Cell therapy and the safety of embryonic stem cell-derived grafts

Transfection, selection, and colony-picking of human induced pluripotent stem cells TALEN-targeted with a GFP gene into the AAVS1 safe harbor

Targeted transgene addition can provide persistent gene expression while circumventing the gene silencing and insertional mutagenesis caused by viral vector mediated random integration. This protocol describes a universal and efficient transgene targeted addition platform in human iPSCs based on utilization of validated open-source TALENs and a gene-trap-like donor to deliver transgenes into a safe harbor locus. Importantly, effective gene editing is rate-limited by the delivery efficiency of gene editing vectors. Therefore, this protocol first focuses on preparation of iPSCs for transfection to achieve high nuclear delivery efficiency. When iPSCs are dissociated into single cells using a gentle-cell dissociation reagent and transfected using an optimized program, >50% cells can be induced to take up the large gene editing vectors. Because the AAVS1 locus is located in the intron of an active gene (PPP1R12C), a splicing acceptor (SA)-linked puromycin resistant gene (PAC) was used to select targeted iPSCs while excluding random integration-only and untransfected cells. This strategy greatly increases the chance of obtaining targeted clones, and can be used in other active gene targeting experiments as well. Two weeks after puromycin selection at the dose adjusted for the specific iPSC line, clones are ready to be picked by manual dissection of large, isolated colonies into smaller pieces that are transferred to fresh medium in a smaller well for further expansion and genetic and functional screening. One can follow this protocol to readily obtain multiple GFP reporter iPSC lines that are useful for in vivo and in vitro imaging and cell isolation.

Porous membrane culture method for expansion of human pluripotent stem cells

For the clinical application of human pluripotent stem cells (hPSCs), it is critical to develop novel culture techniques that completely exclude the use of animal feeder cells and enzyme treatments used in conventional hPSC culture systems. Here, we describe a novel culture method using a porous membrane that allows to maintain stable attachment and expansion of hPSCs, obviates the need for enzyme treatment, and also reduces feeder layer contamination.

Microencapsulation of dopamine neurons derived from human induced pluripotent stem cells

BACKGROUND

Dopamine neurons derived from induced pluripotent stem cells have been widely studied for the treatment of Parkinson's disease. However, various difficulties remain to be overcome, such as tumor formation, fragility of dopamine neurons, difficulty in handling large numbers of dopamine neurons, and immune reactions. In this study, human induced pluripotent stem cell-derived precursors of dopamine neurons were encapsulated in agarose microbeads. Dopamine neurons in microbeads could be handled without specific protocols, because the microbeads protected the fragile dopamine neurons from mechanical stress.

METHODS

hiPS cells were seeded on a Matrigel-coated dish and cultured to induce differentiation into a dopamine neuronal linage. On day 18 of culture, cells were collected from the culture dishes and seeded into U-bottom 96-well plates to induce cell aggregate formation. After 5 days, cell aggregates were collected from the plates and microencapsulated in agarose microbeads. The microencapsulated aggregates were cultured for an additional 45 days to induce maturation of dopamine neurons.

RESULTS

Approximately 60% of all cells differentiated into tyrosine hydroxylase-positive neurons in agarose microbeads. The cells released dopamine for more than 40 days. In addition, microbeads containing cells could be cryopreserved.

CONCLUSION

hiPS cells were successfully differentiated into dopamine neurons in agarose microbeads.

GENERAL SIGNIFICANCE

Agarose microencapsulation provides a good supporting environment for the preparation and storage of dopamine neurons.

Stem cell therapy for glaucoma: science or snake oil?

In recent years there has been substantial progress in developing stem cell treatments for glaucoma. As a downstream approach that targets the underlying susceptibility of retinal ganglion and trabecular meshwork cells, stem cell therapy has the potential to both replace lost, and protect damaged, cells by secreting neurotrophic factors. A variety of sources, including embryonic cells, adult cells derived from the central nervous system, and induced pluripotent stem cells show promise as therapeutic approaches. Even though safety concerns and ethical controversies have limited clinical implementation, some institutions have already commercialized stem cell therapy and are using direct-to-consumer advertising to attract patients with glaucoma. We review the progress of stem cell therapy and its current commercial availability.

Generation of GFP Reporter Human Induced Pluripotent Stem Cells Using AAVS1 Safe Harbor Transcription Activator-Like Effector Nuclease

Generation of a fluorescent GFP reporter line in human induced pluripotent stem cells (hiPSCs) provides enormous potentials in both basic stem cell research and regenerative medicine. A protocol for efficiently generating such an engineered reporter line by gene targeting is highly desired. Transcription activator-like effector nucleases (TALENs) are a new class of artificial restriction enzymes that have been shown to significantly promote homologous recombination by >1000-fold. The AAVS1 (adeno-associated virus integration site 1) locus is a "safe harbor" and has an open chromatin structure that allows insertion and stable expression of transgene. Here, we describe a step-by-step protocol from determination of TALENs activity, hiPSC culture, and delivery of a donor into AAVS1 targeting site, to validation of targeted integration by PCR and Southern blot analysis using hiPSC line, and a pair of open-source AAVS1 TALENs.

Stable enhanced green fluorescent protein expression after differentiation and transplantation of reporter human induced pluripotent stem cells generated by AAVS1 transcription activator-like effector nucleases

Human induced pluripotent stem (hiPS) cell lines with tissue-specific or ubiquitous reporter genes are extremely useful for optimizing in vitro differentiation conditions as well as for monitoring transplanted cells in vivo. The adeno-associated virus integration site 1 (AAVS1) locus has been used as a "safe harbor" locus for inserting transgenes because of its open chromatin structure, which permits transgene expression without insertional mutagenesis. However, it is not clear whether targeted transgene expression at the AAVS1 locus is always protected from silencing when driven by various promoters, especially after differentiation and transplantation from hiPS cells. In this paper, we describe a pair of transcription activator-like effector nucleases (TALENs) that enable more efficient genome editing than the commercially available zinc finger nuclease at the AAVS1 site. Using these TALENs for targeted gene addition, we find that the cytomegalovirus-immediate early enhancer/chicken β-actin/rabbit β-globin (CAG) promoter is better than cytomegalovirus 7 and elongation factor 1α short promoters in driving strong expression of the transgene. The two independent AAVS1, CAG, and enhanced green fluorescent protein (EGFP) hiPS cell reporter lines that we have developed do not show silencing of EGFP either in undifferentiated hiPS cells or in randomly and lineage-specifically differentiated cells or in teratomas. Transplanting cardiomyocytes from an engineered AAVS1-CAG-EGFP hiPS cell line in a myocardial infarcted mouse model showed persistent expression of the transgene for at least 7 weeks in vivo. Our results show that high-efficiency targeting can be obtained with open-source TALENs and that careful optimization of the reporter and transgene constructs results in stable and persistent expression in vitro and in vivo.

Transplantation of photoreceptors derived from human Muller glia restore rod function in the P23H rat

Müller glia possess stem cell characteristics that have been recognized to be responsible for the regeneration of injured retina in fish and amphibians. Although these cells are present in the adult human eye, they are not known to regenerate human retina in vivo. Human Müller glia with stem cell characteristics (hMSCs) can acquire phenotypic and genotypic characteristics of rod photoreceptors in vitro, suggesting that they may have potential for use in transplantation strategies to treat human photoreceptor degenerations. Much work has been undertaken in rodents using various sources of allogeneic stem cells to restore photoreceptor function, but the effect of human Müller glia-derived photoreceptors in the restoration of rod photoreceptor function has not been investigated. This study aimed to differentiate hMSCs into photoreceptor cells by stimulation with growth and differentiation factors in vitro to upregulate gene and protein expression of CRX, NR2E3, and rhodopsin and various phototransduction markers associated with rod photoreceptor development and function and to examine the effect of subretinal transplantation of these cells into the P23H rat, a model of primary photoreceptor degeneration. Following transplantation, hMSC-derived photoreceptor cells migrated and integrated into the outer nuclear layer of the degenerated retinas and led to significant improvement in rod photoreceptor function as shown by an increase in a-wave amplitude and slope using scotopic flash electroretinography. These observations suggest that hMSCs can be regarded as a cell source for development of cell-replacement therapies to treat human photoreceptor degenerations and may also offer potential for the development of autologous transplantation.

Technological progress and challenges towards cGMP manufacturing of human pluripotent stem cells based therapeutic products for allogeneic and autologous cell therapies

Recent technological advances in the generation, characterization, and bioprocessing of human pluripotent stem cells (hPSCs) have created new hope for their use as a source for production of cell-based therapeutic products. To date, a few clinical trials that have used therapeutic cells derived from hESCs have been approved by the Food and Drug Administration (FDA), but numerous new hPSC-based cell therapy products are under various stages of development in cell therapy-specialized companies and their future market is estimated to be very promising. However, the multitude of critical challenges regarding different aspects of hPSC-based therapeutic product manufacturing and their therapies have made progress for the introduction of new products and clinical applications very slow. These challenges include scientific, technological, clinical, policy, and financial aspects. The technological aspects of manufacturing hPSC-based therapeutic products for allogeneic and autologous cell therapies according to good manufacturing practice (cGMP) quality requirements is one of the most important challenging and emerging topics in the development of new hPSCs for clinical use. In this review, we describe main critical challenges and highlight a series of technological advances in all aspects of hPSC-based therapeutic product manufacturing including clinical grade cell line development, large-scale banking, upstream processing, downstream processing, and quality assessment of final cell therapeutic products that have brought hPSCs closer to clinical application and commercial cGMP manufacturing.

hESC expansion and stemness are independent of connexin forty-three-mediated intercellular communication between hESCs and hASC feeder cells

Background

Human embryonic stem cells (hESCs) are a promising and powerful source of cells for applications in regenerative medicine, tissue engineering, cell-based therapies, and drug discovery. Many researchers have employed conventional culture techniques using feeder cells to expand hESCs in significant numbers, although feeder-free culture techniques have recently been developed. In regard to stem cell expansion, gap junctional intercellular communication (GJIC) is thought to play an important role in hESC survival and differentiation. Indeed, it has been reported that hESC-hESC communication through connexin 43 (Cx43, one of the major gap junctional proteins) is crucial for the maintenance of hESC stemness during expansion. However, the role of GJIC between hESCs and feeder cells is unclear and has not yet been reported.

Methodology/Principal Findings

This study therefore examined whether a direct Cx43-mediated interaction between hESCs and human adipose-derived stem cells (hASCs) influences the maintenance of hESC stemness. Over 10 passages, hESCs cultured on a layer of Cx43-downregulated hASC feeder cells showed normal morphology, proliferation (colony growth), and stemness, as assessed by alkaline phosphatase (AP), OCT4 (POU5F1-Human gene Nomenclature Database), SOX2, and NANOG expression.

Conclusions/Significance

These results demonstrate that Cx43-mediated GJIC between hESCs and hASC feeder cells is not an important factor for the conservation of hESC stemness and expansion.

A microfluidic impedance flow cytometer for identification of differentiation state of stem cells

This paper presents a microfluidic electrical impedance flow cytometer (FC) for identifying the differentiation state of single stem cells. This device is comprised of a novel dual micropore design, which not only enhances the processing throughput, but also allows the associated electrodes to be used as a reference for one another. A signal processing algorithm, based on the support vector machine (SVM) theory, and a data classification method were developed to automate the identification of sample types and cell differentiation state based on measured impedance values. The device itself was fabricated using a combination of standard and soft lithography techniques to generate a PDMS-gold electrode construct. Experimental testing with non-biological particles and mouse embryonic carcinoma cells (P19, undifferentiated and differentiated) was carried out using a range of excitation frequencies. The effects of the frequency and the interrogation parameters on sample identification performance were investigated. It was found that the real and imaginary part of the detected impedance signal were adequate for distinguishing the undifferentiated P19 cells from non-biological polystyrene beads at all tested frequencies. A higher frequency and an opacity index were required to resolve the undifferentiated and differentiated P19 cells by capturing capacitive changes in electrophysiological properties arising from differentiation. The experimental results demonstrated salient accuracy of the device and algorithm, and established its feasibility for non-invasive, label-free identification of the differentiation state of the stem cells.

Optimisation of a stirred bioreactor through the use of a novel holographic correlation velocimetry flow measurement technique

We describe a method for measuring three dimensional (3D) velocity fields of a fluid at high speed, by combining a correlation-based approach with in-line holography. While this method utilizes tracer particles contained within the flow, our method does not require the holographic reconstruction of 3D images. The direct flow reconstruction approach developed here allows for measurements at seeding densities in excess of the allowable levels for techniques based on image or particle reconstruction, thus making it suited for biological flow measurement, such as the flow in bioreactor. We outline the theory behind our method, which we term Holographic Correlation Velocimetry (HCV), and subsequently apply it to both synthetic and laboratory data. Moreover, because the system is based on in-line holography, it is very efficient with regard to the use of light, as it does not rely on side scattering. This efficiency could be utilized to create a very high quality system at a modest cost. Alternatively, this efficiency makes the system appropriate for high-speed flows and low exposure times, which is essential for imaging dynamic systems.

Cell based therapy in Parkinsonism

Parkinson's disease (PD) is a synucleinopathy-induced chronic progressive neurodegenerative disorder, worldwide affecting about 5 million humans. As of yet, actual therapies are symptomatic, and neuroprotective strategies are an unmet need. Due to their capability to transdifferentiate, to immune modulate and to increase neuroplasticity by producing neurotrophic factors, adult stem cells (ASC) might fill this gap. Preclinical research in 6-hydroxydopamine (6-OHDA) and/or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned animals established persistent improvements of motor behavior after ASC-treatment. Histological/histochemical measurements in these animals evidenced an intracerebral applied ASC-induced increase of Tyrosine Hydroxylase-positive (TH+) cells with increased striatal dopamine levels, suggesting cell rescue. Likewise, clinical experience with subventricular applied ASCs in PD patients, although limited, is encouraging, evidencing neurorescue especially during the early phase of the disease. In multiple system atrophy (MSA) or progressive supranuclear palsy (PSP) patients, though, only marginal reduced progression of natural progression could be established after subventricular or intravasal ASC implantations.

Immunoreactivity of Pluripotent Markers SSEA-5 and L1CAM in Human Tumors, Teratomas, and Induced Pluripotent Stem Cells

Pluripotent stem cell markers can be useful for diagnostic evaluation of human tumors. The novel pluripotent marker stage-specific embryonic antigen-5 (SSEA-5) is expressed in undifferentiated human induced pluripotent cells (iPSCs), but little is known about SSEA-5 expression in other primitive tissues (e.g., human tumors). We evaluated SSEA-5 immunoreactivity patterns in human tumors, cell lines, teratomas, and iPS cells together with another pluripotent cell surface marker L1 cell adhesion molecule (L1CAM). We tested two hypotheses: (1) SSEA-5 and L1CAM would be immunoreactive and colocalized in human tumors; (2) SSEA-5 and L1CAM immunoreactivity would persist in iPSCs following retinal differentiating treatment. SSEA-5 immunofluorescence was most pronounced in primitive tumors, such as embryonal carcinoma. In tumor cell lines, SSEA-5 was highly immunoreactive in Capan-1 cells, while L1CAM was highly immunoreactive in U87MG cells. SSEA-5 and L1CAM showed colocalization in undifferentiated iPSCs, with immunopositive iPSCs remaining after 20 days of retinal differentiating treatment. This is the first demonstration of SSEA-5 immunoreactivity in human tumors and the first indication of SSEA-5 and L1CAM colocalization. SSEA-5 and L1CAM warrant further investigation as potentially useful tumor markers for histological evaluation or as markers to monitor the presence of undifferentiated cells in iPSC populations prior to therapeutic use.

Transforming pluripotency: an exon-level study of malignancy-specific transcripts in human embryonal carcinoma and embryonic stem cells

To circumvent difficulties of isolating pure populations of cancer stem cells (CSCs) for the purpose of identifying malignancy-specific gene expression, we have compared exon-resolution transcriptomic profiles of 5 embryonal carcinoma (EC) cell lines, a histological subtype of germ cell tumor (GCT), to their nonmalignant caricature, specifically 6 human embryonic stem (ES) cell lines. Both cell types are readily accessible, and were purified for undifferentiated cells only. We identified a set of 28 differentially expressed genes, many of which had cancer and stemness roles. Overexpression of the recently discovered pluripotency gene NR5A2 in malignant EC cells revealed an intriguing indication of how WNT-mediated dysregulation of pluripotency is involved with malignancy. Expression of these 28 genes was further explored within 2 publically available data sets of primary EC tumors and normal testis. At the exon-level, alternative splicing events were detected in ZNF195, DNMT3B, and PMF1, and alternative promoters were detected for ASH2L and ETV5. These events were validated by reverse transcriptase-polymerase chain reaction-based methods in EC and ES lines, where the alternative splicing event in the de novo DNA methyltransferase DNMT3B may have functional consequences. In conclusion, we have identified malignancy-specific gene expression differences within a rigorous pluripotent stem cell context. These findings are of particular interest for both GCT and ES cell biology, and, in general, to the concept of CSCs.

Modification of a purification and expansion method for human embryonic stem cell-derived cardiomyocytes

OBJECTIVE

This study aimed to develop a simple and efficient purification method for human embryonic stem cell (hESC)-derived cardiomyocytes (CMs) using a low-glucose culture system. In addition, we investigated whether intercellular adhesion between single hESC-CMs plays a critical role in enhancing proliferation of purified hESC-CMs.

METHOD

hESCs were cultured in suspension to form human embryoid bodies (hEBs) from which ∼15% contracting clusters were derived after 15-20 days in culture. To purify CMs from contracting hEBs, we first manually isolated contracting clumps that were re-cultured on gelatin-coated plates with media containing a low concentration of glucose. The purified hESC-CMs were cultured at different densities to examine whether cell-cell contact enhances proliferation of hESC-CMs.

RESULTS

Purified CMs demonstrated spontaneous contraction and strongly expressed the CM-specific markers cardiac troponin T and slow myosin heavy chain. We investigated the purification efficiency by examining the expression levels of cardiac-related genes and the expression of MitoTracker Red dye. In addition, purified hESC-CMs in low-glucose culture demonstrated a 1.5-fold increase in their proliferative capacity compared to those cultured as single hESC-CMs.

CONCLUSION

A low level of glucose is efficient in purifying hESC-CMs and intercellular adhesion between individual hESC-CMs plays a critical role in enhancing hESC-CM proliferation.

Recent Advances towards the Clinical Application of Stem Cells for Retinal Regeneration

Retinal degenerative diseases constitute a major cause of irreversible blindness in the world. Stem cell-based therapies offer hope for these patients at risk of or suffering from blindness due to the deterioration of the neural retina. Various sources of stem cells are currently being investigated, ranging from human embryonic stem cells to adult-derived induced pluripotent stem cells as well as human Müller stem cells, with the first clinical trials to investigate the safety and tolerability of human embryonic stem cell-derived retinal pigment epithelium cells having recently commenced. This review aims to summarize the latest advances in the development of stem cell strategies for the replacement of retinal neurons and their supportive cells, the retinal pigment epithelium (RPE) affected by retinal degenerative conditions. Particular emphasis will be given to the advances in stem cell transplantation and the challenges associated with their translation into clinical practice.

Teratocarcinoma Formation in Embryonic Stem Cell-Derived Neural Progenitor Hippocampal Transplants

Embryonic stem cells (ESCs) hold great therapeutic potential due to their ability to differentiate into cells of the three primary germ layers, which can be used to repopulate disease-damaged tissues. In fact, two cell therapies using ESC derivatives are currently in phase I clinical trials. A main concern in using ESCs and their derivatives for cell transplantation is the ability of undifferentiated ESCs to generate tumors in the host. Positive selection steps are often included in protocols designed to generate particular cell types from ESCs; however, the transition from ESC to progenitor cell or terminally differentiated cell is not synchronous, and residual undifferentiated cells often remain. In our transplants of ESC-derived neural progenitors (ESNPs) into the adult mouse hippocampus, we have observed the formation of teratocarcinomas. We set out to reduce teratocarcinoma formation by enrichment of ESNPs using fluorescence-activated cell sorting (FACS) and have found that, although enrichment prior to transplant reduces the overall rate of teratocarcinoma formation, the tumorigenicity of cell batches can vary widely, even after FACS enrichment to as much as 95% ESNPs. Our data suggest that this variability may be due to the percentage of residual ESCs remaining in the transplant cell population and to the presence of pluripotent epiblast-like cells, not previously identified in transplant batches. Our data emphasize the need for stringent characterization of transplant cell populations that will be used for cell replacement therapies in order to reduce the risk of tumor formation.

A review and update on the current status of stem cell therapy and the retina

INTRODUCTION OR BACKGROUND

Many diseases of the retina result in irreversible visual loss. Stem cell (SC) therapy is a rapidly developing field and represents a novel approach to replace non-functioning neuro-retinal cells.

SOURCES OF DATA

A systematic computerized literature search was conducted on PubMed (http://www.ncbi.nlm.nih.gov/pubmed/).

AREAS OF AGREEMENT

The use of stem cells (SCs) in animal models of retinal diseases has resulted in improvement in visual function and performance. SC therapy represents an exciting prospect in restoring vision. Areas of controversy The use of human embryonic SCs raises ethical concerns.

GROWING POINTS

Human trials using SCs in retinal diseases have recently been approved.

AREAS TIMELY FOR DEVELOPING RESEARCH

The success of SCs in retinal therapy depends not only on implanted cell survival, but also on how well SCs migrate, integrate and form synapses. Further research will be needed to overcome these hurdles.

Process engineering of human pluripotent stem cells for clinical application

Human pluripotent stem cells (hPSCs), including embryonic and induced pluripotent stem cells, constitute an extremely attractive tool for cell therapy. However, flexible platforms for the large-scale production and storage of hPSCs in tightly controlled conditions are necessary to deliver high-quality cells in relevant quantities to satisfy clinical demands. Here we discuss the main principles for the bioprocessing of hPSCs, highlighting the impact of environmental factors, novel 3D culturing approaches and integrated bioreactor strategies for controlling hPSC culture outcome. Knowledge on hPSC bioprocessing accumulated during recent years provides important insights for the establishment of more robust production platforms and should potentiate the implementation of novel hPSC-based therapies.

[Embryonic stem cells in the treatment of severe cardiac insufficiency]

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which optimizing cardiac specification of the embryonic stem cells, purifying the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis and controlling the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a pre-requisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Embryonic stem cells for severe heart failure: why and how?

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which the optimization of the cardiac specification of the embryonic stem cells, the purification of the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis, and the control of the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a prerequisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted, and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Empowering adult stem cells for myocardial regeneration

Treatment strategies for heart failure remain a high priority for ongoing research due to the profound unmet need in clinical disease coupled with lack of significant translational progress. The underlying issue is the same whether the cause is acute damage, chronic stress from disease, or aging: progressive loss of functional cardiomyocytes and diminished hemodynamic output. To stave off cardiomyocyte losses, a number of strategic approaches have been embraced in recent years involving both molecular and cellular approaches to augment myocardial structure and performance. Resultant excitement surrounding regenerative medicine in the heart has been tempered by realizations that reparative processes in the heart are insufficient to restore damaged myocardium to normal functional capacity and that cellular cardiomyoplasty is hampered by poor survival, proliferation, engraftment, and differentiation of the donated population. To overcome these limitations, a combination of molecular and cellular approaches must be adopted involving use of genetic engineering to enhance resistance to cell death and increase regenerative capacity. This review highlights biological properties of approached to potentiate stem cell-mediated regeneration to promote enhanced myocardial regeneration, persistence of donated cells, and long-lasting tissue repair. Optimizing cell delivery and harnessing the power of survival signaling cascades for ex vivo genetic modification of stem cells before reintroduction into the patient will be critical to enhance the efficacy of cellular cardiomyoplasty. Once this goal is achieved, then cell-based therapy has great promise for treatment of heart failure to combat the loss of cardiac structure and function associated with acute damage, chronic disease, or aging.

Preconditioning approach in stem cell therapy for the treatment of infarcted heart

Nearly two decades of research in regenerative medicine have been focused on the development of stem cells as a therapeutic option for treatment of the ischemic heart. Given the ability of stem cells to regenerate the damaged tissue, stem-cell-based therapy is an ideal approach for cardiovascular disorders. Preclinical studies in experimental animal models and clinical trials to determine the safety and efficacy of stem cell therapy have produced encouraging results that promise angiomyogenic repair of the ischemically damaged heart. Despite these promising results, stem cell therapy is still confronted with issues ranging from uncertainty about the as-yet-undetermined "ideal" donor cell type to the nonoptimized cell delivery strategies to harness optimal clinical benefits. Moreover, these lacunae have significantly hampered the progress of the heart cell therapy approach from bench to bedside for routine clinical applications. Massive death of donor cells in the infarcted myocardium during acute phase postengraftment is one of the areas of prime concern, which immensely lowers the efficacy of the procedure. An overview of the published data relevant to stem cell therapy is provided here and the various strategies that have been adopted to develop and optimize the protocols to enhance donor stem cell survival posttransplantation are discussed, with special focus on the preconditioning approach.

Musashi1 expression cells derived from mouse embryonic stem cells can be enriched in side population isolated by fluorescence activated cell sorter

Background

Purifying stem cells is an inevitable process for further investigation and cell-therapy. Sorting side population (SP) cells is generally regarded as an effective method to enrich for progenitor cells. This study was to explore whether sorting SP could enrich for the Musashi1 (Msi1) positive cells from Msi1 high expression cells (Msi1^high cells) derived from mouse embryonic stem cells (ESCs) in vitro.

Results

In this study, Msi1^high cell population derived from ESCs were stained by Hoechst 33342, and then the SP and non-SP (NSP) fractions were analyzed and sorted by fluorescence activated cell sorter. Subsequently, the expressions of Msi1 and other markers for neural and intestinal stem cells in SP and NSP were respectively detected. SP and NSP cells were hypodermically engrafted into the backs of NOD/SCID mice to form grafts. The developments of neural and intestinal epithelial cells in these grafts were investigated. SP fraction was identified and isolated from Msi1^high cell population. The expression of Msi1 in SP fraction was significantly higher than that in NSP fraction and unsorted Msi1^high cells (P< 0.05). Furthermore, the markers for neural cells and intestinal epithelial cells were more highly expressed in the grafts from SP fraction than those from NSP fraction (P< 0.05).

Conclusions

SP fraction, isolated from Msi1^high cells, contains almost all the Msi1-positive cells and has the potential to differentiate into neural and intestinal epithelial cells in vivo. Sorting SP fraction could be a convenient and practical method to enrich for Msi1-positive cells from the differentiated cell population derived from ESCs.

Cell therapy for multiple sclerosis

The spontaneous recovery observed in the early stages of multiple sclerosis (MS) is substituted with a later progressive course and failure of endogenous processes of repair and remyelination. Although this is the basic rationale for cell therapy, it is not clear yet to what degree the MS brain is amenable for repair and whether cell therapy has an advantage in comparison to other strategies to enhance endogenous remyelination. Central to the promise of stem cell therapy is the therapeutic plasticity, by which neural precursors can replace damaged oligodendrocytes and myelin, and also effectively attenuate the autoimmune process in a local, nonsystemic manner to protect brain cells from further injury, as well as facilitate the intrinsic capacity of the brain for recovery. These fundamental immunomodulatory and neurotrophic properties are shared by stem cells of different sources. By using different routes of delivery, cells may target both affected white matter tracts and the perivascular niche where the trafficking of immune cells occur. It is unclear yet whether the therapeutic properties of transplanted cells are maintained with the duration of time. The application of neural stem cell therapy (derived from fetal brain or from human embryonic stem cells) will be realized once their purification, mass generation, and safety are guaranteed. However, previous clinical experience with bone marrow stromal (mesenchymal) stem cells and the relative easy expansion of autologous cells have opened the way to their experimental application in MS. An initial clinical trial has established the probable safety of their intravenous and intrathecal delivery. Short-term follow-up observed immunomodulatory effects and clinical benefit justifying further clinical trials.

Plasticity of cells and ex vivo production of red blood cells

The supply of transfusable red blood cells (RBCs) is not sufficient in many countries. If transfusable RBCs could be produced abundantly from certain resources, it would be very useful. Our group has developed a method to produce enucleated RBCs efficiently from hematopoietic stem/progenitor cells present in umbilical cord blood. More recently, it was reported that enucleated RBCs could be abundantly produced from human embryonic stem (ES) cells. The common obstacle for application of these methods is that they require very high cost to produce sufficient number of RBCs that are applicable in the clinic. If erythroid cell lines (immortalized cell lines) able to produce transfusable RBCs ex vivo were established, they would be valuable resources. Our group developed a robust method to obtain immortalized erythroid cell lines able to produce mature RBCs. To the best of our knowledge, this was the first paper to show the feasibility of establishing immortalized erythroid progenitor cell lines able to produce enucleated RBCs ex vivo. This result strongly suggests that immortalized human erythroid progenitor cell lines able to produce mature RBCs ex vivo can also be established.

Real-time monitoring of neural differentiation of human mesenchymal stem cells by electric cell-substrate impedance sensing

Stem cells are useful for cell replacement therapy. Stem cell differentiation must be monitored thoroughly and precisely prior to transplantation. In this study we evaluated the usefulness of electric cell-substrate impedance sensing (ECIS) for in vitro real-time monitoring of neural differentiation of human mesenchymal stem cells (hMSCs). We cultured hMSCs in neural differentiation media (NDM) for 6 days and examined the time-course of impedance changes with an ECIS array. We also monitored the expression of markers for neural differentiation, total cell count, and cell cycle profiles. Cellular expression of neuron and oligodendrocyte markers increased. The resistance value of cells cultured in NDM was automatically measured in real-time and found to increase much more slowly over time compared to cells cultured in non-differentiation media. The relatively slow resistance changes observed in differentiating MSCs were determined to be due to their lower growth capacity achieved by induction of cell cycle arrest in G0/G1. Overall results suggest that the relatively slow change in resistance values measured by ECIS method can be used as a parameter for slowly growing neural-differentiating cells. However, to enhance the competence of ECIS for in vitro real-time monitoring of neural differentiation of MSCs, more elaborate studies are needed.

[Stem cells in the amniotic fluid: the new chance of regenerative medicine]

Amniotic fluid has been used in prenatal diagnosis for more than decades. It yields a simple and reliable screening and diagnostic tool for a variety of congenital malformations and genetic diseases such as chromosomal aberrations, neural tube defects or storage diseases. Nowadays the widening knowledge provides evidence that amniotic fluid is not only a screening and diagnostic tool, but it may be also the source of the effective therapy of several congenital and adult disorders. A subset of cells, the so-called stem cells were found in the amniotic fluid as well as the placenta, and they proved to be capable of maintaining prolonged undifferentiated proliferation. Stem cells are able to differentiate into multiple tissue types, originating from the three germ layers. In the near future stem cells isolated from amniotic fluid or placenta and stored by cryopreservation may play a significant role in regenerative medicine. Congenital malformations as well as certain diseases in adults might be treated by tissues coming from progenitor cells of amniotic fluid stem cell origin. This study gives a summary of the main characteristics of amniotic fluid stem cells and it also presents important examples of their possible clinical application.

The tumorigenicity of human embryonic and induced pluripotent stem cells

The unique abilities of human pluripotent stem cells to self-renew and to differentiate into cells of the three germ layers make them an invaluable tool for the future of regenerative medicine. However, the same properties also make them tumorigenic, and therefore hinder their clinical application. Hence, the tumorigenicity of human embryonic stem cells (HESCs) has been extensively studied. Until recently, it was assumed that human induced pluripotent stem cells (HiPSCs) would behave like their embryonic counterparts in respect to their tumorigenicity. However, a rapidly accumulating body of evidence suggests that there are important genetic and epigenetic differences between these two cell types, which seem to influence their tumorigenicity.

Cytotoxic antibody fragments for eliminating undifferentiated human embryonic stem cells

Human embryonic stem cells (hESC) possess great potential for applications in regenerative medicine due to their ability to differentiate into any cell type in the body. However, it is crucial to remove residual undifferentiated hESC from the differentiated population to avoid teratoma formation in vivo. The monoclonal antibody, mAb 84, has been shown to bind and kill undifferentiated hESC and is very useful for the elimination of contaminating undifferentiated hESC prior to transplantation. As mAb 84 is an IgM, its large size may impede penetration into embryoid bodies (EB) or cell clumps. To improve penetration, four antibody fragment formats of mAb 84 were engineered and expressed in Escherichia coli: Fab 84, scFv 84, scFv 84-diabody and scFv 84-HTH. All 4 fragments bound specifically to hESC, but only scFv 84-HTH, a single chain variable fragment with a dimerizing helix-turn-helix motif, could recapitulate the cytotoxicity of mAb 84 on multiple hESC lines. The results suggest that multivalency and flexibility between the antigen-binding sites may be essential features required for killing of hESC by mAb 84 and its derivatives. Imaging of EB treated with scFv 84-HTH or mAb 84 showed an even distribution of scFv 84-HTH throughout the EB whereas mAb 84 was localized more to the periphery.

The Janus face of pluripotent stem cells--connection between pluripotency and tumourigenicity

Pluripotent stem cells have gained special attraction because of their almost unlimited proliferation and differentiation capacity in vitro. These properties substantiate the potential of pluripotent stem cells in basic research and regenerative medicine. Here three types of in vitro cultured pluripotent stem cells (embryonic carcinoma, embryonic stem and induced pluripotent stem cells) are compared in their historical context with respect to their different origin and properties. It became evident that tumourigenicity is an inherent property of pluripotent cells based on p53 down-regulation, expression of tumour-related genes and high telomerase activity that allow unlimited proliferation. In addition, culture-adapted genetic and epigenetic changes may induce tumourigenicity of pluripotent cells. The use of stem cells in regenerative medicine, however, requires non-malignant cell types and strategies that circumvent stages of malignancy.Reprogramming strategies of adult somatic cells that avoid the tumourigenic state of pluripotency may offer alternatives for future biomedical application.

Embryonic stem cells in non-human primates: An overview of neural differentiation potential

Non-human primate (NHP) embryonic stem (ES) cells show unlimited proliferative capacities and a great potential to generate multiple cell lineages. These properties make them an ideal resource both for investigating early developmental processes and for assessing their therapeutic potential in numerous models of degenerative diseases. They share the same markers and the same properties with human ES cells, and thus provide an invaluable transitional model that can be used to address the safety issues related to the clinical use of human ES cells. Here, we review the available information on the derivation and the specific features of monkey ES cells. We comment on the capacity of primate ES cells to differentiate into neural lineages and the current protocols to generate self-renewing neural stem cells. We also highlight the signalling pathways involved in the maintenance of these neural cell types. Finally, we discuss the potential of monkey ES cells for neuronal differentiation.

Induced differentiation of neural stem cells of astrocytic origin to motor neurons in the rat

Destruction of the motor neurons will lead to loss of innervation of the somatic muscle, which has long been considered an illness with no remedy. The only possible treatment is to substitute the injured motor neurons by neurons differentiated from stem cells. It has been recently reported that embryonic stems cells can be induced to differentiate to motor neurons. However, the use of embryonic stem cells has innate problems. The ideal source of motor neurons should be the cells from the patients themselves, which have the potential to be induced to motor neurons. Our previous study demonstrated that mature astrocyte has the potential of being dedifferentiated to neural stem cell. The present study was aimed to investigate if the neural stem cells of astrocytic origin can be induced to motor neurons. The results demonstrated that neural stem cells of astrocytic origin could be induced to differentiate into motor neurons and their progenitor cells with rich harvest. Further, it has been reported that astrocytes can be readily obtained via biopsy from the cerebral cortex of the patient, rendering autologous transplantation possible. In conclusion, matured astrocytes can be induced to motor neurons and be autologously transplanted to patients suffering from motor neuron destruction.

Red blood cell production from immortalized progenitor cell line

The supply of transfusable red blood cells (RBCs) is not sufficient in many countries. If immortalized erythroid progenitor cell lines able to produce transfusable RBCs in vitro were established, they would be valuable resources. However, such cell lines have not been established. We have developed a robust method to establish immortalized erythroid progenitor cell lines following the induction of hematopoietic differentiation of mouse embryonic stem (ES) cells and have established many immortalized erythroid progenitor cell lines so far. Although their precise characteristics varied among cell lines, each of these lines could differentiate in vitro into more mature erythroid cells, including enucleated RBCs. Following transplantation of these erythroid cells into mice suffering from acute anemia, the cells proliferated transiently, subsequently differentiated into functional RBCs, and significantly ameliorated the acute anemia. Considering the number of human ES cell lines that have been established so far and the number of induced pluripotent stem cell lines that will be established in future, the intensive testing of a number of these lines for establishing immortalized erythroid progenitor cell lines may allow the establishment of such cell lines similar to the mouse erythroid progenitor cell lines.

Current approaches and future prospects for stem cell rescue and regeneration of the retina and optic nerve

The 3 most common causes of visual impairment and legal blindness in developed countries (age-related macular degeneration, glaucoma, and diabetic retinopathy) share 1 end point: the loss of neural cells of the eye. Although recent treatment advances can slow down the progression of these conditions, many individuals still suffer irreversible loss of vision. Research is aimed at developing new treatment strategies to rescue damaged photoreceptors and retinal ganglion cells (RGC) and to replace lost cells by transplant. The neuroprotective and regenerative potential of stem and progenitor cells from a variety of sources has been explored in models of retinal disease and ganglion cell loss. Continuous intraocular delivery of neurotrophic factors via stem cells (SC) slows down photoreceptor cells and RGC loss in experimental models. Following intraocular transplantation, SC are capable of expressing proteins and of developing a morphology characteristic of photoreceptors or RGC. Recently, recovery of vision has been achieved for the first time in a rodent model of retinal dystrophy, using embryonic SC differentiated into photoreceptors prior to transplant. This indicates that clinically significant synapse formation and acquisition of the functional properties of retinal neurons, and restoration of vision, are distinct future possibilities.

Therapeutic liver reconstitution with murine cells isolated long after death

BACKGROUND & AIMS

Due to the shortage of donor organs, many patients needing liver transplantation cannot receive one. For some liver diseases, hepatocyte transplantation could be a viable alternative, but donor cells currently are procured from the same sources as whole organs, and thus the supply is severely limited.

METHODS

Here, we investigated the possibility of isolating viable hepatocytes for liver cell therapy from the plentiful source of morgue cadavers. To determine the utility of this approach, cells were isolated from the livers of non-heart-beating cadaveric mice long after death and transplanted into fumarylacetoacetate hydrolase-deficient mice, a model for the human metabolic liver disease hereditary tyrosinemia type I and a stringent in vivo model for hepatic cell transplantation.

RESULTS

Surprisingly, complete and therapeutic liver repopulation could be achieved with hepatocytes derived up to 27 hours post mortem.

CONCLUSIONS

Competitive repopulation experiments showed that cadaveric liver cells had a repopulation capacity similar to freshly isolated hepatocytes. Importantly, viable hepatocytes also could be isolated from cadaveric primate liver (monkey and human) efficiently. These data provide evidence that non-heart-beating donors could be a suitable source of hepatocytes for much longer time periods than previously thought possible.

Adult retinal stem cells revisited

Recent advances in retinal stem cell research have raised the possibility that these cells have the potential to be used to repair or regenerate diseased retina. Various cell sources for replacement of retinal neurons have been identified, including embryonic stem cells, the adult ciliary epithelium, adult Müller stem cells and induced pluripotent stem cells (iPS). However, the true stem cell nature of the ciliary epithelium and its possible application in cell therapies has now been questioned, leaving other cell sources to be carefully examined as potential candidates for such therapies. The need for identification of the ontogenetic state of grafted stem cells in order to achieve their successful integration into the murine retina has been recognized. However, it is not known whether the same requirements may apply to achieve transplant cell integration into the adult human eye. In addition, the existence of natural barriers for stem cell transplantation, including microglial accumulation and abnormal extracellular matrix deposition have been demonstrated, suggesting that several obstacles need to be overcome before such therapies may be implemented. This review addresses recent scientific developments in the field and discusses various strategies that may be potentially used to design cell based therapies to treat human retinal disease.

Regulatory considerations for the development of autologous induced pluripotent stem cell therapies

Induced pluripotent stem (iPS) cells offer tremendous opportunity for the creation of autologous cellular therapies, in which gene correction or the avoidance of immune response issues are desirable. In addition, iPS cells avoid the ethical concerns raised by the sourcing of human embryonic stem cells (hESCs) from embryos. iPS cells share many characteristics with hESCs and it is anticipated that existing experience with hESCs will translate to rapid progress in moving iPS cell-derived products toward clinical trials. While the potential clinical value for these products is considerable, the nature of current manufacturing paradigms for autologous iPS cell products raises considerable regulatory concerns. Here, the regulatory challenges posed by autologous iPS cell-derived products are examined. We conclude that there will be considerable regulatory concerns primarily relating to reproducibility of the manufacturing process and safety testing within clinically limited time constraints. Demonstrating safety of the final cell product in an autologous setting will be the single greatest obstacle to progressing autologous iPS cell-based therapies into the clinic.

Progenitor cells for regenerative medicine and consequences of ART and cloning-associated epimutations

The "holy grail" of regenerative medicine is the identification of an undifferentiated progenitor cell that is pluripotent, patient specific, and ethically unambiguous. Such a progenitor cell must also be able to differentiate into functional, transplantable tissue, while avoiding the risks of immune rejection. With reports detailing aberrant genomic imprinting associated with assisted reproductive technologies (ART) and reproductive cloning, the idea that human embryonic stem cells (hESCs) derived from surplus in vitro fertilized embryos or nuclear transfer ESCs (ntESCs) harvested from cloned embryos may harbor dangerous epigenetic errors has gained attention. Various progenitor cell sources have been proposed for human therapy, from hESCs to ntESCs, and from adult stem cells to induced pluripotent stem cells (iPS and piPS cells). This review highlights the advantages and disadvantages of each of these technologies, with particular emphasis on epigenetic stability.

Human embryonic stem cell differentiation on periodontal ligament fibroblasts

Human embryonic stem cells' (hESCs) unlimited proliferative potential and differentiation capability to all somatic cell types made them potential cell source in different cell-based tissue engineering strategies as well as various experimental applications in fields such as developmental biology, pharmacokinetics, toxicology, and genetics. Periodontal tissue engineering aims to improve the outcome of regenerative therapies which have variable success rates when contemporary techniques are used. Cell-based therapies may offer potential advantage in overcoming the inherent limitations associated with guided tissue-regeneration procedures, such as dependency on defect type and size and the pool and capacity of progenitor cells resident in the wound area. Elucidation of developmental mechanisms of different periodontal tissues may also contribute to valuable knowledge based upon which the future therapies can be designed. Prior to the realization of such a potential, protocols for the differentiation of pluripotent hESCs into periodontal ligament fibroblastic cells (PDLF) as common progenitors for ligament, cementum, and alveolar bone tissue need to be developed. The present protocol describes methods associated with the guided differentiation of hESCs by the use of coculture with adult PDLFs, and the resulting change of morphotype and phenotype of the pluripotent embryonic stem cells toward fibroblastic and osteoblastic lineages.

Induced human pluripotent stem cells: promises and open questions

Adult cells have been reprogrammed into induced pluripotent stem (iPS) cells by introducing pluripotency-associated transcription factors. Here, we discuss recent advances and challenges of in vitro reprogramming and future prospects of iPS cells for their use in diagnosis and cell therapy. The generation of patient-specific iPS cells for clinical application requires alternative strategies, because genome-integrating viral vectors may cause insertional mutagenesis. Moreover, when suitable iPS cell lines will be available, efficient and selective differentiation protocols are needed to generate transplantable grafts. Finally, we point to the requirement of a regulatory framework necessary for the commercial use of iPS cells.