861. Neonatal Gene Therapy with a Lentiviral Vector Results in Therapeutic Levels of α-Galactosidase A Correction in Fabry Mice

Abstract

Fabry diseaseis a lysosomal storage disease caused by a systemic deficiency of α-galactosidase A (α-gal A) activity. Humans affected with Fabry disease respond to enzyme replacement therapy (ERT), however frequent infusions are required, strong antibody responses develop, and the long-term benefits in key organs are unknown or inadequate. Life-long correction of inherited or acquired disorders by a single non-invasive treatment is the ultimate goal of most gene therapy research. One of the strategies toward this aim is neonatal gene transfer. In the case of lysosomal storage disorders such as Fabry disease, this approach could prevent the disease progression at a very early stage before irreversible organ damage occurs. Lentiviral vectors (LVs) are well suited to this application because of their ability to confer stable, long-term expression of transgenes in a broad host range. LVs are also known to be refractory to inactivation by complement in human serum. Here we explore use of single intravenous injection of a VSV-g pseudotyped LV system to deliver the α-gal A cDNA in order to correct Fabry disease. We have synthesized an HIV-1-based LV that encodes the human α\-gal A cDNA and a cell surface marker human CD25 (huCD25) in a bicistronic format. In in vitro studies we first established efficient transduction of Fabry patient fibroblasts and Fabry mouse primary bone marrow stromal cells. High levels of α-gal A activity (up to 69-fold above normal) were detected in cell lysates and secreted into the culture media. In an in vivo study, neonatal Fabry mice were injected intravenously through the temporal vein with 100 μgl of concentrated LV (1 × 107 functional viral particles/ml determined by huCD25 expression in HeLa cells) at 2 to 3 days after birth. The survival rate was 92.3% (12/13) in the treated group, 83.3% (5/6) in the PBS injected control group. No hematological abnormalities or huCD25 expression on ononuclear cells was observed in peripheral blood. In plasma from Fabry mice injected once with the therapeutic LV, we observed that α-gal A activity rose to ~110.0% of normal levels (35.7 ± 34.7%, n = 12) 6 weeks after injection. The persistence of enzyme activity in our mice is encouraging since a previous report of ERT in Fabry mice showed rapid clearance of this enzyme (T1/2 = ~5min) in plasma. Numerous studies are underway to gauge long-term corrective effects mediated by this simple vector delivery method in Fabry mice. Organ α-gal A activity and Gb3 clearance in clinically relevant organs will be assessed. Anti-human α-gal A antibody levels in plasma will be quantified throughout the experiment. Since it is important to know the systemic biodistribution of vector for pre-clinical safety and efficacy assessments, we will further investigate the distribution of transduced cells by tracking the co-expressed cell surface marker huCD25. To our knowledge, this study is the first report of using neonatal LV-mediated gene therapy to achieve long-term correction in any disease model. These results suggest that this facile LV delivery system may offer significant long-term therapeutic advantages for a variety of gene therapy applications.