Gene Therapy for Diseases of the Central Nervous System

We use recombinant adenovirus (5), retrovirus, lentivirus (6,7) and adenoassociated virus vectors (8) for gene transfer to the central nervous system. Our research has focused on understanding the tropism of the recombinant virus vectors, their impact on the host, and their ability to provide for long-term expression and correction of neurodegenerative phenotypes. Gene therapy to disease models enables us to test how replacement of gene function alters the progression of central nervous system disease in animal models. Our laboratory also investigates how the vectors interact with cells and how the host responds to the vector.



Our laboratory uses a murine model of the mucopolysaccharidoses (MPS), an inherited genetic disorder that causes systemic disease and neurodegeneration in humans, initiated after the onset of disease (9), affects the brain. The MPS VII model provides us with a unique opportunity to test both novel vectors and delivery approaches, with the results applicable to multiple childhood onset neurodegenerative diseases due to a deficiency in a lysosomal enzyme. We were the first to demonstrate that a focal delivery of the enzyme deficient in MPS VII, ß-glucuronidase, could dramatically diminish the lysosomal storage product, a hallmark of the disease, globally throughout the brain (5). Recently we developed a novel approach to improve the distribution of enzyme secreted from transduced CNS cells by perturbing serum osmolality (10). We also demonstrated that global correction of systemic and neurodegenerative disease can result after gene delivery to brain and liver (9). Our most recent studies show that viral-based gene therapy vectors can halt the progressive disease in brain and eye, and importantly allow for recovery of neurological function.





We have begun to apply what we have learned in the MPS VII model to ceroid lipofuscinoses type II (CLN2). This neurodegenerative disease affects children at ages 2-3, with death occurring generally within the first decade. We have found that gene transfer of the lysosomal enzyme deficient in ceroid lipofuscinoses type II, called CLN2, results in widespread distribution (11).

We are also studying neuroprogenitor populations within the CNS. We are using a combination of cell biology and gene transfer technology to test if specific classes of cells within the brain are suitable as a delivery vehicle for brain gene replacement therapy. Experiments are also underway to determine if progenitor cell populations differ between diseased and normal brain.

A common hallmark of many neurological diseases is degeneration of the retina. We have found that the retina can be readily targeted with recombinant viral vectors, with reduction of disease phenotypes after gene transfer (12,13). We are now targeting specialized vectors for their ability to transduce specific cells within the retina (14). Finally we are developing regulated vectors.

Merged fluorescent micrograph of a 10µm section from a mouse retina after a 0.5 µl subretinal injection of AAV5CMVnlsGFP. Transduced cells represented by green nuclei are found mainly in the outer nuclear layer (ONL). Section was counter stained with DAPI to identify retinal cell layers and is represented by blue nuclei.

GCI = ganglion cell layer;
IPL = inner plexiform layer;
INL = inner nuclear layer;
OPL = outer plexiform layer;
ONL = outer nuclear layer;
OS = photoreceptor outer segment layer;
RPE = retinal pigmented epithelium

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References:

5. A Ghodsi et al. Hum Gene Ther 9:2331-2340, 1998.
6. JM Alisky et al. NeuroReport 11(12):2669-2673, 2000.
7. T Derksen et al. J. Gene Med 4(5); 463-469, 2002.
8. BL Davidson et al. PNAS 97(7):3428-3432, 2000.
9. CS Stein et al. J Virol 73(4):3424-3429, 1999.
10. A Ghodsi et al. Exp Neurol 160(1):109-116, 1999.
11. RE Haskell et al. Gene Ther. 10(1):34-42, 2003.
12. T Li et al. Invest Ophthalmol Vis Sci 35:2543-2549, 1994.
13. T Li & BL Davidson. PNAS 92:7700-7704, 1995.
14. A Lotery et al. Hum Gene Ther 13:689-696, 2002.