439. Prolonged Expression of Secreted Enzymes in Dogs After Liver Delivery of Sleeping Beauty Transposons: Implications for Non-Viral Gene Therapy of Mucopolysaccharidoses Types I and VII

The non-viral integrating vector the Sleeping Beauty (SB) transposon system is efficient in treating systemic monogenic diseases in mice including mucopolysaccharidosis (MPS) types I and VII caused by α-iduronidase (IDUA) and β-glucuronidase (GUSB) deficiency, respectively. More recently we have used modified approaches of the hydrodynamic procedure to deliver therapeutic transposons to dog liver. Reproducible delivery and transposition in dogs are about 1% the levels in mice. Using a transgenic canine reporter secreted alkaline phosphatase (cSEAP), in the absence of immune suppression we can detect transgenic protein for up to six weeks post infusion using catheter-mediated hydrodynamic delivery. A proof-of-principle immunomodulation using GdCl3 to block macrophages in liver and spleen prolonged the presence of the cSEAP protein in circulation from 6 weeks to up to at least 5 months after a single vector infusion. We achieved stabilized activity in one dog at about 2-fold of baseline values. Durability of cSEAP in serum was inversely correlated with transient increase of liver enzymes ALT and AST in response to the vector delivery procedure, pointing to the deleterious effect of hepatocellular toxicity on transgene maintenance. However, GdCl3 immunomodulation was ineffective for repeat vector infusions, suggesting a possibility of an alternative, more potent immunosuppression regimen. Evidence of transposition was obtained with the most efficient transposase SB100X but not with SB11. For transgenic IDUA and GUSB, therapeutic activity in serum peaked at 50-350% of wild-type at 2-4 days post-treatment, but lasted only a few days. The differences in levels and duration of detection of cSEAP in the blood compared to those of IDUA and GUSB may be in part due to the facilitated uptake of lysosomal enzymes into cells compared to cSEAP. Longer endurance of transgenic proteins at therapeutic levels may be possible in SB-treated dogs using alternative immunosuppressive regimens.