855. Stable Transduction of Hepatocytes Following Intravenous Retroviral Gene Therapy in Seven-Week-Old Dogs with Mucopolysaccharidosis (MPS) VII

Abstract

Mucopolysaccharidosis (MPS) VII is a lysosomal storage disease due to deficient -glucuronidase (GUSB) activity. We previously reported that IV injection of 310E9 transducing units (TU)/kg of a retroviral vector (RV) expressing GUSB into newborn MPS VII dogs resulted in transduction of hepatocytes, which secreted GUSB into blood and has been stable for more than 3 years. One MPS VII animal that was treated with human hepatocyte growth factor (HGF) prior to neonatal IV injection of 1210E9 U/kg of the same RV had dramatically higher serum levels, possibly due to the HGF or the higher dose of RV. In all 4 of the neonatally treated dogs followed more than 3 years, clinical signs were minimal, and provirus and expression of GUSB were detected by PCR in peripheral blood indicating transduction of hematopoietic stem cells. Because most MPS patients are not diagnosed until 1–2 years of age, we tested if post-weaning, 7-week-old MPS VII dogs could be treated by injecting a total dose of 1.7-2.210E9 TU/kg of RV IV administered over 4 days. Four dogs were pre-treated over 24 h with 2.5 mg/kg of HGF divided every 3 h (HGF/RV); 3 were only given RV. At 6 months of age, the HGF/RV- and RV-treated dogs had 184+/-109 U/ml (54% normal) and 49.7+/-11 (14% normal) U/ml of serum GUSB activity, respectively (ANOVA, p=0.079). The serum activity was stable in each dog for as long as 10 months with a range of from 14% to 83% of normal. Liver biopsies at 1 week (N=4) and 12 weeks (N=3) post treatment had GUSB activity of 83.3+/48.9 U/ml (8.4% normal) and 85.5+/-65.7 U/ml (8.7% normal), respectively, with normal GAG concentration of 3.03+/-0.79 ug/mg protein and 3.77+/-0.51 ug/mg protein, respectively (normal average 4.1 ug/mg protein, affected average 12.7 ug/mg protein). Clinically, 3 of the 7 dogs could still stand or walk at 6 months of age, however, 4 could not. Cornea cloudiness was present to variable degrees from minor to severe, and all dogs had some degree of mitral valve insufficiency by ultrasound. The clinical phenotype was not correlated with the serum GUSB activity. None of these dogs had PCR-detectable provirus in peripheral blood. We conclude that 1) 7-week-old MPS VII dogs were able to achieve stable serum GUSB activity for as long as 10 months at levels that were similar to that achieved with neonatal administration of RV, 2) GUSB expression occurred in the liver by 1 week and reduced hepatic GAG storage to normal, and 3) There was only modest improvement in gait, suggesting that bone and joint disease was not as well corrected with gene therapy at 7 weeks as it was with neonatal gene therapy.