TREATMENT OF A NEURODEGENERATIVE LYSOSOMAL STORAGE DISEASE, MPS VII, WITH MICROENCAPSULATED RECOMBINANT CELLS.

Colin J.D. Ross¹ ,Stephanie A. Maier¹, Martin Ralph², and Patricia L. Chang ^1,3.

¹ Dept. Pediatrics, McMaster University,Hamilton, Ontario, Canada , ² Dept of Psychology, University of Toronto, Toronto, Ontario, Canada, ³ Dept. Biology, McMaster University, Hamilton, Ontario, Canada. (changp@mcmaster.ca)

Neurodegenerative diseases caused by lysosomal enzyme deficiencies are catastrophic illnesses with both peripheral organ and central nervous system abnormalities. We used the mucopolysaccharidosis type VII (MPS VII) mouse with b -glucuronidase deficiency to develop an alternative cell-based method of gene therapy. In this approach, a "universal" cell line engineered to secrete the missing enzyme is implanted directly into all recipients requiring the same enzyme replacement. The cells, though non-autologous in origin, were rendered immunologically protected by encapsulation in immuno-isolating microcapsules. Using this strategy, we implanted b -glucuronidase-secreting fibroblasts enclosed in alginate microcapsules into mutant MPS VII mice. When implanted into the abdominal cavity, these microcapsules led to restoration of b -glucuronidase activity in the plasma (reaching 66% of normal by 2 weeks post-implantation), and in the peripheral organs (liver, kidney and spleen). Concomitantly, the intralysosomal accumulation of undegraded glycosaminoglycans was dramatically reduced for the duration of the 8-week experiment. In addition, the elevated secondary lysosomal enzymes, b -hexosaminidase and a -galactosidase, were also reduced. While the treated mutants developed an antigenic response against the replacement enzyme, limiting the long-term efficacy of the delivery, this response could be abolished transiently with a single treatment of purified anti-CD4 antibody. This should provide a possible approach to overcome a potential problem in patients with cross-reacting-material-negative mutations who may react against the replacement enzymes as foreign antigens. The neurological deficits and the pathological manifestation of the lysosomal storage disease in the central nervous system of the mutants were similarly treated by implanting microencapsulated recombinant cells into the lateral ventricles of the brain. This treatment resulted in delivery of b -glucuronidase throughout most of the central nervous system and reversal of the histological pathology, as well as reduction of the previously elevated secondary lysosomal enzymes, b -hexosaminidase and a -galactosidase in the brain. The behavioural abnormality of the mutants (unstable and fragmented circadian rhythm) was also significantly improved, while the expected deterioration in neuromotor functions that would have occurred in the untreated mutants was prevented. Hence, this alternative cell-based gene therapy demonstrates the proof of principle in reversing the biochemical, histological and behavioural pathology in the MPS VII mice, and provides a potentially cost-effective and nonviral treatment applicable to all lysosomal storage diseases.