In mammals, nitrogen is excreted from the body in the form of urea. Inborn errors of metabolism involving enzymes of the urea cycle may lead to hyperammonemia, coma, mental retardation, and sometimes death. These metabolic defects could be corrected if a safe, effective, and long-lasting means of delivering the proper urea cycle gene to the liver could be achieved. No current gene therapy vector is able to fulfill this requirement. The goal of this proposal is to advance a new system for gene delivery to the liver based on the insect baculovirus, AcMNPV. Preliminary studies demonstrate that this vector is able to deliver a reporter gene into primary cultures of hepatocytes at frequencies exceeding many conventional viral vectors, and is also capable of delivering genes to the mammalian liver in vivo. This vector system accommodates larger inserts (greater than 20kb), grows to higher titers, and is easier to manipulate than many conventional vectors. A further advantage of using an insect virus rather than a mammalian virus for gene therapy is an increased level of safety, since AcMNPV is unable to replicate in mammalian cells. The objectives of this proposal include: 1) to test the hypothesis that the metabolic defects of citrullinemic liver cells can be corrected using a modified AcMNPV vector, 2) to test the hypothesis that long-term expression of a transduced gene can be achieved in mammalian cells targeted by AcMNPV, 3) to test the hypothesis that none of the AcMNPV viral genes are expressed in mammalian cells, and 4) to test the hypothesis that AcMNPV vectors can be used to deliver genes to the liver by portal vein injection. These studies will enhance the capabilities of this important new gene delivery system and provide a critical assessment of its potential for treatment of inborn errors of the urea cycle. The development of this new gene therapy vector is important not only for treatment of inborn errors of the urea cycle but other disorders of the liver as well.
