Delivery of a Retroviral Vector Expressing Human β-Glucuronidase to the Liver and Spleen Decreases Lysosomal Storage in Mucopolysaccharidosis VII Mice

Mucopolysaccharidosis VII (MPS VII) is caused by β-glucuronidase (β-gluc) deficiency and results in lysosomal storage due to the inability to degrade glycosaminoglycans. Transfer of a β-gluc gene into the liver reduces hepatic pathology as well as storage in other organs via uptake of secreted protein. A Moloney murine leukemia-based retroviral vector expressing the human β-gluc cDNA was injected intravascularly into MPS VII mice during hepatocyte replication, which was induced with im injection of an adenoviral vector that transiently expressed hepatocyte growth factor (Ad.CMV.HGF). This procedure resulted in transduction of ~1% of hepatocytes, 1% of normal liver enzyme activity, and a reduction in lysosomal storage in the liver at 3.5 months. Surprisingly, controls that received retroviral vector without HGF had transduction of non-parenchymal cells in the liver, significant levels of enzyme and RNA in the liver at 2 but not 3.5 months, and reduced lysosomal storage at 3.5 months. Transduction was also achieved in the replicating cells of the spleen, where lysosomal storage was reduced. An approach using a retroviral vector without a growth factor might temporarily reduce lysosomal storage in the liver and spleen in humans. Addition of HGF might be used to augment and prolong gene transfer.