Lentiviral vectors have demonstrated great potential as gene therapy vectors mediating efficient ex vivo and in vivo gene delivery and long-term transgene expression in both dividing and nondividing cells. However, for clinical studies it must be demonstrated that lentiviral vector preparations are safe and not contaminated by replication-competent recombinants related to the parental pathogenic virus. Here we describe a sensitive assay for the detection of replication-competent lentiviruses (RCL) in large-scale preparations of HIV-based lentiviral vectors. This RCL assay for lentiviral vectors is based on the principles used for retroviral vectors, using a highly permissive cell line, C8166-45, for RCL amplification and an appropriate positive control virus to establish the assay sensitivity. The assay is capable of detecting 1 RCL infectious unit in a background of 2.5 x 10(8) transducing units of vector in a single test culture. Statistically representative samples from large-scale lentiviral vector productions were assayed using multiple test cultures for each lot. Overall, a total of 1.4 x 10(10) transducing units of vector from 10 independent 14-liter production lots were screened and no RCL was detected. We propose to implement this assay as a release testing for clinical-grade lentiviral vector preparations intended for gene therapy clinical trials.

Replication-deficient lentiviral vectors (LV) have been shown to enable the stable genetic modification of multiple cell types in vivo. We demonstrate here that vascular and hepatic delivery of a third-generation HIV-derived lentiviral vector encoding human Factor IX (LV-hFIX) produced potentially therapeutic serum levels of hFIX protein with no vector-mediated local or systemic toxicity of adult mice. Portal vein administration produced the highest serum levels of hFIX and demonstrated proportionally higher levels of gene transfer to the liver with up to 4% of hepatocytes expressing hFIX. Vascular delivery of a lentiviral vector encoding GFP resulted in genetic modification of up to 12% of liver cells. Cell proliferation was not required for hepatocyte transduction with either vector. Serum hFIX levels reached 4% of normal levels following vascular LV-mediated hFIX gene transfer and remained stable for months following vector administration.

Previous experiments have demonstrated the stable expression of factor IX (FIX) protein in mice and canine models of hemophilia B following portal vein gene transfer with a recombinant adeno-associated virus (rAAV) vector encoding FIX. Here, we present the results of studies that further optimized the rAAV vector transgene cassette used to express FIX and explored the use of the less-invasive intravenous (i.v.) route of vector administration for the treatment of hemophilia B. First, a liver-specific promoter was evaluated in conjunction with cis-acting regulatory elements in mice. Constructs that included both the b-globin intron and the woodchuck hepatitis virus post-transcriptional regulatory element resulted in the highest level of FIX expression in vivo. Using this optimized vector, we demonstrate that i.v. injection was feasible for hepatic gene transfer in mice, achieving 70-80% of portal vein expression levels of FIX. In further studies using the Chapel Hill strain of hemophilia B dogs, we demonstrate for the first time FIX expression and partial correction of the bleeding disorder following i.v. administration of an AAV vector.

Abstract-Inhibition of proliferative neointima formed by vascular smooth muscle cells is a potential target in preventing angioplasty-induced restenosis. We have created a potent antiproliferative by fusing the active regions of the p27 and p16 cell cycle inhibitors. Intravascular delivery of a replication-deficient adenoviral vector (AV) encoding this p27-p16 fusion protein, named W9, inhibited balloon injury-induced neointimal hyperplasia in rabbit carotid arteries. In a therapeutically more relevant model, AV-W9 was delivered to balloon-injured porcine coronary arteries in vivo using an infusion catheter. Of the three coronary arteries, two were injured with a 15-mm balloon catheter and either were left untreated or were treated with 10 12 viral particles of either AV-W9 or a control null virus. AV-W9 treatment significantly inhibited neointimal hyperplasia in this porcine arterial balloon injury model compared with untreated or control virus-treated vessels. The average intimal area of the AV-W9 -treated group 10 days after balloon injury and treatment was 0.42Ϯ0.36 mm 2 , whereas the AV-null group demonstrated an intimal area of 0.70Ϯ0.52 mm 2 . At day 10 the average intimal thickness of the AV-W9 -treated vessels was 9.1 m (nϭ5, ϫ20 magnification) compared with 21.2 m (nϭ5, ϫ20 magnification) in control virus-treated vessels. This trend was also observed at 28 days after balloon injury and gene transfer during which AV-W9 -treated vessels demonstrated an average intimal thickness of 4.7 m (nϭ8, ϫ20 magnification) compared with 13.3 m (nϭ3, ϫ20 magnification) in control virus-treated vessels and 7.3 m (nϭ5, ϫ20 magnification) in the sham-treated vessels. The AV-W9 treatment was safe and well tolerated. These data suggest that AV-W9 gene therapy may be useful in preventing angioplasty-induced intimal hyperplasia in the coronary artery. Key Words: p27 Ⅲ p16 Ⅲ restenosis Ⅲ gene therapy V ascular smooth muscle cell (SMC) proliferation is induced in response to the overextension of coronary and peripheral arteries occurring during balloon angioplasty. This hyperproliferative response is believed to be a critical event in the therapy-associated complication of vessel reocclusion resulting from restenosis. Manipulation of the normal cell cycle control mechanisms in vascular SMCs at the angioplasty site has been suggested as a means of preventing the restenosis. [1][2][3][4][5][6][7][8][9][10][11][12] The negative regulators of cell cycle progression, the cyclin-dependent kinase (CDK) inhibitors (CDKis), fall into the following two structurally distinct families: the INK4 family comprising p15, p16, p18, and p19, and the CIP/KIP family comprising p21, p27, and p57. [13][14][15][16][17] Members of the INK4 and CIP/KIP families normally act in concert to regulate cell proliferation. We combined representative members of each family to create more potent cytostatic agents.A series of p27 KIP1 and p16 INK4b fusion genes were created and introduced into the E1 region of an E1-deleted replication-deficient adenoviral vec...