Medical Updates
Ciliary neurotrophic factor (CNTF) for human retinal degeneration: Phase I trial of CNTF delivered by Encapsulated cell intraocular implants
1. Paul A. Sieving,
2. Rafael C. Caruso,
3. Weng Tao,
4. Hanna R. Coleman,
5. Darby J. S. Thompson¶,
6. Keri R. Fullmer¶, and
7. Ronald A. Bush†
+ Author Affiliations
1. National Eye Institute and
2. National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892;
3. §Neurotech USA, Lincoln, RI 02865; and
4. ¶The EMMES Corporation, Rockville, MD 20850
Communicated by John E. Dowling, Harvard University, Cambridge, MA, January 12, 2006 (received for review November 22, 2005)
Abstract
Neurotrophic factors are agents with a promising ability to retard progression of neurodegenerative diseases and are effective in slowing photoreceptor degeneration in animal models of retinitis pigmentosa. Here we report a human clinical trial of a neurotrophic factor for retinal neurodegeneration. In this Phase I safety trial, human ciliary neurotrophic factor (CNTF) was delivered by cells transfected with the human CNTF gene and sequestered within capsules that were surgically implanted into the vitreous of the eye. The outer membrane of the encapsulated cell implant is semipermeable to allow CNTF to reach the retina. Ten participants received CNTF implants in one eye. When the implants were removed after 6 months, they contained viable cells with minimal cell loss and gave CNTF output at levels previously shown to be therapeutic for retinal degeneration in rcd1 dogs. Although the trial was not powered to form a judgment as to clinical efficacy, of seven eyes for which visual acuity could be tracked by conventional reading charts, three eyes reached and maintained improved acuities of 10–15 letters, equivalent to two- to three-line improvement on standard Snellen acuity charts. A surgically related choroidal detachment in one eye resulted in a transient acuity decrease that resolved with conservative management. This Phase I trial indicated that CNTF is safe for the human retina even with severely compromised photoreceptors. The approach to delivering therapeutic proteins to degenerating retinas using encapsulated cell implants may have application beyond disease caused by genetic mutations.
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Encapsulated cell-based delivery of CNTF reduces photoreceptor degeneration in animal models of Retinitis Pigmentosa.
Tao W, Wen R, Goddard MB, Sherman SD, O'Rourke PJ, Stabila PF, Bell WJ, Dean BJ, Kauper KA, Budz VA, Tsiaras WG, Acland GM, Pearce-Kelling S, Laties AM, Aguirre GD.
Neurotech USA, Lincoln, Rhode Island 02865, USA. w.tao@neurotech.fr
Abstract
PURPOSE: The objective of the present study was to evaluate the therapeutic efficacy of ciliary neurotrophic factor (CNTF) delivered through encapsulated cells directly into the vitreous of the eye in an rcd1 canine model of retinitis pigmentosa. The dose-range effect of the treatment was also investigated. METHODS: Polymer membrane capsules (1.0 cm in length and 1.0 mm in diameter) were loaded with mammalian cells that were genetically engineered to secrete CNTF. The cell-containing capsules were then surgically implanted into the vitreous of one eye of rcd1 dogs at 7 weeks of age, when retinal degeneration is in progress but not complete. The contralateral eyes were not treated. The capsules remained in the eyes for 7 weeks. At the end of the studies, the capsules were explanted, and CNTF output and cell viability were evaluated. The eyes were processed for histologic evaluation. RESULTS: In each animal, the number of rows of photoreceptor nuclei in the outer nuclear layer (ONL) was significantly higher in the eye that received a CNTF-secreting implant than in the untreated contralateral eye. No adverse effects were observed on the retina in the treated eyes. The explanted capsules produced a low level of CNTF. The cells in the capsules remained viable and densely distributed throughout. CONCLUSIONS: CNTF delivered through encapsulated cells directly into the vitreous of the eye protects photoreceptors in the PDE6B-deficient rcd1 canine model. Furthermore, sparing of photoreceptors appeared dose-dependent with minimum protection observed at CNTF doses of 0.2 to 1.0 ng/d. Incrementally greater protection was achieved at higher doses. The surgically implanted, cell-containing capsules were well tolerated, and the cells within the capsule remained viable for the 7-week implantation interval. These results suggest that encapsulated cell therapy may provide a safe and effective strategy for treating retinal disorders in humans.
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