Strategies for retinal cell generation from human pluripotent stem cells

Expansion of induced pluripotent stem cells under consideration of bioengineering aspects: part 2

The manufacturing of allogeneic cell therapeutics based on human-induced pluripotent stem cells (hiPSCs) holds considerable potential to revolutionize the accessibility and affordability of modern healthcare. However, achieving the cell yields necessary to ensure robust production hinges on identifying suitable and scalable single-use (SU) bioreactor systems. While specific stirred SU bioreactor types have demonstrated proficiency in supporting hiPSC expansion at L-scale, others, notably instrumented SU multiplate and fixed-bed bioreactors, remain relatively unexplored. By characterizing these bioreactors using both computational fluid dynamics and experimental bioengineering methods, operating ranges were identified for the Xpansion® 10 and Ascent™ 1 m2 bioreactors in which satisfactory hiPSC expansion under serum-free conditions was achieved. These operating ranges were shown not only to effectively limit cell exposure to wall shear stress but also facilitated sufficient oxygen transfer and mixing. Through their application, almost 5 × 109 viable cells could be produced within 5 days, achieving expansion factors of up to 35 without discernable impact on cell viability, identity, or differentiation potential. Key Points •Bioengineering characterizations allowed the identification of operating ranges that supported satisfactory hiPSC expansion •Both the Xpansion® 10 multiplate and Ascent™ 1 m2 fixed-bed reactor accommodated the production of almost 5 × 109 viable cells within 5 days •Exposing the hiPSCs to a median wall shear stress of up to 8.2 × 10-5 N cm-2 did not impair quality.

Regeneration of the Retina Using Pluripotent Stem Cells: A Comprehensive Review

Retinitis pigmentosa and age-related macular degeneration are the most frequent causes of irreversible visual impairment in the world. Existing therapeutic methods could be more effective, underscoring the necessity of new treatments. Reconstructing the retinal photoreceptors through the transplantation of human pluripotent stem cells, representing an attractive approach for restoring vision, has gained momentum. This paper gives an exhaustive account of what has been known in this field, the discoveries made, and the recent progress. This review paper outlines the retina's organisation, cell types, the pathophysiology of retinal injury/degeneration, and the reasoning behind using pluripotent stem cells in retinal regeneration. This article investigates differentiation strategies, molecular components that dictate cell type specification, and the recreation of retinal development in vitro, genetically engineering and manipulating epigenetic marks using various techniques for driving specific cell fates and improving therapy efficacy. Subretinal injection methods, cell encapsulation techniques, scaffold-based approaches, cell sheet transplantation, and their impact on integrating implanted cells into a functional retina are thoroughly reviewed. Using bioengineering approaches, biomaterials and growth factors form a favourable micro-ambience for grafted cells. Issues around safety and efficacy (tumorigenicity, immunological rejection, and long-term integration/functionality) are explored. Moreover, the paper emphasises the significance of rigorous characterisation, immunomodulatory strategies, and clinical and pre-clinical studies to ensure the safety and effectiveness of retinal regeneration therapy. Future perspectives and challenges are presented, looking at fine-tuning differentiation strategies, improving functional integration and regulatory aspects, and using co-therapy and supportive treatments.

Suspension culture improves iPSC expansion and pluripotency phenotype

BACKGROUND

Induced pluripotent stem cells (iPSCs) offer potential to revolutionize regenerative medicine as a renewable source for islets, dopaminergic neurons, retinal cells, and cardiomyocytes. However, translation of these regenerative cell therapies requires cost-efficient mass manufacturing of high-quality human iPSCs. This study presents an improved three-dimensional Vertical-Wheel® bioreactor (3D suspension) cell expansion protocol with comparison to a two-dimensional (2D planar) protocol.

METHODS

Sendai virus transfection of human peripheral blood mononuclear cells was used to establish mycoplasma and virus free iPSC lines without common genetic duplications or deletions. iPSCs were then expanded under 2D planar and 3D suspension culture conditions. We comparatively evaluated cell expansion capacity, genetic integrity, pluripotency phenotype, and in vitro and in vivo pluripotency potential of iPSCs.

RESULTS

Expansion of iPSCs using Vertical-Wheel® bioreactors achieved 93.8-fold (IQR 30.2) growth compared to 19.1 (IQR 4.0) in 2D (p < 0.0022), the largest expansion potential reported to date over 5 days. 0.5 L Vertical-Wheel® bioreactors achieved similar expansion and further reduced iPSC production cost. 3D suspension expanded cells had increased proliferation, measured as Ki67⁺ expression using flow cytometry (3D: 69.4% [IQR 5.5%] vs. 2D: 57.4% [IQR 10.9%], p = 0.0022), and had a higher frequency of pluripotency marker (Oct4⁺Nanog⁺Sox2⁺) expression (3D: 94.3 [IQR 1.4] vs. 2D: 52.5% [IQR 5.6], p = 0.0079). q-PCR genetic analysis demonstrated a lack of duplications or deletions at the 8 most commonly mutated regions within iPSC lines after long-term passaging (> 25). 2D-cultured cells displayed a primed pluripotency phenotype, which transitioned to naïve after 3D-culture. Both 2D and 3D cells were capable of trilineage differentiation and following teratoma, 2D-expanded cells generated predominantly solid teratomas, while 3D-expanded cells produced more mature and predominantly cystic teratomas with lower Ki67⁺ expression within teratomas (3D: 16.7% [IQR 3.2%] vs.. 2D: 45.3% [IQR 3.0%], p = 0.002) in keeping with a naïve phenotype.

CONCLUSION

This study demonstrates nearly 100-fold iPSC expansion over 5-days using our 3D suspension culture protocol in Vertical-Wheel® bioreactors, the largest cell growth reported to date. 3D expanded cells showed enhanced in vitro and in vivo pluripotency phenotype that may support more efficient scale-up strategies and safer clinical implementation.

Comparison of human amniotic membrane decellularisation approaches for hESC-derived RPE cells culture

Objective

Recent clinical studies have shown that the transplantation of functional retinal pigment epithelium (RPE) cells can prevent the onset of RPE degeneration in age-related macular degeneration. This study aimed to investigate the potential of human amniotic membrane (hAM) as a viable scaffold for the growth and proliferation of pluripotent-derived RPE cells.

Methods and analysis

Three enzymatic hAM de-epithelialisation methods (thermolysin, trypsin-EDTA and dispase II) were assessed by histological analysis and optical coherence tomography (OCT). We generated RPE cells from a human embryonic stem cell (hESC) line subjected to spontaneous differentiation in feeder-free conditions. The hESC-derived RPE cells were seeded over denuded hAM at a density of 2.0×10⁵ cells/cm² and maintained in culture for up to 4 weeks. Immnofluorescence was carried out to evaluate the development of a confluent monolayer of RPE cells on the top of the hAM. Conditioned medium was collected to measure pigment epithelium-derived factor (PEDF) concentration by ELISA.

Results

Laminin α5 and collagen IV staining confirmed the efficiency of the de-epithelialisation process. In particular, thermolysin showed good retention of tissue integrity on OCT images and greater preservation of the hAM basement membrane. The hESC-derived RPE cells formed patches of pigmented cells interspersed along the denuded hAM, but failed to form a regular sheet of RPE cells. These cells expressed typical RPE markers, such as PMEL17 and RPE65, but they secreted low levels of PEDF.

Conclusion

The biological variability of the hAM could influence the adhesion and the expansion of hESC-derived RPE cells. Further studies are required to verify whether a non-confluent monolayer might represent a limit to transplantation.

Binary Colloidal Crystals (BCCs) Modulate the Retina-related Gene Expression of hBMSCs – A Preliminary Study

Surface topography-induced lineage commitment of human bone marrow stem cells (hBMSCs) has been reported. However, this effect on hBMSC differentiation toward retinal pigment epithelium (RPE)-like cells has not been explored. Herein, a family of cell culture substrates called binary colloidal crystals (BCCs) was used to stimulate hBMSCs into RPE-like cells without induction factors. Two BCCs, named SiPS (silica (Si)/polystyrene (PS)) and SiPSC (Si/carboxylated PS), having similar surface topographies but different surface chemistry was used for cell culture. The result showed that cell proliferation was no difference between the two BCCs and tissue culture polystyrene (TCPS) control. However, the cell attachment, spreading area, and aspect ratio between surfaces were significantly changed. For example, cells displayed more elongated on SiPS (aspect ratio ~7.0) than those on SiPSC and TCPS (~2.0). The size of focal adhesions on SiPSC (~1.6 µm²) was smaller than that on the TCPS (~2.5 µm²). qPCR results showed that hBMSCs expressed higher RPE progenitor genes (i.e., MITF and PAX6) on day 15, and mature RPE genes (i.e., CRALBP and RPE65) on day 30 on SiPS than TCPS. On the other hand, the expression of optical vesicle or neuroretina genes (i.e., MITF and VSX2) was upregulated on day 15 on SiPSC compared to the TCPS. This study reveals that hBMSCs could be modulated into different cell subtypes depending on the BCC combinations. This study shows the potential of BCCs in controlling stem cell differentiation.

Brain and Retinal Organoids for Disease Modeling: The Importance of In Vitro Blood–Brain and Retinal Barriers Studies

Brain and retinal organoids are functional and dynamic in vitro three-dimensional (3D) structures derived from pluripotent stem cells that spontaneously organize themselves to their in vivo counterparts. Here, we review the main literature data of how these organoids have been developed through different protocols and how they have been technically analyzed. Moreover, this paper reviews recent advances in using organoids to model neurological and retinal diseases, considering their potential for translational applications but also pointing out their limitations. Since the blood–brain barrier (BBB) and blood–retinal barrier (BRB) are understood to play a fundamental role respectively in brain and eye functions, both in health and in disease, we provide an overview of the progress in the development techniques of in vitro models as reliable and predictive screening tools for BBB and BRB-penetrating compounds. Furthermore, we propose potential future directions for brain and retinal organoids, in which dedicated biobanks will represent a novel tool for neuroscience and ophthalmology research.

Tracking the Transplanted Neurosphere in Retinal Pigment Epithelium Degeneration Model

Introduction

Retinal Pigment Epithelium (RPE) layer deterioration is a leading cause of Age-Related Macular Degeneration (AMD), i.e., the most significant reason for irreversible blindness. The present study aimed to track the Neurosphere-Derived (NS) from Bone Marrow Stromal Stem Cells (BMSCs) grafted into the sub-retinal space (destruction of the RPE layer by sodium iodate).

Methods

RPE degeneration model was performed using the injection of 5% sodium iodate performed in the retro-orbital sinus of Wistar rats. BMSCs were extracted from the examined rat femur and induced into NS, using EGF, bFGF, and B27. BrdU-NS labeled cells were transplanted into the sub-retinal space. For detecting BMSCs and NS markers, immunocytochemistry was performed. Moreover, immunohistochemical was conducted for tracking the transplanted cells in the RPE and sensory retina.

Results

The immunocytochemistry of BMSCs cells displayed the expression of mesenchymal stem cells markers (CD90; 99%±1), CD166 (98%±2), CD44 (99%±1). Additionally, the expression of neural lineage markers in NS, such as SOX2, OCT4, Nanog, Nestin, and Neurofilaments (68, 160, 200) revealed the differentiation from BMSCs. Tracking BrdU-NS labeled suggested these aggregations in most layers of the retina.

Conclusion

Our study data indicated that BMSCs derived neurosphere had the potential to migrate in injured retinal and integrate into the neurosensory retina. These data can be useful in finding safe cells for replacement therapy in AMD.

A Systematic Review on Transplantation Studies of the Retinal Pigment Epithelium in Animal Models

The retinal pigment epithelium (RPE) and the adjacent light-sensitive photoreceptors form a single functional unit lining the back of the eye. Both cell layers are essential for normal vision. RPE degeneration is usually followed by photoreceptor degeneration and vice versa. There are currently almost no effective therapies available for RPE disorders such as Stargardt disease, specific types of retinitis pigmentosa, and age-related macular degeneration. RPE replacement for these disorders, especially in later stages of the disease, may be one of the most promising future therapies. There is, however, no consensus regarding the optimal RPE source, delivery strategy, or the optimal experimental host in which to test RPE replacement therapy. Multiple RPE sources, delivery methods, and recipient animal models have been investigated, with variable results. So far, a systematic evaluation of the (variables influencing) efficacy of experimental RPE replacement parameters is lacking. Here we investigate the effect of RPE transplantation on vision and vision-based behavior in animal models of retinal degenerated diseases. In addition, we aim to explore the effect of RPE source used for transplantation, the method of intervention, and the animal model which is used.

METHODS

In this study, we systematically identified all publications concerning transplantation of RPE in experimental animal models targeting the improvement of vision (e.g., outcome measurements related to the morphology or function of the eye). A variety of characteristics, such as species, gender, and age of the animals but also cell type, number of cells, and other intervention characteristics were extracted from all studies. A risk of bias analysis was performed as well. Subsequently, all references describing one of the following outcomes were analyzed in depth in this systematic review: a-, b-, and c-wave amplitudes, vision-based, thickness analyses based on optical coherence tomography (OCT) data, and transplant survival based on scanning laser ophthalmoscopy (SLO) data. Meta-analyses were performed on the a- and b-wave amplitudes from electroretinography (ERG) data as well as data from vision-based behavioral assays.

RESULTS

original research articles met the inclusion criteria after two screening rounds. Overall, most studies were categorized as unclear regarding the risk of bias, because many experimental details were poorly reported. Twenty-three studies reporting one or more of the outcome measures of interest were eligible for either descriptive (thickness analyses based on OCT data; n = 2) or meta-analyses. RPE transplantation significantly increased ERG a-wave (Hedges' g 1.181 (0.471-1.892), n = 6) and b-wave (Hedges' g 1.734 (1.295-2.172), n = 42) amplitudes and improved vision-based behavior (Hedges' g 1.018 (0.826-1.209), n = 96). Subgroup analyses revealed a significantly increased effect of the use of young and adolescent animals compared to adult animals. Moreover, transplanting more cells (in the range of 105 versus in the range of 104) resulted in a significantly increased effect on vision-based behavior as well. The origin of cells mattered as well. A significantly increased effect was found on vision-based behavior when using ARPE-19 and OpRegen® RPE.

CONCLUSIONS

This systematic review shows that RPE transplantation in animal models for retinal degeneration significantly increases a- and b- wave amplitudes and improves vision-related behavior. These effects appear to be more pronounced in young animals, when the number of transplanted cells is larger and when ARPE-19 and OpRegen® RPE cells are used. We further emphasize that there is an urgent need for improving the reporting and methodological quality of animal experiments, to make such studies more comparable.

Teratogenic Rubella Virus Alters the Endodermal Differentiation Capacity of Human Induced Pluripotent Stem Cells

The study of congenital virus infections in humans requires suitable ex vivo platforms for the species-specific events during embryonal development. A prominent example for these infections is rubella virus (RV) which most commonly leads to defects in ear, heart, and eye development. We applied teratogenic RV to human induced pluripotent stem cells (iPSCs) followed by differentiation into cells of the three embryonic lineages (ecto-, meso-, and endoderm) as a cell culture model for blastocyst- and gastrulation-like stages. In the presence of RV, lineage-specific differentiation markers were expressed, indicating that lineage identity was maintained. However, portrait analysis of the transcriptomic expression signatures of all samples revealed that mock- and RV-infected endodermal cells were less related to each other than their ecto- and mesodermal counterparts. Markers for definitive endoderm were increased during RV infection. Profound alterations of the epigenetic landscape including the expression level of components of the chromatin remodeling complexes and an induction of type III interferons were found, especially after endodermal differentiation of RV-infected iPSCs. Moreover, the eye field transcription factors RAX and SIX3 and components of the gene set vasculogenesis were identified as dysregulated transcripts. Although iPSC morphology was maintained, the formation of embryoid bodies as three-dimensional cell aggregates and as such cellular adhesion capacity was impaired during RV infection. The correlation of the molecular alterations induced by RV during differentiation of iPSCs with the clinical signs of congenital rubella syndrome suggests mechanisms of viral impairment of human development.

Organ-On-A-Chip Technologies for Advanced Blood-Retinal Barrier Models

The blood-retinal barrier (BRB) protects the retina by maintaining an adequate microenvironment for neuronal function. Alterations of the junctional complex of the BRB and consequent BRB breakdown in disease contribute to a loss of neuronal signaling and vision loss. As new therapeutics are being developed to prevent or restore barrier function, it is critical to implement physiologically relevant in vitro models that recapitulate the important features of barrier biology to improve disease modeling, target validation, and toxicity assessment. New directions in organ-on-a-chip technology are enabling more sophisticated 3-dimensional models with flow, multicellularity, and control over microenvironmental properties. By capturing additional biological complexity, organs-on-chip can help approach actual tissue organization and function and offer additional tools to model and study disease compared with traditional 2-dimensional cell culture. This review describes the current state of barrier biology and barrier function in ocular diseases, describes recent advances in organ-on-a-chip design for modeling the BRB, and discusses the potential of such models for ophthalmic drug discovery and development.

CRISPR Activation Enhances In Vitro Potency of AAV Vectors Driven by Tissue-Specific Promoters

Validation of gene transfer vectors containing tissue-specific promoters in cell-based functional assays poses a formidable challenge for gene therapy product development. Here, we describe a novel approach based on CRISPR/dCas9 transcriptional activation to achieve robust transgene expression from transgene cassettes containing tissue or cell type-specific promoters after infection with AAV vectors in cell-based systems. Guide RNA sequences targeting two promoters that are highly active within mammalian photoreceptors were screened in a novel promoter activation assay. Using this screen, we generated and characterized stable cell lines that co-express dCas9.VPR and top-performing guide RNA candidates. These cells exhibit potent activation of proviral plasmids after transfection or after infection with AAV vectors delivering transgene cassettes carrying photoreceptor-specific promoters. In addition, we interrogated mechanisms to optimize this platform through the addition of multiple guide RNA sequences and co-expression of the universal adeno-associated virus receptor (AAVR). Collectively, this investigation identifies a rapid and broadly applicable strategy to enhance in vitro expression and to evaluate potency of AAV vectors that rely upon cell or tissue-specific regulatory elements.

A Mini Review: Moving iPSC-Derived Retinal Subtypes Forward for Clinical Applications for Retinal Degenerative Diseases

Patient-derived human-induced pluripotent stem cells (iPSCs) have been critical in advancing our understanding of the underlying mechanisms of numerous retinal disorders. Many of these retinal disorders have no effective treatment and result in severe visual impairment and even blindness. Among the retinal degenerative diseases modeled by iPSCs are age-related macular degeneration (AMD), glaucoma, Leber congenital amaurosis (LCA), retinitis pigmentosa (RP), and autosomal dominant retinitis pigmentosa (adRP). In addition to studying retinal disease ontogenesis and pathology, hiPSCs have clinical and pharmacological applications, such as developing drug screening and gene therapy approaches and new cell-based clinical treatments. Recent studies have primarily focused on three retinal cell fates - retinal pigmented epithelium cells (RPE), retinal ganglion cells (RGCs), and photoreceptor cells - and have demonstrated that hiPSCs have great potential for increasing our knowledge of and developing treatments for retinal degenerative disorders.