Salutary responses to adeno-associated viral (AAV) gene therapy have been reported in the mouse model of Sandhoff disease (SD), a neurodegenerative lysosomal storage disease caused by deficiency of β-N-acetylhexosaminidase (Hex). While untreated mice reach the humane endpoint by 4.1 months of age, mice treated by a single intracranial injection of vectors expressing human hexosaminidase may live a normal life span of 2 years. When treated with the same therapeutic vectors used in mice, two cats with SD lived to 7.0 and 8.2 months of age, compared with an untreated life span of 4.5 ± 0.5 months (n = 11). Because a pronounced humoral immune response to both the AAV1 vectors and human hexosaminidase was documented, feline cDNAs for the hexosaminidase α- and β-subunits were cloned into AAVrh8 vectors. Cats treated with vectors expressing feline hexosaminidase produced enzymatic activity >75-fold normal at the brain injection site with little evidence of an immune infiltrate. Affected cats treated with feline-specific vectors by bilateral injection of the thalamus lived to 10.4 ± 3.7 months of age (n = 3), or 2.3 times as long as untreated cats. These studies support the therapeutic potential of AAV vectors for SD and underscore the importance of species-specific cDNAs for translational research.

Progressive debilitating neurological defects characterize feline GM1 gangliosidosis, a lysosomal storage disease caused by deficiency of lysosomal β-galactosidase. No effective therapy exists for affected children, who often die before age 5. In the current study, an adeno-associated viral vector carrying the therapeutic gene was injected bilaterally into two brain targets (thalamus and deep cerebellar nuclei) of a feline model of GM1 gangliosidosis. Gene therapy normalized β-galactosidase activity and storage throughout the brain and spinal cord. The mean survival of 12 treated GM1 animals was >38 months compared to 8 months for untreated animals. Seven of the 8 treated animals remaining alive demonstrated normalization of disease, with abrogation of many symptoms including gait deficits and postural imbalance. Sustained correction of the GM1 gangliosidosis disease phenotype after limited intracranial targeting by gene therapy in a large animal model suggests that this approach may be useful for treating the human version of this lysosomal storage disorder.

BackgroundGM1-gangliosidosis is a glycosphingolipid (GSL) lysosomal storage disease caused by a genetic deficiency of acid β-galactosidase (βgal), which results in the accumulation of GM1-ganglioside and its asialo-form (GA1) primarily in the CNS. Age of onset ranges from infancy to adulthood, and excessive ganglioside accumulation produces progressive neurodegeneration and psychomotor retardation in humans. Currently, there are no effective therapies for the treatment of GM1-gangliosidosis.Methodology/Principal FindingsIn this study we examined the effect of thalamic infusion of AAV2/1-βgal vector in adult GM1 mice on enzyme distribution, activity, and GSL content in the CNS, motor behavior, and survival. Six to eight week-old GM1 mice received bilateral injections of AAV vector in the thalamus, or thalamus and deep cerebellar nuclei (DCN) with pre-determined endpoints at 1 and 4 months post-injection, and the humane endpoint, or 52 weeks of age. Enzyme activity was elevated throughout the CNS of AAV-treated GM1 mice and GSL storage nearly normalized in most structures analyzed, except in the spinal cord which showed ∼50% reduction compared to age-matched untreated GM1 mice spinal cord. Survival was significantly longer in AAV-treated GM1 mice (52 wks) than in untreated mice. However the motor performance of AAV-treated GM1 mice declined over time at a rate similar to that observed in untreated GM1 mice.Conclusions/SignificanceOur studies show that the AAV-modified thalamus can be used as a ‘built-in’ central node network for widespread distribution of lysosomal enzymes in the mouse cerebrum. In addition, this study indicates that thalamic delivery of AAV vectors should be combined with additional targets to supply the cerebellum and spinal cord with therapeutic levels of enzyme necessary to achieve complete correction of the neurological phenotype in GM1 mice.

The treatment of malignant glioma is currently ineffective. Oncolytic viruses are being explored as a means to selectively lyse tumor cells in the brain. We have engineered a mutant herpes simplex virus type 1 with deletions in the viral UL39 and g 1 34.5 genes and an insertion of the two prodrug activating genes, CYP2B1 and secreted human intestinal carboxylesterase. Each of these can convert the inactive prodrugs, cyclophosphamide and irinotecan (CPT-11), into their active metabolites, respectively. This new oncolytic virus (MGH2) displays increased antitumor efficacy against human glioma cells both in vitro and in vivo when combined with cyclophosphamide and CPT-11. Importantly, cyclophosphamide, CPT-11, or the combination of cyclophosphamide and CPT-11 does not significantly affect oncolytic virus replication. Therefore, MGH2 provides effective multimodal therapy for gliomas in preclinical models when combined with these chemotherapy agents. (Cancer Res 2005; 65(15): 6850-7)