HIGH-EFFICIENCY RETROVIRUS-MEDIATED GENE-TRANSFER INTO THE LIVERS OF MICE

Recombinant retroviral vectors represent an attractive means of transf erring genes into the liver because they integrate in the host cell ge nome and result in permanent gene expression. However, efficient gene transfer is limited by the requirement of active cell division for int egration. Surgical partial hepatectomy has been the traditional method of inducing hepatocellular proliferation, but this invasive approach would be difficult to justify in clinical gene therapy. As an alternat ive, we used a recombinant adenovirus expressing a nonsecreted form of urokinase plaminogen activator (Ad.PGKmuPA), which results in liver r egeneration over a period of 8 days. When a high-titer retroviral vect or was continuously infused into the portal vein of mice during this p eriod of hepatocyte proliferation, 33.5% of hepatocytes were stably tr ansduced, In addition, high-level expression of a secreted transgene r eporter was sustained for at least 48 weeks (length of experiment). We investigated the influence of vector titer on the in vivo transductio n efficiency in our system, and found that the total number of infecti ous retroviral particles delivered per target cell is a critical facto r. The results presented here demonstrate the ability to obtain a high gene transfer efficiency and long-term gene expression in hepatocytes in vivo without the need for surgical hepatectomy, The two-vector sys tem described here may be of clinical relevance, as the level of hepat ic gene transfer achieved has potential to be curative for a large num ber of genetic liver diseases.