Stem cell therapy for retinal disease:

Exploring Stem-Cell-Based Therapies for Retinal Regeneration

The escalating prevalence of retinal diseases-notably, age-related macular degeneration and hereditary retinal disorders-poses an intimidating challenge to ophthalmic medicine, often culminating in irreversible vision loss. Current treatments are limited and often fail to address the underlying loss of retinal cells. This paper explores the potential of stem-cell-based therapies as a promising avenue for retinal regeneration. We review the latest advancements in stem cell technology, focusing on embryonic stem cells (ESCs), pluripotent stem cells (PSCs), and mesenchymal stem cells (MSCs), and their ability to differentiate into retinal cell types. We discuss the challenges in stem cell transplantation, such as immune rejection, integration into the host retina, and functional recovery. Previous and ongoing clinical trials are examined to highlight the therapeutic efficacy and safety of these novel treatments. Additionally, we address the ethical considerations and regulatory frameworks governing stem cell research. Our analysis suggests that while stem-cell-based therapies offer a groundbreaking approach to treating retinal diseases, further research is needed to ensure long-term safety and to optimize therapeutic outcomes. This review summarizes the clinical evidence of stem cell therapy and current limitations in utilizing stem cells for retinal degeneration, such as age-related macular degeneration, retinitis pigmentosa, and Stargardt's disease.

Molecular and cellular imaging of the eye

The application of molecular and cellular imaging in ophthalmology has numerous benefits. It can enable the early detection and diagnosis of ocular diseases, facilitating timely intervention and improved patient outcomes. Molecular imaging techniques can help identify disease biomarkers, monitor disease progression, and evaluate treatment responses. Furthermore, these techniques allow researchers to gain insights into the pathogenesis of ocular diseases and develop novel therapeutic strategies. Molecular and cellular imaging can also allow basic research to elucidate the normal physiological processes occurring within the eye, such as cell signaling, tissue remodeling, and immune responses. By providing detailed visualization at the molecular and cellular level, these imaging techniques contribute to a comprehensive understanding of ocular biology. Current clinically available imaging often relies on confocal microscopy, multi-photon microscopy, PET (positron emission tomography) or SPECT (single-photon emission computed tomography) techniques, optical coherence tomography (OCT), and fluorescence imaging. Preclinical research focuses on the identification of novel molecular targets for various diseases. The aim is to discover specific biomarkers or molecular pathways associated with diseases, allowing for targeted imaging and precise disease characterization. In parallel, efforts are being made to develop sophisticated and multifunctional contrast agents that can selectively bind to these identified molecular targets. These contrast agents can enhance the imaging signal and improve the sensitivity and specificity of molecular imaging by carrying various imaging labels, including radionuclides for PET or SPECT, fluorescent dyes for optical imaging, or nanoparticles for multimodal imaging. Furthermore, advancements in technology and instrumentation are being pursued to enable multimodality molecular imaging. Integrating different imaging modalities, such as PET/MRI (magnetic resonance imaging) or PET/CT (computed tomography), allows for the complementary strengths of each modality to be combined, providing comprehensive molecular and anatomical information in a single examination. Recently, photoacoustic microscopy (PAM) has been explored as a novel imaging technology for visualization of different retinal diseases. PAM is a non-invasive, non-ionizing radiation, and hybrid imaging modality that combines the optical excitation of contrast agents with ultrasound detection. It offers a unique approach to imaging by providing both anatomical and functional information. Its ability to utilize molecularly targeted contrast agents holds great promise for molecular imaging applications in ophthalmology. In this review, we will summarize the application of multimodality molecular imaging for tracking chorioretinal angiogenesis along with the migration of stem cells after subretinal transplantation in vivo.

Innovative Technologies for Optimized Artificial Vision

Despite significant advances in the treatment of severe eye diseases, certain forms of blindness cannot be cured or improved to this day. These include, for example, retinitis pigmentosa, a hereditary degeneration of photoreceptors. Technology approaches with implantable visual prostheses based on electrical stimulation of remaining neurons in the retina or cortex, have already been tested in a number of patients with limited results. New findings in the biology of these diseases as well as new technological developments give hope for better results in the future.

In Utero Fetal Therapy: Stem Cells, Cell Transplantation, Gene Therapy, and CRISPR-Cas9

In utero fetal therapy offers the opportunity to prevent and treat diseases with a cellular or genetic basis. Components of successful fetal treatment include isolation of a replacement cell population, in utero stem cell transplantation, cell engraftment with fetal immune tolerance, and ongoing cell function. Fetal gene therapy with CRISPR-Cas9 represents an exciting potential therapy for genetic diseases not amenable to gene supplementation via adenoviral vector transduction. These fetal therapies have unique ethical and safety considerations. Clinical trials for in utero cell therapy are underway, as additional discoveries in stem cell biology and gene therapy move closer to clinical translation.

Stem Cell-Derived Exosomes Potential Therapeutic Roles in Cardiovascular Diseases

Owing to myocardial abnormalities, cardiac ailments are considered to be the major cause of morbidity and mortality worldwide. According to a recent study, membranous vesicles that are produced naturally, termed as "exosomes", have emerged as the potential candidate in the field of cardiac regenerative medicine. A wide spectrum of stem cells has also been investigated in the treatment of cardiovascular diseases (CVD). Exosomes obtained from the stem cells are found to be cardioprotective and offer great hope in the treatment of CVD. The basic nature of exosomes is to deal with the intracellular delivery of both proteins and nucleic acids. This activity of exosomes helps us to rely on them as the attractive pharmaceutical delivery agents. Most importantly, exosomes derived from microRNAs (miRNAs) hold great promise in assessing the risk of CVD, as they serve as notable biomarkers of the disease. Exosomes are small, less immunogenic, and lack toxicity. These nanovesicles harbor immense potential as a therapeutic entity and would provide fruitful benefits if consequential research were focused on their upbringing and development as a useful diagnostic and therapeutic tool in the field of medicine.

Visual properties of human retinal ganglion cells

The retinal output is the sole source of visual information for the brain. Studies in non-primate mammals estimate that this information is carried by several dozens of retinal ganglion cell types, each informing the brain about different aspects of a visual scene. Even though morphological studies of primate retina suggest a similar diversity of ganglion cell types, research has focused on the function of only a few cell types. In human retina, recordings from individual cells are anecdotal or focus on a small subset of identified types. Here, we present the first systematic ex-vivo recording of light responses from 342 ganglion cells in human retinas obtained from donors. We find a great variety in the human retinal output in terms of preferences for positive or negative contrast, spatio-temporal frequency encoding, contrast sensitivity, and speed tuning. Some human ganglion cells showed similar response behavior as known cell types in other primate retinas, while we also recorded light responses that have not been described previously. This first extensive description of the human retinal output should facilitate interpretation of primate data and comparison to other mammalian species, and it lays the basis for the use of ex-vivo human retina for in-vitro analysis of novel treatment approaches.

Intravitreal Use of a Bone Marrow Mononuclear Fraction (BMMF) Containing CD34+ Cells in Patients with Stargardt Type Macular Dystrophy

To assess the therapeutic potential and the safety of intravitreous use of a bone marrow mononuclear fraction (BMMF) containing CD34+ cells in patients with Stargardt type macular dystrophy. The study was conducted on 10 patients with Stargardt dystrophy with worse eye visual acuity ≤ 20/125. A bone marrow aspirate was obtained from all patients, and after processing in the cell therapy center (CTC), 0.1 ml of the intravitreous BMMF suspension was injected into the eye with worse visual acuity. A sham injection was performed in the contralateral eye. The patients were evaluated at baseline and one, three, and six months after the injection. All of them were submitted to measurement of best corrected visual acuity (BCVA), microperimetry, multifocal electroretinography (mfERG) and full field electroretinography (ffERG), autofluorescence (AF), and optical coherence tomography (OCT). Fluorescein angiography was also performed before and six months after the injection. All patients completed the six-month period of evaluation. Mean visual acuity of the treated eye was 1.1 logMAR (20/250) before intravitreous (IV) injection, 0.96 logMAR (20/200+2) one month after injection, and 0.92 logMAR (20/160-1) 3 months after injection. In the untreated eye, mean VA was 1.0 logMAR (20/200) at baseline and 0.96 logMAR (20/200+2) and 0.94 logMAR (20/160-2) one and three months after injection, respectively. In the treated group, VA at baseline ranged from best acuity of 20/125-1 to worst acuity of 20/640+2, going through 20/100+2 and 20/400 during the first month. In the untreated group, BCVA ranged from 20/100+2 to 20/400 at baseline and from 20/100 to 20/400 after one month. The results for the treated group differed significantly at all follow-up times, whereas no significant difference was observed in the untreated group. Regarding the mean sensitivity of microperimetry, although there was improvement throughout all months, a significant difference occurred only during the first month. In the untreated eye, there was no significant difference in any analysis. Angiofluoresceinography did not reveal neovessel formation or tumor growth. The remaining exams were used in order to aid the diagnosis. The results indicate that the use of intravitreous BMMF in patients with Stargardt dystrophy is safe and is associated with a discrete improvement of BCVA and microperimetry in the treated eye compared to the untreated one.

Intravenous Infusion of Umbilical Cord Mesenchymal Stem Cells Maintains and Partially Improves Visual Function in Patients with Advanced Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a hereditary retinal degeneration disease with no effective therapeutic approaches. Inflammatory and immune disorders are thought to play an important role in the pathogenesis of RP. Human umbilical cord mesenchymal stem cells (UCMSCs), with multiple biological functions such as anti-inflammation and immunoregulation, have been applied in different systemic diseases. We conducted a phase I/II clinical trial aiming to evaluate the safety and efficacy of intravenous administration of UCMSCs in advanced RP patients. All 32 subjects were intravenously infused with one dose of 10⁸ UCMSCs and were followed up for 12 months. No serious local or systemic adverse effects occurred in the whole follow-up. Most patients improved their best corrected visual acuity (BCVA) in the first 3 months. The proportions of patients with improved or maintained BCVA were 96.9%, 95.3%, 93.8%, 95.4%, 90.6%, and 90.6% at the 1st, 2nd, 3rd, 6th, 9th, and 12th month follow-up, respectively. Most of the patients (81.3%) maintained or improved their visual acuities for 12 months. The average NEI VFQ-25 questionnaire scores were significantly improved at the third month (P < 0.05). The average visual field sensitivity and flash visual evoked potential showed no significant difference (P = 0.185, P = 0.711). Our results indicated that the intravenous infusion of UCMSCs was safe for advanced RP patients. Most of the patients improved or maintained their visual functions in a long term. The life qualities were improved significantly in the first 3 months, suggesting that the intravenous infusion of UCMSCs may be a promising therapeutic approach for advanced RP patients.

Laminin modification subretinal bio-scaffold remodels retinal pigment epithelium-driven microenvironment in vitro and in vivo

Advanced age-related macular degeneration (AMD) may lead to geographic atrophy or fibrovascular scar at macular, dysfunctional retinal microenvironment, and cause profound visual loss. Recent clinical trials have implied the potential application of pluripotent cell-differentiated retinal pigment epithelial cells (dRPEs) and membranous scaffolds implantation in repairing the degenerated retina in AMD. However, the efficacy of implanted membrane in immobilization and supporting the viability and functions of dRPEs, as well as maintaining the retinal microenvironment is still unclear. Herein we generated a biomimetic scaffold mimicking subretinal Bruch's basement from plasma modified polydimethylsiloxane (PDMS) sheet with laminin coating (PDMS-PmL), and investigated its potential functions to provide a subretinal environment for dRPE-monolayer grown on it. Firstly, compared to non-modified PDMS, PDMS-PmL enhanced the attachment, proliferation, polarization, and maturation of dRPEs. Second, PDMS-PmL increased the polarized tight junction, PEDF secretion, melanosome pigment deposit, and phagocytotic-ability of dRPEs. Third, PDMS-PmL was able to carry a dRPEs/photoreceptor-precursors multilayer retina tissue. Finally, the in vivo subretinal implantation of PDMS-PmL in porcine eyes showed well-biocompatibility up to 2-year follow-up. Notably, multifocal ERGs at 2-year follow-up revealed well preservation of macular function in PDMS-PmL, but not PDMS, transplanted porcine eyes. Trophic PEDF secretion of macular retina in PDMS-PmL group was also maintained to preserve retinal microenvironment in PDMS-PmL eyes at 2 year. Taken together, these data indicated that PDMS-PmL is able to sustain the physiological morphology and functions of polarized RPE monolayer, suggesting its potential of rescuing macular degeneration in vivo.

Intravitreal use of bone marrow mononuclear fraction containing CD34+ stem cells in patients with atrophic age-related macular degeneration

Purpose

To evaluate the therapeutic potential and safety of intravitreal injections of bone marrow mononuclear fraction (BMMF) containing CD34⁺ cells in patients with atrophic age-related macular degeneration (AMD).

Methods

Ten patients with atrophic AMD and best-corrected visual acuity (BCVA) in the worse-seeing eye of ≤20/100 were enrolled in this study. The bone marrow from all patients was aspirated and processed for mononuclear cell separation. A 0.1 mL suspension of BMMF CD34⁺ cells was injected into the vitreous cavity of the worse-seeing eye. Patients were evaluated at Baseline and 1,3,6,9 and 12 months after injection. Ophthalmic evaluation included BCVA measurement, microperimetry, infrared imaging, fundus autofluorescence and SD-optical coherence tomography at all study visits. Fluorescein angiography was performed at Baseline and at 6 and 12 months after intravitreal therapy.

Results

All patients completed the 6-month follow-up, and six completed the 12-month follow-up. Prior to the injection, mean BCVA was 1.18 logMAR (20/320⁻¹), ranging from 20/125 to 20/640⁻², and improved significantly at every follow-up visit, including the 12-month one, when BCVA was 1.0 logMAR (20/200) (P<0.05). Mean sensitivity threshold also improved significantly at 6, 9 and 12 months after treatment (P<0.05). Considering the area of atrophy identified by fundus autofluorescence, significant mean BCVA and mean sensitivity threshold improvement were observed in patients with the smallest areas of atrophy. Fluorescein angiography did not identify choroidal new vessels or tumor growth.

Conclusion

The use of intravitreal BMMF injections in patients with AMD is safe and is associated with significant improvement in BCVA and macular sensitivity threshold. Patients with small areas of atrophy have a better response. The paracrine effect of CD34⁺ cells may explain the functional improvement observed; however, larger series of patients are necessary to confirm these preliminary findings.

Immunocytochemical Profiling of Cultured Mouse Primary Retinal Cells

Primary retinal cell cultures and immunocytochemistry are important experimental platforms in ophthalmic research. Translation of retinal cells from their native environment to the in vitro milieu leads to cellular stress, jeopardizing their in vivo phenotype features. Moreover, the specificity and stability of many retinal immunochemical markers are poorly evaluated in retinal cell cultures. Hence, we here evaluated the expression profile of 17 retinal markers, that is, recoverin, rhodopsin, arrestin, Chx10, PKC, DCX, CRALBP, GS, vimentin, TPRV4, RBPMS, Brn3a, β-tubulin III, NeuN, MAP2, GFAP, and synaptophysin. At 7 and 18 days of culture, the marker expression profiles of mouse postnatal retinal cells were compared with their age-matched in vivo retinas. We demonstrate stable in vitro expression of all markers, except for arrestin and CRALBP. Differences in cellular expression and location of some markers were observed, both over time in culture and compared with the age-matched retina. We hypothesize that these differences are likely culture condition dependent. Taken together, we suggest a thorough evaluation of the antibodies in specific culture settings, before extrapolating the in vitro results to an in vivo setting. Moreover, the identification of specific cell types may require a combination of different genes expressed or markers with structural information.

Cell therapy for retinal disease

PURPOSE OF REVIEW

The following review will provide an update on stem cell therapy with a focus on completed and ongoing human trials.

RECENT FINDINGS

Significant progress has brought stem cell therapy from proof-of-concept animal models to human clinical trials. Although in its infancy, valuable safety and efficacy data are starting to emerge from trials looking at cell therapies for age-related macular degeneration, Stargardt's macular dystrophy, retinitis pigmentosa, and ischemic retinopathies.

SUMMARY

Although clinical trials continue to enroll and evaluate stem cell therapy in patients with retinal diseases, preliminary results using both cellular replacement and trophic models have provided initial support for this exciting therapy. Results of these pivotal trials will form a key foundation for moving forward toward the ultimate goal of preventing blinding disease.

Modeling autosomal dominant optic atrophy using induced pluripotent stem cells and identifying potential therapeutic targets

Background

Many retinal degenerative diseases are caused by the loss of retinal ganglion cells (RGCs). Autosomal dominant optic atrophy is the most common hereditary optic atrophy disease and is characterized by central vision loss and degeneration of RGCs. Currently, there is no effective treatment for this group of diseases. However, stem cell therapy holds great potential for replacing lost RGCs of patients. Compared with embryonic stem cells, induced pluripotent stem cells (iPSCs) can be derived from adult somatic cells, and they are associated with fewer ethical concerns and are less prone to immune rejection. In addition, patient-derived iPSCs may provide us with a cellular model for studying the pathogenesis and potential therapeutic agents for optic atrophy.

Methods

In this study, iPSCs were obtained from patients carrying an OPA1 mutation (OPA1^+/−-iPSC) that were diagnosed with optic atrophy. These iPSCs were differentiated into putative RGCs, which were subsequently characterized by using RGC-specific expression markers BRN3a and ISLET-1.

Results

Mutant OPA1^+/−-iPSCs exhibited significantly more apoptosis and were unable to efficiently differentiate into RGCs. However, with the addition of neural induction medium, Noggin, or estrogen, OPA1^+/−-iPSC differentiation into RGCs was promoted.

Conclusions

Our results suggest that apoptosis mediated by OPA1 mutations plays an important role in the pathogenesis of optic atrophy, and both noggin and β-estrogen may represent potential therapeutic agents for OPA1-related optic atrophy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0264-1) contains supplementary material, which is available to authorized users.

Electrically evoked potentials in an ovine model for the evaluation of visual prosthesis efficacy

Visual prostheses are becoming a reality as a therapy to restore functional vision to the blind. New stimulation strategies and novel electrode designs are contributing to accelerate the development of such devices triggering the interest of scientists, clinicians and the blind community worldwide. In this scenario, there is a need for large animal models that are suitable for preclinical testing of retinal neuroprostheses. This study presents an electrophysiology assessment of an ovine model for single and simultaneous electrode stimulation from the suprachoroidal space, using symmetric biphasic current pulses with a monopolar return configuration. Visually and electrically evoked potentials were recorded using supradural surface electrodes, showing charge thresholds comparable to those in humans. This model represents an alternative to feline or canine models with analogous activation levels and an eye anatomy similar to that of humans.

Exosomes and Their Therapeutic Potentials of Stem Cells

Exosomes, a group of vesicles originating from the multivesicular bodies (MVBs), are released into the extracellular space when MVBs fuse with the plasma membrane. Numerous studies indicate that exosomes play important roles in cell-to-cell communication, and exosomes from specific cell types and conditions display multiple functions such as exerting positive effects on regeneration in many tissues. It is widely accepted that the therapeutic potential of stem cells may be mediated largely by the paracrine factors, so harnessing the paracrine effects of stem and progenitor cells without affecting these living, replicating, and potentially pluripotent cell populations is an advantage in terms of safety and complexity. Ascending evidence indicated that exosomes might be the main components of paracrine factors; thus, understanding the role of exosomes in each subtype of stem cells is far-reaching. In this review, we discuss the functions of exosomes from different types of stem cells and emphasize the therapeutic potentials of exosomes, providing an alternative way of developing strategies to cure diseases.

Human umbilical tissue-derived cells rescue retinal pigment epithelium dysfunction in retinal degeneration

Retinal pigment epithelium (RPE) cells perform many functions crucial for retinal preservation and vision. RPE cell dysfunction results in various retinal degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration (AMD). Currently, there are no effective treatments for retinal degeneration except for a small percentage of individuals with exudative AMD. Cell therapies targeting RPE cells are being developed in the clinic for the treatment of retinal degeneration. Subretinal injection of human umbilical tissue-derived cells (hUTC) in the Royal College of Surgeons (RCS) rat model of retinal degeneration was shown to preserve photoreceptors and visual function. However, the precise mechanism remains unclear. Here, we demonstrate that hUTC rescue phagocytic dysfunction in RCS RPE cells in vitro. hUTC secrete receptor tyrosine kinase (RTK) ligands brain-derived neurotrophic factor (BDNF), hepatocyte growth factor (HGF), and glial cell-derived neurotrophic factor (GDNF), as well as opsonizing bridge molecules milk-fat-globule-epidermal growth factor 8 (MFG-E8), growth arrest-specific 6 (Gas6), thrombospondin (TSP)-1, and TSP-2. The effect of hUTC on phagocytosis rescue in vitro is mimicked by recombinant human proteins of these factors and is abolished by siRNA-targeted gene silencing in hUTC. The bridge molecules secreted from hUTC bind to the photoreceptor outer segments and facilitate their ingestion by the RPE. This study elucidates novel cellular mechanisms for the repair of RPE function in retinal degeneration through RTK ligands and bridge molecules, and demonstrates the potential of using hUTC for the treatment of retinal degenerative diseases.

Mesenchymal stem cells in regenerative medicine: Focus on articular cartilage and intervertebral disc regeneration

Musculoskeletal disorders represent a major cause of disability and morbidity globally and result in enormous costs for health and social care systems. Development of cell-based therapies is rapidly proliferating in a number of disease areas, including musculoskeletal disorders. Novel biological therapies that can effectively treat joint and spine degeneration are high priorities in regenerative medicine. Mesenchymal stem cells (MSCs) isolated from bone marrow (BM-MSCs), adipose tissue (AD-MSCs) and umbilical cord (UC-MSCs) show considerable promise for use in cartilage and intervertebral disc (IVD) repair. This review article focuses on stem cell-based therapeutics for cartilage and IVD repair in the context of the rising global burden of musculoskeletal disorders. We discuss the biology MSCs and chondroprogenitor cells and specifically focus on umbilical cord/Wharton's jelly derived MSCs and examine their potential for regenerative applications. We also summarize key components of the molecular machinery and signaling pathways responsible for the control of chondrogenesis and explore biomimetic scaffolds and biomaterials for articular cartilage and IVD regeneration. This review explores the exciting opportunities afforded by MSCs and discusses the challenges associated with cartilage and IVD repair and regeneration. There are still many technical challenges associated with isolating, expanding, differentiating, and pre-conditioning MSCs for subsequent implantation into degenerate joints and the spine. However, the prospect of combining biomaterials and cell-based therapies that incorporate chondrocytes, chondroprogenitors and MSCs leads to the optimistic view that interdisciplinary approaches will lead to significant breakthroughs in regenerating musculoskeletal tissues, such as the joint and the spine in the near future.

Cell-based therapy approaches: the hope for incurable diseases

Cell therapies aim to repair the mechanisms underlying disease initiation and progression, achieved through trophic effect or by cell replacement. Multiple cell types can be utilized in such therapies, including stem, progenitor or primary cells. This review covers the current state of cell therapies designed for the prominent disorders, including cardiovascular, neurological (Parkinson's disease, amyotrophic lateral sclerosis, stroke, spinal cord injury), autoimmune (Type 1 diabetes, multiple sclerosis, Crohn's disease), ophthalmologic, renal, liver and skeletal (osteoarthritis) diseases. Various cell therapies have reached advanced clinical trial phases with potential marketing approvals in the near future, many of which are based on mesenchymal stem cells. Advances in pluripotent stem cell research hold great promise for regenerative medicine. The information presented in this review is based on the analysis of the cell therapy collection detailed in LifeMap Discovery(®) (LifeMap Sciences Inc., USA) the database of embryonic development, stem cell research and regenerative medicine.

Ocular stem cells: a status update!

Stem cells are unspecialized cells that have been a major focus of the field of regenerative medicine, opening new frontiers and regarded as the future of medicine. The ophthalmology branch of the medical sciences was the first to directly benefit from stem cells for regenerative treatment. The success stories of regenerative medicine in ophthalmology can be attributed to its accessibility, ease of follow-up and the eye being an immune-privileged organ. Cell-based therapies using stem cells from the ciliary body, iris and sclera are still in animal experimental stages but show potential for replacing degenerated photoreceptors. Limbal, corneal and conjunctival stem cells are still limited for use only for surface reconstruction, although they might have potential beyond this. Iris pigment epithelial, ciliary body epithelial and choroidal epithelial stem cells in laboratory studies have shown some promise for retinal or neural tissue replacement. Trabecular meshwork, orbital and sclera stem cells have properties identical to cells of mesenchymal origin but their potential has yet to be experimentally determined and validated. Retinal and retinal pigment epithelium stem cells remain the most sought out stem cells for curing retinal degenerative disorders, although treatments using them have resulted in variable outcomes. The functional aspects of the therapeutic application of lenticular stem cells are not known and need further attention. Recently, embryonic stem cell-derived retinal pigment epithelium has been used for treating patients with Stargardts disease and age-related macular degeneration. Overall, the different stem cells residing in different components of the eye have shown some success in clinical and animal studies in the field of regenerative medicine.

Stemistry: the control of stem cells in situ using chemistry

A new paradigm for drug research has emerged, namely the deliberate search for molecules able to selectively affect the proliferation, differentiation, and migration of adult stem cells within the tissues in which they exist. Recently, there has been significant interest in medicinal chemistry toward the discovery and design of low molecular weight molecules that affect stem cells and thus have novel therapeutic activity. We believe that a successful agent from such a discover program would have profound effects on the treatment of many long-term degenerative disorders. Among these conditions are examples such as cardiovascular decay, neurological disorders including Alzheimer's disease, and macular degeneration, all of which have significant unmet medical needs. This perspective will review evidence from the literature that indicates that discovery of such agents is achievable and represents a worthwhile pursuit for the skills of the medicinal chemist.

Rat BMSCs initiate retinal endogenous repair through NGF/TrkA signaling

Müller cells can completely repair retinal injury by acting as endogenous stem/progenitor cells in lower-order vertebrates. However, a safe and effective approach to activate progenitor potential of retinal Müller cells in higher-order vertebrates, which rarely re-enter the cell cycle, is a bottleneck problem. In the present study, Royal College of Surgeon's (RCS) rats were subjected to rat bone marrow mesenchymal stem cells (rBMSCs) subretinal space transplantation. Electroretinography (ERG) recordings showed that the b-wave amplitudes and ONL thicknesses statistically increased after transplantation. The number of Müller cells expressing proliferative, stem/progenitor and neuronal markers significantly increased after rBMSCs transplantation in vivo or after co-culturing with rBMSCs in vitro. The cultured rBMSCs could secrete nerve growth factor (NGF). In addition, we confirmed that NGF or NGF-neutralizing antibody could activate or depress Müller cells dedifferentiation, both in vivo and in vitro. Furthermore, Müller cells expressing high levels of the NGF receptor neurotrophic tyrosine kinase receptor type 1 (TrkA) were observed in the retinas of rats transplanted with rBMSCs. Moreover, the protein expression of downstream elements of NGF/TrkA signaling, such as p-PI3K, p-Akt and p-CREB, increased in Müller cells in the retinas of rBMSCs-treated rats in vivo or in Müller cells co-cultured with rBMSCs in vitro. Blocking TrkA with K-252a reduced the number of dedifferentiated Müller cells and the expression of NGF/TrkA signaling in vitro. Thus, rBMSCs might initiate endogenous regenerative mechanisms, which may constitute a new therapeutic strategy for retinal dystrophic diseases.

Histologic and spectroscopic study of pluripotent stem cells after implant in ocular traumatic injuries in a murine model

Introduction

Ocular trauma is defined as a trauma caused by blunt or penetrating mechanisms on the eyeball and its peripheral structures, causing damage with different degrees of affection with temporary or permanent visual function compromise. Ocular trauma is a major cause of preventable blindness worldwide; it constitutes 7% of all corporal injury and 10% to 15% of all eye diseases. Regenerative medicine research has opened up the possibility to use stem cells as a source of cell replacement, so that experimental studies on embryonic stem cells and bone marrow stem cells have been carried out. In this study, we analyzed the histopathological and spectroscopic changes in ocular tissue with trauma, treated with mouse pluripotent stem cells.

Methods

Firstly, mouse embryonic stem cells were seeded. Subsequently, the obtained cells were implanted in a murine model of scleral and retinal damage at the first, second, and fourth weeks post-trauma. At week 12 post-trauma, the eyes were enucleated for histopathologic study (inflammatory response and histological integrity) and spectroscopic analysis by Fourier transform infrared spectroscopy in the attenuated total reflection configuration. Data were analyzed by one-way analysis of variance.

Results

Histopathological results showed that the experimental groups treated with stem cells presented a decrease in the inflammatory response, and the histological integrity was restored, which contrasted with the experimental group treated with saline solution. Moreover, in the spectroscopic analysis, characteristic bands of biological samples were observed in all tissues, highlighting in healthy tissues the presence of C = O bond at 1,745 cm^-1, which was not observed in the injured and treated tissues. Also, the absorption spectrum of the tissues treated with embryonic stem cells showed bands whose intensity was high at around 1,080 to 1,070 cm^-1. It has been reported that these bands are characteristic of pluripotent stem cells.

Conclusions

The implant of embryonic stem cells could be a useful therapeutic treatment after traumatic eye injuries or many other eye diseases to reduce the inflammatory response and restore histological integrity. Furthermore, the spectroscopic technique could be used as a complementary technique for detecting stem cell incorporation into various tissues.

Quantitative assessment of barriers to the clinical development and adoption of cellular therapies: A pilot study

There has been a large increase in basic science activity in cell therapy and a growing portfolio of cell therapy trials. However, the number of industry products available for widespread clinical use does not match this magnitude of activity. We hypothesize that the paucity of engagement with the clinical community is a key contributor to the lack of commercially successful cell therapy products. To investigate this, we launched a pilot study to survey clinicians from five specialities and to determine what they believe to be the most significant barriers to cellular therapy clinical development and adoption. Our study shows that the main concerns among this group are cost-effectiveness, efficacy, reimbursement, and regulation. Addressing these concerns can best be achieved by ensuring that future clinical trials are conducted to adequately answer the questions of both regulators and the broader clinical community.

Differentiation of human limbal-derived induced pluripotent stem cells into limbal-like epithelium

Limbal epithelial stem cell (LESC) deficiency (LSCD) leads to corneal abnormalities resulting in compromised vision and blindness. LSCD can be potentially treated by transplantation of appropriate cells, which should be easily expandable and bankable. Induced pluripotent stem cells (iPSCs) are a promising source of transplantable LESCs. The purpose of this study was to generate human iPSCs and direct them to limbal differentiation by maintaining them on natural substrata mimicking the native LESC niche, including feederless denuded human amniotic membrane (HAM) and de-epithelialized corneas. These iPSCs were generated with nonintegrating vectors from human primary limbal epithelial cells. This choice of parent cells was supposed to enhance limbal cell differentiation from iPSCs by partial retention of parental epigenetic signatures in iPSCs. When the gene methylation patterns were compared in iPSCs to parental LESCs using Illumina global methylation arrays, limbal-derived iPSCs had fewer unique methylation changes than fibroblast-derived iPSCs, suggesting retention of epigenetic memory during reprogramming. Limbal iPSCs cultured for 2 weeks on HAM developed markedly higher expression of putative LESC markers ABCG2, ΔNp63α, keratins 14, 15, and 17, N-cadherin, and TrkA than did fibroblast iPSCs. On HAM culture, the methylation profiles of select limbal iPSC genes (including NTRK1, coding for TrkA protein) became closer to the parental cells, but fibroblast iPSCs remained closer to parental fibroblasts. On denuded air-lifted corneas, limbal iPSCs even upregulated differentiated corneal keratins 3 and 12. These data emphasize the importance of the natural niche and limbal tissue of origin in generating iPSCs as a LESC source with translational potential for LSCD treatment.

Major challenges in vitreoretinal surgery

Since the first vitrectomy surgery was used for treatment of vitreoretinal diseases, surgical techniques and instrumentation have been rapidly improved in the past decades. However, there are complicated vitreoretinal diseases that cannot be successfully treated, even with state-of-the-art surgeries. The outcomes of some complicated cases are still poor due to different reasons and debates still remain in some areas regarding what are the best treatments. There is still a lack of full understanding on many complicated vitreoretinal diseases, such as the molecular basis of proliferative vitreoretinopathy (PVR), the role of scleral buckling (SB) in the management of rhegmatogenous retinal detachment (RRD), the optimal surgical consideration for pediatric RD, and the possibility of surgical management for various retinal degenerations and congenital retinal anomalies. This review discusses the current understandings of some complicated vitreoretinal diseases.

Therapeutic effect of bone marrow mesenchymal stem cells on laser-induced retinal injury in mice

Stem cell therapy has shown encouraging results for neurodegenerative diseases. The retina provides a convenient locus to investigate stem cell functions and distribution in the nervous system. In the current study, we investigated the therapeutic potential of bone marrow mesenchymal stem cells (MSCs) by systemic transplantation in a laser-induced retinal injury model. MSCs from C57BL/6 mice labeled with green fluorescent protein (GFP) were injected via the tail vein into mice after laser photocoagulation. We found that the average diameters of laser spots and retinal cell apoptosis were decreased in the MSC-treated group. Interestingly, GFP-MSCs did not migrate to the injured retina. Further examination revealed that the mRNA expression levels of glial fibrillary acidic protein and matrix metalloproteinase-2 were lower in the injured eyes after MSC transplantation. Our results suggest that intravenously injected MSCs have the ability to inhibit retinal cell apoptosis, reduce the inflammatory response and limit the spreading of damage in the laser-injured retina of mice. Systemic MSC therapy might play a role in neuroprotection, mainly by regulation of the intraocular microenvironment.

Chitosan feasibility to retain retinal stem cell phenotype and slow proliferation for retinal transplantation

Retinal stem cells (RSCs) are promising in cell replacement strategies for retinal diseases. RSCs can migrate, differentiate, and integrate into retina. However, RSCs transplantation needs an adequate support; chitosan membrane (ChM) could be one, which can carry RSCs with high feasibility to support their integration into retina. RSCs were isolated, evaluated for phenotype, and subsequently grown on sterilized ChM and polystyrene surface for 8 hours, 1, 4, and 11 days for analysing cell adhesion, proliferation, viability, and phenotype. Isolated RSCs expressed GFAP, PKC, isolectin, recoverin, RPE65, PAX-6, cytokeratin 8/18, and nestin proteins. They adhered (28 ± 16%, 8 hours) and proliferated (40 ± 20 cells/field, day 1 and 244 ± 100 cells/field, day 4) significantly low (P < 0.05) on ChM. However, they maintained similar viability (>95%) and phenotype (cytokeratin 8/18, PAX6, and nestin proteins expression, day 11) on both surfaces (ChM and polystyrene). RSCs did not express alpha-SMA protein on both surfaces. RSCs express proteins belonging to epithelial, glial, and neural cells, confirming that they need further stimulus to reach a final destination of differentiation that could be provided in in vivo condition. ChM does not alternate RSCs behaviour and therefore can be used as a cell carrier so that slow proliferating RSCs can migrate and integrate into retina.

The global landscape of stem cell clinical trials

AIM

To provide a comprehensive analysis of clinical trials (CTs) listed in worldwide registries involving new applications for stem cell-based treatments and account for the role of industry.

MATERIALS & METHODS

We developed a data set of 4749 stem cell CTs up to 2013 in worldwide registries. We defined 1058 novel CTs (i.e., trials that were not observational in nature; did not involve an established stem cell therapy for an established indication, such as hematopoietic stem cells for leukemia; and did not investigate supportive measures). Based on trial descriptions, we manually coded these for eight additional elements.

RESULTS

Our analysis details the characteristics of novel stem cell CTs (e.g., stem cell types being tested, disease being targeted, and whether interventions were autologous or allogeneic), geotemporal trends, and private sector involvement as sponsor or collaborator.

CONCLUSION

The field is progressing at a steady pace with emerging business models for stem cell therapeutics. However, therapeutic rhetoric must be tempered to reflect current clinical and research realities.

Nanofiber for cardiovascular tissue engineering

INTRODUCTION

Organ/tissue replacement therapy is inherently difficult for application in the tissue engineering field due to immune rejection that limits the long-term efficacy of implanted devices. As the application of tissue engineering in the biomedical field has steadily expanded, stem cells have emerged as a viable option to promote the immune acceptance of implantable devices and to expedite alleviation of the pathological conditions. With various novel scaffolds being introduced, nanofibers which have a three-dimensional architecture can be considered as an efficient carrier for stem cells.

AREAS COVERED

This article reviews the novel tissue engineering processes involved with nanofiber and stem cells. Topics such as the fabrication of nanofiber via electrospinning techniques, the interaction between nanofiber scaffold and specific cell and advanced techniques to enhance the stability of stem cells are delineated in detail. In addition, cardiovascular applications of nanofiber scaffolds loaded with stem cells are examined from a clinical perspective.

EXPERT OPINION

Electrospun nanofibers have been intensively explored as a tool for the architecture control of cardiovascular tissue engineering due to their tunable physicochemical properties. The modification of nanofiber with biological cues, which provide rapid differentiation of stem cells into a specific lineage and protect stem cells under the harsh conditions (i.e., hypoxia), will significantly enhance therapeutic efficacies of transplanted cells. A combination of nanofiber carriers and stem cell therapy for tissue regeneration seems to pose enormous potential for the treatment of cardiac diseases including atherosclerosis and myocardial infarction.

Gene therapy for blindness

Sight-restoring therapy for the visually impaired and blind is a major unmet medical need. Ocular gene therapy is a rational choice for restoring vision or preventing the loss of vision because most blinding diseases originate in cellular components of the eye, a compartment that is optimally suited for the delivery of genes, and many of these diseases have a genetic origin or genetic component. In recent years we have witnessed major advances in the field of ocular gene therapy, and proof-of-concept studies are under way to evaluate the safety and efficacy of human gene therapies. Here we discuss the concepts and recent advances in gene therapy in the retina. Our review discusses traditional approaches such as gene replacement and neuroprotection and also new avenues such as optogenetic therapies. We conjecture that advances in gene therapy in the retina will pave the way for gene therapies in other parts of the brain.

eyeGENE(R): a novel approach to combine clinical testing and researching genetic ocular disease

PURPOSE OF REVIEW

Molecular genetics is revolutionizing the diagnosis and treatment of inherited eye diseases. The National Eye Institute of the National Institutes of Health (NIH), in an effort to facilitate future basic and clinical research in inherited eye disease, created The National Ophthalmic Disease Genotyping and Phenotyping Network (eyeGENE). This review describes the process and utility of the eyeGENE program as it relates to ophthalmic clinical practice.

RECENT FINDINGS

Over the last few years, genetic testing of specific genes associated with inherited eye conditions is becoming the standard practice. Vision research and human clinical trials relying on molecular genetic testing of individuals with inherited eye conditions are becoming more common. Eye healthcare professionals must consider the options to assist patients in obtaining genetic testing results and locating trials or studies that may have benefit.

SUMMARY

eyeGENE is a DNA repository and patient registry for inherited eye diseases coupled to phenotypic descriptors and molecular genetic information. Through eyeGENE, healthcare professionals throughout the United States and Canada can obtain Clinical Laboratory Improvement Amendments-certified clinical molecular genetic results on their patients. Researchers may request access to a de-identified database of phenotype and genotype information about eyeGENE participants and DNA aliquots for their research studies. eyeGENE also offers participants the option of being included in a patient registry, whereby they may be re-contacted if an approved clinical study for which they might qualify is offered.

Differentiation of human embryonic stem cells using size-controlled embryoid bodies and negative cell selection in the production of photoreceptor precursor cells

We proposed to optimize the retinal differentiation protocols for human embryonic stem cells (hESCs) by improving cell handling. To improve efficiency, we first focused on the production of just one retinal precursor cell type (photoreceptor precursor cells [PPCs]) rather than the production of a range of retinal cells. Combining information from a number of previous studies, in particular the use of a feeder-free culture medium and taurine plus triiodothyronine supplements, we then assessed the values of using size-controlled embryoid bodies (EBs) and negative cell selection (to remove residual embryonic antigen-4-positive hESCs). Using size-controlled 1000 cell EBs, significant improvements were made, in that 78% CRX+ve PPCs could be produced in just 17 days. This could be increased to 93% PPCs through the added step of negative cell selection. Improved efficiency of PPC production will help in efforts to undertake shorter and larger preclinical studies as a prelude to future clinical trials.

Dawn of ocular gene therapy: implications for molecular diagnosis in retinal disease

Personalized medicine aims to utilize genomic information about patients to tailor treatment. Gene replacement therapy for rare genetic disorders is perhaps the most extreme form of personalized medicine, in that the patients' genome wholly determines their treatment regimen. Gene therapy for retinal disorders is poised to become a clinical reality. The eye is an optimal site for gene therapy due to the relative ease of precise vector delivery, immune system isolation, and availability for monitoring of any potential damage or side effects. Due to these advantages, clinical trials for gene therapy of retinal diseases are currently underway. A necessary precursor to such gene therapies is accurate molecular diagnosis of the mutation(s) underlying disease. In this review, we discuss the application of Next Generation Sequencing (NGS) to obtain such a diagnosis and identify disease causing genes, using retinal disorders as a case study. After reviewing ocular gene therapy, we discuss the application of NGS to the identification of novel Mendelian disease genes. We then compare current, array based mutation detection methods against next NGS-based methods in three retinal diseases: Leber's Congenital Amaurosis, Retinitis Pigmentosa, and Stargardt's disease. We conclude that next-generation sequencing based diagnosis offers several advantages over array based methods, including a higher rate of successful diagnosis and the ability to more deeply and efficiently assay a broad spectrum of mutations. However, the relative difficulty of interpreting sequence results and the development of standardized, reliable bioinformatic tools remain outstanding concerns. In this review, recent advances NGS based molecular diagnoses are discussed, as well as their implications for the development of personalized medicine.