424. Intracranial AAV5 Synergizes with Non-Myeloablative Bone Marrow Transplantation in the Murine Model of Globoid-Cell Leukodystrophy

Abstract

Top of pageAbstract Globoid-cell leukodystrophy (GLD or Krabbe disease) is a neurodegenerative lysosomal storage disease caused by an inherited deficiency in galactosylceramidase (GALC) activity. A murine model of GLD (Twitcher mouse) exists that mimics many of the biochemical and clinical aspects of the human disease. It has been shown previously that bone marrow transplantation (BMT) following myeloablative radiation (800-900 rads) performed in 8-9 day old Twitcher mice significantly increased the average life span (increased from |[sim]|40 to |[sim]|80 days) and reduced the levels of pro-inflammatory cytokines in the brain. Due to the severe developmental damage caused by high dose radiation, we treated newborn Twitcher mice (2 days old) with BMT following myeloreductive (400 rads) rather than myeloablative radiation. The animals had 20-40% normal donor chimerism, low level GALC activity in the brain, and a minor, but significant increase in the average life span (|[sim]|45 days). Unfortunately, the lower radiation dose combined with earlier treatment was less effective than the previous BMT regimen, although there was a minor but global decrease in CD11b(+) cells in the brain. It has been shown that intracranial injections of AAV vectors can improve the anatomical and functional deficits in animal models of other lysosmal storage diseases. We showed previously that injection of AAV2 or AAV5 vectors encoding murine GALC directly into the brains of newborn Twitcher mice resulted in GALC levels of 28% and 2,500% of normal, respectively, and a local reduction in both GFAP(+) and CD11b(+) cells in the brain. Surprisingly, there was only a moderate, albeit significant improvement in average life span (untreated |[sim]|38d, AAV2 |[sim]|45d, AAV5 |[sim]|53d). The AAV data suggest that simply supplying high levels of enzyme to targeted areas is not sufficient to fully correct this disease. Because AAV and myeloreductive BMT target different aspects of the disease to varying degrees (ie. GFAP(+) and CD11b(+) cells; local vs. global reductions), we hypothesized that combining the two therapies would synergize and be more efficacious than either approach alone. We injected newborn Twitcher mice intracranially with AAV5 and then intravenously with 106 GALC(+) bone marrow cells from a normal donor following 400 rads of conditioning radiation (AAV5/BMT-treated). High level GALC activity was measured in the brains of Twitcher mice that received combination AAV5/BMT treatment. The animals receiving the combination AAV5/BMT treatment had a more complete and widespread reduction of both GFAP(+) and CD11b(+) cells than either the AAV5-treated or BMT-treated animals. Interestingly, the average life span of the AAV5/BMT-treated Twitcher mice was 103 days (range = 38-153 days), which is considerably longer than any previous therapeutic approach. Our results suggest that a combination of approaches will likely be required for effective treatment of GLD.