Long Term Expression of TPP-I in Rat and Non-Human Primate Brain Following Administration of AAV2CUhCLN2, a Candidate Gene Therapy Treatment for Late Infantile Neuronal Ceroid Lipofuscinosis
Authors: Dolan Sondhi, Daniel A. Peterson, E. Lela Giannaris, Elizabeth Vassallo, Neil R. Hackett, Christine T. Sanders, Kimberly B. Bjugstad, John R. R. Sladek, Ronald G. Crystal
Journal: Molecular Therapy (2004)

Late infantile neuronal ceroid lipofuscinosis (LINCL), a fatal lysosomal storage disease leading to neurodegeneration, results from mutations in the CLN2 gene which lead to a deficiency of the CLN2 gene product, tripeptidyl peptidase I (TPP-I). The objective of this study was to assess the feasibility of using gene therapy to interrupt the progression of LINCL. Due to the chronic and diffuse nature of the disease, long term TPP-I production is required throughout the brain following gene transfer. In this study, AAV2CUhCLN2, a serotype 2 replication-deficient recombinant adeno-associated virus vector expressing the human CLN2 cDNA from a CMV/β-actin hybrid promoter, was utilized, with the hypothesis that AAV2CUhCLN2 administration to the brain of rat and non-human primates would lead to long-term TPP-I expression. Fisher 344 rats were injected in the left striatum with 1 μl of AAV2 CUhCLN2 (1010 particle units) and sacrificed at 1 to 18 months (n=3/time point), at which time the brains were harvested and analyzed for TPP-I expression by immunohistochemical staining. The volume of detectable TPP-I expression in the brains were calculated throughout the hemisphere using the Cavalieri estimator. This analysis revealed the persistent expression of vector-derived TPP-I in 43 ± 2% of the striatum at 1 month post injection, with expression reaching 46 ± 4 % at 12 months. Vector-derived TPP-I expression was also observed in a fraction of the neurons in up to 10% of the non-striatal volume of the brain of the injected animals beginning at 8 months and continuing through 18 months. Vector-derived TPP-I was also observed in the cerebral cortex of the non-injected hemisphere at 18 months. These distant cell populations were located in several regions with axons terminating in the striatum (the injected region), suggesting retrograde transport of the vector or the secreted TPP-I protein from the axon through the brain. African green monkeys (n=6) received a total dose of 3.6×1011 pu of AAV2CUhCLN2 at 12 locations targeting the caudate nucleus, hippocampus and overlying cortices. Controls received 3.6×1011 pu AAV2CUNull (a similar vector with no transgene) or PBS. The brains were immunohistochemically stained using mouse anti-human TPP-I antibody and multiple immunofluorescent labeling was performed to determine the cell types expressing TPP-I. There was widespread detection of TPP-I in neurons, but not glial cells, at all regions of injection. The distribution of TPP-I positive cells was similar in level at 5 and 13 wk post-administration. The data show that AAV2CUhCLN2 can be transferred to the brain of a rat and non-human primate to yield robust and persistent TPP-I expression, thus paving the way for a clinical study to assess safety and efficacy in human subjects with LINCL.