696. Comparative Study of Lentiviral Vector-Mediated Gene Therapy in Neonatal and Young-Adult MPS I Mice by a Single Intravenous Injection
Authors: Yuli Liu, Hennig Anne, Kovacs Attila, Xu Lingfei, Fu Annabel, Chung Sarah, Ponder Katherine
Journal: Molecular Therapy (2004)

Mucopolysaccharidosis (MPS) I is due to deficient activity of α-L-iduronidase (IDUA) and is the most common MPS syndrome. Hepatic gene therapy might permanently correct the clinical manifestations of this disorder by programming liver cells to secrete IDUA with mannose 6-phosphate (M6P) that could be taken up by cells throughout the rest of the body via the M6P receptor. The canine IDUA cDNA was cloned into a retroviral vector (RV) with a strong liver promoter, and the RV was injected into newborn MPS I mice at a high [1×109 transducing units (TU)/kg] or a low (1×108 TU/kg) dose. This resulted in transduction of liver cells and stable serum IDUA activity in most animals for 8 months at 1241+/-147 and 110+/-31 units (U)/ml, and DNA copy number of 0.17 and 0.014 copies of RV/cell, for the high (N=25) and low dose (N=18) animals, respectively. Three of 18 mice that received the low dose of RV lost expression over time, which appeared to be due to a cytotoxic T lymphocyte response. Although serum IDUA activity was much higher than in normal mice (1 U/ml) or untreated MPS I mice (<0.01 U/ml), only 3% of the IDUA in serum of RV-treated MPS I mice contained M6P. In contrast, 70% of the IDUA in normal mice contained M6P. This suggests that the canine IDUA may be a poor substrate for modification with M6P in murine cells. Nevertheless, for animals that received the high dose of RV, IDUA activity in most organs was at least as high as in normal mice, while IDUA activity in brain was 10% of normal. MPS I mice that received the high dose of RV had normal echocardiograms, electroretinograms (ERG), and auditory brainstem responses (ABR) at 8 months after birth. In the heart, untreated MPS I mice had aortic insufficiency, aortic dilatation [ascending aorta diameter was 3.1 mm for MPS I vs 1.8 mm in high dose RV (p<0.001)], and cardiomegaly [left ventricular internal diameter at diastole of 4.3 mm in MPS I vs. 3.6 mm in high dose RV (p=0.02)]. In visual testing, MPS I mice had a markedly reduced response to light on electroretinograms [the a wave was-124 microvolts in MPS I vs.-329 in high dose RV (p<0.0001) and the b wave was 452 microvolts in MPS I vs. 682 in high dose RV (p=0.002)]. In hearing testing, untreated MPS I mice had a markedly increased threshold for hearing at frequencies of sound of 5 mHz [84 decibels in MPS I vs. 42 for high dose RV (p<0.0001)], 10 mHz [76 decibels for MPS I vs. 24 for high dose RV (p<0.0001)], and 20 mHz [77 decibels in MPS I vs. 55 in high dose RV (p=0.01)]. MPS I mice that received a low dose of RV had no improvements in echocardiograms, and only partial improvements in ERG and ABR. Pathological improvements correlated with clinical improvements. We conclude that neonatal gene therapy with a high dose of RV expressing IDUA corrects the cardiac, visual, and hearing abnormalities of MPS I, while a low dose of RV was less effective. These data help to define a target goal for serum IDUA activity for correcting these major manifestations of disease in MPS I.