365. Long-Term Toxicology Evaluation of AAVrh. 10hARSA Administration to the CNS of Nonhuman Primates to Treat Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD), a lysosomal storage disorder caused by the deficiency of the enzyme arylsulfatase A (ARSA), is a recessive, fatal neurodegenerative lysosomal storage disease associated with intracellular accumulation of sulfatides in the CNS. The disease is fatal, with no approved therapy. The focus of this study is to test the hypothesis that direct CNS administration of AAVrh.10hARSA (AAVrh.10 serotype vector coding for the human ARSA cDNA) to the CNS of nonhuman primates at doses scalable to humans has an acceptable long term safety profile. Safety of intraparenchymal administration of AAVrh. 10hARSA was evaluated following its administration to the CNS of non-human primates (NHPs, African Green monkeys, n=24) at 12 locations in the white matter centrum ovale at two different doses (total dose 2.85×1010 genome copies (gc), equivalent to human clinical dose of 2.85×1011 gc previously used via a similar route of administration in humans, and 1.5×1012 gc, a 1.7-log higher dose, equivalent to a human dose of 1.5×1013 gc). NHPs administered in a similar fashion with AAVNull vector (a vector with an expression cassette without a translatable sequence) and sham (PBS) were used as controls. Target locations were determined using CAT and MRI imaging. The groups (n=6/group) were sacrificed at 1, 13, 26, and 52 wk following vector administration to determine short and long-term effects of treatment. General safety, hematologic, serum chemistry and CNS histopathology parameters were assessed at several time points up to 1 yr after vector administration. Additional in-life safety assessments included behavioral videotaping and CNS monitoring by magnetic resonance imaging (MRI) at 13, 26, and 52 wk post-administration. The vector-administered groups did not differ from the controls in any parameter of general assessment or comprehensive blood profile (complete blood count, chemistry panel). Blinded videotape analysis of NHP behavior pre-surgery and post-administration showed no discernible neurological differences. No significant adverse effects were observed in animals treated with low dose AAVrh. 10hARSA; the only abnormal observation was presence of limited and reversible, minimal to mild T and B cell focal infiltrates at the CNS administration sites, findings that were corroborated by MRI. Animals treated with the higher dose of both the ARSA and Null vectors (1.5×1012 gc) demonstrated significant infiltrates of T cells, B cells and activated microglial cells and/or macrophages in the brain at the sites of administration. Similar observations were made from MRIs images, i.e., the higher dose may be associated with some local adverse effects, although these findings did not have clinical consequences on in-life data, complete blood count, serum chemistry or behavior in these NHPs. Together these findings demonstrate the safety of AAVrh.10hARSA administration at 2.85×1010 gc, equivalent to a human dose of 2.85×1011 gc and support the use of this vector as a vehicle for therapy of MLD.