Differentiation of human embryonic stem cells in serum-free medium reveals distinct roles for bone morphogenetic protein 4, vascular endothelial growth factor, stem cell factor, and fibroblast growth factor 2 in hematopoiesis

Recent advances in the application of induced pluripotent stem cell technology to the study of myeloid malignancies

Acquired myeloid malignancies are a spectrum of clonal disorders known to be caused by sequential acquisition of genetic lesions in hematopoietic stem and progenitor cells, leading to their aberrant self-renewal and differentiation. The increasing use of induced pluripotent stem cell (iPSC) technology to study myeloid malignancies has helped usher a paradigm shift in approaches to disease modeling and drug discovery, especially when combined with gene-editing technology. The process of reprogramming allows for the capture of the diversity of genetic lesions and mutational burden found in primary patient samples into individual stable iPSC lines. Patient-derived iPSC lines, owing to their self-renewal and differentiation capacity, can thus be a homogenous source of disease relevant material that allow for the study of disease pathogenesis using various functional read-outs. Furthermore, genome editing technologies like CRISPR/Cas9 enable the study of the stepwise progression from normal to malignant hematopoiesis through the introduction of specific driver mutations, individually or in combination, to create isogenic lines for comparison. In this review, we survey the current use of iPSCs to model acquired myeloid malignancies including myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), acute myeloid leukemia and MDS/MPN overlap syndromes. The use of iPSCs has enabled the interrogation of the underlying mechanism of initiation and progression driving these diseases. It has also made drug testing, repurposing, and the discovery of novel therapies for these diseases possible in a high throughput setting.

Modulation of WNT, Activin/Nodal, and MAPK Signaling Pathways Increases Arterial Hemogenic Endothelium and Hematopoietic Stem/Progenitor Cell Formation During Human iPSC Differentiation

Several differentiation protocols enable the emergence of hematopoietic stem and progenitor cells (HSPCs) from human-induced pluripotent stem cells (iPSCs), yet optimized schemes to promote the development of HSPCs with self-renewal, multilineage differentiation, and engraftment potential are lacking. To improve human iPSC differentiation methods, we modulated WNT, Activin/Nodal, and MAPK signaling pathways by stage-specific addition of small-molecule regulators CHIR99021, SB431542, and LY294002, respectively, and measured the impact on hematoendothelial formation in culture. Manipulation of these pathways provided a synergy sufficient to enhance formation of arterial hemogenic endothelium (HE) relative to control culture conditions. Importantly, this approach significantly increased production of human HSPCs with self-renewal and multilineage differentiation properties, as well as phenotypic and molecular evidence of progressive maturation in culture. Together, these findings provide a stepwise improvement in human iPSC differentiation protocols and offer a framework for manipulating intrinsic cellular cues to enable de novo generation of human HSPCs with functionality in vivo.

Generation and Functional Characterization of Anti-CD19 Chimeric Antigen Receptor-Natural Killer Cells from Human Induced Pluripotent Stem Cells

Natural killer (NK) cells are a part of innate immunity that can be activated rapidly in response to malignant transformed cells without prior sensitization. Engineering NK cells to express chimeric antigen receptors (CARs) allows them to be directed against corresponding target tumor antigens. CAR-NK cells are regarded as a promising candidate for cellular immunotherapy alternatives to conventional CAR-T cells, due to the relatively low risk of graft-versus-host disease and safer clinical profile. Human induced pluripotent stem cells (iPSCs) are a promising renewable cell source of clinical NK cells. In the present study, we successfully introduced a third-generation CAR targeting CD19, which was validated to have effective signaling domains suitable for NK cells, into umbilical cord blood NK-derived iPSCs, followed by a single-cell clone selection and thorough iPSC characterization. The established single-cell clone of CAR19-NK/iPSCs, which is highly desirable for clinical application, can be differentiated using serum- and feeder-free protocols into functional CAR19-iNK-like cells with improved anti-tumor activity against CD19-positive hematologic cancer cells when compared with wild-type (WT)-iNK-like cells. With the feasibility of being an alternative source for off-the-shelf CAR-NK cells, a library of single-cell clones of CAR-engineered NK/iPSCs targeting different tumor antigens may be created for future clinical application.

Engineering T Cell Development for the Next Generation of Stem Cell-Derived Immunotherapies

Engineered T cells are at the leading edge of clinical cell therapy. T cell therapies have had a remarkable impact on patient care for a subset of hematological malignancies. This foundation has motivated the development of off-the-shelf engineered cell therapies for a broad range of devastating indications. Achieving this vision will require cost-effective manufacturing of precision cell products capable of addressing multiple process and clinical-design challenges. Pluripotent stem cell (PSC)-derived engineered T cells are emerging as a solution of choice. To unleash the full potential of PSC-derived T cell therapies, the field will require technologies capable of robustly orchestrating the complex series of time- and dose-dependent signaling events needed to recreate functional T cell development in the laboratory. In this article, we review the current state of allogenic T cell therapies, focusing on strategies to generate engineered lymphoid cells from PSCs. We highlight exciting recent progress in this field and outline timely opportunities for advancement with an emphasis on niche engineering and synthetic biology.

Modulation of WNT, Activin/Nodal and MAPK Signaling Pathways Increases Arterial Hemogenic Endothelium and Hematopoietic Stem/Progenitor Cell Formation During Human iPSC Differentiation

Several differentiation protocols enable the emergence of hematopoietic stem and progenitor cells (HSPCs) from human induced pluripotent stem cells (iPSCs), yet optimized schemes to promote the development of HSPCs with self-renewal, multilineage differentiation and engraftment potential are lacking. To improve human iPSC differentiation methods, we modulated WNT, Activin/Nodal and MAPK signaling pathways by stage-specific addition of small molecule regulators CHIR99021, SB431542 and LY294002, respectively, and measured the impact on hematoendothelial formation in culture. Manipulation of these pathways provided a synergy sufficient to enhance formation of arterial hemogenic endothelium (HE) relative to control culture conditions. Importantly, this approach significantly increased production of human HSPCs with self-renewal and multilineage differentiation properties, as well as phenotypic and molecular evidence of progressive maturation in culture. Together, these findings provide a stepwise improvement in human iPSC differentiation protocols and offer a framework for manipulating intrinsic cellular cues to enable de novo generation of human HSPCs with functionality in vivo .

Significance Statement

The ability to produce functional HSPCs by differentiation of human iPSCs ex vivo holds enormous potential for cellular therapy of human blood disorders. However, obstacles still thwart translation of this approach to the clinic. In keeping with the prevailing arterial-specification model, we demonstrate that concurrent modulation of WNT, Activin/Nodal and MAPK signaling pathways by stage-specific addition of small molecules during human iPSC differentiation provides a synergy sufficient to promote arterialization of HE and production of HSPCs with features of definitive hematopoiesis. This simple differentiation scheme provides a unique tool for disease modeling, in vitro drug screening and eventual cell therapies.

De Novo Generation of Human Hematopoietic Stem Cells from Pluripotent Stem Cells for Cellular Therapy

The ability to manufacture human hematopoietic stem cells (HSCs) in the laboratory holds enormous promise for cellular therapy of human blood diseases. Several differentiation protocols have been developed to facilitate the emergence of HSCs from human pluripotent stem cells (PSCs). Most approaches employ a stepwise addition of cytokines and morphogens to recapitulate the natural developmental process. However, these protocols globally lack clinical relevance and uniformly induce PSCs to produce hematopoietic progenitors with embryonic features and limited engraftment and differentiation capabilities. This review examines how key intrinsic cues and extrinsic environmental inputs have been integrated within human PSC differentiation protocols to enhance the emergence of definitive hematopoiesis and how advances in genomics set the stage for imminent breakthroughs in this field.

Dendritic cells generated from induced pluripotent stem cells and by direct reprogramming of somatic cells

Novel and exciting avenues allow generating dendritic cells (DC) by reprogramming of somatic cells. DC are obtained from induced pluripotent stem cells (iPS cells), referred to as ipDC, and by direct reprogramming of cells toward DC, referred to as induced DC (iDC). iPS cells represent pluripotent stem cells generated by reprogramming of somatic cells and can differentiate into all cell types of the body, including DC. This makes iPS cells and ipDC derived thereof useful for studying various DC subsets, acquiring high cell numbers for research and clinical use, or applying genome editing to generate DC with wanted properties. Thereby, ipDC overcome limitations in specific DC subsets, which are only found in low abundance in blood or lymphoid organs. iDC are generated by direct reprogramming of somatic cells with a specific set of transcription factors and offer an avenue to obtain DC without a pluripotent cell intermediate. ipDC and iDC retain patient and disease-specific mutations and this opens new perspectives for studying DC in disease. This review summarizes the current techniques used to generate ipDC and iDC, and the types and functionality of the DC generated.

Induced Pluripotent Stem Cells as a Tool for Modeling Hematologic Disorders and as a Potential Source for Cell-Based Therapies

The breakthrough in human induced pluripotent stem cells (hiPSCs) has revolutionized the field of biomedical and pharmaceutical research and opened up vast opportunities for drug discovery and regenerative medicine, especially when combined with gene-editing technology. Numerous healthy and patient-derived hiPSCs for human disease modeling have been established, enabling mechanistic studies of pathogenesis, platforms for preclinical drug screening, and the development of novel therapeutic targets/approaches. Additionally, hiPSCs hold great promise for cell-based therapy, serving as an attractive cell source for generating stem/progenitor cells or functional differentiated cells for degenerative diseases, due to their unlimited proliferative capacity, pluripotency, and ethical acceptability. In this review, we provide an overview of hiPSCs and their utility in the study of hematologic disorders through hematopoietic differentiation. We highlight recent hereditary and acquired genetic hematologic disease modeling with patient-specific iPSCs, and discuss their applications as instrumental drug screening tools. The clinical applications of hiPSCs in cell-based therapy, including the next-generation cancer immunotherapy, are provided. Lastly, we discuss the current challenges that need to be addressed to fulfill the validity of hiPSC-based disease modeling and future perspectives of hiPSCs in the field of hematology.

Large-scale generation of megakaryocytes from human embryonic stem cells using transgene-free and stepwise defined suspension culture conditions

Objectives

Ex vivo engineered production of megakaryocytes (MKs) and platelets (PLTs) from human pluripotent stem cells is an alternative approach to solve shortage of donor‐donated PLTs in clinics and to provide induced PLTs for transfusion. However, low production yields are observed and the generation of clinically applicable MKs and PLTs from human pluripotent stem cells without genetic modifications still needs to be improved.

Materials and Methods

We defined an optimal, stepwise and completely xeno‐free culture protocol for the generation of MKs from human embryonic stem cells (hESCs). To generate MKs from hESCs on a large scale, we improved the monolayer induction manner to define three‐dimensional (3D) and sphere‐like differentiation systems for MKs by using a special polystyrene CellSTACK culture chamber.

Results

The 3D manufacturing system could efficiently generate large numbers of MKs from hESCs within 16‐18 days of continuous culturing. Each CellSTACK culture chamber could collect on an average 3.4 × 10⁸ CD41⁺ MKs after a three‐stage orderly induction process. MKs obtained from hESCs via 3D induction showed significant secretion of IL‐8, thrombospondin‐1 and MMP9. The induced cells derived from hESCs in our culture system were shown to have the characteristics of MKs as well as the function to form proPLTs and release PLTs. Furthermore, we generated clinically applicable MKs from clinical‐grade hESC lines and confirmed the biosafety of these cells.

Conclusions

We developed a simple, stepwise, 3D and completely xeno‐free/feeder‐free/transgene‐free induction system for the generation of MKs from hESCs. hESC‐derived MKs were shown to have typical MK characteristics and PLT formation ability. This study further enhances the clinical applications of MKs or PLTs derived from pluripotent stem cells.

Stem-cell-derived human microglia transplanted into mouse brain to study human disease

Microglia are critically involved in complex neurological disorders with a strong genetic component, such as Alzheimer's disease, Parkinson's disease and frontotemporal dementia. Although mouse microglia can recapitulate aspects of human microglia physiology, they do not fully capture the human genetic aspects of disease and do not reproduce all human cell states. Primary cultures of human microglia or microglia derived from human induced pluripotent stem cells (PSCs) are difficult to maintain in brain-relevant cell states in vitro. Here we describe MIGRATE (microglia in vitro generation refined for advanced transplantation experiments, which provides a combined in vitro differentiation and in vivo xenotransplantation protocol to study human microglia in the context of the mouse brain. This article details an accurate, step-by-step workflow that includes in vitro microglia differentiation from human PSCs, transplantation into the mouse brain and quantitative analysis of engraftment. Compared to current differentiation and xenotransplantation protocols, we present an optimized, faster and more efficient approach that yields up to 80% chimerism. To quantitatively assess engraftment efficiency by flow cytometry, access to specialized flow cytometry is required. Alternatively, the percentage of chimerism can be estimated by standard immunohistochemical analysis. The MIGRATE protocol takes ~40 d to complete, from culturing PSCs to engraftment efficiency assessment.

Multilineage differentiation potential of hematoendothelial progenitors derived from human induced pluripotent stem cells

BACKGROUND

Human induced pluripotent stem cells (hiPSCs) offer a renewable source of cells for the generation of hematopoietic cells for cell-based therapy, disease modeling, and drug screening. However, current serum/feeder-free differentiation protocols rely on the use of various cytokines, which makes the process very costly or the generation of embryoid bodies (EBs), which are labor-intensive and can cause heterogeneity during differentiation. Here, we report a simple feeder and serum-free monolayer protocol for efficient generation of iPSC-derived multipotent hematoendothelial progenitors (HEPs), which can further differentiate into endothelial and hematopoietic cells including erythroid and T lineages.

METHODS

Formation of HEPs from iPSCs was initiated by inhibition of GSK3 signaling for 2 days followed by the addition of VEGF and FGF2 for 3 days. The HEPs were further induced toward mature endothelial cells (ECs) in an angiogenic condition and toward T cells by co-culturing with OP9-DL1 feeder cells. Endothelial-to-hematopoietic transition (EHT) of the HEPs was further promoted by supplementation with the TGF-β signaling inhibitor. Erythroid differentiation was performed by culturing the hematopoietic stem/progenitor cells (HSPCs) in a three-stage erythroid liquid culture system.

RESULTS

Our protocol significantly enhanced the number of KDR⁺ CD34⁺ CD31⁺ HEPs on day 5 of differentiation. Further culture of HEPs in angiogenic conditions promoted the formation of mature ECs, which expressed CD34, CD31, CD144, vWF, and ICAM-1, and could exhibit the formation of vascular-like network and acetylated low-density lipoprotein (Ac-LDL) uptake. In addition, the HEPs were differentiated into CD8⁺ T lymphocytes, which could be expanded up to 34-fold upon TCR stimulation. Inhibition of TGF-β signaling at the HEP stage promoted EHT and yielded a large number of HSPCs expressing CD34 and CD43. Upon erythroid differentiation, these HSPCs were expanded up to 40-fold and displayed morphological changes following stages of erythroid development.

CONCLUSION

This protocol offers an efficient and simple approach for the generation of multipotent HEPs and could be adapted to generate desired blood cells in large numbers for applications in basic research including developmental study, disease modeling, and drug screening as well as in regenerative medicine.

Induced pluripotent stem cells and hematological malignancies: A powerful tool for disease modeling and drug development

The derivation of human pluripotent stem cell (iPSC) lines by in vitro reprogramming of somatic cells revolutionized research: iPSCs have been used for disease modeling, drug screening and regenerative medicine for many disorders, especially when combined with cutting-edge genome editing technologies. In hematology, malignant transformation is often a multi-step process, that starts with either germline or acquired genetic alteration, followed by progressive acquisition of mutations combined with the selection of one or more pre-existing clones. iPSCs are an excellent model to study the cooperation between different genetic alterations and to test relevant therapeutic drugs. In this review, we will describe the use of iPSCs for pathophysiological studies and drug testing in inherited and acquired hematological malignancies.

BMP4 and perivascular cells promote hematopoietic differentiation of human pluripotent stem cells in a differentiation stage-specific manner

The efficient and reproducible derivation and maturation of multipotent hematopoietic progenitors from human pluripotent stem cells (hPSCs) requires the recapitulation of appropriate developmental stages and the microenvironment. Here, using serum-, xeno-, and feeder-free stepwise hematopoietic induction protocols, we showed that short-term and high-concentration treatment of hPSCs with bone morphogenetic protein 4 (BMP4) strongly promoted early mesoderm induction followed by increased hematopoietic commitment. This method reduced variations in hematopoietic differentiation among hPSC lines maintained under chemically defined Essential 8 medium compared to those maintained under less-defined mTeSR medium. We also found that perivascular niche cells (PVCs) significantly augmented the production of hematopoietic cells via paracrine signaling mechanisms only when they were present during the hematopoietic commitment phase. A protein array revealed 86 differentially expressed (>1.5-fold) secretion factors in PVC-conditioned medium compared with serum-free control medium, of which the transforming growth factor-β inducible gene H3 significantly increased the number of hematopoietic colony-forming colonies. Our data suggest that BMP4 and PVCs promote the hematopoietic differentiation of hPSCs in a differentiation stage-specific manner. This will increase our understanding of hematopoietic development and expedite the development of hPSC-derived blood products for therapeutic use.

Adding a vital regulatory molecule and support cells to the culture medium can help in the derivation of blood products from stem cells. A team led by Seok-Ho Hong from Kangwon National University in Chuncheon, South Korea, followed a clinical-grade protocol for converting embryonic stem cells or induced pluripotent stem cells from adults into blood cell precursors. The researchers showed that incorporating high doses of a growth factor called bone morphogenetic protein 4 into the standard culture medium for a short period promoted early differentiation toward blood cells. Incorporating so-called perivascular cells taken from umbilical cord blood also enhanced the process through the secretion of signaling molecules that further pushed the stem cells toward differentiating into blood cells. The findings could help improve protocols for making blood products from stem cells for therapeutic purposes.

Expanded potential stem cell media as a tool to study human developmental hematopoiesis in vitro

Pluripotent stem cell (PSC) differentiation in vitro represents a powerful and tractable model to study mammalian development and an unlimited source of cells for regenerative medicine. Within hematology, in vitro PSC hematopoiesis affords novel insights into blood formation and represents an exciting potential approach to generate hematopoietic and immune cell types for transplantation and transfusion. Most studies to date have focused on in vitro hematopoiesis from mouse PSCs and human PSCs. However, differences in mouse and human PSC culture protocols have complicated the translation of discoveries between these systems. We recently developed a novel chemical media formulation, expanded potential stem cell medium (EPSCM), that maintains mouse PSCs in a unique cellular state and extraembryonic differentiation capacity. Herein, we describe how EPSCM can be directly used to stably maintain human PSCs. We further demonstrate that human PSCs maintained in EPSCM can spontaneously form embryoid bodies and undergo in vitro hematopoiesis using a simple differentiation protocol, similar to mouse PSC differentiation. EPSCM-maintained human PSCs generated at least two hematopoietic cell populations, which displayed distinct transcriptional profiles by RNA-sequencing (RNA-seq) analysis. EPSCM also supports gene targeting using homologous recombination, affording generation of an SPI1 (PU.1) reporter PSC line to study and track in vitro hematopoiesis. EPSCM therefore provides a useful tool not only to study pluripotency but also hematopoietic cell specification and developmental-lineage commitment.

Recent Updates on Induced Pluripotent Stem Cells in Hematological Disorders

Over the past decade, enormous progress has been made in the field of induced pluripotent stem cells (iPSCs). Patients' somatic cells such as skin fibroblasts or blood cells can be used to generate disease-specific pluripotent stem cells, which have unlimited proliferation and can differentiate into all cell types of the body. Human iPSCs offer great promises and opportunities for treatments of degenerative diseases and studying disease pathology and drug screening. So far, many iPSC-derived disease models have led to the discovery of novel pathological mechanisms as well as new drugs in the pipeline that have been tested in the iPSC-derived cells for efficacy and potential toxicities. Furthermore, recent advances in genome editing technology in combination with the iPSC technology have provided a versatile platform for studying stem cell biology and regenerative medicine. In this review, an overview of iPSCs, patient-specific iPSCs for disease modeling and drug screening, applications of iPSCs and genome editing technology in hematological disorders, remaining challenges, and future perspectives of iPSCs in hematological diseases will be discussed.

Generation of Hematopoietic Stem and Progenitor Cells from Human Pluripotent Stem Cells

Human pluripotent stem cells (PSCs) have the potential to provide a virtually unlimited supply of cells for transplantation therapy. When combined with recent advances in genome editing technologies, human PSCs could offer various approaches that enable gene therapy, drug discovery, disease modeling, and in vitro modeling of human development. De novo generation of hematopoietic stem cells (HSCs) from human PSCs is an important focus in the field, since it enables autologous HSC transplantation to treat many blood disorders and malignancies. Although culture conditions have been established to generate a broad spectrum of hematopoietic progenitors from human PSCs, it remains a significant challenge to generate bona fide HSCs that possess sustained self-renewal and multilineage differentiation capacities upon transplantation. In this review, recent promising advances in the efforts to generate HSCs and hematopoietic progenitors from human PSCs in vitro and in vivo or from somatic cells are discussed.

From pluripotent stem cells to T cells

The generation of T cells from human pluripotent stem cells (PSCs) opens a valuable experimental window into developmental hematopoiesis and raises the possibility of a new therapeutic approach for T-cell immunotherapy. After directing PSCs through mesoderm and early hematopoietic developmental stages, commitment to the T-cell lineage has been achieved by several groups using coculture with stromal cells that express a notch ligand, recapitulating the critical signals that initiate the first stages of normal T-cell differentiation in the thymus. However, positive selection and the production of mature T cells from human PSCs have been limited to date. Nonetheless, T-lineage cells have been generated from PSCs with tumor antigen specificity either through a prearranged clonal T-cell receptor (TCR) or lentiviral-mediated expression of chimeric antigen receptors. The recent development of a 3D artificial organoid model has demonstrated that PSCs can generate mature conventional T cells that are fully functional and express a diverse TCR repertoire. Introduction of a transgenic TCR at the PSC stage allows for the production of tumor-antigen-specific, mature conventional T cells. The tools of gene editing in PSCs are ideally suited to produce off-the-shelf universal products for T-cell immunotherapy. In this review, we describe the studies that have led to this exciting moment in PSC biology and discuss translation to clinical applications.

Inhibition of MicroRNA-221 and 222 Enhances Hematopoietic Differentiation from Human Pluripotent Stem Cells via c-KIT Upregulation

The stem cell factor (SCF)/c-KIT axis plays an important role in the hematopoietic differentiation of human pluripotent stem cells (hPSCs), but its regulatory mechanisms involving microRNAs (miRs) are not fully elucidated. Here, we demonstrated that supplementation with SCF increases the hematopoietic differentiation of hPSCs via the interaction with its receptor tyrosine kinase c-KIT, which is modulated by miR-221 and miR-222. c-KIT is comparably expressed in undifferentiated human embryonic and induced pluripotent stem cells. The inhibition of SCF signaling via treatment with a c-KIT antagonist (imatinib) during hPSC-derived hematopoiesis resulted in reductions in the yield and multi-lineage potential of hematopoietic progenitors. We found that the transcript levels of miR-221 and miR-222 targeting c-KIT were significantly lower in the pluripotent state than they were in terminally differentiated somatic cells. Furthermore, suppression of miR-221 and miR-222 in undifferentiated hPSC cultures induced more hematopoiesis by increasing c-KIT expression. Collectively, our data implied that the modulation of c-KIT by miRs may provide further potential strategies to expedite the generation of functional blood cells for therapeutic approaches and the study of the cellular machinery related to hematologic malignant diseases such as leukemia.

Early Human Hemogenic Endothelium Generates Primitive and Definitive Hematopoiesis In Vitro

The differentiation of human embryonic stem cells (hESCs) to hematopoietic lineages initiates with the specification of hemogenic endothelium, a transient specialized endothelial precursor of all blood cells. This in vitro system provides an invaluable model to dissect the emergence of hematopoiesis in humans. However, the study of hematopoiesis specification is hampered by a lack of consensus in the timing of hemogenic endothelium analysis and the full hematopoietic potential of this population. Here, our data reveal a sharp decline in the hemogenic potential of endothelium populations isolated over the course of hESC differentiation. Furthermore, by tracking the dynamic expression of CD31 and CD235a at the onset of hematopoiesis, we identified three populations of hematopoietic progenitors, representing primitive and definitive subsets that all emerge from the earliest specified hemogenic endothelium. Our data establish that hemogenic endothelium populations endowed with primitive and definitive hematopoietic potential are specified simultaneously from the mesoderm in differentiating hESCs.

Multivalent biomaterial platform to control the distinct arterial venous differentiation of pluripotent stem cells

Vascular endothelial cells (ECs) differentiated from pluripotent stem cells have enormous potential to be used in a variety of therapeutic areas such as tissue engineering of vascular grafts and re-vascularization of ischemic tissues. To date, various protocols have been developed to differentiate stem cells toward vascular ECs. However, current methods are still not sufficient to drive the distinct arterial venous differentiation. Therefore, developing refined method of arterial-venous differentiation is critically needed to address this gap. Here, we developed a biomaterial platform to mimic multivalent ephrin-B2/EphB4 signaling and investigated its role in the early arterial and venous specification of pluripotent stem cells. Our results show immobilized ephrinB2 or EphB4 on hydrogel substrates have a distinct effect on arterial venous differentiation by regulating several arterial venous markers. When in combination with Wnt pathway agonist or BMP4 signaling, the ephrin-B2/EphB4 biomaterial platform can create diverging EC progenitor populations, demonstrating differential gene expression pattern across a wide range of arterial and venous markers, as well as phenotypic markers such as anti-thrombotic, pro-atherogenic and osteogenic genes, that are consistent with the in vivo expression patterns of arterial and venous ECs. Importantly, this distinct EC progenitor population cannot be achieved by current methods of applying soluble factors or hemodynamic stimuli alone, illustrating that fine-tuning of developmental signals using the biomaterial platform offers a new approach to better control the arterial venous differentiation of stem cells.

Making HSCs in vitro: don't forget the hemogenic endothelium

Generating a hematopoietic stem cell (HSC) in vitro from nonhematopoietic tissue has been a goal of experimental hematologists for decades. Until recently, no in vitro-derived cell has closely demonstrated the full lineage potential and self-renewal capacity of a true HSC. Studies revealing stem cell ontogeny from embryonic mesoderm to hemogenic endothelium to HSC provided the key to inducing HSC-like cells in vitro from a variety of cell types. Here we review the path to this discovery and discuss the future of autologous transplantation with in vitro-derived HSCs as a therapeutic modality.

Directed Differentiation of Primitive and Definitive Hematopoietic Progenitors from Human Pluripotent Stem Cells

One of the major goals for regenerative medicine is the generation and maintenance of hematopoietic stem cells (HSCs) derived from human pluripotent stem cells (hPSCs). Until recently, efforts to differentiate hPSCs into HSCs have predominantly generated hematopoietic progenitors that lack HSC potential, and instead resemble yolk sac hematopoiesis. These resulting hematopoietic progenitors may have limited utility for in vitro disease modeling of various adult hematopoietic disorders, particularly those of the lymphoid lineages. However, we have recently described methods to generate erythro-myelo-lymphoid multilineage definitive hematopoietic progenitors from hPSCs using a stage-specific directed differentiation protocol, which we outline here. Through enzymatic dissociation of hPSCs on basement membrane matrix-coated plasticware, embryoid bodies (EBs) are formed. EBs are differentiated to mesoderm by recombinant BMP4, which is subsequently specified to the definitive hematopoietic program by the GSK3β inhibitor, CHIR99021. Alternatively, primitive hematopoiesis is specified by the PORCN inhibitor, IWP2. Hematopoiesis is further driven through the addition of recombinant VEGF and supportive hematopoietic cytokines. The resulting hematopoietic progenitors generated using this method have the potential to be used for disease and developmental modeling, in vitro.

Craniometaphyseal Dysplasia Mutations in ANKH Negatively Affect Human Induced Pluripotent Stem Cell Differentiation into Osteoclasts

We identified osteoclast defects in craniometaphyseal dysplasia (CMD) using an easy-to-use protocol for differentiating osteoclasts from human induced pluripotent stem cells (hiPSCs). CMD is a rare genetic bone disorder, characterized by life-long progressive thickening of craniofacial bones and abnormal shape of long bones. hiPSCs from CMD patients with an in-frame deletion of Phe377 or Ser375 in ANKH are more refractory to in vitro osteoclast differentiation than control hiPSCs. To exclude differentiation effects due to genetic variability, we generated isogenic hiPSCs, which have identical genetic background except for the ANKH mutation. Isogenic hiPSCs with ANKH mutations formed fewer osteoclasts, resorbed less bone, expressed lower levels of osteoclast marker genes, and showed decreased protein levels of ANKH and vacuolar proton pump v-ATP6v0d2. This proof-of-concept study demonstrates that efficient and reproducible differentiation of isogenic hiPSCs into osteoclasts is possible and a promising tool for investigating mechanisms of CMD or other osteoclast-related disorders.

Human haematopoietic stem cell development: from the embryo to the dish

Haematopoietic stem cells (HSCs) emerge during embryogenesis and give rise to the adult haematopoietic system. Understanding how early haematopoietic development occurs is of fundamental importance for basic biology and medical sciences, but our knowledge is still limited compared with what we know of adult HSCs and their microenvironment. This is particularly true for human haematopoiesis, and is reflected in our current inability to recapitulate the development of HSCs from pluripotent stem cells in vitro In this Review, we discuss what is known of human haematopoietic development: the anatomical sites at which it occurs, the different temporal waves of haematopoiesis, the emergence of the first HSCs and the signalling landscape of the haematopoietic niche. We also discuss the extent to which in vitro differentiation of human pluripotent stem cells recapitulates bona fide human developmental haematopoiesis, and outline some future directions in the field.

Induced Pluripotent Stem Cell for the Study and Treatment of Sickle Cell Anemia

Sickle cell anemia (SCA) is a monogenic disease of high mortality, affecting millions of people worldwide. There is no broad, effective, and safe definitive treatment for SCA, so the palliative treatments are the most used. The establishment of an in vitro model allows better understanding of how the disease occurs, besides allowing the development of more effective tests and treatments. In this context, iPSC technology is a powerful tool for basic research and disease modeling, and a promise for finding and screening more effective and safe drugs, besides the possibility of use in regenerative medicine. This work obtained a model for study and treatment of SCA using iPSC. Then, episomal vectors were used for reprogramming peripheral blood mononuclear cells to obtain integration-free iPSC. Cells were collected from patients treated with hydroxyurea and without treatment. The iPSCP Bscd lines were characterized for pluripotent and differentiation potential. The iPSC lines were differentiated into HSC, so that we obtained a dynamic and efficient protocol of CD34+CD45+ cells production. We offer a valuable tool for a better understanding of how SCA occurs, in addition to making possible the development of more effective drugs and treatments and providing better understanding of widely used treatments, such as hydroxyurea.

Hematopoietic Developmental Potential of Human Pluripotent Stem Cell Lines Is Accompanied by the Morphology of Embryoid Bodies and the Expression of Endodermal and Hematopoietic Markers

The potential clinical applications of hematopoietic stem cells (HSCs) derived from human pluripotent stem cells (hPSCs) are limited by the difficulty of recapitulating embryoid hematopoiesis and by the unknown differentiation potential of hPSC lines. To evaluate their hematopoietic developmental potential, available hPSC lines were differentiated by an embryoid body (EB) suspension culture in serum-free medium supplemented with three different cytokine mixes (CMs). The hPSC differentiation status was investigated by the flow cytometry expression profiles of cell surface molecules, and the gene expression of pluripotency and differentiation markers over time was evaluated by real-time reverse transcription polymerase chain reaction (qRT-PCR). hPSC lines differed in several aspects of the differentiation process, including the absolute yield of hematopoietic progenitors, the proportion of hematopoietic progenitor populations, and the effect of various CMs. The ability to generate hematopoietic progenitors was then associated with the morphology of the developing EBs, the expression of the endodermal markers AFP and SOX17, and the hematopoietic transcription factor RUNX1. These findings deepen the knowledge about the hematopoietic propensity of hPSCs and identify its variability as an aspect that must be taken into account before the usage of hPSC-derived HSCs in downstream applications.

A view of human haematopoietic development from the Petri dish

Human pluripotent stem cells (hPSCs) provide an unparalleled opportunity to establish in vitro differentiation models that will transform our approach to the study of human development. In the case of the blood system, these models will enable investigation of the earliest stages of human embryonic haematopoiesis that was previously not possible. In addition, they will provide platforms for studying the origins of human blood cell diseases and for generating de novo haematopoietic stem and progenitor cell populations for cell-based regenerative therapies.

CD13 and ROR2 Permit Isolation of Highly Enriched Cardiac Mesoderm from Differentiating Human Embryonic Stem Cells

The generation of tissue-specific cell types from human embryonic stem cells (hESCs) is critical for the development of future stem cell-based regenerative therapies. Here, we identify CD13 and ROR2 as cell-surface markers capable of selecting early cardiac mesoderm emerging during hESC differentiation. We demonstrate that the CD13+/ROR2+ population encompasses pre-cardiac mesoderm, which efficiently differentiates to all major cardiovascular lineages. We determined the engraftment potential of CD13+/ROR2+ in small (murine) and large (porcine) animal models, and demonstrated that CD13+/ROR2+ progenitors have the capacity to differentiate toward cardiomyocytes, fibroblasts, smooth muscle, and endothelial cells in vivo. Collectively, our data show that CD13 and ROR2 identify a cardiac lineage precursor pool that is capable of successful engraftment into the porcine heart. These markers represent valuable tools for further dissection of early human cardiac differentiation, and will enable a detailed assessment of human pluripotent stem cell-derived cardiac lineage cells for potential clinical applications.

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CD13 and ROR2 separate hESC-derived MIXL1+ mesoderm from MIXL1+ endoderm

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CD13 and ROR2 select for a population of highly enriched pre-cardiac mesoderm

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CD13+/ROR2+ cells derived from hESCs engraft into porcine, but not murine hearts

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CD13+/ROR2+ cells differentiate to all major cardiac lineages in the pig heart

Progress towards generation of human haematopoietic stem cells

De novo generation of haematopoietic stem cells from different human pluripotent stem cell sources remains a high priority for haematology and regenerative medicine. At present, efficient derivation of functional haematopoietic stem cells with the capability for definitive in vivo engraftment and multi-lineage potential remains challenging. Here, we discuss recent progress and strategies to overcome obstacles that have thwarted past efforts. In addition, we review promising advances in the generation of mature blood lineages and the potential of induced pluripotent stem cells.

Concise Review: Recent Advances in the In Vitro Derivation of Blood Cell Populations

: Hematopoietic cell-based therapies are currently available treatment options for many hematological and nonhematological disorders. However, the scarcity of allogeneic donor-derived cells is a major hurdle in treating these disorders. Embryonic stem cell-based directed differentiation and direct reprogramming of somatic cells provide excellent tools for the potential generation of hematopoietic stem cells usable in the clinic for cellular therapies. In addition to blood stem cell transplantation, mature blood cells such as red blood cells, platelets, and engineered T cells have also been increasingly used to treat several diseases. Besides cellular therapies, induced blood progenitor cells generated from autologous sources (either induced pluripotent stem cells or somatic cells) can be useful for disease modeling of bone marrow failures and acquired blood disorders. However, although great progress has been made toward these goals, we are still far from the use of in vitro-derived blood products in the clinic. We review the current state of knowledge on the directed differentiation of embryonic stem cells and the reprogramming of somatic cells toward the generation of blood stem cells and derivatives.

SIGNIFICANCE

Hematopoietic cell-based therapies are currently available treatment options for many hematological and nonhematological disorders. However, the scarcity of allogeneic donor-derived cells is a major hurdle in treating these disorders. The current state of knowledge on the directed differentiation of embryonic stem cells and the reprogramming of somatic cells toward the generation of blood stem cells and derivatives is reviewed.

Lost in translation: pluripotent stem cell-derived hematopoiesis

Pluripotent stem cells (PSCs) such as embryonic stem cells or induced pluripotent stem cells represent a promising cell type to gain novel insights into human biology. Understanding the differentiation process of PSCs in vitro may allow for the identification of cell extrinsic/intrinsic factors, driving the specification process toward all cell types of the three germ layers, which may be similar to the human in vivo scenario. This would not only lay the ground for an improved understanding of human embryonic development but would also contribute toward the generation of novel cell types used in cell replacement therapies. In this line, especially the developmental process of mesodermal cells toward the hematopoietic lineage is of great interest. Therefore, this review highlights recent progress in the field of hematopoietic specification of pluripotent stem cell sources. In addition, we would like to shed light on emerging factors controlling primitive and definitive hematopoietic development and to highlight recent approaches to improve the differentiation potential of PSC sources toward hematopoietic stem/progenitor cells. While the generation of fully defined hematopoietic stem cells from PSCs remains challenging in vitro, we here underline the instructive role of cell extrinsic factors such as cytokines for the generation of PSC-derived mature hematopoietic cells. Thus, we have comprehensively examined the role of cytokines for the derivation of mature hematopoietic cell types such as macrophages, granulocytes, megakaryocytes, erythrocytes, dendritic cells, and cells of the B- and T-cell lineage.

High-Efficiency Serum-Free Feeder-Free Erythroid Differentiation of Human Pluripotent Stem Cells Using Small Molecules

This article describes a highly efficient, fully feeder-free, serum-free method for erythroid differentiation of induced pluripotent stem cells and human embryonic stem cells, including a clinical-grade line, that is amenable to scale-up and as such will be of significant value for basic and translational studies of hematopoiesis and erythropoiesis.

This article describes a good manufacturing practice (GMP)-compatible, feeder-free and serum-free method to produce large numbers of erythroid cells from human pluripotent stem cells (hPSCs), either embryonic or induced. This multistep protocol combines cytokines and small molecules to mimic and surpass the early stages of development. It produces, without any selection or sorting step, a population of cells in which 91.8% ± 5.4% express CD34 at day 7, 98.6% ± 1.3% express CD43 at day 10, and 99.1% ± 0.95% of cells are CD235a positive by day 31 of the differentiation process. Moreover, this differentiation protocol supports extensive expansion, with a single hPSC producing up to 150 hematopoietic progenitor cells by day 10 and 50,000–200,000 erythroid cells by day 31. The erythroid cells produced exhibit a definitive fetal hematopoietic type, with 90%–95% fetal globin and variable proportion of embryonic and adult globin at the protein level. The presence of small molecules during the differentiation protocol has quantitative and qualitative effects; it increases the proportion of adult globin and decreases the proportion of embryonic globin. Given its level of definition, this system provides a powerful tool for investigation of the mechanisms governing early hematopoiesis and erythropoiesis, including globin switching and enucleation. The early stages of the differentiation protocol could also serve as a starting point for the production of endothelial cells and other hematopoietic cells, or to investigate the production of long-term reconstituting hematopoietic stem cells from hPSCs.

Significance

This differentiation protocol allows the production of a large amount of erythroid cells from pluripotent stem cells. Its efficiency is compatible with that of in vitro red blood cell production, and it can be a considerable asset for studying developmental erythropoiesis and red blood cell enucleation, thereby aiding both basic and translational research. In addition to red cells, the early stages of the protocol could also be used as a starting point for the large-scale production of other hematopoietic cell types, including the ultimate goal of generating long-term reconstituting hematopoietic stem cells.

Medial HOXA genes demarcate haematopoietic stem cell fate during human development

Pluripotent stem cells (PSC) may provide a potential source of haematopoietic stem/progenitor cells (HSPCs) for transplantation; however, unknown molecular barriers prevent the self-renewal of PSC-HSPCs. Using two-step differentiation, human embryonic stem cells (hESCs) differentiated in vitro into multipotent haematopoietic cells that had CD34⁺CD38^−/loCD90⁺CD45⁺GPI-80⁺ foetal liver (FL) HSC immunophenotype, but displayed poor expansion potential and engraftment ability. Transcriptome analysis of immunophenotypic hESC-HSPCs revealed that, despite their molecular resemblance to FL-HSPCs, medial HOXA genes remained suppressed. Knockdown of HOXA7 disrupted FL-HSPC function and caused transcriptome dysregulation that resembled hESC-derived progenitors. Overexpression of medial HOXA genes prolonged FL-HSPC maintenance but was insufficient to confer self-renewal to hESC-HSPCs. Stimulation of retinoic acid signalling during endothelial-to-haematopoietic transition induced the HOXA cluster and other HSC/definitive haemogenic endothelium genes, and prolonged HSPC maintenance in culture. Thus, retinoic acid signalling-induced medial HOXA gene expression marks the establishment of the definitive HSC fate and controls HSC identity and function.

A Multi-Lineage Screen Reveals mTORC1 Inhibition Enhances Human Pluripotent Stem Cell Mesendoderm and Blood Progenitor Production

Human pluripotent stem cells (hPSCs) exist in heterogeneous micro-environments with multiple subpopulations, convoluting fate-regulation analysis. We patterned hPSCs into engineered micro-environments and screened responses to 400 small-molecule kinase inhibitors, measuring yield and purity outputs of undifferentiated, neuroectoderm, mesendoderm, and extra-embryonic populations. Enrichment analysis revealed mammalian target of rapamycin (mTOR) inhibition as a strong inducer of mesendoderm. Dose responses of mTOR inhibitors such as rapamycin synergized with Bone Morphogenetic protein 4 (BMP4) and activin A to enhance the yield and purity of BRACHYURY-expressing cells. Mechanistically, small interfering RNA knockdown of RAPTOR, a component of mTOR complex 1, phenocopied the mesendoderm-enhancing effects of rapamycin. Functional analysis during mesoderm and endoderm differentiation revealed that mTOR inhibition increased the output of hemogenic endothelial cells 3-fold, with a concomitant enhancement of blood colony-forming cells. These data demonstrate the power of our multi-lineage screening approach and identify mTOR signaling as a node in hPSC differentiation to mesendoderm and its derivatives.

Efficient differentiation of human embryonic stem cells to arterial and venous endothelial cells under feeder- and serum-free conditions

Background

Heterogeneity of endothelial cells (ECs) is a hallmark of the vascular system which may impact the development and management of vascular disorders. Despite the tremendous progress in differentiation of human embryonic stem cells (hESCs) towards endothelial lineage, differentiation into arterial and venous endothelial phenotypes remains elusive. Additionally, current differentiation strategies are hampered by inefficiency, lack of reproducibility, and use of animal-derived products.

Methods

To direct the differentiation of hESCs to endothelial subtypes, H1- and H9-hESCs were seeded on human plasma fibronectin and differentiated under chemically defined conditions by sequential modulation of glycogen synthase kinase-3 (GSK-3), basic fibroblast growth factor (bFGF), bone morphogenetic protein 4 (BMP4) and vascular endothelial growth factor (VEGF) signaling pathways for 5 days. Following the initial differentiation, the endothelial progenitor cells (CD34⁺CD31⁺ cells) were sorted and terminally differentiated under serum-free conditions to arterial and venous ECs. The transcriptome and secretome profiles of the two distinct populations of hESC-derived arterial and venous ECs were characterized. Furthermore, the safety and functionality of these cells upon in vivo transplantation were characterized.

Results

Sequential modulation of hESCs with GSK-3 inhibitor, bFGF, BMP4 and VEGF resulted in stages reminiscent of primitive streak, early mesoderm/lateral plate mesoderm, and endothelial progenitors under feeder- and serum-free conditions. Furthermore, these endothelial progenitors demonstrated differentiation potential to almost pure populations of arterial and venous endothelial phenotypes under serum-free conditions. Specifically, the endothelial progenitors differentiated to venous ECs in the absence of VEGF, and to arterial phenotype under low concentrations of VEGF. Additionally, these hESC-derived arterial and venous ECs showed distinct molecular and functional profiles in vitro. Furthermore, these hESC-derived arterial and venous ECs were nontumorigenic and were functional in terms of forming perfused microvascular channels upon subcutaneous implantation in the mouse.

Conclusions

We report a simple, rapid, and efficient protocol for directed differentiation of hESCs into endothelial progenitor cells capable of differentiation to arterial and venous ECs under feeder-free and serum-free conditions. This could offer a human platform to study arterial–venous specification for various applications related to drug discovery, disease modeling and regenerative medicine in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0260-5) contains supplementary material, which is available to authorized users.

The Use of Patient-Specific Induced Pluripotent Stem Cells (iPSCs) to Identify Osteoclast Defects in Rare Genetic Bone Disorders

More than 500 rare genetic bone disorders have been described, but for many of them only limited treatment options are available. Challenges for studying these bone diseases come from a lack of suitable animal models and unavailability of skeletal tissues for studies. Effectors for skeletal abnormalities of bone disorders may be abnormal bone formation directed by osteoblasts or anomalous bone resorption by osteoclasts, or both. Patient-specific induced pluripotent stem cells (iPSCs) can be generated from somatic cells of various tissue sources and in theory can be differentiated into any desired cell type. However, successful differentiation of hiPSCs into functional bone cells is still a challenge. Our group focuses on the use of human iPSCs (hiPSCs) to identify osteoclast defects in craniometaphyseal dysplasia. In this review, we describe the impact of stem cell technology on research for better treatment of such disorders, the generation of hiPSCs from patients with rare genetic bone disorders and current protocols for differentiating hiPSCs into osteoclasts.

In Vitro Differentiation of Embryonic Stem Cells into Hematopoietic Lineage: Towards Erythroid Progenitor's Production

Embryonic stem cells (ESCs) differentiation via embryoid body (EB) formation is an established method that generates the three germ layers. However, EB differentiation poses several problems including formation of heterogeneous cell populations. Herein, we described a differentiation protocol on enhancing mesoderm derivation from murine ESCs (mESCs) using conditioned medium (CM) from HepG2 cells. We used this technique to direct hematopoiesis by generating "embryoid-like" colonies (ELCs) from murine (m) ESCs without following standard formation of EBs. Our CM-mESCs group yielded an almost fivefold increase in ELC formation (p ≤ 0.05) and higher expression of mesoderm genes;-Brachyury-T, Goosecoid, and Flk-1 compared with control mESCs group. Hematopoietic colony formation from CM-mESCs was also enhanced by twofold at days 7 and 14 with earlier colony commitment compared to control mESCs (p ≤ 0.05). This early clonogenic capacity was confirmed morphologically by the presence of nucleated erythrocytes and macrophages as early as day 7 in culture using standard 14-day colony-forming assay. Early expression of hematopoietic primitive (ζ-globin) and definitive (β-globin) erythroid genes and proteins was also observed by day 7 in the CM-treated culture. These data indicate that hematopoietic cells more quickly differentiate from CM-treated, compared with those using standard EB approaches, and provide an efficient bioprocess platform for erythroid-specific differentiation of ESCs.

Early activated hepatic stellate cell-derived molecules reverse acute hepatic injury

AIM: To test whether hepatic stellate cells (HSCs) at different activation stages play different roles in acetaminophen (APAP)-induced acute liver injury (ALI).

METHODS: HSCs were isolated from mouse liver and cultured in vitro. Morphological changes of initiation HSCs [HSCs (5d)] and perpetuation HSCs [HSCs (p3)] were observed by immunofluorescence and transmission electron microscopy. The protective effects of HSC-derived molecules, cell lysates and HSC-conditioned medium (HSC-CM) were tested in vivo by survival and histopathological analyses. Liver injury was determined by measuring aminotransferase levels in the serum and by histologic examination of tissue sections under a light microscope. Additionally, to determine the molecular mediators of the observed protective effects of initiation HSCs, we examined HSC-CM using a high-density protein array.

RESULTS: HSCs (5d) and HSCs (p3) had different morphological and phenotypic traits. HSCs (5d) presented a star-shaped appearance with expressing α-SMA at non-uniform levels between cells. However, HSCs (p3) evolved into myofibroblast-like cells without lipid droplets and expressed a uniform and higher level of α-SMA. HSC-CM (5d), but not HSC-CM (p3), provided a significant survival benefit and showed a dramatic reduction of hepatocellular necrosis and panlobular leukocyte infiltrates in mice exposed to APAP. However, this protective effect was abrogated at higher cell masses, indicating a therapeutic window of effectiveness. Furthermore, the protein array screen revealed that HSC-CM (5d) was composed of many chemokines and growth factors that correlated with inflammatory inhibition and therapeutic activity. When compared with HSC-CM (p3), higher levels of monocyte chemoattractant protein-1, macrophage inflammatory protein-1γ, hepatocyte growth factor, interleukin-10, and matrix metalloproteinase-2, but lower levels of stem cell factor and Fas-Ligand were observed in HSC-CM (5d).

CONCLUSION: These data indicated that initiation HSCs and perpetuation HSCs were different in morphology and protein expression, and provided the first experimental evidence of the potential medical value of initiation HSC-derived molecules in the treatment of ALI.

Cell therapies for treatment of human immunodeficiency virus infection

After the serendipitous discovery of HIV eradication in the "Berlin patient", interest has grown in curing HIV infection by replacing the patient's replication-competent blood cells with infection-resistant ones. At the same time, induced pluripotent stem cell technologies and genetic engineering have boosted cell therapy transfer into the clinic. Currently available cell therapy approaches to attempt to cure HIV infection include the following: (1) Transplantation of autologous or allogeneic cells spontaneously resistant or edited to resist HIV infection; (2) Transplantation of autologous T-lymphocytes spontaneously targeting or redirected against HIV; and (3) Transplantation of autologous cells engineered to work as anti-HIV antibody factories. We review here the preliminary results and potential for future applications of these approaches.

Progress and challenges in generating functional hematopoietic stem/progenitor cells from human pluripotent stem cells

The generation of hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) in vitro holds great potential for providing alternative sources of donor cells for clinical HSC transplantation. However, the low efficiency of current protocols for generating blood lineages and the dysfunction identified in hPSC-derived hematopoietic cells limit their use for full hematopoietic reconstitution in clinics. This review outlines the current understanding of in vitro hematopoietic differentiation from hPSCs, emphasizes the intrinsic and extrinsic molecular mechanisms that are attributed to the aberrant phenotype and function in hPSC-derived hematopoietic cells, pinpoints the current challenges to develop the truly functional HSCs from hPSCs for clinical applications and explores their potential solutions.

Modeling murine yolk sac hematopoiesis with embryonic stem cell culture systems

The onset of hematopoiesis in mammals is defined by generation of primitive erythrocytes and macrophage progenitors in embryonic yolk sac. Laboratories have met the challenge of transient and swiftly changing specification events from ventral mesoderm through multipotent progenitors and maturing lineage-restricted hematopoietic subtypes, by developing powerful in vitro experimental models to interrogate hematopoietic ontogeny. Most importantly, studies of differentiating embryonic stem cell derivatives in embryoid body and stromal coculture systems have identified crucial roles for transcription factor networks (e.g. Gata1, Runx1, Scl) and signaling pathways (e.g. BMP, VEGF, WNT) in controlling stem and progenitor cell output. These and other relevant pathways have pleiotropic biological effects, and are often associated with early embryonic lethality in knockout mice. Further refinement in subsequent studies has allowed conditional expression of key regulatory genes, and isolation of progenitors via cell surface markers (e.g. FLK1) and reporter-tagged constructs, with the purpose of measuring their primitive and definitive hematopoietic potential. These observations continue to inform attempts to direct the differentiation, and augment the expansion, of progenitors in human cell culture systems that may prove useful in cell replacement therapies for hematopoietic deficiencies. The purpose of this review is to survey the extant literature on the use of differentiating murine embryonic stem cells in culture to model the developmental process of yolk sac hematopoiesis.

Tenascin C promotes hematoendothelial development and T lymphoid commitment from human pluripotent stem cells in chemically defined conditions

The recent identification of hemogenic endothelium (HE) in human pluripotent stem cell (hPSC) cultures presents opportunities to investigate signaling pathways that are essential for blood development from endothelium and provides an exploratory platform for de novo generation of hematopoietic stem cells (HSCs). However, the use of poorly defined human or animal components limits the utility of the current differentiation systems for studying specific growth factors required for HE induction and manufacturing clinical-grade therapeutic blood cells. Here, we identified chemically defined conditions required to produce HE from hPSCs growing in Essential 8 (E8) medium and showed that Tenascin C (TenC), an extracellular matrix protein associated with HSC niches, strongly promotes HE and definitive hematopoiesis in this system. hPSCs differentiated in chemically defined conditions undergo stages of development similar to those previously described in hPSCs cocultured on OP9 feeders, including the formation of VE-Cadherin⁺CD73⁻CD235a/CD43⁻ HE and hematopoietic progenitors with myeloid and T lymphoid potential.

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Hemogenic endothelium is generated in a completely defined xenogen-free system

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The system reproduces all stages of hematopoietic development

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Tenascin C enhances hematoendothelial development from pluripotent stem cells

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Tenesacin C uniquely supports T cell specification

Derivation and expansion of PAX7-positive muscle progenitors from human and mouse embryonic stem cells

Cell therapies treating pathological muscle atrophy or damage requires an adequate quantity of muscle progenitor cells (MPCs) not currently attainable from adult donors. Here, we generate cultures of approximately 90% skeletal myogenic cells by treating human embryonic stem cells (ESCs) with the GSK3 inhibitor CHIR99021 followed by FGF2 and N2 supplements. Gene expression analysis identified progressive expression of mesoderm, somite, dermomyotome, and myotome markers, following patterns of embryonic myogenesis. CHIR99021 enhanced transcript levels of the pan-mesoderm gene T and paraxial-mesoderm genes MSGN1 and TBX6; immunofluorescence confirmed that 91% ± 6% of cells expressed T immediately following treatment. By 7 weeks, 47% ± 3% of cells were MYH(+ve) myocytes/myotubes surrounded by a 43% ± 4% population of PAX7(+ve) MPCs, indicating 90% of cells had achieved myogenic identity without any cell sorting. Treatment of mouse ESCs with these factors resulted in similar enhancements of myogenesis. These studies establish a foundation for serum-free and chemically defined monolayer skeletal myogenesis of ESCs.

Self-renewal and cell lineage differentiation strategies in human embryonic stem cells and induced pluripotent stem cells

INTRODUCTION

Since the initial discoveries of human embryonic and induced pluripotent stem cells, many strategies have been developed to utilize the potential of these cells for translational research and disease modeling. The success of these aims and the development of future applications in this area will depend on the ability to generate high-quality and large numbers of differentiated cell types that genetically, epigenetically, and functionally mimic the cells found in the body.

AREAS COVERED

In this review, we highlight the current strategies used to maintain stem cell pluripotency (a measure of stem cell quality), as well as provide an overview of the various differentiation strategies being used to generate cells from all three germ lineages. We also discuss the particular considerations that must be addressed when utilizing these cells for translational therapy, and provide an example of a cell type currently used in clinical trials.

EXPERT OPINION

The major challenge in regenerative medicine and disease modeling will be in generating functional cells of sufficient quality that are physiologically and epigenetically similar to the diverse cells that they are modeled after. By meeting these criteria, these differentiated products can be successfully used in disease modeling, drug/toxicology screens, and cellular replacement therapy.

FOXN1 (GFP/w) reporter hESCs enable identification of integrin-β4, HLA-DR, and EpCAM as markers of human PSC-derived FOXN1(+) thymic epithelial progenitors

Thymic epithelial cells (TECs) play a critical role in T cell maturation and tolerance induction. The generation of TECs from in vitro differentiation of human pluripotent stem cells (PSCs) provides a platform on which to study the mechanisms of this interaction and has implications for immune reconstitution. To facilitate analysis of PSC-derived TECs, we generated hESC reporter lines in which sequences encoding GFP were targeted to FOXN1, a gene required for TEC development. Using this FOXN1^GFP/w line as a readout, we developed a reproducible protocol for generating FOXN1-GFP⁺ thymic endoderm cells. Transcriptional profiling and flow cytometry identified integrin-β4 (ITGB4, CD104) and HLA-DR as markers that could be used in combination with EpCAM to selectively purify FOXN1⁺ TEC progenitors from differentiating cultures of unmanipulated PSCs. Human FOXN1⁺ TEC progenitors generated from PSCs facilitate the study of thymus biology and are a valuable resource for future applications in regenerative medicine.

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FOXN1-GFP reporter hESC lines were generated

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KGF promotes the proliferation of FOXN1-GFP⁺ cells

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FOXN1-GFP⁺ cells express TEC-associated genes

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ITGB4, HLA-DR, and EpCAM can be used to purify FOXN1⁺ TEC progenitors (219)

Induced pluripotent stem cells in hematology: current and future applications

Reprogramming somatic cells into induced pluripotent stem (iPS) cells is nowadays approaching effectiveness and clinical grade. Potential uses of this technology include predictive toxicology, drug screening, pathogenetic studies and transplantation. Here, we review the basis of current iPS cell technology and potential applications in hematology, ranging from disease modeling of congenital and acquired hemopathies to hematopoietic stem and other blood cell transplantation.

Dendritic cells derived from pluripotent stem cells: Potential of large scale production

Human pluripotent stem cells (hPSCs), including human embryonic stem cells and human induced pluripotent stem cells, are promising sources for hematopoietic cells due to their unlimited growth capacity and the pluripotency. Dendritic cells (DCs), the unique immune cells in the hematopoietic system, can be loaded with tumor specific antigen and used as vaccine for cancer immunotherapy. While autologous DCs from peripheral blood are limited in cell number, hPSC-derived DCs provide a novel alternative cell source which has the potential for large scale production. This review summarizes recent advances in differentiating hPSCs to DCs through the intermediate stage of hematopoietic stem cells. Step-wise growth factor induction has been used to derive DCs from hPSCs either in suspension culture of embryoid bodies (EBs) or in co-culture with stromal cells. To fulfill the clinical potential of the DCs derived from hPSCs, the bioprocess needs to be scaled up to produce a large number of cells economically under tight quality control. This requires the development of novel bioreactor systems combining guided EB-based differentiation with engineered culture environment. Hence, recent progress in using bioreactors for hPSC lineage-specific differentiation is reviewed. In particular, the potential scale up strategies for the multistage DC differentiation and the effect of shear stress on hPSC differentiation in bioreactors are discussed in detail.

c-Met inhibition in a HOXA9/Meis1 model of CN-AML

BACKGROUND

Hematopoiesis is a paradigm for developmental processes, hierarchically organized, with stem cells at its origin. Hematopoietic stem cells (HSCs) replenish progenitor and precursor cells of multiple lineages, which normally differentiate into short-lived mature circulating cells. Hematopoiesis has provided insight into the molecular basis of tissue homeostasis and malignancy. Malignant hematopoiesis, in particular acute myeloid leukemia (AML), results from impaired development or differentiation of HSCs and progenitors. Co-overexpression of HOX and TALE genes, particularly the HOXA cluster and MEIS1, is associated with AML. Clinically relevant models of AML are required to advance drug development for an aging patient cohort.

RESULTS

Molecular analysis identified altered gene, microRNA, and protein expression in HOXA9/Meis1 leukemic bone marrow compared to normal controls. A candidate drug screen identified the c-Met inhibitor SU11274 for further analysis. Altered cell cycle status, apoptosis, differentiation, and impaired colony formation were shown for SU11274 in AML cell lines and primary leukemic bone marrow.

CONCLUSIONS

The clonal HOXA9/Meis1 AML model is amenable to drug screening analysis. The data presented indicate that human AML cells respond in a similar manner to the HOXA9/Meis1 cells, indicating pre-clinical relevance of the mouse model.