Ciliary neurotrophic factor delivered by encapsulated cell intraocular implants for treatment of geographic atrophy in age-related macular degeneration.

There is no treatment available for vision loss associated with advanced dry age-related macular degeneration (AMD) or geographic atrophy (GA). In a pilot, proof of concept phase 2 study, we evaluated ciliary neurotrophic factor (CNTF) delivered via an intraocular encapsulated cell technology implant for the treatment of GA. We designed a multicenter, 1-y, double-masked, sham-controlled dose-ranging study. Patients with GA were randomly assigned to receive a high-or low-dose implant or sham surgery. The primary endpoint was the change in best corrected visual acuity (BCVA) at 12 mo. CNTF treatment resulted in a dose-dependent increase in retinal thickness. This change was followed by visual acuity stabilization (loss of less than 15 letters) in the high-dose group (96.3%) compared with low-dose (83.3%) and sham (75%) group. A subgroup analysis of those with baseline BCVA at 20/63 or better revealed that 100% of patients in the high-dose group lost <15 letters compared with 55.6% in the combined low-dose/sham group (P = 0.033). There was a 0.8 mean letter gain in the high-dose group compared with a 9.7 mean letter loss in the combined low-dose/sham group (P = 0.0315). Both the implant and the implant procedure were well-tolerated. These findings suggest that CNTF delivered by the encapsulated cell technology implant appears to slow the progression of vision loss in GA, especially in eyes with 20/63 or better vision at baseline.

The sucrose challenge symptoms test optimized for diagnosis of congenital sucrase isomaltase deficiency.

BACKGROUND: Congenital sucrase isomaltase deficiency (CSID), an inherited carbohydrate malabsorption disorder, is difficult to diagnose because of overlapping symptoms with other gastrointestinal (GI) diseases. An at-home study was conducted in CSID and healthy adults to evaluate the diagnostic utility of self-reported GI symptoms following administration of a sucrose challenge. METHODS: This study investigated the optimum symptom scoring with a sucrose challenge symptoms test (SCST) for diagnosing CSID in 45 confirmed patients and 118 healthy controls. Subjects self-reported the severity of GI symptoms using a 10-point Likert scale after ingesting 50 grams of sucrose on an empty stomach. The receiver operator characteristics curve (ROC) was used to identify the diagnostic variable with the highest Youden Index, a measure of diagnostic performance. RESULTS: All six symptoms were significantly worse in the CSID group within 2 hours after the sucrose challenge. The diagnostic variable with the highest Youden Index was worsening in global symptoms scores at 1- and 2-hours (11.7 [CSID] vs 3.2 [Controls]; P<0.001.) Optimized by gender, the sensitivity and specificity for this diagnostic variable were 87% and 81%, respectively. CONCLUSIONS: The SCST is a simple, non-invasive at-home test that can aid in a CSID diagnosis.

CD24-Siglec axis is an innate immune checkpoint against metaflammation and metabolic disorder.

The molecular interactions that regulate chronic inflammation underlying metabolic disease remain largely unknown. Since the CD24-Siglec interaction regulates inflammatory response to danger-associated molecular patterns (DAMPs), we have generated multiple mouse strains with single or combined mutations of Cd24 or Siglec genes to explore the role of the CD24-Siglec interaction in metaflammation and metabolic disorder. Here, we report that the CD24-Siglec-E axis, but not other Siglecs, is a key suppressor of obesity-related metabolic dysfunction. Inactivation of the CD24-Siglec-E pathway exacerbates, while CD24Fc treatment alleviates, diet-induced metabolic disorders, including obesity, dyslipidemia, insulin resistance, and nonalcoholic steatohepatitis (NASH). Mechanistically, sialylation-dependent recognition of CD24 by Siglec-E induces SHP-1 recruitment and represses metaflammation to protect against metabolic syndrome. A first-in-human study of CD24Fc (NCT02650895) supports the significance of this pathway in human lipid metabolism and inflammation. These findings identify the CD24-Siglec-E axis as an innate immune checkpoint against metaflammation and metabolic disorder and suggest a promising therapeutic target for metabolic disease.

Ciliary neurotrophic factor for macular telangiectasia type 2: results from a phase 1 safety trial.

PURPOSE: To evaluate the safety and tolerability of intraocular delivery of ciliary neurotrophic factor (CNTF) using an encapsulated cell implant for the treatment of macular telangiectasia type 2. DESIGN: An open-label safety trial conducted in 2 centers enrolling 7 participants with macular telangiectasia type 2. METHODS: The participant's more severely affected eye (worse baseline visual acuity) received the high-dose implant of CNTF. Patients were followed for a period of 36 months. The primary safety outcome was a change in the parameters of the electroretinogram (ERG). Secondary efficacy outcomes were changes in visual acuity, en face measurements of the optical coherence tomography of the disruption in the ellipsoid zone, and microperimetry when compared with baseline. RESULTS: The ERG findings demonstrated a reduction in the amplitude of the scotopic b-wave in 4 participants 3 months after implantation (month 3). All parameters returned to baseline values by month 12 and remained so at month 36 with no clinical impact on dark adaptation. There was no change in visual acuity compared with baseline. The area of the defect as measured functionally by microperimetry and structurally by the en face OCT imaging of the ellipsoid zone loss appeared unchanged from baseline. CONCLUSIONS: The intraocular delivery of CNTF in the encapsulated cell implant appeared to be safe and well tolerated in eyes with macular telangiectasia type 2. Further evaluation in a randomized controlled clinical trial is warranted to test for efficacy.

Photoreceptor protection by cardiotrophin-1 in transgenic rats with the rhodopsin mutation s334ter.

PURPOSE: This work examines the effects of cardiotrophin (CT)-1 on photoreceptor survival in transgenic rats that carry the rhodopsin mutation S334ter. METHODS: Recombinant CT-1 was injected intravitreally into eyes of heterozygous animals. Photoreceptor survival was analyzed by histology. Phosphorylation of signal transducer and activator of transcription1 (STAT1), STAT3, extracellular signal-regulated kinase (ERK), or Akt was assessed by immunoblot analysis. Localization of phosphorylated STAT3 was determined by immunocytochemistry. RESULTS: Heterozygous S334ter rats experience rapid photoreceptor degeneration. By postnatal day (PD)20, the outer nuclear layer (ONL) retained only 1 to 2 rows of nuclei compared with 10 to 12 rows in wild-type animals. Repeated administration of CT-1 resulted in significant survival of photoreceptors. At PD20, a CT-1-treated eye (2 micro g/2 micro L every 3 days, starting at PD9) had six to seven rows of nuclei, and the vehicle-treated eyes had only one to two rows. At PD30, eyes treated every 3 days still had five to six rows of nuclei, in contrast to no rows to one row in vehicle-treated eyes. Eyes treated every 4 days retained three to four rows, whereas eyes treated every 5 days had two to three rows. There was a significant increase in phosphorylated STAT1 and -3 in the retina after CT-1 injection. The increase in phosphorylated STAT3 was colocalized with glutamine synthetase, a Müller cell marker, by immunocytochemistry. CONCLUSIONS: These results indicate that CT-1 promotes photoreceptor survival and that Müller cells probably mediate this effect. They also suggest that sustained delivery of the protein is essential for long-term rescue of photoreceptors.

Encapsulated cell-based intraocular delivery of ciliary neurotrophic factor in normal rabbit: dose-dependent effects on ERG and retinal histology.

PURPOSE: ERG and histologic changes were investigated in normal rabbits after intravitreal implantation of encapsulated cell technology (ECT) devices releasing ciliary neurotrophic factor (CNTF). METHODS: Fifteen adult New Zealand White albino rabbits had ECT devices secreting CNTF at 22, 5, or 0 ng/d implanted in the superior temporal quadrant of the left eye. The low dose has been shown to produce substantial rescue of photoreceptors in the rcd1 canine model of retinal degeneration. Right eyes were untreated. Ganzfeld dark- and light-adapted ERGs and clinical observations were performed at 5, 15, and 25 days after implantation. Rod a-waves and rod and cone b-waves and outer nuclear layer (ONL) morphology were evaluated at 25 days. RESULTS: Clinical examination showed minimal changes in a few CNTF-treated eyes, including vitreous membranes and engorgement of iris vessels at day 25. Retinas appeared normal. CNTF did not significantly affect the rod a- or b-waves, although the b-wave amplitude tended to be larger in CNTF-treated retinas at low flash intensities. The cone b-wave amplitude was significantly reduced in high-dose eyes at some flash intensities. The ONL area in high-dose eyes was significantly greater because of increased thickness than in fellow retinas. ONL cell size was significantly increased, and staining density decreased in CNTF-treated retinas. CONCLUSIONS: CNTF, given by intravitreal ECT device at doses that protect photoreceptors in a canine model of retinal degeneration (5 ng/d), did not adversely affect either rod or cone ERG function of normal rabbit retina. The cone ERG was more sensitive to suppression being reduced, at low flash intensities, by 22 ng/d. Dose-related changes in the ONL and photoreceptor cell nuclei did not represent a toxic effect, because they were not associated with deficits in the rod ERG over a broad range of intensities.

Encapsulated cell-based delivery of CNTF reduces photoreceptor degeneration in animal models of retinitis pigmentosa.

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.

Sustained secretion of ciliary neurotrophic factor to the vitreous, using the encapsulated cell therapy-based NT-501 intraocular device.

The objective of this study was to evaluate the in vivo secretion profile of ciliary neurotrophic factor (CNTF) from either of two genetically engineered cell lines contained in the encapsulated cell therapy (ECT)-based NT-501 device. ECT devices were loaded with either a low or high CNTF-secreting cell line and implanted into rabbit eyes for 1, 3, 7, 14, 30, 60, 90, 135, 180, or 365 days. After explantation, the vitreous was sampled and devices were allowed to incubate in endothelial serum-free medium for 24 h at 37 degrees C. Both the vitreous and the conditioned medium were assayed for CNTF using an ELISA. Device and vitreous CNTF, were plotted against time, and regression analysis was used to calculate half-life. Devices loaded with either cell line showed stable in vivo output for the duration of the study, with populations of healthy cells remaining in the device at study termination. For the low-dose CNTF-secreting cell line, with the final time point at 6 months, the halflife was estimated as 71 days, whereas the high-dose devices, with a final time point of 1 year, had an associated half-life of approximately 198 days. The NT-501 device is capable of delivering CNTF to the vitreous for at least 1 year. This ECT-based device, which has been shown to be safe and effective by our group, is a well-engineered ECT-based controlled delivery system capable of protein output on the order of years.

CNGB3-achromatopsia clinical trial with CNTF: diminished rod pathway responses with no evidence of improvement in cone function.

PURPOSE: Ciliary neurotrophic factor (CNTF) protects rod photoreceptors from retinal degenerative disease in multiple nonhuman models. Thus far, CNTF has failed to demonstrate rod protection in trials for human retinitis pigmentosa. Recently, CNTF was found to improve cone photoreceptor function in a canine CNGB3 achromatopsia model. This study explores whether this finding translates to humans with CNGB3 achromatopsia. METHODS: A five-subject, open-label Phase I/II study was initiated by implanting intraocular microcapsules releasing CNTF (nominally 20 ng/d) into one eye each of CNGB3 achromat participants. Fellow eyes served as untreated controls. Subjects were followed for 1 year. RESULTS: Pupil constriction in treated eyes gave evidence of intraocular CNTF release. Additionally, scotopic ERG responses were reduced, and dark-adapted psychophysical absolute thresholds were increased, attributable to diminished rod or rod pathway activity. Optical coherence tomography revealed that the cone-rich fovea underwent structural changes as the foveal hyporeflective zone (HRZ) became diminished in CNTF-treated eyes. No objectively measurable enhancement of cone function was found by assessments of visual acuity, mesopic increment sensitivity threshold, or the photopic ERG. Careful measurements of color hue discrimination showed no change. Nonetheless, subjects reported beneficial changes of visual function in the treated eyes, including reduced light sensitivity and aversion to bright light, which may trace to decreased effective ambient light from the pupillary constriction; further they noted slowed adaptation to darkness, consistent with CNTF action on rod photoreceptors. CONCLUSIONS: Ciliary neurotrophic factor did not measurably enhance cone function, which reveals a species difference between human and canine CNGB3 cones in response to CNTF. (ClinicalTrials.gov number, NCT01648452.).

Randomized trial of ciliary neurotrophic factor delivered by encapsulated cell intraocular implants for retinitis pigmentosa.

PURPOSE: To evaluate the safety and effect on visual function of ciliary neurotrophic factor delivered via an intraocular encapsulated cell implant for the treatment of retinitis pigmentosa (RP). DESIGN: Ciliary neurotrophic factor for late-stage retinitis pigmentosa study 3 (CNTF3; n = 65) and ciliary neurotrophic factor for early-stage retinitis pigmentosa study 4 (CNTF4; n = 68) were multicenter, sham-controlled dose-ranging studies. METHODS: Patients were randomly assigned to receive a high- or low-dose implant in 1 eye and sham surgery in the fellow eye. The primary endpoints were change in best-corrected visual acuity (BCVA) at 12 months for CNTF3 and change in visual field sensitivity at 12 months for CNTF4. Patients had the choice of retaining or removing the implant at 12 months for CNTF3 and 24 months for CNTF4. RESULTS: There were no serious adverse events related to either the encapsulated cell implant or the surgical procedure. In CNTF3, there was no change in acuity in either ciliary neurotrophic factor- or sham-treated eyes at 1 year. In CNTF4, eyes treated with the high-dose implant showed a significant decrease in sensitivity while no change was seen in sham- and low dose-treated eyes at 12 months. The decrease in sensitivity was reversible upon implant removal. In both studies, ciliary neurotrophic factor treatment resulted in a dose-dependent increase in retinal thickness. CONCLUSIONS: Long-term intraocular delivery of ciliary neurotrophic factor is achieved by the encapsulated cell implant. Neither study showed therapeutic benefit in the primary outcome variable.

CNTF and retina.

Ciliary neurotrophic factor (CNTF) is one of the most studied neurotrophic factors for neuroprotection of the retina. A large body of evidence demonstrates that CNTF promotes rod photoreceptor survival in almost all animal models. Recent studies indicate that CNTF also promotes cone photoreceptor survival and cone outer segment regeneration in the degenerating retina and improves cone function in dogs with congenital achromotopsia. In addition, CNTF is a neuroprotective factor and an axogenesis factor for retinal ganglion cells (RGCs). This review focuses on the effects of exogenous CNTF on photoreceptors and RGCs in the mammalian retina and the potential clinical application of CNTF for retinal degenerative diseases.

Two-year intraocular delivery of ciliary neurotrophic factor by encapsulated cell technology implants in patients with chronic retinal degenerative diseases.

PURPOSE: To evaluate the pharmacokinetics of ciliary neurotrophic factor (CNTF) delivered over a period of up to 2 years by an intraocular encapsulated cell technology (ECT) implant in patients with retinitis pigmentosa (RP) and geographic atrophy (GA). METHODS: Patients from phase 1 RP (CNTF1); phase 2 GA (CNTF2); and phase 2 late and early stage RP (CNTF3, and CNTF4) studies received an ECT-CNTF implant, designated as "NT-501," in one eye. Per protocol, all implants (n = 10) were removed at 6 months from the CNTF1 study patients. Explant for the phase 2 studies was optional, but several patients were explanted at 12, 18, and 24 months post implant. A small amount of vitreous sample was collected at the time of explant. The rate of CNTF secretion from the explants and the corresponding vitreous CNTF levels were evaluated for each time point. Serum samples from these patients were evaluated for CNTF, anti-CNTF antibodies, and antibodies to the encapsulated cells. RESULTS: NT-501 implants produced CNTF consistently over a 2-year period. The calculated half-life of CNTF in the vitreous continuously delivered by ECT implants was 51 months, with CNTF levels statistically equivalent between the 6- and 24-month implant period. CNTF, anti-CNTF antibodies, and antibodies to the encapsulated cells were not detected in the serum of patients. CONCLUSIONS: This retrospective study demonstrated that the intraocular ECT implant has a favorable pharmacokinetic profile for the treatment of chronic retinal degenerative diseases without systemic exposure. (ClinicalTrials.gov numbers, NCT00063765, NCT00447954, NCT00447980, NCT00447993.).

Longitudinal study of cone photoreceptors during retinal degeneration and in response to ciliary neurotrophic factor treatment.

PURPOSE: To study cone photoreceptor structure and function in patients with inherited retinal degenerations treated with sustained-release ciliary neurotrophic factor (CNTF). METHODS: Two patients with retinitis pigmentosa and one with Usher syndrome type 2 who participated in a phase 2 clinical trial received CNTF delivered by an encapsulated cell technology implant in one eye and sham surgery in the contralateral eye. Patients were followed longitudinally over 30 to 35 months. Adaptive optics scanning laser ophthalmoscopy (AOSLO) provided high-resolution images at baseline and at 3, 6, 12, 18, and 24 months. AOSLO measures of cone spacing and density and optical coherence tomography measures of retinal thickness were correlated with visual function, including visual acuity (VA), visual field sensitivity, and full-field electroretinography (ERG). RESULTS: No significant changes in VA, visual field sensitivity, or ERG responses were observed in either eye of the three patients over 24 months. Outer retinal layers were significantly thicker in CNTF-treated eyes than in sham-treated eyes (P < 0.005). Cone spacing increased by 2.9% more per year in sham-treated eyes than in CNTF-treated eyes (P < 0.001, linear mixed model), and cone density decreased by 9.1%, or 223 cones/degree(2) more per year in sham-treated than in CNTF-treated eyes (P = 0.002, linear mixed model). CONCLUSIONS: AOSLO images provided a sensitive measure of disease progression and treatment response in patients with inherited retinal degenerations. Larger studies of cone structure using high-resolution imaging techniques are urgently needed to evaluate the effect of CNTF treatment in patients with inherited retinal degenerations.

CNTF induces regeneration of cone outer segments in a rat model of retinal degeneration.

BACKGROUND: Cone photoreceptors are responsible for color and central vision. In the late stage of retinitis pigmentosa and in geographic atrophy associated with age-related macular degeneration, cone degeneration eventually causes loss of central vision. In the present work, we investigated cone degeneration secondary to rod loss in the S334ter-3 transgenic rats carrying the rhodopsin mutation S334ter. METHODOLOGY/PRINCIPAL FINDINGS: Recombinant human ciliary neurotrophic factor (CNTF) was delivered by intravitreal injection to the left eye of an animal, and vehicle to the right eye. Eyes were harvested 10 days after injection. Cone outer segments (COS), and cell bodies were identified by staining with peanut agglutinin and cone arrestin antibodies in whole-mount retinas. For long-term treatment with CNTF, CNTF secreting microdevices were implanted into the left eyes at postnatal day (PD) 20 and control devices into the right eyes. Cone ERG was recorded at PD 160 from implanted animals. Our results demonstrate that an early sign of cone degeneration is the loss of COS, which concentrated in many small areas throughout the retina and is progressive with age. Treatment with CNTF induces regeneration of COS and thus reverses the degeneration process in early stages of cone degeneration. Sustained delivery of CNTF prevents cones from degeneration and helps them to maintain COS and light-sensing function. CONCLUSIONS/SIGNIFICANCE: Loss of COS is an early sign of secondary cone degeneration whereas cell death occurs much later. At early stages, degenerating cones are capable of regenerating outer segments, indicating the reversal of the degenerative process. Sustained delivery of CNTF preserves cone cells and their function. Long-term treatment with CNTF starting at early stages of degeneration could be a viable strategy for preservation of central vision for patients with retinal degenerations.

CREB1/ATF1 activation in photoreceptor degeneration and protection.

PURPOSE: The cAMP response element binding protein 1 (CREB1) and activating transcription factor 1 (ATF1) are closely related members of the bZIP superfamily of transcription factors. Both are activated in response to a wide array of stimuli, including cellular stress. This study was conducted to assess the CREB1/ATF1 pathway in photoreceptor disease and protection. METHODS: The expression levels of p-CREB1, CREB1, and ATF1 were examined by immunoblot and immunohistochemistry in normal canine retina and retinas of several canine models of retinal degeneration (rcd1, rcd2, erd, prcd, XLPRA1, XLPRA2, T4R RHO). Humans retinas affected with age-related macular degeneration (AMD) were also examined. p-CREB1/ATF1 immunolabeling was assessed in normal and rcd1 dogs treated with ciliary neurotrophic factor (CNTF), to examine the effect of a neuroprotective stimulus on activation of CREB1/ATF1. RESULTS: Native CREB1 and ATF1 as well as phosphorylated CREB1/ATF1 was examined in normal canine retina by immunoblot. The p-CREB1 antibody identified phosphorylated CREB1 and ATF1 and labeled the inner retina only in normal dogs. In degenerate canine and human retinas, strong immunolabeling appeared in rod and cone photoreceptors, indicating increased expression of native CREB1 and ATF1, as well as increased phosphorylation of these proteins. Retinal protection by CNTF in rcd1 dogs was accompanied by a significant increase in the number of p-CREB1/ATF1-labeled photoreceptor nuclei. CONCLUSIONS: Positive association of CREB1/ATF1 phosphorylation with photoreceptor protection suggests that it may contribute to an innate protective response. These data identify a signaling mechanism in rods and cones of potential importance for therapies of RP and AMD.

Application of encapsulated cell technology for retinal degenerative diseases.

Ophthalmic disorders represent a rapidly growing disease area that is associated with the ageing population. Their sight is threatened by age-related macular degeneration, diabetic retinopathy, glaucoma and/or retinitis pigmentosa (RP). Few effective treatments for these disorders are available at present, in part due to lack of effective delivery of therapeutic molecules to the retina. Encapsulated cell technology (ECT) allows the controlled, continuous and long-term administration of protein drugs in the eye, where therapeutic agents are needed, and does not subject the host to the systemic exposure. Furthermore, the implants can be retrieved, providing an added level of safety. Ciliary neurotrophic factor (CNTF) has been shown to protect the retina from degeneration in 13 animal models, and ECT-based delivery of CNTF protected photoreceptors in the rcd1 dog model of RP.

CNTF induces dose-dependent alterations in retinal morphology in normal and rcd-1 canine retina.

Ciliary neurotrophic factor (CNTF) provides morphologic preservation of rods in several animal models of retinitis pigmentosa (RP). However, CNTF may alter photoreceptor morphology and rod photoreceptor differentiation in vitro, as well as affecting normal retinal electrophysiology. In addition, the capacity of CNTF to support other cell types affected secondarily in RP (cones and ganglion cells) is unclear. The purposes of this study were to examine the effects of CNTF upon a canine model of RP, the rod-cone degeneration (rcd-1) dog. Archival tissue from a previous study assessing the capacity of CNTF to rescue photoreceptors in rcd-1 dogs was used. One eye was treated for 7 weeks before being explanted. The contralateral eye was untreated. A total of 23 rcd-1 dogs and seven control dogs (four untreated and three CNTF-treated) were used. Morphometric data describing outer and inner nuclear layer thickness, inner retinal thickness, cones and ganglion cells were collected at nine evenly spaced points along each retina and analysed using a mixed effects model. Immunohistochemistry was performed on a subset of 11 dogs for expression of rhodopsin, human cone arrestin (hCAR) and recoverin. CNTF protected the outer nuclear layer and increased inner retinal thickness in a dose-dependent manner (both were maximal at CNTF doses of 1-6 ng day-1). Significant cone loss or reduction of inner nuclear layer width in rcd-1 did not occur in this model, therefore we were unable to assess the protective effect of CNTF upon these parameters. CNTF did not afford significant ganglion cell protection. CNTF induced morphologic changes in rods and ganglion cells, as well as reducing expression of hCAR and rhodopsin, but not recoverin. The dose of CNTF which provided optimal outer nuclear layer protection also resulted in several other effects, including altered ganglion cell morphology, increased thickness of the entire retina, and reduced expression of some phototransduction proteins. These changes were more marked in rcd-1 retinas than in wild-type retinas. This implies that the consequences of CNTF treatment may be substantially influenced by the cellular context into which it is introduced.

Ciliary neurotrophic factor (CNTF) for human retinal degeneration: phase I trial of CNTF delivered by encapsulated cell intraocular implants.

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.