Subretinal Implantation of a Human Embryonic Stem Cell-Derived Retinal Pigment Epithelium Monolayer in a Porcine Model

Pig Models in Retinal Research and Retinal Disease

The pig has been used as a large animal model in biomedical research for many years and its use continues to increase because induced mutations phenocopy several inherited human diseases. In addition, they are continuous breeders, can be propagated by artificial insemination, have large litter sizes (on the order of mice), and can be genetically manipulated using all of the techniques that are currently available in mice. The pioneering work of Petters and colleagues set the stage for the use of the pig as a model of inherited retinal disease. In the last 10 years, the pig has become a model of choice where specific disease-causing mutations that are not phenocopied in rodents need to be studied and therapeutic approaches explored. The pig is not only used for retinal eye disease but also for the study of the cornea and lens. This review attempts to show how broad the use of the pig has become and how it has contributed to the assessment of treatments for eye disease. In the last 10 years, there have been several reviews that included the use of the pig in biomedical research (see body of the review) that included information about retinal disease. None directly discuss the use of the pig as an animal model for retinal diseases, including inherited diseases, where a single genetic mutation has been identified or for multifactorial diseases such as glaucoma and diabetic retinopathy. Although the pig is used to explore diseases of the cornea and lens, this review focuses on how and why the pig, as a large animal model, is useful for research in neural retinal disease and its treatment.

Ocular barriers as a double-edged sword: preventing and facilitating drug delivery to the retina

In recent decades, the growing of the aging population in the world brings increasingly heavy burden of vision-threatening retinal diseases. One of the biggest challenges in the treatment of retinal diseases is the effective drug delivery to the diseased area. Due to the existence of multiple anatomical and physiological barriers of the eye, commonly used oral drugs or topical eye drops cannot effectively reach the retinal lesions. Innovations in new drug formulations and delivery routes have been continuously applied to improve current drug delivery to the back of the eye. Unique ocular anatomical structures or physiological activities on these ocular barriers, in turn, can facilitate drug delivery to the retina if compatible formulations or delivery routes are properly designed or selected. This paper focuses on key barrier structures of the eye and summarizes advances of corresponding drug delivery means to the retina, including various local drug delivery routes by invasive approaches, as well as systemic eye drug delivery by non-invasive approaches.

[Optogenetics and cell replacement in retinology : Regenerative ophthalmology-What we can do!]

For many degenerative retinal diseases that progressively lead to blindness, no treatment options are available so far. In recent years, several innovative therapies have been experimentally explored, which are promising because they are independent of the genetic cause of the degenerative disease. One of these is optogenetics, which involves light-sensitive proteins that selectively act as ion channels or ion pumps to control the potential of the treated cell. Thus, these cells can be stimulated or inhibited by light, quasi functionally remote controlled. In this way artificial photoreceptors are induced from the remaining cells, which has already been successfully employed in animal experiments. This type of treatment is already being tested on patients and leads to an improvement in vision, but so far only data from one patient are available. The use of optogenetics additionally requires special eyeglasses to adapt the light impulses in adequate strength and wavelength for the respective optogenes. Another exciting approach is cell replacement therapy of retinal pigment epithelium (RPE) and photoreceptor cells to exchange degenerated cell material. This appears to be very successful for RPE cells in clinical trials. Obtaining human photoreceptors from stem cells is technically possible, but very laborious. The integration of the transplanted photoreceptors into the host retinal tissue also needs further optimization for broader clinical applications; however, both cell replacement and optogenetics approaches are promising, so that the translation from basic research into clinical application will be successful.

Stem cell-derived retinal pigment epithelium transplantation in age-related macular degeneration: recent advances and challenges

PURPOSE OF REVIEW

Age-related macular degeneration (AMD) is one of the leading causes of irreversible vision loss in the world with more than 80% of the prevalence accounted for by the nonneovascular (NNAMD) or 'dry' form of the disease. NNAMD does not have any definitive treatment once vision loss has ensued and presents a major unmet medical need. This review will highlight stem cell-based therapies that are a promising form of treatment for advanced NNAMD.

RECENT FINDINGS

In the past decade, clinical trials utilizing both induced pluripotent stem cell-derived RPE and human embryonic stem cell-derived RPE have been aggressively pursued as potential treatments of RPE loss and prevention of overlying neurosensory atrophy. While promising preliminary results demonstrating safety and potential efficacy have been published, new challenges have also been identified. These include selecting the most appropriate cell-based therapy, identifying and managing potential immune response as well as characterizing anatomic and functional efficacy. In this review, we will discuss some of these challenges in light of the available data from several early phase clinical trials and discuss the strategies that are being considered to further advance the field.

SUMMARY

Cell-based therapies demonstrate promising potential to treat advanced stages of NNAMD. Several early phase clinical trials using both induced pluripotent stem cells (iPSC) and human embryonic stem cell derived (hESC) have demonstrated safety and preliminary signs of efficacy and highlighted remaining challenges which appear surmountable. These challenges include development of selection criteria for use of cell suspensions versus RPE sheets, especially in light of immunological properties of RPE that are intrinsic to the status of RPE differentiation in each of these cell formulations.

Retina stem cells, hopes and obstacles

Retinal degeneration is a major contributor to visual dysfunction worldwide. Although it comprises several eye diseases, loss of retinal pigment epithelial (RPE) and photoreceptor cells are the major contributors to their pathogenesis. Early therapies included diverse treatments, such as provision of anti-vascular endothelial growth factor and many survival and trophic factors that, in some cases, slow down the progression of the degeneration, but do not effectively prevent it. The finding of stem cells (SC) in the eye has led to the proposal of cell replacement strategies for retina degeneration. Therapies using different types of SC, such as retinal progenitor cells (RPCs), embryonic SC, pluripotent SCs (PSCs), induced PSCs (iPSCs), and mesenchymal stromal cells, capable of self-renewal and of differentiating into multiple cell types, have gained ample support. Numerous preclinical studies have assessed transplantation of SC in animal models, with encouraging results. The aim of this work is to revise the different preclinical and clinical approaches, analyzing the SC type used, their efficacy, safety, cell attachment and integration, absence of tumor formation and immunorejection, in order to establish which were the most relevant and successful. In addition, we examine the questions and concerns still open in the field. The data demonstrate the existence of two main approaches, aimed at replacing either RPE cells or photoreceptors. Emerging evidence suggests that RPCs and iPSC are the best candidates, presenting no ethical concerns and a low risk of immunorejection. Clinical trials have already supported the safety and efficacy of SC treatments. Serious concerns are pending, such as the risk of tumor formation, lack of attachment or integration of transplanted cells into host retinas, immunorejection, cell death, and also ethical. However, the amazing progress in the field in the last few years makes it possible to envisage safe and effective treatments to restore vision loss in a near future.

A modified protocol for isolation of retinal microglia from the pig

Microglia are the resident immune cells in the retina. To investigate their properties and behaviour, a reliable and yielding procedure to culture them is necessary. We here describe a way of isolation of microglial cells from the porcine retina, as pig eyes are similar to human eyes in size, structure and vasculature, including similarities in proteins and pathways. Retina was isolated from fresh pig eyes, dissociated by a mixture of collagenase, hyaluronidase and DNAse, and passed through a cell strainer. After triple centrifugation with decreasing velocity and re-suspension, cells were seeded into poly-d-lysine coated culture flasks and cultured using DMEM and macrophage-colony stimulating factor (M-CSF). Number of cells increased gradually during the first 10-14 days, till they could be split and used for experiments. Identity of isolated cells as microglia was assessed by immunostaining against the microglia/macrophage markers Iba1, CD11b, CD68, CD45 and TMEM119. Phagocytic function of microglia could be demonstrated by phagocytosis of fluorescence beads and their response to lipopolysaccharide (LPS). As a conclusion, we developed a protocol for isolation and cultivation of pig retinal microglial cells that are suitable for research in the laboratory.

Creating an Ocular Biofactory: Surgical Approaches in Gene Therapy for Acquired Retinal Diseases

ABSTRACT

Gene therapy offers the potential to treat inherited retinal disorders and deliver sustained therapy for acquired retinal diseases. In the latter case, host cells can be harnessed to produce non-native proteins that have beneficial properties, such as antivascular endothelial growth factor activity, transforming the eye into an ocular "biofactory." Several gene therapy programs have entered clinical testing for delivery to the vitreous, subretinal, and suprachoroidal space. Improved viral vectors and refined surgical techniques are critical to successful delivery of therapeutic products to the target tissue. In this review, we discuss the development of gene therapy products aimed at acquired retinal diseases and the surgical techniques utilized to achieve targeted delivery.