO THE LIVER BY RECEPTOR-TARGETED UPTAKE

Receptor-mediated gene transfer has been used to introduce genes Into tissues of animals in vivo. The genes introduced by this approach have been transiently expressed at low levels in animal tissues. High leve ls of expression, for longer periods, have been attained by the induct ion of cell division (i.e., partial hepatectomy) or disruption of lyso somal degradation of the DNA. We have studied the correlation of speci fic structural features on the DNA/ligand complexes with their ability to efficiently introduce DNA into the livers of intact animals. A chi meric gene containing the phosphoenolpyruvate carboxykinase gene promo ter (nucleotides -460 to +73) linked to the structural gene for human factor IX (PEPCK-hFIX gene) was condensed with galactosylated poly(L-l ysine) by titration with NaCl, resulting in complexes of defined size (10-12 nm in diameter) and shape. The PEPCK-hFIX gene complex was inje cted into the caudal vena cava of adult rats and the conjugated DNA wa s specifically targeted to the livers of the animals; no detectable DN A was noted in other tissues. The plasmid containing the PEPCK-hFIX ge ne was found as an episome in the livers of the rats 32 days after inj ection of the DNA complex. Human factor IX DNA, mRNA, and functional p rotein were detected up to 140 days after administration of the DNA co mplex (the duration of the experiment). Transcription from the PEPCK p romoter could be induced over the entire course of the experiment by f eeding the rats a high-protein, carbohydrate-free diet. We conclude th at the structure of the DNA/ligand complexes is of key importance for the successful introduction of genes into the tissues of animals by re ceptor-mediated endocytosis.