Integrated platform for production and purification of human pluripotent stem cell-derived neural precursors. Stem Cell Rev Rep. 2014;10:151-161. [PMID: 24221956 DOI: 10.1007/s12015-013-9482-z]

The cell replacement therapeutic potential of human pluripotent stem cells

INTRODUCTION

The remarkable ability of human pluripotent stem cells (hPSCs) to differentiate into specialized cells of the human body emphasizes their immense potential in treating various diseases. Advances in hPSC technology are paving the way for personalized and allogeneic cell-based therapies. The first-in-human studies showed improved treatment of diseases with no adverse effects, which encouraged the industrial production of this type of medicine. To ensure the quality, safety and efficacy of hPSC-based products throughout their life cycle, it is important to monitor and control their clinical translation through good practices (GxP) regulations. Understanding these rules in advance will help ensure that the industrial development of hPSC-derived products for widespread clinical implementation is feasible and progresses rapidly.

AREAS COVERED

In this review, we discuss the key translational obstacles of hPSCs, outline the current hPSC-based clinical trials, and present a workflow for putative clinical hPSC-based products. Finally, we highlight some future therapeutic opportunities for hPSC-derivatives.

EXPERT OPINION

hPSC-based products continue to show promise for the treatment of a variety of diseases. While clinical trials support the relative safety and efficacy of hPSC-based products, further investigation is required to explore the clinical challenges and achieve exclusive regulations for hPSC-based cell therapies.

Xeno-Free Integrated Platform for Robust Production of Cardiomyocyte Sheets from hiPSCs

Human induced pluripotent stem cells (hiPSCs) can be efficiently differentiated into cardiomyocytes (CMs), which can be used for cardiac disease modeling, for drug screening, and to regenerate damaged myocardium. Implementation of xeno-free culture systems is essential to fully explore the potential of these cells. However, differentiation using xeno-free adhesion matrices often results in low CM yields and lack of functional CM sheets, capable of enduring additional maturation stages. Here, we established a xeno-free CM differentiation platform using TeSR/Synthemax, including a replating step and integrated with two versatile purification/enrichment metabolic approaches. Results showed that the replating step was essential to reestablish a fully integrated, closely-knit CM sheet. In addition, replating contributed to increase the cTnT expression from 65% to 75% and the output from 2.2 to 3.1 CM per hiPSC, comparable with the efficiency observed when using TeSR/Matrigel. In addition, supplementation with PluriSin1 and Glu-Lac+ medium allowed increasing the CM content over 80% without compromising CM sheet integrity or functionality. Thus, this xeno-free differentiation platform is a reliable and robust method to produce hiPSC-derived CMs, increasing the possibility of using these cells safely for a wide range of applications.

Neural Stem Cells and Methods for Their Generation From Induced Pluripotent Stem Cells in vitro

Neural stem cells (NSCs) provide promising approaches for investigating embryonic neurogenesis, modeling of the pathogenesis of diseases of the central nervous system, and for designing drug-screening systems. Such cells also have an application in regenerative medicine. The most convenient and acceptable source of NSCs is pluripotent stem cells (embryonic stem cells or induced pluripotent stem cells). However, there are many different protocols for the induction and differentiation of NSCs, and these result in a wide range of neural cell types. This review is intended to summarize the knowledge accumulated, to date, by workers in this field. It should be particularly useful for researchers who are beginning investigations in this area of cell biology.

Towards Multi-Organoid Systems for Drug Screening Applications

A low percentage of novel drug candidates succeed and reach the end of the drug discovery pipeline, mainly due to poor initial screening and assessment of the effects of the drug and its metabolites over various tissues in the human body. For that, emerging technologies involving the production of organoids from human pluripotent stem cells (hPSCs) and the use of organ-on-a-chip devices are showing great promise for developing a more reliable, rapid and cost-effective drug discovery process when compared with the current use of animal models. In particular, the possibility of virtually obtaining any type of cell within the human body, in combination with the ability to create patient-specific tissues using human induced pluripotent stem cells (hiPSCs), broadens the horizons in the fields of drug discovery and personalized medicine. In this review, we address the current progress and challenges related to the process of obtaining organoids from different cell lineages emerging from hPSCs, as well as how to create devices that will allow a precise examination of the in vitro effects generated by potential drugs in different organ systems.

Label-Free Separation of Induced Pluripotent Stem Cells with Anti-SSEA-1 Antibody Immobilized Microfluidic Channel

When induced pluripotent stem cells (iPSCs) are routinely cultured, the obtained cells are a heterogeneous mixture, including feeder cells and partially differentiated cells. Therefore, a purification process is required to use them in a clinical stage. We described a label-free separation of iPSCs using a microfluidic channel. Antibodies against stage-specific embryonic antigen 1 (SSEA-1) was covalently immobilized on the channel coated with a phospholipid polymer. After injection of the heterogeneous cell suspension containing iPSCs, the velocity of cell movement under a liquid flow condition was measured. The mean velocity of the cell movement was 2.1 mm/sec in the unmodified channel, while that in the channel with the immobilized-antibody was 0.4 mm/sec. The eluted cells were fractionated by eluting time. As a result, the SSEA-1 positive iPSCs were mainly contained in later fractions, and the proportion of iPSCs was increased from 43% to 82% as a comparison with the initial cell suspension. These results indicated that iPSCs were selectively separated by the microfluidic channel. This channel is a promising device for label-free separation of iPSCs based on their pluripotent state.

Mesenchymal Stem Cell Magnetization: Magnetic Multilayer Microcapsule Uptake, Toxicity, Impact on Functional Properties, and Perspectives for Magnetic Delivery

Mesenchymal stem cells (MSCs) are widely used in cell therapy due to their convenience, multiline differentiation potential, reproducible protocols, and biological properties. The potential of MSCs to impregnate magnetic microcapsules and their possible influence on cell function and ability to response to magnetic field have been explored. Interestingly, the cells suspended in media show much higher ability in internalization of microcapsules, then MSCs adhere into the surface. There is no significant effect of microcapsules on cell toxicity compared with other cell line-capsule internalization reported in literature. Due to internalization of magnetic capsules by the cells, such cell engineering platform is responsive to external magnetic field, which allows to manipulate MSC migration. Magnetically sorted MSCs are capable to differentiation as confirmed by their conversion to adipogenic and osteogenic cells using standard protocols. There is a minor effect of capsule internalization on cell adhesion, though MSCs are still able to form spheroid made by dozen of thousand MSCs. This work demonstrates the potential of use of microcapsule impregnated MSCs to carry internalized micron-sized vesicles and being navigated with external magnetic signaling.

Scaling up a chemically-defined aggregate-based suspension culture system for neural commitment of human pluripotent stem cells

The demand of high cell numbers for applications in cellular therapies and drug screening requires the development of scalable platforms capable to generating highly pure populations of tissue-specific cells from human pluripotent stem cells. In this work, we describe the scaling-up of an aggregate-based culture system for neural induction of human induced pluripotent stem cells (hiPSCs) under chemically-defined conditions. A combination of non-enzymatic dissociation and rotary agitation was successfully used to produce homogeneous populations of hiPSC aggregates with an optimal (140 μm) and narrow distribution of diameters (coefficient of variation of 21.6%). Scalable neural commitment of hiPSCs as 3D aggregates was performed in 50 mL spinner flasks, and the process was optimized using a factorial design approach, involving parameters such as agitation rate and seeding density. We were able to produce neural progenitor cell cultures, that at the end of a 6-day neural induction process contained less than 3% of Oct4-positive cells and that, after replating, retained more than 60% of Pax6-positive neural cells. The results here presented should set the stage for the future generation of a clinically relevant number of human neural progenitors for transplantation and other biomedical applications using controlled, automated and reproducible large-scale bioreactor culture systems.

A Compendium of Preparation and Application of Stem Cells in Parkinson's Disease: Current Status and Future Prospects

Parkinson's Disease (PD) is a progressively neurodegenerative disorder, implicitly characterized by a stepwise loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and explicitly marked by bradykinesia, rigidity, resting tremor and postural instability. Currently, therapeutic approaches available are mainly palliative strategies, including L-3,4-dihydroxy-phenylalanine (L-DOPA) replacement therapy, DA receptor agonist and deep brain stimulation (DBS) procedures. As the disease proceeds, however, the pharmacotherapeutic efficacy is inevitably worn off, worse still, implicated by side effects of motor response oscillations as well as L-DOPA induced dyskinesia (LID). Therefore, the frustrating status above has propeled the shift to cell replacement therapy (CRT), a promising restorative therapy intending to secure a long-lasting relief of patients' symptoms. By far, stem cell lines of multifarious origins have been established, which can be further categorized into embryonic stem cells (ESCs), neural stem cells (NSCs), induced neural stem cells (iNSCs), mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). In this review, we intend to present a compendium of preparation and application of multifarious stem cells, especially in relation to PD research and therapy. In addition, the current status, potential challenges and future prospects for practical CRT in PD patients will be elaborated as well.

Spatial and temporal control of cell aggregation efficiently directs human pluripotent stem cells towards neural commitment

3D suspension culture is generally considered a promising method to achieve efficient expansion and controlled differentiation of human pluripotent stem cells (hPSCs). In this work, we focused on developing an integrated culture platform for expansion and neural commitment of hPSCs into neural precursors using 3D suspension conditions and chemically-defined culture media. We evaluated different inoculation methodologies for hPSC expansion as 3D aggregates and characterized the resulting cultures in terms of aggregate size distribution. It was demonstrated that upon single-cell inoculation, after four days of culture, 3D aggregates were composed of homogenous populations of hPSC and were characterized by an average diameter of 139 ± 26 μm, which was determined to be the optimal size to initiate neural commitment. Temporal analysis revealed that upon neural specification it is possible to maximize the percentage of neural precursor cells expressing the neural markers Sox1 and Pax6 after nine days of culture. These results highlight our ability to define a robust method for production of hPSC-derived neural precursors that minimizes processing steps and that constitutes a promising alternative to the traditional planar adherent culture system due to a high potential for scaling-up.

Clinical-scale purification of pluripotent stem cell derivatives for cell-based therapies

Human pluripotent stem cells (hPSCs) have the potential to revolutionize cell-replacement therapies because of their ability to self renew and differentiate into nearly every cell type in the body. However, safety concerns have delayed the clinical translation of this technology. One cause for this is the capacity that hPSCs have to generate tumors after transplantation. Because of the challenges associated with achieving complete differentiation into clinically relevant cell types, the development of safe and efficient strategies for purifying committed cells is essential for advancing hPSC-based therapies. Several purification strategies have now succeeded in generating non-tumorigenic and homogeneous cell-populations. These techniques typically enrich for cells by either depleting early committed populations from teratoma-initiating hPSCs or by positively selecting cells after differentiation. Here we review the working principles behind separation methods that have facilitated the safe and controlled application of hPSC-derived cells in laboratory settings and pre-clinical research. We underscore the need for improving and integrating purification strategies within differentiation protocols in order to unlock the therapeutic potential of hPSCs.

Purification of human induced pluripotent stem cell-derived neural precursors using magnetic activated cell sorting

Neural precursor (NP) cells derived from human induced pluripotent stem cells (hiPSCs), and their neuronal progeny, will play an important role in disease modeling, drug screening tests, central nervous system development studies, and may even become valuable for regenerative medicine treatments. Nonetheless, it is challenging to obtain homogeneous and synchronously differentiated NP populations from hiPSCs, and after neural commitment many pluripotent stem cells remain in the differentiated cultures. Here, we describe an efficient and simple protocol to differentiate hiPSC-derived NPs in 12 days, and we include a final purification stage where Tra-1-60+ pluripotent stem cells (PSCs) are removed using magnetic activated cell sorting (MACS), leaving the NP population nearly free of PSCs.

Pluripotent stem cell-derived neural stem cells: From basic research to applications

Basic research on pluripotent stem cells is designed to enhance understanding of embryogenesis, whereas applied research is designed to develop novel therapies and prevent diseases. Attainment of these goals has been enhanced by the establishment of embryonic stem cell lines, the technological development of genomic reprogramming to generate induced-pluripotent stem cells, and improvements in vitro techniques to manipulate stem cells. This review summarizes the techniques required to generate neural cells from pluripotent stem cells. In particular, this review describes current research applications of a simple neural differentiation method, the neural stem sphere method, which we developed.

Electrical maturation of neurons derived from human embryonic stem cells

In-vitro neuronal differentiation of human pluripotent stem cells has become a widely used tool in disease modeling and prospective regenerative medicine. Most studies evaluate neurons molecularly and only a handful of them use electrophysiological tools to directly indicate that these are genuine neurons. Therefore, the specific timing of development of intrinsic electrophysiological properties and synaptic capabilities remains poorly understood. Here we describe a systematic analysis of developing neurons derived in-vitro from human embryonic stem cells (hESCs). We show that hESCs differentiated in-vitro into early embryonic neurons, displaying basically mature morphological and electrical features as early as day 37. This early onset of action potential discharges suggests that first stages of neurogenesis in humans are already associated with electrical maturation. Spike frequency, amplitude, duration, threshold and after hyperpolarization were found to be the most predictive parameters for electrical maturity. Furthermore, we were able to detect spontaneous synaptic activity already at these early time-points, demonstrating that neuronal connectivity can develop concomitantly with the gradual process of electrical maturation. These results highlight the functional properties of hESCs in the process of their development into neurons. Moreover, our results provide practical tools for the direct measurement of functional maturity, which can be reproduced and implemented for stem cell research of neurogenesis in general, and neurodevelopmental disorders in particular.