235. The Route of Vector Delivery Impacts the Therapeutic Effects of AAV-Mediated Gene Therapy in Adult Mucopolysaccharidosis IIIB Mice

Abstract

Mucopolysaccharidosis (MPS) IIIB is an inherited lysosomal storage disease with severe neurological involvement, due to the deficiency of |[alpha]|-N-Acetylglucosaminidase (NaGlu). A critical factor impacting therapeutic development for MPS IIIB is how to efficiently deliver the therapeutic materials into the central nervous system (CNS) to correct the global neurological pathology, which is the cause of high mortality and premature death in MPS IIIB patients. Three delivery strategies, an intravenous (IV) or an intracisternal (IC) injection or combination of an IV and an IC infusion, were considered in studying the therapeutic consequences of adeno-associated viral (AAV) CNS gene delivery in adult MPS IIIB mice. Pretreatment with an IV infusion of mannitol was conducted to facilitate the CNS entry of IV delivered AAV vector and to enhance the dispersion of IC injected vector in the CNS. A therapeutic AAV serotype 2 viral vector (AAV2-CMV-hNaGlu) was used in this study, expressing human NaGlu and controlled by the CMV promoter. Following an IV administration of mannitol, AAV2-CMV-hNaGlu was delivered into young adult MPS IIIB mice by an IV injection (4-8|[times]|1011 viral particles) or by an IC infusion (5|[times]|1010 viral particles), or in combination. In MPS IIIB mice receiving an IV delivery of AAV vector, 20-100% of normal level of NaGlu activity was detected in liver, and the correction of lysosomal storage was observed to be complete in liver and partial in spleen, heart, lung, intestine and skeletal muscle. Intracisternal AAV delivery resulted in a histopathological decrease of lysosomal storage and the expression of functional NaGlu in broad brain areas. No somatic correction of lysosomal storage or detectable NaGlu enzyme activity was observed after IC injection. The therapeutic benefit was also shown by delayed occurrence of neurological symptoms and significantly increased life span in all three treated groups of MPS IIIB mice. The impact of AAV-mediated gene therapy on the life span of MPS IIIB mice was greater in mice treated with a combination of IV and IC delivery (11.1-18.4 months) than by IV (9.2-11.5 months) or IC (10.3-14.0 months) delivery alone, compared with that of non-treated MPS IIIB mice (7.9-11.0 months). In addition, animal behavior studies demonstrated significantly improved activity levels in 31% (5/16) of IV+IC treated MPS IIIB mice, while 48% (13/27) of IV+IC treated mice showed improved performance in a visual cue task. This study demonstrated the great potential of combining IV and IC delivery for improving the AAV CNS gene delivery and developing AAV gene therapy for treating MPS IIIB patients.