403. Long-Term, High alpha-L-iduronidase Expression in MPS I Dogs Following Neonatal, Intravenous, Retroviral Vector Gene Therapy

Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to deficient activity of alpha-L-iduronidase (IDUA). Manifestations include bone and joint disease, heart disease, and neurological dysfunction. The MPS I dog has a G to A transition in the donor splice site of intron 1 creating a premature termination codon at the exon-intron junction. The disease in the dog resembles the clinical manifestation in humans. We treated six MPS I dogs at three days of age intravenously with 2.5 to 10.1 |[times]| 10E9 (mean 3.6+/-2.9 SD) transducing units (TU)/kg of a retroviral vector (RV) expressing canine IDUA from the human 1-antitrypsin promoter (hAAT-cIDUA-WPRE). The group had 22-749 nmol/ml/hr of serum IDUA activity (mean = 337+/-334; normal = 14.6 +/-2.4, N = 7) (Fig. 1). The 3 oldest dogs at more than 1 year of age have stable activity at 1.3x, 2.1x, and 41|[times]| normal. The serum activity was not proportional to the dose. Clinically in the dog, early manifestations of MPS I are much less severe than those of MPS VII previously reported. Early signs include facial dysmorphia, prolapse of the 3rd eyelid, corneal clouding, mitral valve insufficiency, and joint disease. The 3 RV-treated dogs at 1 year of age showed improvement in corneal clouding, facial dysmorphia, 3rd eyelid prolapse, and valvular heart disease. Corneal clouding scores were 0/3,1/3, and 0/3 for the RV-treated dogs (serum IDUA activity of 35, 22, and 684 nmol/ml/h, respectively) compared with scores of 2/3 for four 6 month-old untreated MPS I dogs. Scores for facial dysmorphia were 0/4 for all RV-treated dogs compared to 2-3/4 for 3 untreated dogs. No treated MPS I dog exhibited 3rd eyelid prolapse, a sign seen in all untreated dogs. At 1 year of age, none of the 3 RV-treated dogs had a cardiac murmur, whereas two of the three oldest untreated MPS I dogs had a grade 2/6 murmur of mitral insufficiency. Two untreated dogs were euthanized at 1 year of age due to signs of severe cervical spinal cord disease, no signs of which are present in any of the treated dogs, the oldest of which is 17 months. One dog was treated with 1.3X10E9 TU/kg at 7 weeks of age and at 6 weeks post-treatment has 2.9 nmol/ml/hr (17% of normal) IDUA activity in serum (I-173, Fig. 1), which has been stable since 4 days post-transduction. These data show that in contrast to previous treatment modalities, neonatal, intravenous, RV gene therapy was successful in producing stable serum IDUA levels in MPS I dogs, improving early clinical disease.