Age-related macular degeneration (AMD) remains a major cause of blindness, with dysfunction and loss of retinal pigment epithelium (RPE) central to disease progression. We engineered an RPE patch comprising a fully differentiated, human embryonic stem cell (hESC)-derived RPE monolayer on a coated, synthetic basement membrane. We delivered the patch, using a purpose-designed microsurgical tool, into the subretinal space of one eye in each of two patients with severe exudative AMD. Primary endpoints were incidence and severity of adverse events and proportion of subjects with improved best-corrected visual acuity of 15 letters or more. We report successful delivery and survival of the RPE patch by biomicroscopy and optical coherence tomography, and a visual acuity gain of 29 and 21 letters in the two patients, respectively, over 12 months. Only local immunosuppression was used long-term. We also present the preclinical surgical, cell safety and tumorigenicity studies leading to trial approval. This work supports the feasibility and safety of hESC-RPE patch transplantation as a regenerative strategy for AMD.

/pdf/phase-1-clinical-study-of-an-embryonic-stem-cell-derived-4vohryqfba.pdf

Phase 1 clinical study of an embryonic stem cell-derived retinal pigment epithelium patch in age-related macular degeneration.

Human induced pluripotent stem cells (iPSCs) have great promise for cellular therapy, but it is unclear if they have the same potential as human embryonic stem cells (hESCs) to differentiate into specialized cell types. Ocular cells such as the retinal pigmented epithelium (RPE) are of particular interest because they could be used to treat degenerative eye diseases, including age-related macular degeneration and retinitis pigmentosa. We show here that iPSCs generated using Oct4, Sox2, Nanog, and Lin28 can spontaneously differentiate into RPE cells, which can then be isolated and cultured to form highly differentiated RPE monolayers. RPE derived from iPSCs (iPS-RPE) were analyzed with respect to gene expression, protein expression, and rod outer segment phagocytosis, and compared with cultured fetal human RPE (fRPE) and RPE derived from hESCs (hESC-RPE). iPS-RPE expression of marker mRNAs was quantitatively similar to that of fRPE and hESC-RPE, and marker proteins were appropriately expressed and localized in polarized monolayers. Levels of rod outer segment phagocytosis by iPS-RPE, fRPE, and hESC-RPE were likewise similar and dependent on integrin αvβ5. This work shows that iPSCs can differentiate into functional RPE that are quantitatively similar to fRPE and hESC-RPE and further supports the finding that iPSCs are similar to hESCs in their differentiation potential. STEM CELLS 2009;27:2427–2434

https://stemcellsjournals.onlinelibrary.wiley.com/doi/pdf/10.1002/stem.189

Derivation of Functional Retinal Pigmented Epithelium from Induced Pluripotent Stem Cells

Transformation of somatic cells with a set of embryonic transcription factors produces cells with the pluripotent properties of embryonic stem cells (ESCs). These induced pluripotent stem (iPS) cells have the potential to differentiate into any cell type, making them a potential source from which to produce cells as a therapeutic platform for the treatment of a wide range of diseases. In many forms of human retinal disease, including age-related macular degeneration (AMD), the underlying pathogenesis resides within the support cells of the retina, the retinal pigment epithelium (RPE). As a monolayer of cells critical to photoreceptor function and survival, the RPE is an ideally accessible target for cellular therapy. Here we report the differentiation of human iPS cells into RPE. We found that differentiated iPS-RPE cells were morphologically similar to, and expressed numerous markers of developing and mature RPE cells. iPS-RPE are capable of phagocytosing photoreceptor material, in vitro and in vivo following transplantation into the Royal College of Surgeons (RCS) dystrophic rat. Our results demonstrate that iPS cells can be differentiated into functional iPS-RPE and that transplantation of these cells can facilitate the short-term maintenance of photoreceptors through phagocytosis of photoreceptor outer segments. Long-term visual function is maintained in this model of retinal disease even though the xenografted cells are eventually lost, suggesting a secondary protective host cellular response. These findings have identified an alternative source of replacement tissue for use in human retinal cellular therapies, and provide a new in vitro cellular model system in which to study RPE diseases affecting human patients.

/pdf/protective-effects-of-human-ips-derived-retinal-pigment-xuvqi0knt9.pdf

Protective effects of human iPS-derived retinal pigment epithelium cell transplantation in the retinal dystrophic rat.

We have applied research on the visual psychophysics of reading to low vision assessment. Research on different aspects of the reading process found that reading rate rather than reading comprehension is more sensitive to variations in a subject’s visual functioning or the stimulus properties of print. The research identified four different visual factors that significantly affect reading rate: (1) acuity reserve [print size relative to acuity threshold], (2) contrast reserve [print contrast relative to contrast threshold], (3) field of view [number of letters visible], and (4) in cases of maculopathy, central scotoma size. Our research indicates that fluent reading rates can be attained with a restricted field of view, as little as four characters. However, attainment of fluent reading levels requires that print size and contrast should be several times threshold and the diameter of a central scotoma should be less than 22°. Although important clinical studies are lacking, we derived specific visual requirements for different reading rates from published experimental research to provide a starting point and to illustrate how visual requirements could be derived, even with poor correlations. Research has made significant progress toward the development of a comprehensive low vision assessment that will allow the practitioner to identify visual impediments to reading, other than reduced visual acuity. Having more fully characterized a visual impairment, the practitioner may tailor devices or interventions to the individual’s needs and capabilities.

Visual requirements for reading

Specific cells within the early mammalian embryo have the capacity to generate all somatic lineages plus the germline. This property of pluripotency is confined to the epiblast, a transient tissue that persists for only a few days. In vitro, however, pluripotency can be maintained indefinitely through derivation of stem cell lines. Pluripotent stem cells established from the newly formed epiblast are known as embryonic stem cells (ESCs), whereas those generated from later stages are called postimplantation epiblast stem cells (EpiSCs). These different classes of pluripotent stem cell have distinct culture requirements and gene expression programs, likely reflecting the dynamic development of the epiblast in the embryo. In this chapter we review current understanding of how the epiblast forms and relate this to the properties of derivative stem cells. We discuss whether ESCs and EpiSCs are true counterparts of different phases of epiblast development or are culture-generated phenomena. We also consider the proposition that early epiblast cells and ESCs may represent a naive ground state without any prespecification of lineage choice, whereas later epiblasts and EpiSCs may be primed in favor of particular fates.

/pdf/pluripotency-in-the-embryo-and-in-culture-3ulrvmoau6.pdf

Pluripotency in the Embryo and in Culture

Autologous transplantation of the retinal pigment epithelium and choroid in the treatment of neovascular age-related macular degeneration.

Purpose: We propose a case selection algorithm to assess suitability for macular translocation for subfoveal neovascular membrane (CNV) secondary to age-related macular degeneration. The algorithm is based on preoperative assessment of residual foveal function, as assessed by a slit-lamp fixation task and duration of visual loss, in patients with poor acuity. We validate our slit-lamp fixation task against an objective analysis (Nidek MP-1 Microperimetry) and proceed to examine surgical outcomes as selected by the algorithm.



Methods:  A prospective series of 27 consecutive patients with CNV underwent translocation at Moorfields Eye Hospital, London between May 2003 and May 2006.



Results:  Validation of the slit-lamp fixation task revealed 100% concordance in classification of fixation between the slit-lamp task and the microperimeter. At an average follow up of 12.2 months, the mean Early Treatment of Diabetic Retinopathy Study distance acuity improved from logMAR 0.88 to 0.68 (P < 0.03). Sixty-six per cent of patients achieved an acuity of ≤logMAR 0.8 (6/30), 22% an acuity of ≤logMAR 0.3 (6/12) and 33% gained three lines of acuity. The mean MN Read reading acuity improved from logMAR 1.23 to 0.91 (P < 0.01). Forty-four per cent of patients achieved an acuity of ≥logMAR 0.7 (N10), 15% an acuity of ≥logMAR 0.4 (N5) and 44% gained three lines of acuity.



Discussion:  We have demonstrated a simple case selection algorithm that is based on residual foveal function and suggests good outcomes. The strongest indicators of foveal function are fixation characteristics and duration of visual loss. In contrast to previous studies, our algorithm suggests good outcomes independently of preoperative visual acuity and CNV characteristics.

Andrew B. Milliken

Papers

Autologous transplantation of the retinal pigment epithelium and choroid in the treatment of neovascular age-related macular degeneration.

New algorithm for assessing patient suitability for macular translocation surgery.