Retinitis Pigmentosa

Retinitis pigmentosa (RP) is an inherited disorder of the retina and is the sixth leading cause of blindness. Whereas current clinical strategies are primarily palliative in nature, research in animal models demonstrates that neurotrophic factors inhibit retinal degeneration caused by RP. Studies in the rd model of retinal degeneration demonstrated that CNTF gene transfer maintains retinal morphology,[17] and later studies in the rcdl dog model[18] using intravitreal implants of encapsulated CNTF-secret-ing cells demonstrated a dose-dependent preservation of rods. In the dog studies, untreated eyes showed, on

Table 2 Diseases for which cell encapsulation is being applied

Disease/model

Hormonal and whole-organ diseases Diabetes

Hypoparathyroidism Kidney failure

Growth hormone deficiency Single-gene diseases Hemophilia

Lysosomal storage disease Age-related/Neurodegenerative-diseases Age-related motor decline Amyotrophic lateral sclerosis Alzheimer's disease

Huntington's disease

Parkinson's disease

Retinitis pigmentosa

Spinal cord damage Oncology Colon cancer Glioblastoma

HER-2/neu positive tumors

Leukemia

Ovarian cancer Other

Acute and chronic pain Clinical trials

Amyotrophic lateral sclerosis Chronic pain

Diabetes

Huntington's disease Hypoparathyroidism Pancreatic cancer

Retinitis pigmentosa

Encapsulated cell/experimental paradigm

Islets in rodents and dogs Parathyroid tissue in rats Orally delivered Escherichia coli bacteria to rats

Growth hormone-producing cells in dogs

Factor 9 cells in rats Beta-glucuronidase cells in mice

Catecholamine and GDNF cells in rats CNTF-producing cells in mice NGF cells in rat and primates

NGF and CNTF cells in rats and primates

Catecholamine and GDNF cells in rat and primate brain

Human cells secreting hCNTF

into the vitreous

BDNF cells in rats iNOS cells (tet-regulated system) in mice Endostatin cells in mice and rats

IL-2 fused with anti-HER-2/neu antibody in mice Hybridoma producing antibodies to p15E in mice iNOS cells (tet-regulated system) in mice

Chromaffin cells in rats

CNTF cells intrathecally Chromaffin cells in subarachnoid space

Human islets intraperitoneally CNTF cells into ventricles Parathyroid tissue CYP2B1 cells in tumor vessel

CNTF cells in eye

Results

Normoglycemia for 2 years Normocalcemia for 30 weeks Normalized urea metabolism

Hormone secretion for 1 year

Cell survival and secretion Behavioral normalization

Improvement in motor function Protection of motor neurons Protection of cholinergic neurons, improved memory Protection of neurons, improved behavior

Improved behavior, protection of dopaminergic neurons Rod preservation

Outgrowth of neurites

Enhanced survival

Reduced tumor growth, enhanced survival

Modest survival benefit Enhanced survival Enhanced survival, cures Reduced pain

Sustained delivery, no toxicity Prolonged cell survival, no pain reduction in phase II trials Insulin independence for 9 months Delivery for 6 months Successful in two patients Local tumor growth controlled, well tolerated Ongoing average, three layers of the outer nuclear layer, while treated eyes showed between three and six layers. The distribution of retinal preservation was homogenous throughout the retina. These experiments paved the way for the recently initiated clinical trials by Neurotech USA. Patients diagnosed with RP have received intravitreal implants of an immunoisolatory membrane containing a human epithelial cell line engineered to secrete CNTF. Results from this phase I safety study are anticipated in 2004-2005.

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