In utero gene therapy with AAV viral vectors in an inherited lysosomal storage disease animal model

Neurogenetic diseases typically have globally distributed lesions. Pathology usually develops early in life requiring early diagnosis and treatment to achieve a more complete remission in the adult. We investigated therapy using adeno-associated virus vectors injected into the fetal brain, prior to the onset of pathology, in a mouse model of a lysosomal storage disease. First, we tested adeno-associated virus (AAV) vector serotypes 1 and 2 in the fetal brain, and analyzed the long-term effects on tumor development and germline transmission. A single injection of AAV1 into the ventricle at 15.5 days of gestation resulted in widespread distribution and life-long expression of the normal gene in the brain and spinal cord. There was no detectable vector transduction after an in utero intraventricular injection with AAV2. Injecting AAV1 into the fetal brain restricted vector transduction to the cells of the CNS, with no evidence of germline transmission, and did not increase the incidence of neoplasia later in life. We next analyzed the vector tropism and transduction patterns. There was a reproducible AAV1 transduction pattern in many structures of the brain at 1 month of age, with AAV1 targeting primarily neurons. Vector gene expression was maintained in most of the structures at 12 months postpartum. There were vector positive cells in brain structures with active neurogenesis in the adult (dentate gyrus and subventricular zone), suggesting that AAV1 transduced neural progenitor cells at the time of the in utero injection. The final experiments investigated the therapeutic benefits of AAV1 gene transfer to the brain of fetal MPS VII mice. The extensive distribution of normal enzyme throughout the CNS completely prevented the development of storage lesions in the brain and spinal cord. No vector transfer was found outside the CNS, including in gonads, but a small amount of enzyme was present in spleen, liver and lung, consistent with cerebral spinal fluid to venous flow. The peripheral enzyme was so low it did not alter the severe skeletal dysmorphology, which occurs readily when systemic treatment is used in neonates. Unexpectedly, the survival probability of the treated animals was significantly increased. The results indicate that the nervous system disease makes a heretofore unappreciated contribution to the overall physiological health of the animal in this type of disease.