Intracranial delivery of CLN2 reduces brain pathology in a mouse model of classical late infantile neuronal ceroid lipofuscinosis

Classical late infantile neuronal ceroid lipofuscinosis (cLINCL) is a lysosomal storage disorder caused by mutations in CLN2, which encodes lysosomal tripeptidyl peptidase I (TPP1). Lack of TPP1 results in accumulation of autofluorescent storage material and curvilinear bodies in cells throughout the CNS, leading to progressive neurodegeneration and death typically in childhood. In this study, we injected adeno-associated virus (AAV) vectors containing the human CLN2 cDNA into the brains of CLN2(-/-) mice to determine therapeutic efficacy. AAV2(CU)hCLN2 or AAV5(CU)hCLN2 were stereotaxically injected into the motor cortex, thalamus, and cerebellum of both hemispheres at 6 weeks of age, and mice were then killed at 13 weeks after injection. Mice treated with AAV2(CU)hCLN2 and AAV5(CU)hCLN2 contained TPP1 activity at each injection tract that was equivalent to 0.5- and 2-fold that of CLN2(+/+) control mice, respectively. Lysosome-associated membrane protein 1 immunostaining and confocal microscopy showed intracellular targeting of TPP1 to the lysosomal compartment. Compared with control animals, there was a marked reduction of autofluorescent storage in the AAV2(CU)hCLN2 and AAV5(CU)hCLN2 injected brain regions, as well as adjacent regions, including the striatum and hippocampus. Analysis by electron microscopy confirmed a significant decrease in pathological curvilinear bodies in cells. This study demonstrates that AAV-mediated TPP1 enzyme replacement corrects the hallmark cellular pathologies of cLINCL in the mouse model and raises the possibility of using AAV gene therapy to treat cLINCL patients.