Ruth Olmer

Generation of Induced Pluripotent Stem Cells from Human Cord Blood

Induced pluripotent stem cells (iPSCs) may represent an ideal cell source for future regenerative therapies. A critical issue concerning the clinical use of patient-specific iPSCs is the accumulation of mutations in somatic (stem) cells over an organisms lifetime. Acquired somatic mutations are passed onto iPSCs during reprogramming and may be associated with loss of cellular functions and cancer formation. Here we report the generation of human iPSCs from cord blood (CB) as a juvenescent cell source. CBiPSCs show characteristics typical of embryonic stem cells and can be differentiated into derivatives of all three germ layers, including functional cardiomyocytes. For future therapeutic production of autologous and allogeneic iPSC derivatives, CB could be routinely harvested for public and commercial CB banks without any donor risk. CB could readily become available for pediatric patients and, in particular, for newborns with genetic diseases or congenital malformations.

Scalable expansion of human pluripotent stem cells in suspension culture

Routine commercial and clinical applications of human pluripotent stem cells (hPSCs) and their progenies will require increasing cell quantities that cannot be provided by conventional adherent culture technologies. Here we describe a straightforward culture protocol for the expansion of undifferentiated human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) in suspension culture. This culture technique was successfully tested on two hiPSC clones, three hESC lines and on a nonhuman primate ESC line. It is based on a defined medium and single-cell inoculation, but it does not require culture preadaptation, use of microcarriers or any other matrices. Over a time course of 4–7 d, hPSCs can be expanded up to sixfold. Preparation of a high-density culture and its subsequent translation to scalable stirred suspension in Erlenmeyer flasks and stirred spinner flasks are also feasible. Importantly, hPSCs maintain pluripotency and karyotype stability for more than ten passages.

Long term expansion of undifferentiated human iPS and ES cells in suspension culture using a defined medium.

Therapeutic application of stem cell derivatives requires large quantities of cells produced in defined media that cannot be produced via conventional adherent culture. We have applied human induced pluripotent stem (hiPS) cells expressing eGFP under control of the OCT4 promoter to establish the expansion of undifferentiated human embryonic stem (hES) and hiPS cells in suspension culture. A defined culture medium has been identified that results in up to six-fold increase in cell numbers within four days. Our culture system is based on initial single cell dissociation which is critical for standardized process inoculation. HES / hiPS cells were expanded for up to 17 passages. The cells maintained a stable karyotype, their expression of pluripotency markers and their potential to differentiate into derivatives of all three germ layers. The ability to expand HES / hiPS cells in a scalable suspension culture represents a critical step towards standardized production in stirred bioreactors.

Transplantation and tracking of human-induced pluripotent stem cells in a pig model of myocardial infarction: assessment of cell survival, engraftment, and distribution by hybrid single photon emission computed tomography/computed tomography of sodium iodide symporter transgene expression

Background— Evaluation of novel cellular therapies in large-animal models and patients is currently hampered by the lack of imaging approaches that allow for long-term monitoring of viable transplanted cells. In this study, sodium iodide symporter (NIS) transgene imaging was evaluated as an approach to follow in vivo survival, engraftment, and distribution of human-induced pluripotent stem cell (hiPSC) derivatives in a pig model of myocardial infarction. Methods and Results— Transgenic hiPSC lines stably expressing a fluorescent reporter and NIS (NISpos-hiPSCs) were established. Iodide uptake, efflux, and viability of NISpos-hiPSCs were assessed in vitro. Ten (±2) days after induction of myocardial infarction by transient occlusion of the left anterior descending artery, catheter-based intramyocardial injection of NISpos-hiPSCs guided by 3-dimensional NOGA mapping was performed. Dual-isotope single photon emission computed tomographic/computed tomographic imaging was applied with the use of 123I to follow donor cell survival and distribution and with the use of 99mTC-tetrofosmin for perfusion imaging. In vitro, iodide uptake in NISpos-hiPSCs was increased 100-fold above that of nontransgenic controls. In vivo, viable NISpos-hiPSCs could be visualized for up to 15 weeks. Immunohistochemistry demonstrated that hiPSC-derived endothelial cells contributed to vascularization. Up to 12 to 15 weeks after transplantation, no teratomas were detected. Conclusions— This study describes for the first time the feasibility of repeated long-term in vivo imaging of viability and tissue distribution of cellular grafts in large animals. Moreover, this is the first report demonstrating vascular differentiation and long-term engraftment of hiPSCs in a large-animal model of myocardial infarction. NISpos-hiPSCs represent a valuable tool to monitor and improve current cellular treatment strategies in clinically relevant animal models.Background— Evaluation of novel cellular therapies in large-animal models and patients is currently hampered by the lack of imaging approaches that allow for long-term monitoring of viable transplanted cells. In this study, sodium iodide symporter (NIS) transgene imaging was evaluated as an approach to follow in vivo survival, engraftment, and distribution of human-induced pluripotent stem cell (hiPSC) derivatives in a pig model of myocardial infarction. Methods and Results— Transgenic hiPSC lines stably expressing a fluorescent reporter and NIS (NISpos-hiPSCs) were established. Iodide uptake, efflux, and viability of NISpos-hiPSCs were assessed in vitro. Ten (±2) days after induction of myocardial infarction by transient occlusion of the left anterior descending artery, catheter-based intramyocardial injection of NISpos-hiPSCs guided by 3-dimensional NOGA mapping was performed. Dual-isotope single photon emission computed tomographic/computed tomographic imaging was applied with the use of 123I to follow donor cell survival and distribution and with the use of 99mTC-tetrofosmin for perfusion imaging. In vitro, iodide uptake in NISpos-hiPSCs was increased 100-fold above that of nontransgenic controls. In vivo, viable NISpos-hiPSCs could be visualized for up to 15 weeks. Immunohistochemistry demonstrated that hiPSC-derived endothelial cells contributed to vascularization. Up to 12 to 15 weeks after transplantation, no teratomas were detected. Conclusions— This study describes for the first time the feasibility of repeated long-term in vivo imaging of viability and tissue distribution of cellular grafts in large animals. Moreover, this is the first report demonstrating vascular differentiation and long-term engraftment of hiPSCs in a large-animal model of myocardial infarction. NISpos-hiPSCs represent a valuable tool to monitor and improve current cellular treatment strategies in clinically relevant animal models. # Clinical Perspective {#article-title-36}

Controlling Expansion and Cardiomyogenic Differentiation of Human Pluripotent Stem Cells in Scalable Suspension Culture

Summary To harness the potential of human pluripotent stem cells (hPSCs), an abundant supply of their progenies is required. Here, hPSC expansion as matrix-independent aggregates in suspension culture was combined with cardiomyogenic differentiation using chemical Wnt pathway modulators. A multiwell screen was scaled up to stirred Erlenmeyer flasks and subsequently to tank bioreactors, applying controlled feeding strategies (batch and cyclic perfusion). Cardiomyogenesis was sensitive to the GSK3 inhibitor CHIR99021 concentration, whereas the aggregate size was no prevailing factor across culture platforms. However, in bioreactors, the pattern of aggregate formation in the expansion phase dominated subsequent differentiation. Global profiling revealed a culture-dependent expression of BMP agonists/antagonists, suggesting their decisive role in cell-fate determination. Furthermore, metallothionein was discovered as a potentially stress-related marker in hPSCs. In 100 ml bioreactors, the production of 40 million predominantly ventricular-like cardiomyocytes (up to 85% purity) was enabled that were directly applicable to bioartificial cardiac tissue formation.

Cardiac differentiation of human pluripotent stem cells in scalable suspension culture.

Cardiomyocytes (CMs) generated from human pluripotent stem cells (hPSCs) are a potential cell source for regenerative therapies, drug discovery and disease modeling. All these applications require a routine supply of relatively large quantities of in vitro–generated CMs. This protocol describes a suspension culture–based strategy for the generation of hPSC-CMs as cell-only aggregates, which facilitates process development and scale-up. Aggregates are formed for 4 d in hPSC culture medium followed by 10 d of directed differentiation by applying chemical Wnt pathway modulators. The protocol is applicable to static multiwell formats supporting fast adaptation to specific hPSC line requirements. We also demonstrate how to apply the protocol using stirred tank bioreactors at a 100-ml scale, providing a well-controlled upscaling platform for CM production. In bioreactors, the generation of 40–50 million CMs per differentiation batch at >80% purity without further lineage enrichment can been achieved within 24 d.

Cleavage of E-Cadherin and β-Catenin by Calpain Affects Wnt Signaling and Spheroid Formation in Suspension Cultures of Human Pluripotent Stem Cells

The envisioned clinical and industrial use of human pluripotent stem cells and their derivatives has given major momentum to the establishment of suspension culture protocols that enable the mass production of cells. Understanding molecular changes accompanying the transfer from adherent to suspension culture is of utmost importance because this information can have a direct effect on the development of optimized culture conditions. In this study we assessed the gene expression of human embryonic stem cells and induced pluripotent stem cells grown in surface-adherent culture (two-dimensional) versus free-floating suspension culture spheroids (three-dimensional). We combined a quantitative proteomic approach based on stable isotope labeling by amino acids in cell culture with deep-sequencing-based transcriptomics. Cells in three-dimensional culture showed reduced expression of proteins forming structural components of cell–cell and cell–extracellular matrix junctions. However, fully unexpected, we found up-regulation of secreted inhibitors of the canonical Wnt signaling pathway and, concomitantly, a reduction in the level of active β-catenin and in the expression of Wnt target genes. In Western blot analyses the cysteine protease calpain was shown to cleave E-cadherin and β-catenin under three-dimensional culture conditions. Our data allowed the development of a model in which calpain cleavage of E-cadherin induces the disintegration of focal cell contacts and generates a 100-kDa E-cadherin fragment required for the formation of three-dimensional cell–cell contacts in spheroids. The parallel release of β-catenin and its potential activation by calpain cleavage are counterbalanced by the overexpression of soluble Wnt pathway inhibitors. According to this model, calpain has a key function in the interplay between E-cadherin and β-catenin-mediated intercellular adhesion and the canonical Wnt signaling pathway. Supporting this model, we show that pharmacological modulation of calpain activity prevents spheroid formation and causes disassembly of preexisting spheroids into single cells, thereby providing novel strategies for improving suspension culture conditions for human pluripotent stem cells in the future.

Bulk cell density and Wnt/TGFbeta signalling regulate mesendodermal patterning of human pluripotent stem cells.

In vitro differentiation of human pluripotent stem cells (hPSCs) recapitulates early aspects of human embryogenesis, but the underlying processes are poorly understood and controlled. Here we show that modulating the bulk cell density (BCD: cell number per culture volume) deterministically alters anteroposterior patterning of primitive streak (PS)-like priming. The BCD in conjunction with the chemical WNT pathway activator CHIR99021 results in distinct paracrine microenvironments codifying hPSCs towards definitive endoderm, precardiac or presomitic mesoderm within the first 24 h of differentiation, respectively. Global gene expression and secretome analysis reveals that TGFß superfamily members, antagonist of Nodal signalling LEFTY1 and CER1, are paracrine determinants restricting PS progression. These data result in a tangible model disclosing how hPSC-released factors deflect CHIR99021-induced lineage commitment over time. By demonstrating a decisive, functional role of the BCD, we show its utility as a method to control lineage-specific differentiation. Furthermore, these findings have profound consequences for inter-experimental comparability, reproducibility, bioprocess optimization and scale-up.

Transplantation and Tracking of Human Induced Pluripotent Stem Cells in a Pig Model of Myocardial Infarction: Assessment of Cell Survival, Engraftment and Distribution by Hybrid SPECT-CT Imaging of Sodium Iodide Symporter Trangene Expression

Background— Evaluation of novel cellular therapies in large-animal models and patients is currently hampered by the lack of imaging approaches that allow for long-term monitoring of viable transplanted cells. In this study, sodium iodide symporter (NIS) transgene imaging was evaluated as an approach to follow in vivo survival, engraftment, and distribution of human-induced pluripotent stem cell (hiPSC) derivatives in a pig model of myocardial infarction. Methods and Results— Transgenic hiPSC lines stably expressing a fluorescent reporter and NIS (NISpos-hiPSCs) were established. Iodide uptake, efflux, and viability of NISpos-hiPSCs were assessed in vitro. Ten (±2) days after induction of myocardial infarction by transient occlusion of the left anterior descending artery, catheter-based intramyocardial injection of NISpos-hiPSCs guided by 3-dimensional NOGA mapping was performed. Dual-isotope single photon emission computed tomographic/computed tomographic imaging was applied with the use of 123I to follow donor cell survival and distribution and with the use of 99mTC-tetrofosmin for perfusion imaging. In vitro, iodide uptake in NISpos-hiPSCs was increased 100-fold above that of nontransgenic controls. In vivo, viable NISpos-hiPSCs could be visualized for up to 15 weeks. Immunohistochemistry demonstrated that hiPSC-derived endothelial cells contributed to vascularization. Up to 12 to 15 weeks after transplantation, no teratomas were detected. Conclusions— This study describes for the first time the feasibility of repeated long-term in vivo imaging of viability and tissue distribution of cellular grafts in large animals. Moreover, this is the first report demonstrating vascular differentiation and long-term engraftment of hiPSCs in a large-animal model of myocardial infarction. NISpos-hiPSCs represent a valuable tool to monitor and improve current cellular treatment strategies in clinically relevant animal models.Background— Evaluation of novel cellular therapies in large-animal models and patients is currently hampered by the lack of imaging approaches that allow for long-term monitoring of viable transplanted cells. In this study, sodium iodide symporter (NIS) transgene imaging was evaluated as an approach to follow in vivo survival, engraftment, and distribution of human-induced pluripotent stem cell (hiPSC) derivatives in a pig model of myocardial infarction. Methods and Results— Transgenic hiPSC lines stably expressing a fluorescent reporter and NIS (NISpos-hiPSCs) were established. Iodide uptake, efflux, and viability of NISpos-hiPSCs were assessed in vitro. Ten (±2) days after induction of myocardial infarction by transient occlusion of the left anterior descending artery, catheter-based intramyocardial injection of NISpos-hiPSCs guided by 3-dimensional NOGA mapping was performed. Dual-isotope single photon emission computed tomographic/computed tomographic imaging was applied with the use of 123I to follow donor cell survival and distribution and with the use of 99mTC-tetrofosmin for perfusion imaging. In vitro, iodide uptake in NISpos-hiPSCs was increased 100-fold above that of nontransgenic controls. In vivo, viable NISpos-hiPSCs could be visualized for up to 15 weeks. Immunohistochemistry demonstrated that hiPSC-derived endothelial cells contributed to vascularization. Up to 12 to 15 weeks after transplantation, no teratomas were detected. Conclusions— This study describes for the first time the feasibility of repeated long-term in vivo imaging of viability and tissue distribution of cellular grafts in large animals. Moreover, this is the first report demonstrating vascular differentiation and long-term engraftment of hiPSCs in a large-animal model of myocardial infarction. NISpos-hiPSCs represent a valuable tool to monitor and improve current cellular treatment strategies in clinically relevant animal models. # Clinical Perspective {#article-title-36}

Proteomic Analysis of Human Pluripotent Stem Cell Cardiomyogenesis Revealed Altered Expression of Metabolic Enzymes and PDLIM5 Isoforms

Human pluripotent stem cells (hPSCs), both embryonic (hESCs) and induced (hiPSCs), can be differentiated into derivatives of the three germ layers and are promising tools in regenerative medicine. Cardiovascular diseases are the top-ranking cause of premature death worldwide, and cell replacement therapies based on in vitro differentiated cardiomyocytes might provide a promising perspective to cure patients in the future. The molecular processes during hPSC cardiomyogenesis are far from being fully understood, and we thus have focused here on characterizing the proteome along hESC in vitro differentiation into cardiomyocytes (CMs). Stable isotope labeling of amino acids in cell culture was applied to quantitatively assess the proteome throughout defined stages of hESC cardiomyogenesis. Genetically enriched, >90% pure CM populations were used for shotgun proteomics, leading to the identification and quantitative determination of several thousand proteins. Pathway analysis revealed alterations in energy metabolism during cardiomyogenesis. Enzymes of glycolysis were identified as up-regulated upon differentiation, whereas enzymes involved in oxidative phosphorylation were down-regulated in aggregates on day 20 of differentiation (<10% CMs) and reconstituted on day 35 in >90% pure CMs. A structural protein that attracted our attention was the PDZ and LIM domain containing protein 5 (PDLIM5), which was strongly up-regulated during cardiomyogenesis and for which we detected novel stage-specific isoforms. Notably, expression of the 53 kDa isoforms b and g (corresponding to transcript variants 2 and 7) of PDLIM5 occurred simultaneously to the onset of expression of the early cardiac transcription factor NKX2.5, known to play a key role in cardiac development.