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Articles  |   July 2014
Enhancing RPE Cell-Based Therapy Outcomes for AMD: The Role of Bruch's Membrane
Author Affiliations & Notes
  • Janosch P. Heller
    John van Geest Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, United Kingdom
    Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, United Kingdom
  • Keith R. Martin
    John van Geest Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, United Kingdom
    Department of Ophthalmology, NIHR Biomedical Research Centre and Wellcome Trust-MRC Cambridge Stem Cell Institute, University of Cambridge, United Kingdom
  • Correspondence: Keith R. Martin, John van Geest Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 0PY, United Kingdom; email: krgm2@cam.ac.uk  
Translational Vision Science & Technology July 2014, Vol.3, 4. doi:10.1167/tvst.3.4.4
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      Janosch P. Heller, Keith R. Martin; Enhancing RPE Cell-Based Therapy Outcomes for AMD: The Role of Bruch's Membrane. Trans. Vis. Sci. Tech. 2014;3(4):4. doi: 10.1167/tvst.3.4.4.

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Abstract

Age-related macular degeneration (AMD) is the leading cause of legal blindness in older people in the developed world. The disease involves damage to the part of the retina responsible for central vision. Degeneration of retinal pigment epithelial (RPE) cells, photoreceptors, and choriocapillaris may contribute to visual loss. Over the past decades, scientists and clinicians have tried to replace lost RPE cells in patients with AMD using cells from different sources. In recent years, advances in generating RPE cells from stem cells have been made and clinical trials are currently evaluating the safety and efficiency of replacing the degenerated RPE cell layer with stem cell–derived RPE cells. However, the therapeutic success of transplantation of stem cell–derived RPE cells may be limited unless the transplanted cells can adhere and survive in the long term in the diseased eye. One hallmark of AMD is the altered extracellular environment of Bruch's membrane to which the grafted cells have to adhere. Here, we discuss recent approaches to overcome the inhibitory environment of the diseased eye and to enhance the survival rate of transplanted RPE cells. Our aim is to highlight novel approaches that may have the potential to improve the efficacy of RPE transplantation for AMD in the future.

Introduction
Age-related macular degeneration (AMD) is the major cause of blindness in the elderly in the developed world. 13 The disease is multifactorial and affects the macular region of the eye, which is responsible for central vision (Fig.). 13 Changes to Bruch's membrane and the choriocapillaris frequently occur as AMD develops and are associated with degeneration of the retinal pigment epithelium (RPE). Irreversible structural damage to other retinal layers may also occur as the disease progresses. Worldwide, 30 to 50 million individuals, 4 and up to one-third of the people older than 75 have some form of AMD. 5 The incidence of AMD is increasing in European countries, the United States of America, and Japan. 6 Also, as life expectancy increases, the number of patients suffering from age-related diseases, such as Alzheimer's and AMD, is likely to rise. 7  
Figure.
 
Fundus photographs of healthy and diseased eyes. The photograph of a healthy eye shows normal pigmentation and normal retinal blood vessels. In dry AMD, deposits on Bruch's membrane may be visible at the macula. In addition, depigmented areas of geographic atrophy may be present. In wet AMD, new blood vessels originating from the choroid may give rise to macular edema and hemorrhage.
Figure.
 
Fundus photographs of healthy and diseased eyes. The photograph of a healthy eye shows normal pigmentation and normal retinal blood vessels. In dry AMD, deposits on Bruch's membrane may be visible at the macula. In addition, depigmented areas of geographic atrophy may be present. In wet AMD, new blood vessels originating from the choroid may give rise to macular edema and hemorrhage.
AMD can be classified into the dry and the wet form of the disease (Fig.). 13 Dry AMD often results in gradual loss of central vision accompanied by atrophy of RPE cells. In wet AMD, new blood vessels from the choroid (choroidal neovascularization) may leak, resulting in macular edema and hemorrhage. Although the wet from of the disease only accounts for about 10% of total AMD cases, most available treatments target this form of the disease. Currently, the most widely used treatment for wet AMD involves administration of antibodies against vascular endothelial growth factor to prevent the formation of new blood vessels and to cause those already established to regress. 811 Other available treatments include surgical excision of choroidal neovascular membranes, photodynamic therapy, and radiotherapy. 1215  
RPE cells, critical to the integrity of the outer retina, are often lost relatively early during the development of AMD. RPE cells transport nutrients from the choriocapillaris to the photoreceptors and they phagocytose shed outer segments. 16 They are also involved in maintaining relative immune privilege within the eye as part of the blood–retina barrier. 1618 RPE cells are subject to many stresses caused by the absorption of scattered light, and due to their phagocytic function. As RPE cells age, the efficiency of phagocytosis and subsequent recycling and degradation of waste declines and this may lead to a build-up of toxic waste that is deposited beneath the RPE cells on Bruch's membrane. 19,20 Together with other Bruch's membrane abnormalities this may lead to the dysfunction and ultimately the death of the RPE cells. 21,22 For patients with RPE loss due to AMD, but in whom the photoreceptors and choriocapillaris remain relatively intact, the possibility of transplanting healthy RPE cells to prevent secondary loss of photoreceptors and potentially keep or restore vision has received much recent attention. 
RPE Cell Transplantation in Animal Models
Culture techniques for human RPE cells were established in the early 1980s. 2325 RPE cells can be harvested as single cells or as monolayers. 24,2628 The first transplantations of cultured human RPE cells were performed into monkey eyes in the mid-1980s. 29,30 RPE cells have also been grafted into the eyes of other animals, including rats and rabbits. 3133  
The therapeutic potential of RPE transplantation was highlighted in experiments where RPE cells were grafted into the eyes of the Royal College of Surgeons (RCS) rat. The RCS rat has been used widely as a model of retinal degeneration for decades. 34,35 The degeneration is caused by a naturally occurring mutation in the c-mer proto-oncogene tyrosine kinase (MERTK) gene that codes for a protein essential for the phagocytosis of outer segments. 36,37 Although this animal model can be used to evaluate the survival and function of RPE cell grafts it does not show typical hallmarks of AMD. Li and Turner 31,38 published the first successful transplantation of rat RPE cells into young neonatal and adult Sprague Dawley rats as well as RCS rats. The cells integrated into the host RPE cell layer and repopulated denuded parts of Bruch's membrane. In 1989, another group reported the successful grafting of rat RPE cells into the subretinal space of the RCS rat with reversal of their inherited incapability to phagocytose outer segments. 39 In 1997, Castillo et al. 40 described the transplantation of adult human RPE cells into the RCS model to prevent retinal degeneration. In addition, transplantation of the human RPE cell lines, ARPE19 41 and h1RPE7 into the RCS model can stop the progression of retinal degeneration. 4246 As well as assaying phagocytosis of outer segments after transplantation, the ability of RPE cells to prevent retinal degeneration has been assessed functionally, for example by measuring the effects on the pupillary light reflex and by electroretinography. 4245,47,48 Additionally, Schwann cells, 49 fetal human RPE cells, 50 neonatal rat RPE cells, 51 olfactory ensheathing cells, 52 human central nervous stem cells, 53 and other cell types have been transplanted into the RCS rat. 
Transplantation of Stem Cell–Derived RPE Cells
In addition to the above mentioned cell types, stem cell–derived RPE cells have been used in RPE transplantation studies. Human embryonic stem cells (HESCs) are pluripotent cells harvested from the inner cell mass of day-5 human blastocysts that are leftover from in vitro fertilizations. 54 HESCs possess the potential to differentiate into every cell type of the body and they are essentially immortal because they can be expanded in culture without differentiation. 55,56 HESC-derived RPE cells were first derived from an ESC/stromal cell (PA6) coculture system inducing neuronal differentiation. 57,58 RPE cells have also been derived from mouse ESCs. 59 Several other studies have been published where RPE cells were derived from HESCs using a spontaneous differentiation protocol. 6072 HESC-derived RPE cells express many RPE cell markers including MERTK and the 65-kDa RPE-specific protein (RPE65), and the cells are able to perform the functions of RPE cells such as phagocytosis of rod outer segments or latex beads. 60,61,64,65,67,72  
Besides random differentiation, RPE cells have been derived from HESCs through embryoid body formation/neural differentiation. 63,64,66,6871,73 These cells express RPE-specific markers and phagocytose outer segments. 63,64,66,6871,73 Stem cell–derived RPE cells behave more like fetal RPE cells compared with adult RPE cells. The cells express genes that are essential for the function of RPE cells and that are normally not found in RPE cell lines. 6466,72,74,75  
HESC-derived RPE cells have been used for transplantation into rat and mouse models of retinal degeneration and the cells were able to rescue visual function. 63,66,67,72,73 Lu et al. 66 transplanted HESC-derived RPE cells subretinally into rat and mouse models of retinal degeneration and Stargardt's disease. A few cells survived for over 220 days and they maintained some visual function. Additionally, no teratoma formation or any other pathological reaction was observed. 66 HESC-derived RPE cells are currently being used in human clinical trials and first results were published in 2012. 76 HESC-derived RPE cells were transplanted as a cell solution into one patient with Stargardt's disease and one patient with dry AMD. Although the cells did not form a functional monolayer in the patients, slight improvements in visual acuity in both patients was observed. 76 However, it should be noted that the measured visual acuity in retested AMD patients can sometimes improve over time due to changes in eccentric fixation, where a slightly different part of the retina is used to view central visual targets. This mechanism could also explain why there was some improvement in the fellow eye, which received no RPE cells. Thus, careful experimental design and cautious interpretation of results are essential to be sure that any change in visual acuity is truly due to an RPE transplant. Yet the preliminary findings are certainly suggestive and the results of later phase studies are awaited with interest. 
In addition to HESCs, human induced pluripotent stem cells (iPSCs) have been used to derive RPE cells. iPSCs are reprogrammed somatic cells that share many similarities with HESCs. They are also pluripotent and can be expanded in culture to a theoretically infinite degree. 7781 RPE cells were derived from iPSCs using the spontaneous differentiation method. 60,65,82,83 Additionally, iPSCs have been used to derive RPE cells through embryoid body formation/neural differentiation 68,71,8487 or through directed differentiation. 88 The iPSC-derived RPE cells also expressed several RPE markers and fulfilled RPE functions as well as being able to replace RPE cells after transplantation. 60,65,82,83,85,8789 Most recently, RIKEN and the Foundation for Biomedical Research and Innovation, Japan, jointly applied to conduct a clinical trial using iPSC-derived RPE cells to treat AMD, 90,91 so active development of this approach appears likely in the near future. 
The use of stem cells in regenerative medicine carries the risk of tumor formation and immune rejection. 66,92 Because of its immune privilege, 17 cells transplanted into the eye may survive for longer than in other parts of the body. However, xenografts of RPE cells can still be targeted and destroyed by the recipient 93 and in animals, immunosuppression did not help to protect RPE allografts from destruction by the recipient's immune system, 94,95  
Although RPE cells derived from embryonic stem cells seem to be relatively safe in terms of tumor risk post transplantation, 66 it has been reported that these cells can dedifferentiate into neural rosettes. 72 In the latest human clinical trial, the transplanted HESC-derived RPE cells did not appear to cause any serious side effects, although data from only two patients have been published so far. 76  
In addition, iPSC-derived RPE cells lead to a more rapid host cell rejection after subretinal transplantation compared with HESC-derived RPE cells. 61 This rejection might be due to the reprogramming of the somatic cells into iPSCs using integrative viruses. 96 The use of nonintegrative episomal viruses to reprogram cells generates pluripotent cells that are less immunogenic and more similar to HESCs. 97,98 In addition, the use of a Sendai virus, 99 directed mRNA 100 or proteins 101 to reprogram the cells might overcome immunogenic problems. 96 Recently, Hou et al. 102 found a way to induce pluripotency in mice somatic cells using chemical compounds alone. Four of these compounds are already used in clinical trials. The researchers are now trying the same approach on human cells. 102 To overcome the stem cell–associated tumor risk human fibroblasts have been differentiated directly into RPE-like cells by overexpressing RPE-specific transcription factors. 103 Also this approach uses retroviruses to overexpress the transcription factors which might lead to complications in vivo. Patient-derived iPSCs might overcome the host immune response but they will still carry AMD susceptibility loci that might lead to AMD features post transplantation. 96 Targeted gene repair to genetically correct AMD associated mutations prior to transplantation might overcome this problem. 85  
Primary RPE Cell Transplantation into Human Patients
Following encouraging results in animal models, grafting of RPE cells was tested in human patients using a variety of techniques. In some studies, healthy autologous RPE from the periphery of the eye was transplanted into the macular region of the same eye to replace the diseased foveal RPE cells. This autologous transplantation involved either RPE cells alone or a patch of RPE cells together with the underlying choroid. 104115 In the first of these studies, Peyman et al. 112 transplanted RPE cells into the eyes of two patients with advanced AMD. For one of the two cases visual improvement was achieved for several months, but the other did not show any positive effects. Improved instrumentation to minimize damage of healthy tissue as well as improvements in the delivery method of RPE cell suspensions or sheets have made RPE cell transplantation somewhat easier and safer, but the technique is still difficult, time-consuming, and may lead to retinal detachment during the harvesting of peripheral RPE cells. 116118 To date, a total of more than 30 homologous and 230 autologous RPE transplantations have been reported. 119  
A comparison between the grafting of a RPE cell suspension and transplantation of an RPE sheet did not find significant differences with some improvement in visual acuity observed. 107 However, transplantation of a uniform layer has proven difficult because the grafts tend to wrinkle up or contract after grafting, forming thin patches or multilayered folds. 120 On the other hand, RPE cell suspensions alone may not survive in the diseased environment of an aged Bruch's membrane, 121 and the therapeutic success of transplantation of RPE cell solutions may be limited if few cells adhere to diseased Bruch's membrane or fail to survive for long enough to show a positive effect. The rejection rate due to inflammation seemed to be a major problem in some studies and this may be a bigger problem in wet than dry AMD as this type of the disease involves a greater compromise of the retinal–blood barrier. 122 The extracellular environment to which the cells have to adhere plays an important role in the survival of the transplanted RPE cells. 123129 It has been shown that RPE cells undergo apoptosis if they do not adhere fast enough. 125,127 The lack of adhesion can be explained through molecular changes on Bruch's membrane that result from age-related deposition of anti-adhesive molecules and a decline in normal integrin ligands that would promote the attachment of the transplanted cells. 
Moreover, in wet AMD, surgical approaches face the problem that choroidal new vessels have grown from the choroid through Bruch's membrane into the retina and have altered the environment of Bruch's membrane in the process. Prior to transplantation of RPE cells, choroidal neovascular membranes can be excised and RPE cells can be seeded on the denuded area. 130,131 After subretinal choroidal neovascular removal, the endogenous RPE layer displays a certain wound healing ability but the RPE cells are not able to cover the exposed deeper layers of the diseased Bruch's membrane completely and progressive atrophy of the choriocapillaris frequently occurs. 132,133  
Binder et al. 104,105 showed that autologous macular transplantation led to some visual improvement after choroidal neovascular removal. The clinical study comparing membrane excision alone with simultaneous RPE transplantation found a small improvement in visual acuity for near but not for distance. 104 Other studies showed that the debridement of Bruch's membrane followed by transplantation of autologous RPE cells led to a repopulation of the cleaned area of Bruch's membrane and a prevention of photoreceptor loss. 33 In 2007, MacLaren et al. 111 reported that their autologous transplantation after choroidal neovascular excision led to visual function improvements and that the graft survived until the 6-month time point. However, surgery-associated complications remained high. 111  
In addition to age-related changes to Bruch's membrane that can at least in part be held responsible for a failure of survival of grafted RPE cells, mechanical damage due to the transplantation itself may result in poorer adhesion of the graft. Techniques that are used to excise choroidal neovascular membranes in wet AMD can result in damage or removal of the basement membrane of Bruch's membrane. 134 The RPE basement membrane is the best substrate for transplanted RPE cells and its removal has serious consequences for RPE survival, as has been shown ex vivo. 123,124,127,135,136  
In addition to using autologous RPE cells, allotransplantation has been performed in human patients. 122,137140 In one study, grafted fetal RPE cells resurfaced the denuded Bruch's membrane after removal of choroidal neovascular membranes and the cells survived for up to 3 months in the five patients. 137 However, at the 12-month follow-up, most of the patients reported further visual loss compared with the pre-operative vision. 137 In nonexudative AMD, fetal RPE cell suspension grafts showed positive effects and stabilized visual acuity. However, in disciform lesions and in dry geographic atrophy AMD, the transplants did not lead to visual improvement. 122,140 Transplantation of allogeneic fetal RPE grafts is associated with a high rejection rate without immunosuppression, especially in wet AMD cases. 138 Autologous transplantation of a sheet of adult RPE cells has also been studied in one clinical trial. 139 Although no improvements in visual acuity were observed, the adult RPE monolayer was not rejected by the host and it appeared healthy up to 1 year after transplantation. 139  
Enhancing the Adhesion and Survival of Transplanted RPE Cells
As mentioned above, transplanted RPE cells show limited adhesion and survival after transplantation into human eyes. Ex vivo models played an important role in determining the survival rate of RPE cells after transplantation. By comparing the attachment rate of RPE cells seeded on Bruch's membrane from young and old donors, researchers have demonstrated that aged Bruch's membrane does not support adhesion, survival, differentiation, and function of grafted RPE cells. 15,123,127129,141 Age-related debris in all layers of Bruch's membrane might account for the lack of adhesion. 126 That RPE cells behave differently on Bruch's membranes from differently aged donors has further been evaluated with gene expression profiles; RPE cells seeded on aged Bruch's membrane upregulate 12 genes and downregulate eight compared with younger membranes. 142  
Sugino et al. 143 compared the fate of fetal and HESC-derived RPE cells on aged and AMD Bruch's membrane. Both cell types were able to resurface parts of the membranes after 3 weeks. However, even after successful adhesion of the grafted RPE cells, the changes on Bruch's membrane hindered the formation of a functional monolayer of RPE cells. 143 This study emphasizes that stem cell–derived RPE cells behave similarly to fetal RPE cells in a diseased Bruch's membrane environment and new approaches are required to overcome the inhibitory environment to ensure RPE cell resurfacing of Bruch's membrane. 
The interaction of RPE cells with Bruch's membrane is mediated mostly via β1-containing integrins, which bind to a variety of extracellular ligands including laminin, fibronectin, vitronectin, and collagen IV. 144146 Further studies have shown that laminin and fibronectin facilitated the attachment of RPE cells and prevented RPE apoptosis most effectively. 125,147 The upper-most layers of Bruch's membrane are rich in these two extracellular matrix molecules 148,149 and exposure of deeper layers of the membrane will result in disturbed adhesion of RPE cells. Therefore, it is important to enable the RPE cells to cope with the extracellular environment that they will encounter after transplantation. 147,150  
One approach to enhance the binding of transplanted RPE cells in the pathological environment is to provide the RPE cells with a more favorable substrate. However, in vivo, the addition of poly-L-lysine in combination with RPE translocation did not show any positive effects, 114 although this failure might have been due to a permeabilization of the grafted RPE cells by the poly-L-lysine itself. Nevertheless, in vitro, the alteration of the extracellular matrix (ECM) composition of Bruch's membrane through the addition of conditioned media helped the attachment of seeded RPE cells to aged Bruch's membrane. 126,151153 Another approach is to increase the surface levels of integrins. It has been shown that uncultured RPE cells from aged donors fail to adhere, survive, or function on Bruch's membrane. 124,127,135,154 Thus, Gullapalli et al. 155 tested the effect of long-term culturing on the adhesion rate of the RPE cells. The long-term culture increased the expression levels of α-integrins, which has a positive effect on the adhesion of RPE cells to Bruch's membrane and its components. 155 In addition to long-term culturing of the RPE cells, genetic manipulation to overexpress integrins can be used to enhance RPE adhesion. As an example, overexpression of the integrin α6β4 led to an increased binding and proliferation of RPE cells on all layers of Bruch's membrane. Manipulation of this integrin through site directed mutagenesis disrupted the adhesion and proliferation of the RPE cells on Bruch's membrane. 156 Additionally, our group has shown that overexpression of α9 integrin in ARPE19 cells enhanced the adhesion of the cells to Bruch's membrane explants from donors with wet AMD. 147  
As well as changing the integrins exposed on the surface of cells, the activation state of these cell surface integrins can be controlled from within the cell (inside-out signaling). This mechanism promotes the cellular binding to extracellular ligands and the linkage of the integrins to the cytoskeleton. 157 Several researchers have investigated the role of integrin activation in improving cell adhesion, migration, and neurite outgrowth. 158163 In addition, it has been shown that inhibitory factors can influence the activation state of integrins and decrease the ability of the cells to interact with their extracellular environment. 159,162,163 It is therefore possible to change the expression profile of integrins or their activation state to promote the adhesion of RPE cells to pathological Bruch's membrane prior to transplantation. It has been shown in ARPE19 cells that the addition of manganese as a broad integrin activator 164 or the administration of the monoclonal antibody TS2/16 165,166 enhances the adhesion as well as migration of the cells to Bruch's membrane components as well as in our studies with Bruch's membrane explants. 147 Furthermore, recent unpublished data from our laboratory shows that the application of manganese as well as the overexpression of kindlin-1, an intracellular binding partner, and activator of integrins, 162,167169 enhances the adhesion, spreading as well as migration of primary rat RPE cells on Bruch's membrane components and rat Bruch's membrane explants (Heller JP, et al. IOVS. 2011;52:ARVO E-Abstract 936). Upregulation of anti-adhesive molecules such as tenascin-C has been reported, particularly in wet AMD. 147,170,171 The application of manganese, as well as the overexpression of kindlin-1 or α9 integrin, in primary rat RPE cells can overcome the inhibitory effects of TN-C and the chondroitin sulfate proteoglycan aggrecan and promote the adhesion, spreading and migration on these pathological Bruch's membrane components (Heller JP, et al. IOVS. 2011;52:ARVO E-Abstract 936). Hence, in an environment where inhibitory molecules are more abundant than pro-adhesive molecules like laminin and fibronectin, the modulation of RPE cell integrins could potentially enhance the survival rate of transplanted RPE cells. 147,150 Therefore, this approach might overcome age-related pathological changes on Bruch's membrane as well as surgical damage caused by the excision of choroidal neovascular membranes. 
To overcome the problems of forming a functional monolayer post transplantation, RPE cells can be grafted as a polarized monolayer growing on a scaffold. This can circumvent the problems of de- and redifferentiation of the RPE cells as well as avoiding the low attachment rate of the grafted RPE cells. Natural membranes including biologically-derived basal lamina, amniotic membrane, Descemet's membrane and lens capsule have been used as substrates for RPE cells. 121,172 Additionally, artificial Bruch's membrane substrates including parylene films, 173,174 plasma polymers, 175 polyamide nanofibres, 176 polyester membranes, 177 polyimide, 178 and modified polytetrafluoroethylene 175 have been proposed. 179 However, the use of some types of artificial membranes carries the risk of biological contamination and disease transmission. 172 Encouraging results have been described by the group of Peter Coffey at the Institute of Ophthalmology in London, UK and the University of California at Santa Barbara and his collaborators using a coated, nonbiodegradable polyester membrane with HESC-derived RPE cells. 61,72 A clinical trial of these approaches is planned to commence in the near future. 
In a recent study, Diniz et al. 173 compared the survival of 10,000 cells transplanted as a suspension versus 2700 cells seeded on a parylene membrane. The cells grafted as a monolayer survived better, and the cells in solution often formed aggregates or clumps in the immunocompromised rat model. However, the transplantation of a cell solution is technically easier and causes less trauma and biocompatibility issues. 173 Again, this emphasizes that the use of a RPE cell solution might be the easier approach to replace lost RPE cells in AMD. The results from our laboratory using primary rat RPE as well as ARPE19 cells suggest that in future transplantation studies the integrin abundance on the cell surface as well as the integrin activation state of stem cell–derived RPE cells should be altered prior to transplantation to ensure satisfying adhesion to and interaction with the aged and diseased Bruch's membrane 147 (Heller JP, et al. IOVS. 2011;52:ARVO E-Abstract 936). 
Conclusion
Although the results of many of the animal studies performed in models of AMD are encouraging, it is important to remember that there is no model that fully replicates the human disease. All of the animal models used to study AMD have limitations and the results should therefore be interpreted with caution, particularly with regard to how they apply to the human condition. In particular, models differ with regard to the mechanisms of RPE cell loss, the importance of inflammation and the recruitment of other cells during the degenerative process. Better animal models of AMD are an important goal for future research. 
Nevertheless, approaches using RPE cell transplantation to treat AMD are reaching a very exciting stage. However, the recent results from the Advanced Cell Technology–sponsored trial using HESC-derived RPE cells showed that no functional monolayer was formed by the transplanted cells. Additionally, signs of cell clumping were detected in one patient. 76 More patients are needed in this trial to assess the potential of the transplanted cells to replace the diseased RPE cells. However, the low attachment and spreading rate of the transplanted RPE cells might be avoidable, either through the use of genetic engineering to overexpress integrins or integrin activators in the RPE cells, 147,150,156 or through the use of RPE cells growing on scaffolds. Planned clinical trials will evaluate the effectiveness of RPE cell monolayers rather than cell suspensions. 61,72 In addition, the clinical trial will evaluate the feasibility of this technique in human patients as compared with the easier grafting of a cell suspension. The clinical trial in Japan will show whether the use of iPSC-derived cells is a safe tool for regenerative medicine, and whether transplantation of iPSC-derived RPE cells can be a potential treatment for macular degeneration in human patients. 90,91 In addition, several banks for iPSC lines are going to be established in many parts of the world, including the United States, Europe, and Japan. These banks will enable the use of HLA-matched cells for transplantation to reduce the risk of graft rejection by the patients. The results of these trials may well have important implications for future AMD therapy and are awaited with great interest. 
Nevertheless, the transplantation of RPE cells alone might not be sufficient if AMD has progressed to a stage when photoreceptors are affected too. Simultaneous or sequential grafting of RPE cells together with photoreceptor precursor cells could potentially be used as a treatment for more advanced AMD as the transplantation of developing rods has been shown to be effective in several animal models of inherited retinopathies. 180,181 2164  
Acknowledgments
This article was supported by grants from the Cambridge Eye Trust and the Medical Research Council. 
Disclosure: J.P. Heller, None; K.R. Martin, None 
References
de Jong PT Age-related macular degeneration. N Engl J Med . 2006; 355: 1474– 1485. [CrossRef] [PubMed]
Jager RD Mieler WF Miller JW Age-related macular degeneration. N Engl J Med . 2008; 358: 2606– 2617. [CrossRef] [PubMed]
Ambati J Fowler BJ Mechanisms of age-related macular degeneration. Neuron . 2012; 75: 26– 39. [CrossRef] [PubMed]
Gehrs KM Anderson DH Johnson LV Hageman GS Age-related macular degeneration–emerging pathogenetic and therapeutic concepts. Ann Med . 2006; 38: 450– 471. [CrossRef] [PubMed]
Zarbin MA Current concepts in the pathogenesis of age-related macular degeneration. Arch Ophthalmol . 2004; 122: 598– 614. [CrossRef] [PubMed]
Bird AC The Bowman lecture. Towards an understanding of age-related macular disease. Eye (Lond) . 2003; 17: 457– 466. [CrossRef] [PubMed]
Friedman DS O'Colmain BJ Munoz B et al . Prevalence of age-related macular degeneration in the United States. Arch Ophthalmol . 2004; 122: 564– 572. [CrossRef] [PubMed]
Bopp S Anti-VEGF for neovascular ARMD: visual improvement as the goal of therapy? Br J Ophthalmol . 2007; 91: 1259– 1260. [CrossRef] [PubMed]
Wu L Martinez-Castellanos MA Quiroz-Mercado H et al . Twelve-month safety of intravitreal injections of bevacizumab (Avastin(R)): results of the Pan-American Collaborative Retina Study Group (PACORES). Graefes Arch Clin Exp Ophthalmol . 2008; 246: 81– 87. [CrossRef] [PubMed]
Martin DF Maguire MG Ying GS et al . Ranibizumab and bevacizumab for neovascular age-related macular degeneration. N Engl J Med . 2011; 364: 1897– 1908. [CrossRef] [PubMed]
Heier JS Brown DM Chong V et al . Intravitreal aflibercept (VEGF trap-eye) in wet age-related macular degeneration. Ophthalmology . 2012; 119: 2537– 2548. [CrossRef] [PubMed]
Soubrane G Bressler NM Treatment of subfoveal choroidal neovascularisation in age related macular degeneration: focus on clinical application of verteporfin photodynamic therapy. Br J Ophthalmol . 2001; 85: 483– 495. [CrossRef] [PubMed]
Silva RA Moshfeghi AA Kaiser PK et al . Radiation treatment for age-related macular degeneration. Semin Ophthalmol . 2011; 26: 121– 130. [CrossRef] [PubMed]
Petrarca R Jackson TL Radiation therapy for neovascular age-related macular degeneration. Clin Ophthalmol . 2011; 5: 57– 63. [CrossRef] [PubMed]
Binder S Stanzel BV Krebs I Glittenberg C Transplantation of the RPE in AMD. Prog Retin Eye Res . 2007; 26: 516– 554. [CrossRef] [PubMed]
Strauss O The retinal pigment epithelium in visual function. Physiol Rev . 2005; 85: 845– 881. [CrossRef] [PubMed]
Taylor AW Ocular immune privilege. Eye (Lond) . 2009; 23: 1885– 1889. [CrossRef] [PubMed]
Rizzolo LJ Peng S Luo Y Xiao W Integration of tight junctions and claudins with the barrier functions of the retinal pigment epithelium. Prog Retin Eye Res . 2011; 30: 296– 323. [CrossRef] [PubMed]
Kinnunen K Petrovski G Moe MC et al . Molecular mechanisms of retinal pigment epithelium damage and development of age-related macular degeneration. Acta Ophthalmol . 2012; 90: 299– 309. [CrossRef] [PubMed]
Sparrow JR Hicks D Hamel CP The retinal pigment epithelium in health and disease. Curr Mol Med . 2010; 10: 802– 823. [CrossRef] [PubMed]
Dunaief JL Dentchev T Ying GS Milam AH The role of apoptosis in age-related macular degeneration. Arch Ophthalmol . 2002; 120: 1435– 1442. [CrossRef] [PubMed]
Del Priore LV Kuo YH Tezel TH Age-related changes in human RPE cell density and apoptosis proportion in situ. Invest Ophthalmol Vis Sci . 2002; 43: 3312– 3318. [PubMed]
Boulton ME Marshall J Mellerio J Human retinal pigment epithelial cells in tissue culture: a means of studying inherited retinal diseases. Birth Defects Orig Artic Ser . 1982; 18: 101– 118. [PubMed]
Flood MT Gouras P Kjeldbye H Growth characteristics and ultrastructure of human retinal pigment epithelium in vitro. Invest Ophthalmol Vis Sci . 1980; 19: 1309– 1320. [PubMed]
Hu DN Del Monte MA Liu S Maumenee IH Morphology, phagocytosis, and vitamin A metabolism of cultured human retinal pigment epithelium. Birth Defects Orig Artic Ser . 1982; 18: 67– 79. [PubMed]
Ho TC Del Priore LV Kaplan HJ Tissue culture of retinal pigment epithelium following isolation with a gelatin matrix technique. Exp Eye Res . 1997; 64: 133– 139. [CrossRef] [PubMed]
Mayerson PL Hall MO Clark V Abrams T An improved method for isolation and culture of rat retinal pigment epithelial cells. Invest Ophthalmol Vis Sci . 1985; 26: 1599– 1609. [PubMed]
Tezel TH Del Priore LV Kaplan HJ Harvest and storage of adult human retinal pigment epithelial sheets. Curr Eye Res . 1997; 16: 802– 809. [CrossRef] [PubMed]
Gouras P Flood MT Kjedbye H et al . Transplantation of cultured human retinal epithelium to Bruch's membrane of the owl monkey's eye. Curr Eye Res . 1985; 4: 253– 265. [CrossRef] [PubMed]
Gouras P Flood MT Kjeldbye H Transplantation of cultured human retinal cells to monkey retina. Anais da Academia Brasileira de Ciencias . 1984; 56: 431– 443. [PubMed]
Li LX Turner JE Transplantation of retinal pigment epithelial cells to immature and adult rat hosts: short- and long-term survival characteristics. Exp Eye Res . 1988; 47: 771– 785. [CrossRef] [PubMed]
Lopez R Gouras P Brittis M Kjeldbye H Transplantation of cultured rabbit retinal epithelium to rabbit retina using a closed-eye method. Invest Ophthalmol Vis Sci . 1987; 28: 1131– 1137. [PubMed]
Phillips SJ Sadda SR Tso MO et al . Autologous transplantation of retinal pigment epithelium after mechanical debridement of Bruch's membrane. Curr Eye Res . 2003; 26: 81– 88. [CrossRef] [PubMed]
Bok D Hall MO The role of the pigment epithelium in the etiology of inherited retinal dystrophy in the rat. J Cell Biol . 1971; 49: 664– 682. [CrossRef] [PubMed]
Mullen RJ LaVail MM Inherited retinal dystrophy: primary defect in pigment epithelium determined with experimental rat chimeras. Science . 1976; 192: 799– 801. [CrossRef] [PubMed]
D'Cruz PM Yasumura D Weir J et al . Mutation of the receptor tyrosine kinase gene Mertk in the retinal dystrophic RCS rat. Hum Mol Genet . 2000; 9: 645– 651. [CrossRef] [PubMed]
Gal A Li Y Thompson DA et al . Mutations in MERTK, the human orthologue of the RCS rat retinal dystrophy gene, cause retinitis pigmentosa. Nat Genet . 2000; 26: 270– 271. [CrossRef] [PubMed]
Li LX Turner JE Inherited retinal dystrophy in the RCS rat: prevention of photoreceptor degeneration by pigment epithelial cell transplantation. Exp Eye Res . 1988; 47: 911– 917. [CrossRef] [PubMed]
Lopez R Gouras P Kjeldbye H et al . Transplanted retinal pigment epithelium modifies the retinal degeneration in the RCS rat. Invest Ophthalmol Vis Sci . 1989; 30: 586– 588. [PubMed]
Castillo BVJr del Cerro M White RM et al . Efficacy of nonfetal human RPE for photoreceptor rescue: a study in dystrophic RCS rats. Exp Neurol . 1997; 146: 1– 9. [CrossRef] [PubMed]
Dunn KC Aotaki-Keen AE Putkey FR Hjelmeland LM ARPE-19, a human retinal pigment epithelial cell line with differentiated properties. Exp Eye Res . 1996; 62: 155– 169. [CrossRef] [PubMed]
Coffey PJ Girman S Wang SM et al . Long-term preservation of cortically dependent visual function in RCS rats by transplantation. Nat Neurosci . 2002; 5: 53– 56. [CrossRef] [PubMed]
Gias C Jones M Keegan D et al . Preservation of visual cortical function following retinal pigment epithelium transplantation in the RCS rat using optical imaging techniques. Eur J Neurosci . 2007; 25: 1940– 1948. [CrossRef] [PubMed]
Girman SV Wang S Lund RD Cortical visual functions can be preserved by subretinal RPE cell grafting in RCS rats. Vision Res . 2003; 43: 1817– 1827. [CrossRef] [PubMed]
Lund RD Adamson P Sauve Y et al . Subretinal transplantation of genetically modified human cell lines attenuates loss of visual function in dystrophic rats. Proc Natl Acad Sci U S A . 2001; 98: 9942– 9947. [CrossRef] [PubMed]
Wang S Lu B Wood P Lund RD Grafting of ARPE-19 and Schwann cells to the subretinal space in RCS rats. Invest Ophthalmol Vis Sci . 2005; 46: 2552– 2560. [CrossRef] [PubMed]
Sauve Y Klassen H Whiteley SJ Lund RD Visual field loss in RCS rats and the effect of RPE cell transplantation. Exp Neurol . 1998; 152: 243– 250. [CrossRef] [PubMed]
Whiteley SJ Litchfield TM Coffey PJ Lund RD Improvement of the pupillary light reflex of Royal College of Surgeons rats following RPE cell grafts. Exp Neurol . 1996; 140: 100– 104. [CrossRef] [PubMed]
Lawrence JM Sauve Y Keegan DJ et al . Schwann cell grafting into the retina of the dystrophic RCS rat limits functional deterioration. Royal College of Surgeons. Invest Ophthalmol Vis Sci . 2000; 41: 518– 528. [PubMed]
Little CW Cox C Wyatt J et al . Correlates of photoreceptor rescue by transplantation of human fetal RPE in the RCS rat. Exp Neurol . 1998; 149: 151– 160. [CrossRef] [PubMed]
Seaton AD Sheedlo HJ Turner JE A primary role for RPE transplants in the inhibition and regression of neovascularization in the RCS rat. Invest Ophthalmol Vis Sci . 1994; 35: 162– 169. [PubMed]
Huo SJ Li YC Xie J et al . Transplanted olfactory ensheathing cells reduce retinal degeneration in Royal College of Surgeons rats. Curr Eye Res . 2012; 37: 749– 758. [CrossRef] [PubMed]
McGill TJ Cottam B Lu B et al . Transplantation of human central nervous system stem cells - neuroprotection in retinal degeneration. Eur J Neurosci . 2012; 35: 468– 477. [CrossRef] [PubMed]
Thomson JA Itskovitz-Eldor J Shapiro SS et al . Embryonic stem cell lines derived from human blastocysts. Science . 1998; 282: 1145– 1147. [CrossRef] [PubMed]
Amit M Carpenter MK Inokuma MS et al . Clonally derived human embryonic stem cell lines maintain pluripotency and proliferative potential for prolonged periods of culture. Dev Biol . 2000; 227: 271– 278. [CrossRef] [PubMed]
Reubinoff BE Pera MF Fong CY et al . Embryonic stem cell lines from human blastocysts: somatic differentiation in vitro. Nat Biotechnol . 2000; 18: 399– 404. [CrossRef] [PubMed]
Haruta M Sasai Y Kawasaki H et al . In vitro and in vivo characterization of pigment epithelial cells differentiated from primate embryonic stem cells. Invest Ophthalmol Vis Sci . 2004; 45: 1020– 1025. [CrossRef] [PubMed]
Kawasaki H Suemori H Mizuseki K et al . Generation of dopaminergic neurons and pigmented epithelia from primate ES cells by stromal cell-derived inducing activity. Proc Natl Acad Sci U S A . 2002; 99: 1580– 1585. [CrossRef] [PubMed]
Hirano M Yamamoto A Yoshimura N et al . Generation of structures formed by lens and retinal cells differentiating from embryonic stem cells. Dev Dyn . 2003; 228: 664– 671. [CrossRef] [PubMed]
Buchholz DE Hikita ST Rowland TJ et al . Derivation of functional retinal pigmented epithelium from induced pluripotent stem cells. Stem Cells (Dayton, Ohio) . 2009; 27: 2427– 2434. [CrossRef] [PubMed]
Carr AJ Vugler A Lawrence J et al . Molecular characterization and functional analysis of phagocytosis by human embryonic stem cell-derived RPE cells using a novel human retinal assay. Mol Vis . 2009; 15: 283– 295. [PubMed]
Gong J Sagiv O Cai H et al . Effects of extracellular matrix and neighboring cells on induction of human embryonic stem cells into retinal or retinal pigment epithelial progenitors. Exp Eye Res . 2008; 86: 957– 965. [CrossRef] [PubMed]
Idelson M Alper R Obolensky A et al . Directed differentiation of human embryonic stem cells into functional retinal pigment epithelium cells. Cell Stem Cell . 2009; 5: 396– 408. [CrossRef] [PubMed]
Klimanskaya I Hipp J Rezai KA et al . Derivation and comparative assessment of retinal pigment epithelium from human embryonic stem cells using transcriptomics. Cloning Stem Cells . 2004; 6: 217– 245. [CrossRef] [PubMed]
Liao JL Yu J Huang K et al . Molecular signature of primary retinal pigment epithelium and stem-cell-derived RPE cells. Hum Mol Genet . 2010; 19: 4229– 4238. [CrossRef] [PubMed]
Lu B Malcuit C Wang S et al . Long-term safety and function of RPE from human embryonic stem cells in preclinical models of macular degeneration. Stem Cells (Dayton, Ohio) . 2009; 27: 2126– 2135. [CrossRef] [PubMed]
Lund RD Wang S Klimanskaya I et al . Human embryonic stem cell-derived cells rescue visual function in dystrophic RCS rats. Cloning Stem Cells . 2006; 8: 189– 199. [CrossRef] [PubMed]
Meyer JS Shearer RL Capowski EE et al . Modeling early retinal development with human embryonic and induced pluripotent stem cells. Proc Natl Acad Sci U S A . 2009; 106: 16698– 16703. [CrossRef] [PubMed]
Nistor G Seiler MJ Yan F et al . Three-dimensional early retinal progenitor 3D tissue constructs derived from human embryonic stem cells. J Neurosci Methods . 2010; 190: 63– 70. [CrossRef] [PubMed]
Osakada F Ikeda H Sasai Y Takahashi M Stepwise differentiation of pluripotent stem cells into retinal cells. Nat Protoc . 2009; 4: 811– 824. [CrossRef] [PubMed]
Osakada F Jin ZB Hirami Y et al . In vitro differentiation of retinal cells from human pluripotent stem cells by small-molecule induction. J Cell Sci . 2009; 122: 3169– 3179. [CrossRef] [PubMed]
Vugler A Carr AJ Lawrence J et al . Elucidating the phenomenon of HESC-derived RPE: anatomy of cell genesis, expansion and retinal transplantation. Exp Neurol . 2008; 214: 347– 361. [CrossRef] [PubMed]
Park UC Cho MS Park JH et al . Subretinal transplantation of putative retinal pigment epithelial cells derived from human embryonic stem cells in rat retinal degeneration model. Clin Exp Reprod Med . 2011; 38: 216– 221. [CrossRef] [PubMed]
Lamba DA Reh TA Microarray characterization of human embryonic stem cell--derived retinal cultures. Invest Ophthalmol Vis Sci . 2011; 52: 4897– 4906. [CrossRef] [PubMed]
Osakada F Ikeda H Mandai M et al . Toward the generation of rod and cone photoreceptors from mouse, monkey and human embryonic stem cells. Nat Biotechnol . 2008; 26: 215– 224. [CrossRef] [PubMed]
Schwartz SD Hubschman JP Heilwell G et al . Embryonic stem cell trials for macular degeneration: a preliminary report. Lancet . 2012; 379: 713– 720. [CrossRef] [PubMed]
Okita K Yamanaka S Induced pluripotent stem cells: opportunities and challenges. Philos Trans R Soc Lond B Biol Sci . 2011; 366: 2198– 2207. [CrossRef] [PubMed]
Park IH Lerou PH Zhao R et al . Generation of human-induced pluripotent stem cells. Nat Protoc . 2008; 3: 1180– 1186. [CrossRef] [PubMed]
Takahashi K Tanabe K Ohnuki M et al . Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell . 2007; 131: 861– 872. [CrossRef] [PubMed]
Takahashi K Yamanaka S Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell . 2006; 126: 663– 676. [CrossRef] [PubMed]
Yu J Vodyanik MA Smuga-Otto K et al . Induced pluripotent stem cell lines derived from human somatic cells. Science . 2007; 318: 1917– 1920. [CrossRef] [PubMed]
Carr AJ Vugler AA Hikita ST et al . Protective effects of human iPS-derived retinal pigment epithelium cell transplantation in the retinal dystrophic rat. PLoS ONE . 2009; 4: e8152. [CrossRef] [PubMed]
Ukrohne TU Westenskow PD Kurihara T et al . Generation of retinal pigment epithelial cells from small molecules and OCT4 reprogrammed human induced pluripotent stem cells. Stem Cells Transl Med . 2012; 1: 96– 109. [CrossRef] [PubMed]
Hirami Y Osakada F Takahashi K et al . Generation of retinal cells from mouse and human induced pluripotent stem cells. Neurosci Lett . 2009; 458: 126– 131. [CrossRef] [PubMed]
Meyer JS Howden SE Wallace KA et al . Optic vesicle-like structures derived from human pluripotent stem cells facilitate a customized approach to retinal disease treatment. Stem Cells (Dayton, Ohio) . 2011; 29: 1206– 1218. [CrossRef] [PubMed]
Rowland TJ Blaschke AJ Buchholz DE et al . Differentiation of human pluripotent stem cells to retinal pigmented epithelium in defined conditions using purified extracellular matrix proteins. J Tissue Eng Regen Med . 2013; 7: 642– 653. [CrossRef] [PubMed]
Vaajasaari H Ilmarinen T Juuti-Uusitalo K et al . Toward the defined and xeno-free differentiation of functional human pluripotent stem cell-derived retinal pigment epithelial cells. Mol Vis . 2011; 17: 558– 575. [PubMed]
Westenskow PD Moreno SK Krohne TU et al . Using flow cytometry to compare the dynamics of photoreceptor outer segment phagocytosis in iPS-derived RPE cells. Invest Ophthalmol Vis Sci . 2012; 53: 6282– 6290. [CrossRef] [PubMed]
Kokkinaki M Sahibzada N Golestaneh N Human induced pluripotent stem-derived retinal pigment epithelium (RPE) cells exhibit ion transport, membrane potential, polarized vascular endothelial growth factor secretion, and gene expression pattern similar to native RPE. Stem Cells (Dayton, Ohio) . 2011; 29: 825– 835. [CrossRef] [PubMed]
Cyranoski D Stem cells cruise to clinic. Nature . 2013; 494: 413. [CrossRef] [PubMed]
Song PP Inagaki Y Sugawara Y Kokudo N Perspectives on human clinical trials of therapies using iPS cells in Japan: reaching the forefront of stem-cell therapies. Biosci Trends . 2013; 7: 157– 158. [PubMed]
Utermohlen O Baschuk N Abdullah Z et al . Immunologic hurdles of therapeutic stem cell transplantation. Biol Chem . 2009; 390: 977– 983. [CrossRef] [PubMed]
Grisanti S Szurman P Jordan J et al . Xenotransplantation of retinal pigment epithelial cells into RCS rats. Jpn J Ophthalmol . 2002; 46: 36– 44. [CrossRef] [PubMed]
Crafoord S Algvere PV Kopp ED Seregard S Cyclosporine treatment of RPE allografts in the rabbit subretinal space. Acta Ophthalmol Scand . 2000; 78: 122– 129. [CrossRef] [PubMed]
Del Priore LV Ishida O Johnson EW et al . Triple immune suppression increases short-term survival of porcine fetal retinal pigment epithelium xenografts. Invest Ophthalmol Vis Sci . 2003; 44: 4044– 4053. [CrossRef] [PubMed]
Carr AJ Smart MJ Ramsden CM et al . Development of human embryonic stem cell therapies for age-related macular degeneration. Trends Neurosci . 2013; 36: 385– 395. [CrossRef] [PubMed]
Liu Y Cheng D Li Z et al . The gene expression profiles of induced pluripotent stem cells (iPSCs) generated by a non-integrating method are more similar to embryonic stem cells than those of iPSCs generated by an integrating method. Genet Mol Biol . 2012; 35: 693– 700. [CrossRef] [PubMed]
Zhao T Zhang ZN Rong Z Xu Y Immunogenicity of induced pluripotent stem cells. Nature . 2011; 474: 212– 215. [CrossRef] [PubMed]
Fusaki N Ban H Nishiyama A et al . Efficient induction of transgene-free human pluripotent stem cells using a vector based on Sendai virus, an RNA virus that does not integrate into the host genome. Proc Jpn Acad Ser B Phys Biol Sci . 2009; 85: 348– 362. [CrossRef] [PubMed]
Warren L Manos PD Ahfeldt T et al . Highly efficient reprogramming to pluripotency and directed differentiation of human cells with synthetic modified mRNA. Cell Stem Cell . 2010; 7: 618– 630. [CrossRef] [PubMed]
Kim D Kim CH Moon JI et al . Generation of human induced pluripotent stem cells by direct delivery of reprogramming proteins. Cell Stem Cell . 2009; 4: 472– 476. [CrossRef] [PubMed]
Hou P Li Y Zhang X et al . Pluripotent stem cells induced from mouse somatic cells by small-molecule compounds. Science . 2013; 341: 651– 654. [CrossRef] [PubMed]
Zhang K Liu GH Yi F et al . Direct conversion of human fibroblasts into retinal pigment epithelium-like cells by defined factors. Protein Cell . 2014; 5: 48– 58 [CrossRef] [PubMed]
Binder S Krebs I Hilgers RD et al . Outcome of transplantation of autologous retinal pigment epithelium in age-related macular degeneration: a prospective trial. Invest Ophthalmol Vis Sci . 2004; 45: 4151– 4160. [CrossRef] [PubMed]
Binder S Stolba U Krebs I et al . Transplantation of autologous retinal pigment epithelium in eyes with foveal neovascularization resulting from age-related macular degeneration: a pilot study. Am J Ophthalmol . 2002; 133: 215– 225. [CrossRef] [PubMed]
Chen FK Uppal GS MacLaren RE et al . Long-term visual and microperimetry outcomes following autologous retinal pigment epithelium choroid graft for neovascular age-related macular degeneration. Clin Experiment Ophthalmol . 2009; 37: 275– 285. [CrossRef] [PubMed]
Falkner-Radler CI Krebs I Glittenberg C et al . Human retinal pigment epithelium (RPE) transplantation: outcome after autologous RPE-choroid sheet and RPE cell-suspension in a randomised clinical study. Br J Ophthalmol . 2011; 95: 370– 375. [CrossRef] [PubMed]
Heussen FM Fawzy NF Joeres S et al . Autologous translocation of the choroid and RPE in age-related macular degeneration: 1-year follow-up in 30 patients and recommendations for patient selection. Eye (Lond) . 2008; 22: 799– 807. [CrossRef] [PubMed]
Joussen AM How complete is successful? “Autologous retinal pigment epithelium and choriod translocation in patients with exsudative age-related macular degeneration: a short-term follow-up.” by van Meurs Jan, none van Biesen. PR Graefes Arch Clin Exp Ophthalmol . 2003; 241: 966– 967. [CrossRef]
Joussen AM Heussen FM Joeres S et al . Autologous translocation of the choroid and retinal pigment epithelium in age-related macular degeneration. Am J Ophthalmol . 2006; 142: 17– 30. [CrossRef] [PubMed]
MacLaren RE Uppal GS Balaggan KS et al . Autologous transplantation of the retinal pigment epithelium and choroid in the treatment of neovascular age-related macular degeneration. Ophthalmology . 2007; 114: 561– 570. [CrossRef] [PubMed]
Peyman GA Blinder KJ Paris CL et al . A technique for retinal pigment epithelium transplantation for age-related macular degeneration secondary to extensive subfoveal scarring. Ophthalmic Surg . 1991; 22: 102– 108. [PubMed]
Stanga PE Kychenthal A Fitzke FW et al . Retinal pigment epithelium translocation after choroidal neovascular membrane removal in age-related macular degeneration. Ophthalmology . 2002; 109: 1492– 1498. [CrossRef] [PubMed]
van Meurs JC ter Averst E Hofland LJ et al . Autologous peripheral retinal pigment epithelium translocation in patients with subfoveal neovascular membranes. Br J Ophthalmol . 2004; 88: 110– 113. [CrossRef] [PubMed]
van Meurs JC Van Den Biesen PR Autologous retinal pigment epithelium and choroid translocation in patients with exudative age-related macular degeneration: short-term follow-up. Am J Ophthalmol . 2003; 136: 688– 695. [CrossRef] [PubMed]
Thomas MA Dickinson JD Melberg NS et al . Visual results after surgical removal of subfoveal choroidal neovascular membranes. Ophthalmology . 1994; 101: 1384– 1396. [CrossRef] [PubMed]
Thomas MA Ibanez HE Instruments for submacular surgery. Retina . 1994; 14: 84– 87. [CrossRef] [PubMed]
Thomas MA Kaplan HJ Surgical removal of subfoveal neovascularization in the presumed ocular histoplasmosis syndrome. Am J Ophthalmol . 1991; 111: 1– 7. [CrossRef] [PubMed]
Wong IY Poon MW Pang RT et al . Promises of stem cell therapy for retinal degenerative diseases. Graefes Arch Clin Exp Ophthalmol . 2011; 249: 1439– 1448. [CrossRef] [PubMed]
Siqueira RC Autologous transplantation of retinal pigment epithelium in age related macular degeneration [article in Portuguese]. Arquivos brasileiros de oftalmologia . 2009; 72: 123– 130. [CrossRef] [PubMed]
Binder S Scaffolds for retinal pigment epithelium (RPE) replacement therapy. Br J Ophthalmol . 2011; 95: 441– 442. [CrossRef] [PubMed]
Algvere PV Berglin L Gouras P et al . Transplantation of RPE in age-related macular degeneration: observations in disciform lesions and dry RPE atrophy. Graefes Arch Clin Exp Ophthalmol . 1997; 235: 149– 158. [CrossRef] [PubMed]
Del Priore LV Tezel TH Reattachment rate of human retinal pigment epithelium to layers of human Bruch's membrane. Arch Ophthalmol . 1998; 116: 335– 341. [CrossRef] [PubMed]
Tezel TH Del Priore LV Repopulation of different layers of host human Bruch's membrane by retinal pigment epithelial cell grafts. Invest Ophthalmol Vis Sci . 1999; 40: 767– 774. [PubMed]
Tezel TH Del Priore LV Reattachment to a substrate prevents apoptosis of human retinal pigment epithelium. Graefes Arch Clin Exp Ophthalmol . 1997; 235: 41– 47. [CrossRef] [PubMed]
Tezel TH Del Priore LV Kaplan HJ Reengineering of aged Bruch's membrane to enhance retinal pigment epithelium repopulation. Invest Ophthalmol Vis Sci . 2004; 45: 3337– 3348. [CrossRef] [PubMed]
Tezel TH Kaplan HJ Del Priore LV Fate of human retinal pigment epithelial cells seeded onto layers of human Bruch's membrane. Invest Ophthalmol Vis Sci . 1999; 40: 467– 476. [PubMed]
Gullapalli VK Sugino IK Van Patten Y et al . Retinal pigment epithelium resurfacing of aged submacular human Bruch's membrane. Trans Am Ophthalmol Soc . 2004; 102: 123– 137, discussion 137–128. [PubMed]
Gullapalli VK Sugino IK Van Patten Y et al . Impaired RPE survival on aged submacular human Bruch's membrane. Exp Eye Res . 2005; 80: 235– 248. [CrossRef] [PubMed]
Bindewald A Roth F Van Meurs J Holz FG Transplantation of retinal pigment pithelium (RPE) following CNV removal in patients with AMD. Techniques, results, outlook [article in German]. Ophthalmologe . 2004; 101: 886– 894. [CrossRef] [PubMed]
Treumer F Bunse A Klatt C Roider J Autologous retinal pigment epithelium-choroid sheet transplantation in age related macular degeneration: morphological and functional results. Br J Ophthalmol . 2007; 91: 349– 353. [CrossRef] [PubMed]
Castellarin AA Nasir M Sugino IK Zarbin MA Progressive presumed choriocapillaris atrophy after surgery for age-related macular degeneration. Retina . 1998; 18: 143– 149. [CrossRef] [PubMed]
Castellarin AA Nasir MA Sugino IK Zarbin MA Clinicopathological correlation of primary and recurrent choroidal neovascularisation following surgical excision in age related macular degeneration. Br J Ophthalmol . 1998; 82: 480– 487. [CrossRef] [PubMed]
Grossniklaus HE Hutchinson AK Capone AJr et al . Clinicopathologic features of surgically excised choroidal neovascular membranes. Ophthalmology . 1994; 101: 1099– 1111. [CrossRef] [PubMed]
Tsukahara I Ninomiya S Castellarin A et al . Early attachment of uncultured retinal pigment epithelium from aged donors onto Bruch's membrane explants. Exp Eye Res . 2002; 74: 255– 266. [CrossRef] [PubMed]
Wang H Ninomiya Y Sugino IK Zarbin MA Retinal pigment epithelium wound healing in human Bruch's membrane explants. Invest Ophthalmol Vis Sci . 2003; 44: 2199– 2210. [CrossRef] [PubMed]
Algvere PV Berglin L Gouras P Sheng Y Transplantation of fetal retinal pigment epithelium in age-related macular degeneration with subfoveal neovascularization. Graefes Arch Clin Exp Ophthalmol . 1994; 232: 707– 716. [CrossRef] [PubMed]
Algvere PV Gouras P Dafgard Kopp E. Long-term outcome of RPE allografts in non-immunosuppressed patients with AMD. Eur J Ophthalmol . 1999; 9: 217– 230. [PubMed]
Tezel TH Del Priore LV Berger AS Kaplan HJ Adult retinal pigment epithelial transplantation in exudative age-related macular degeneration. Am J Ophthalmol . 2007; 143: 584– 595. [CrossRef] [PubMed]
Weisz JM Humayun MS De Juan EJr et al . Allogenic fetal retinal pigment epithelial cell transplant in a patient with geographic atrophy. Retina . 1999; 19: 540– 545. [CrossRef] [PubMed]
Sun K Cai H Tezel TH et al . Bruch's membrane aging decreases phagocytosis of outer segments by retinal pigment epithelium. Mol Vis . 2007; 13: 2310– 2319. [PubMed]
Cai H Del Priore LV Gene expression profile of cultured adult compared to immortalized human RPE. Mol Vis . 2006; 12: 1– 14. [PubMed]
Sugino IK Sun Q Wang J et al . Comparison of FRPE and human embryonic stem cell-derived RPE behavior on aged human Bruch's membrane. Invest Ophthalmol Vis Sci . 2011; 52: 4979– 4997. [CrossRef] [PubMed]
Chu PG Grunwald GB Functional inhibition of retinal pigment epithelial cell-substrate adhesion with a monoclonal antibody against the beta 1 subunit of integrin. Invest Ophthalmol Vis Sci . 1991; 32: 1763– 1769. [PubMed]
Han J Yan XL Han QH et al . Integrin beta1 subunit signaling is involved in the directed migration of human retinal pigment epithelial cells following electric field stimulation. Ophthalmic Res . 2011; 45: 15– 22. [CrossRef] [PubMed]
Ho TC Del Priore LV Reattachment of cultured human retinal pigment epithelium to extracellular matrix and human Bruch's membrane. Invest Ophthalmol Vis Sci . 1997; 38: 1110– 1118. [PubMed]
Afshari FT Kwok JC Andrews MR et al . Integrin activation or alpha 9 expression allows retinal pigmented epithelial cell adhesion on Bruch's membrane in wet age-related macular degeneration. Brain . 2010; 133: 448– 464. [CrossRef] [PubMed]
Booij JC Baas DC Beisekeeva J et al . The dynamic nature of Bruch's membrane. Prog Retin Eye Res . 2010; 29: 1– 18. [CrossRef] [PubMed]
Das A Frank RN Zhang NL Turczyn TJ Ultrastructural localization of extracellular matrix components in human retinal vessels and Bruch's membrane. Arch Ophthalmol . 1990; 108: 421– 429. [CrossRef] [PubMed]
Afshari FT Fawcett JW Improving RPE adhesion to Bruch's membrane. Eye . 2009.
Del Priore LV Tezel TH Kaplan HJ Maculoplasty for age-related macular degeneration: reengineering Bruch's membrane and the human macula. Prog Retin Eye Res . 2006; 25: 539– 562. [CrossRef] [PubMed]
Sugino IK Gullapalli VK Sun Q et al . Cell-deposited matrix improves retinal pigment epithelium survival on aged submacular human Bruch's membrane. Invest Ophthalmol Vis Sci . 2011; 52: 1345– 1358. [CrossRef] [PubMed]
Sugino IK Rapista A Sun Q et al . A method to enhance cell survival on Bruch's membrane in eyes affected by age and age-related macular degeneration. Invest Ophthalmol Vis Sci . 2011; 52: 9598– 9609. [CrossRef] [PubMed]
Zarbin MA Analysis of retinal pigment epithelium integrin expression and adhesion to aged submacular human Bruch's membrane. Trans Am Ophthalmol Soc . 2003; 101: 499– 520. [PubMed]
Gullapalli VK Sugino IK Zarbin MA Culture-induced increase in alpha integrin subunit expression in retinal pigment epithelium is important for improved resurfacing of aged human Bruch's membrane. Exp Eye Res . 2008; 86: 189– 200. [CrossRef] [PubMed]
Fang IM Yang CH Yang CM Chen MS Overexpression of integrin alpha6 and beta4 enhances adhesion and proliferation of human retinal pigment epithelial cells on layers of porcine Bruch's membrane. Exp Eye Res . 2009; 88: 12– 21. [CrossRef] [PubMed]
Humphries MJ Integrin activation: the link between ligand binding and signal transduction. Curr Opin Cell Biol . 1996; 8: 632– 640. [CrossRef] [PubMed]
Gorelik M Orukari I Wang J et al . Use of MR cell tracking to evaluate targeting of glial precursor cells to inflammatory tissue by exploiting the very late antigen-4 docking receptor. Radiology . 2012; 265: 175– 185. [CrossRef] [PubMed]
Hu F Strittmatter SM The N-terminal domain of Nogo-A inhibits cell adhesion and axonal outgrowth by an integrin-specific mechanism. J Neurosci . 2008; 28: 1262– 1269. [CrossRef] [PubMed]
Lemons ML Condic ML Combined integrin activation and intracellular cAMP cause Rho GTPase dependent growth cone collapse on laminin-1. Exp Neurol . 2006; 202: 324– 335. [CrossRef] [PubMed]
Seales EC Jurado GA Brunson BA et al . Hypersialylation of beta1 integrins, observed in colon adenocarcinoma, may contribute to cancer progression by up-regulating cell motility. Cancer Res . 2005; 65: 4645– 4652. [CrossRef] [PubMed]
Tan CL Andrews MR Kwok JC et al . Kindlin-1 enhances axon growth on inhibitory chondroitin sulfate proteoglycans and promotes sensory axon regeneration. J Neurosci . 2012; 32: 7325– 7335. [CrossRef] [PubMed]
Tan CL Kwok JC Patani R et al . Integrin activation promotes axon growth on inhibitory chondroitin sulfate proteoglycans by enhancing integrin signaling. J Neurosci . 2011; 31: 6289– 6295. [CrossRef] [PubMed]
Gailit J Ruoslahti E Regulation of the fibronectin receptor affinity by divalent cations. J Biol Chem . 1988; 263: 12927– 12932. [PubMed]
Humphries MJ Monoclonal antibodies as probes of integrin priming and activation. Biochem Soc Trans . 2004; 32: 407– 411. [CrossRef] [PubMed]
Tsuchida J Ueki S Saito Y Takagi J Classification of ‘activation' antibodies against integrin beta1 chain. FEBS Lett . 1997; 416: 212– 216. [CrossRef] [PubMed]
Shattil SJ Kim C Ginsberg MH The final steps of integrin activation: the end game. Nat Rev Mol Cell Biol . 2010; 11: 288– 300. [CrossRef] [PubMed]
Lai-Cheong JE Parsons M McGrath JA The role of kindlins in cell biology and relevance to human disease. Int J Biochem Cell Biol . 2010; 42: 595– 603. [CrossRef] [PubMed]
Moser M Legate KR Zent R Fassler R The tail of integrins, talin, and kindlins. Science . 2009; 324: 895– 899. [CrossRef] [PubMed]
Fasler-Kan E Wunderlich K Hildebrand P et al . Activated STAT 3 in choroidal neovascular membranes of patients with age-related macular degeneration. Ophthalmologica . 2005; 219: 214– 221. [CrossRef] [PubMed]
Nicolo M Piccolino FC Zardi L et al . Detection of tenascin-C in surgically excised choroidal neovascular membranes. Graefes Arch Clin Exp Ophthalmol . 2000; 238: 107– 111. [CrossRef] [PubMed]
John S Natarajan S Parikumar P et al . Choice of cell source in cell-based therapies for retinal damage due to age-related macular degeneration: a review. J Ophthalmol . 2013; 2013: 465169. [PubMed]
Diniz B Thomas PB Ribeiro RM et al . Subretinal implantation of retinal pigment epithelial cells derived from human embryonic stem cells - improved survival when implanted as a monolayer. Invest Ophthalmol Vis Sci . 2013; 54: 5087– 5096. [CrossRef] [PubMed]
Hu Y Liu L Lu B et al . A novel approach for subretinal implantation of ultrathin substrates containing stem cell-derived retinal pigment epithelium monolayer. Ophthalmic Res . 2012; 48: 186– 191. [CrossRef] [PubMed]
Kearns V Mistry A Mason S et al . Plasma polymer coatings to aid retinal pigment epithelial growth for transplantation in the treatment of age related macular degeneration. J Mater Sci Mater Med . 2012; 23: 2013– 2021. [CrossRef] [PubMed]
Li Y Tang L Comparison of growth of human fetal RPE cells on electrospun nanofibers and etched pore polyester membranes [article in Chinese]. Zhong Nan Da Xue Xue Bao Yi Xue Ban . 2012; 37: 433– 440. [PubMed]
Stanzel BV Liu Z Brinken R et al . Subretinal delivery of ultrathin rigid-elastic cell carriers using a metallic shooter instrument and biodegradable hydrogel encapsulation. Invest Ophthalmol Vis Sci . 2012; 53: 490– 500. [CrossRef] [PubMed]
Subrizi A Hiidenmaa H Ilmarinen T et al . Generation of hESC-derived retinal pigment epithelium on biopolymer coated polyimide membranes. Biomaterials . 2012; 33: 8047– 8054. [CrossRef] [PubMed]
Hynes SR Lavik EB A tissue-engineered approach towards retinal repair: scaffolds for cell transplantation to the subretinal space. Graefes Arch Clin Exp Ophthalmol . 2010; 248: 763– 778. [CrossRef] [PubMed]
Barber AC Hippert C Duran Y et al . Repair of the degenerate retina by photoreceptor transplantation. Proc Natl Acad Sci U S A . 2013; 110: 354– 359. [CrossRef] [PubMed]
Pearson RA Barber AC Rizzi M et al . Restoration of vision after transplantation of photoreceptors. Nature . 2012; 485: 99– 103. [CrossRef] [PubMed]
Figure.
 
Fundus photographs of healthy and diseased eyes. The photograph of a healthy eye shows normal pigmentation and normal retinal blood vessels. In dry AMD, deposits on Bruch's membrane may be visible at the macula. In addition, depigmented areas of geographic atrophy may be present. In wet AMD, new blood vessels originating from the choroid may give rise to macular edema and hemorrhage.
Figure.
 
Fundus photographs of healthy and diseased eyes. The photograph of a healthy eye shows normal pigmentation and normal retinal blood vessels. In dry AMD, deposits on Bruch's membrane may be visible at the macula. In addition, depigmented areas of geographic atrophy may be present. In wet AMD, new blood vessels originating from the choroid may give rise to macular edema and hemorrhage.
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