853. Efficacy of AAV-Mediated Expression of Acid Sphingomyelinase at Correcting the Visceral and Pulmonary Manifestations of Niemann-Pick B Disease
Authors: C. M. Barbon, R. J. Ziegler, S. D. Bercury, M. Cherry, C. Li, E. Schuchman, R. J. Desnick, M. J. Lukason, S. Lonning, S. H. Cheng
Journal: Molecular Therapy (2004)

Niemann-Pick B disease (NPD) is an inheritable lysosomal storage disease in which the deficient activity of the lysosomal hydrolase, acid sphingomyelinase (ASM), results in the intracellular accumulation of sphingomyelin. Accumulation is most strikingly evidenced by the presence of enlarged, often multinucleated myeloid-lineage cells in bone marrow, lung, liver, and spleen. In particular, the presence of lung infiltrates of engorged alveolar macrophages is frequently referenced in human lung biopsies and at autopsy. In NPD patients, significant morbidity is attributed to protracted pulmonary decline and recurrent respiratory infections, underscoring the importance of achieving efficacy in this organ. Systemic administration of either an AAV2/1 or 2/8 pseudotyped vector encoding human ASM under the transcriptional control of a liver-restricted promoter into acid sphingomyelinase knockout mice (ASMKO) resulted in expression of therapeutic levels of the enzyme. Transduction and subsequent expression, which was primarily hepatic-restricted, was approximately 50–100-fold higher with the AAV2/8 than with the AAV2/1 vector. Furthermore, the high levels attained using the AAV2/8 vector were readily detected in the circulation by day 4 and were sustained at the end of the 120-day study. Subsequent extrahepatic uptake of the secreted enzyme, presumably via the mannose and mannose 6-phosphate receptors, was associated with a reduction in sphingomyelin levels in all the affected tissues, including the lung. As may be expected, since the levels of expression attained with the AAV2/8 vector were significantly higher, the kinetics of sphingomyelin clearance was more rapid than with the AAV2/1 vector. Biochemical and histological analysis of ASMKO mice at days 60 and 120 post-administration demonstrated a profound reversal of lung pathology concomitant with substrate depletion to basal levels. Correction was also associated with reduced levels of the proinflammatory chemokine, MIP-1, and normalization of the cellularity and cell differentials in the bronchoalveolar lavage fluids (BALF) of treated animals. In contrast to the severe storage inclusions and enzyme-uptake defects shown associated with alveolar macrophages from ASMKO BALF, those isolated from AAV2/8-treated mice demonstrated improved phagocytic activity and displayed morphologies that were more akin to normal macrophages. Hepatic-restricted expression of the human ASM also promoted immune tolerance to the expressed enzyme in the ASMKO mice. No antibodies to the human enzyme were detected in the animals throughout the 120-day study. Hence, AAV2/8-mediated, hepatic-restricted expression of ASM was capable of correcting the visceral storage disease and abrogating the chronic pulmonary inflammatory manifestations shown associated with NPD. This data supports the continued evaluation of the gene delivery system for the treatment of NPD.