Generation of engraftable hematopoietic stem cells from induced pluripotent stem cells by way of teratoma formation. Mol Ther. 2013;21:1424-1431. [PMID: 23670574 DOI: 10.1038/mt.2013.71]

Stepwise dual-release microparticles of BMP-4 and SCF in induced pluripotent stem cell spheroids enhance differentiation into hematopoietic stem cells

Recently, the formation of three-dimensional (3D) cell aggregates known as embryoid bodies (EBs) grown in media supplemented with HSC-specific morphogens has been utilized for the directed differentiation of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), into clinically relevant hematopoietic stem cells (HSCs). However, delivering growth factors and nutrients have become ineffective in inducing synchronous differentiation of cells due to their 3D conformation. Moreover, irregularly sized EBs often lead to the formation of necrotic cores in larger EBs, impairing differentiation. Here, we developed two gelatin microparticles (GelMPs) with different release patterns and two HSC-related growth factors conjugated to them. Slow and fast releasing GelMPs were conjugated with bone morphogenic factor-4 (BMP-4) and stem cell factor (SCF), respectively. The sequential presentation of BMP-4 and SCF in GelMPs resulted in efficient and effective hematopoietic differentiation, shown by the enhanced gene and protein expression of several mesoderm and HSC-related markers, and the increased concentration of released HSC-related cytokines. In the present study, we were able to generate CD34+, CD133+, and FLT3+ cells with similar cellular and molecular morphology as the naïve HSCs that can produce colony units of different blood cells, in vitro.

The use of artificial intelligence in induced pluripotent stem cell-based technology over 10-year period: A systematic scoping review

BACKGROUND

Stem cell research, particularly in the domain of induced pluripotent stem cell (iPSC) technology, has shown significant progress. The integration of artificial intelligence (AI), especially machine learning (ML) and deep learning (DL), has played a pivotal role in refining iPSC classification, monitoring cell functionality, and conducting genetic analysis. These enhancements are broadening the applications of iPSC technology in disease modelling, drug screening, and regenerative medicine. This review aims to explore the role of AI in the advancement of iPSC research.

METHODS

In December 2023, data were collected from three electronic databases (PubMed, Web of Science, and Science Direct) to investigate the application of AI technology in iPSC processing.

RESULTS

This systematic scoping review encompassed 79 studies that met the inclusion criteria. The number of research studies in this area has increased over time, with the United States emerging as a leading contributor in this field. AI technologies have been diversely applied in iPSC technology, encompassing the classification of cell types, assessment of disease-specific phenotypes in iPSC-derived cells, and the facilitation of drug screening using iPSC. The precision of AI methodologies has improved significantly in recent years, creating a foundation for future advancements in iPSC-based technologies.

CONCLUSIONS

Our review offers insights into the role of AI in regenerative and personalized medicine, highlighting both challenges and opportunities. Although still in its early stages, AI technologies show significant promise in advancing our understanding of disease progression and development, paving the way for future clinical applications.

Decoding the universal human chromatin landscape through teratoma-based profiling

Teratoma formation is key for evaluating differentiation of human pluripotent stem cells into embryonic germ layers and serves as a model for understanding stem cell differentiation and developmental processes. Its potential for insights into epigenome and transcriptome profiling is significant. This study integrates the analysis of the epigenome and transcriptome of hESC-generated teratomas, comparing transcriptomes between hESCs and teratomas. It employs cell type-specific expression patterns from single-cell data to deconvolve RNA-Seq data and identify cell types within teratomas. Our results provide a catalog of activating and repressive histone modifications, while also elucidating distinctive features of chromatin states. Construction of an epigenetic signature matrix enabled the quantification of diverse cell populations in teratomas and enhanced the ability to unravel the epigenetic landscape in heterogeneous tissue contexts. This study also includes a single cell multiome atlas of expression (scRNA-Seq) and chromatin accessibility (scATAC-Seq) of human teratomas, further revealing the complexity of these tissues. A histology-based digital staining tool further complemented the annotation of cell types in teratomas, enhancing our understanding of their cellular composition. This research is a valuable resource for examining teratoma epigenomic and transcriptomic landscapes and serves as a model for epigenetic data comparison.

Making Human Hematopoietic Stem Cells Without Transgenes

Creating hematopoietic stem cells (HSCs) capable of multilineage engraft while possessing the ability to self-renew stands as a pivotal achievement within the field of regenerative medicine. However, achieving the generation of these cells without transgene expression or teratoma formation has not been fully accomplished. In a recent publication featured in Cell Stem Cell, Piau et al. document the production of functional HSCs derived from human-induced pluripotent stem cells (hiPSCs). They achieved this through a one-step differentiation protocol that notably does not require any transgene expression. hiPSCs-derived HSCs can engraft and self-renew upon serial transplantation and they are able to reconstitute lymphoid, myeloid, and erythroid compartments. This study presents a promising system to further study human HSC ontogeny, and it might represent a crucial step to obtain HSCs.

A novel Kit mutant rat enables hematopoietic stem cell engraftment without irradiation

Hematopoietic stem cell (HSC) transplantation is extensively studied in mouse models, but their limited scale presents challenges for effective engraftment and comprehensive evaluations. Rats, owing to their larger size and anatomical similarity to humans, offer a promising alternative. In this study, we establish a rat model with the KitV834M mutation, mirroring KitW41 mice often used in KIT signaling and HSC research. KitV834M rats are viable and fertile, displaying anemia and mast cell depletion similar to KitW41 mice. The colony-forming unit assay revealed that the KitV834M mutation leads to reduced proliferation and loss of or decreased pluripotency of hematopoietic stem and progenitor cells (HSPCs), resulting in diminished competitive repopulating capacity of KitV834M HSPCs in competitive transplantation assays. Importantly, KitV834M rats support donor rat-HSC engraftment without irradiation. Leveraging the larger scale of this rat model enhances our understanding of HSC biology and transplantation dynamics, potentially advancing our knowledge in this field.

Cis inhibition of NOTCH1 through JAGGED1 sustains embryonic hematopoietic stem cell fate

Hematopoietic stem cells (HSCs) develop from the hemogenic endothelium (HE) in the aorta- gonads-and mesonephros (AGM) region and reside within Intra-aortic hematopoietic clusters (IAHC) along with hematopoietic progenitors (HPC). The signalling mechanisms that distinguish HSCs from HPCs are unknown. Notch signaling is essential for arterial specification, IAHC formation and HSC activity, but current studies on how Notch segregates these different fates are inconsistent. We now demonstrate that Notch activity is highest in a subset of, GFI1 + , HSC-primed HE cells, and is gradually lost with HSC maturation. We uncover that the HSC phenotype is maintained due to increasing levels of NOTCH1 and JAG1 interactions on the surface of the same cell (cis) that renders the NOTCH1 receptor from being activated. Forced activation of the NOTCH1 receptor in IAHC activates a hematopoietic differentiation program. Our results indicate that NOTCH1-JAG1 cis-inhibition preserves the HSC phenotype in the hematopoietic clusters of the embryonic aorta.

Advancements in medical research using fetal sheep: Implications for human health and treatment methods

Sheep are typically considered as industrial animals that provide wool and meals. However, they play a significant role in medical research in addition to their conventional use. Notably, sheep fetuses are resistant to surgical invasions and can endure numerous manipulations, such as needle puncture and cell transplantation, and surgical operations requiring exposure beyond the uterus. Based on these distinguishing characteristics, we established a chimeric sheep model capable of producing human/monkey pluripotent cell-derived blood cells via the fetal liver. Furthermore, sheep have become crucial as human fetal models, acting as platforms for developing and improving techniques for intrauterine surgery to address congenital disorders and clarifying the complex pharmacokinetic interactions between mothers and their fetuses. This study emphasizes the significant contributions of fetal sheep to advancing human disease understanding and treatment strategies, highlighting their unique characteristics that are not present in other animals.

Impact of the overexpression of the tyrosine kinase receptor RET in the hematopoietic potential of induced pluripotent stem cells (iPSCs)

INTRODUCTION

Previous studies have suggested that the tyrosine kinase receptor RET plays a significant role in the hematopoietic potential in mice and could also be used to expand cord-blood derived hematopoietic stem cells (HSCs). The role of RET in human iPSC-derived hematopoiesis has not been tested so far.

METHODS

To test the implication of RET on the hematopoietic potential of iPSCs, we activated its pathway with the lentiviral overexpression of RETWT or RETC634Y mutation in normal iPSCs. An iPSC derived from a patient harboring the RETC634Y mutation (iRETC634Y) and its CRISPR-corrected isogenic control iPSC (iRETCTRL) were also used. The hematopoietic potential was tested using 2D cultures and evaluated regarding the phenotype and the clonogenic potential of generated cells.

RESULTS

Hematopoietic differentiation from iPSCs with RET overexpression (WT or C634Y) led to a significant reduction in the number and in the clonogenic potential of primitive hematopoietic cells (CD34+/CD38-/CD49f+) as compared to control iPSCs. Similarly, the hematopoietic potential of iRETC634Y was reduced as compared to iRETCTRL. Transcriptomic analyses revealed a specific activated expression profile for iRETC634Y compared to its control with evidence of overexpression of genes which are part of the MAPK network with negative hematopoietic regulator activities.

CONCLUSION

RET activation in iPSCs is associated with an inhibitory activity in iPSC-derived hematopoiesis, potentially related to MAPK activation.

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.

Haematopoietic development and HSC formation in vitro: promise and limitations of gastruloid models

Haematopoietic stem cells (HSCs) are the most extensively studied adult stem cells. Yet, six decades after their first description, reproducible and translatable generation of HSC in vitro remains an unmet challenge. HSC production in vitro is confounded by the multi-stage nature of blood production during development. Specification of HSC is a late event in embryonic blood production and depends on physical and chemical cues which remain incompletely characterised. The precise molecular composition of the HSC themselves is incompletely understood, limiting approaches to track their origin in situ in the appropriate cellular, chemical and mechanical context. Embryonic material at the point of HSC emergence is limiting, highlighting the need for an in vitro model of embryonic haematopoietic development in which current knowledge gaps can be addressed and exploited to enable HSC production. Gastruloids are pluripotent stem cell-derived 3-dimensional (3D) cellular aggregates which recapitulate developmental events in gastrulation and early organogenesis with spatial and temporal precision. Gastruloids self-organise multi-tissue structures upon minimal and controlled external cues, and are amenable to live imaging, screening, scaling and physicochemical manipulation to understand and translate tissue formation. In this review, we consider the haematopoietic potential of gastruloids and review early strategies to enhance blood progenitor and HSC production. We highlight possible strategies to achieve HSC production from gastruloids, and discuss the potential of gastruloid systems in illuminating current knowledge gaps in HSC specification.

Generation of transgene-free hematopoietic stem cells from human induced pluripotent stem cells

Hematopoietic stem cells (HSCs) are the rare cells responsible for the lifelong curative effects of hematopoietic cell (HC) transplantation. The demand for clinical-grade HSCs has increased significantly in recent decades, leading to major difficulties in treating patients. A promising but not yet achieved goal is the generation of HSCs from pluripotent stem cells. Here, we have obtained vector- and stroma-free transplantable HSCs by differentiating human induced pluripotent stem cells (hiPSCs) using an original one-step culture system. After injection into immunocompromised mice, cells derived from hiPSCs settle in the bone marrow and form a robust multilineage hematopoietic population that can be serially transplanted. Single-cell RNA sequencing shows that this repopulating activity is due to a hematopoietic population that is transcriptionally similar to human embryonic aorta-derived HSCs. Overall, our results demonstrate the generation of HSCs from hiPSCs and will help identify key regulators of HSC production during human ontogeny.

Cell-based Therapies for Corneal and Retinal Disorders

Maintenance of the visual function is the desired outcome of ophthalmologic therapies. The shortcomings of the current treatment options, like partial recovery, post-operation failure, rigorous post-operative care, complications, etc., which are usually encountered with the conventional treatment options has warranted newer treatment options that may eliminate the root cause of diseases and minimize the side effects. Cell therapies, a class of regenerative medicines, have emerged as cutting-edge treatment option. The corneal and retinal dystrophies during the ocular disorders are the major cause of blindness, worldwide. Corneal disorders are mainly categorized mainly into corneal epithelial, stromal, and endothelial disorders. On the other hand, glaucoma, retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, Stargardt Disease, choroideremia, Leber congenital amaurosis are then major retinal degenerative disorders. In this manuscript, we have presented a detailed overview of the development of cell-based therapies, using embryonic stem cells, bone marrow stem cells, mesenchymal stem cells, dental pulp stem cells, induced pluripotent stem cells, limbal stem cells, corneal epithelial, stromal and endothelial, embryonic stem cell-derived differentiated cells (like retinal pigment epithelium or RPE), neural progenitor cells, photoreceptor precursors, and bone marrow-derived hematopoietic stem/progenitor cells etc. The manuscript highlights their efficiency, drawbacks and the strategies that have been explored to regain visual function in the preclinical and clinical state associated with them which can be considered for their potential application in the development of treatment.

Generation of a human induced pluripotent stem cell line harboring the infant leukemia-associated fusion gene, KMT2A-AFF1 (IMSUTi002-A-2)

KMT2A-AFF1 (MLL-AF4), formed by chromosomal translocation t(4;11), is observed specifically in infant pro-B acute lymphoblastic leukemia, and the main driver of leukemogenesis. In this study, a human induced pluripotent stem cell (hiPSC) line harboring KMT2A-AFF1 (IMSUTi002-A-2), which has the ability to simultaneously induce the doxycycline-inducible expression of KMT2A-AFF1 and EGFP, was established. This hiPSC can be a powerful model for understanding infant leukemia and risk assessment of leukemogenesis.

Generating hematopoietic cells from human pluripotent stem cells: approaches, progress and challenges

Human pluripotent stem cells (hPSCs) have been suggested as a potential source for the production of blood cells for clinical application. In two decades, almost all types of blood cells can be successfully generated from hPSCs through various differentiated strategies. Meanwhile, with a deeper understanding of hematopoiesis, higher efficiency of generating progenitors and precursors of blood cells from hPSCs is achieved. However, how to generate large-scale mature functional cells from hPSCs for clinical use is still difficult. In this review, we summarized recent approaches that generated both hematopoietic stem cells and mature lineage cells from hPSCs, and remarked their efficiency and mechanisms in producing mature functional cells. We also discussed the major challenges in hPSC-derived products of blood cells and provided some potential solutions. Our review summarized efficient, simple, and defined methodologies for developing good manufacturing practice standards for hPSC-derived blood cells, which will facilitate the translation of these products into the clinic.

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.

The quest for the holy grail: overcoming challenges in expanding human hematopoietic stem cells for clinical use

Hematopoietic stem cell (HSC) transplantation has been the golden standard for many hematological disorders. However, the number of HSCs obtained from several sources, including umbilical cord blood (UCB), often is insufficient for transplantation. For decades, maintaining or even expanding HSCs for therapeutic purposes has been a "holy grail" in stem cell biology. Different methods have been proposed to improve the efficiency of cell expansion and enhance homing potential such as co-culture with stromal cells or treatment with specific agents. Recent progress has shown that this is starting to become feasible using serum-free and well-defined media. Some of these protocols to expand HSCs along with genetic modification have been successfully applied in clinical trials and some others are studied in preclinical and clinical studies. However, the main challenges regarding ex vivo expansion of HSCs such as limited growth potential and tendency to differentiate in culture still need improvements. Understanding the biology of blood stem cells, their niche and signaling pathways has provided possibilities to regulate cell fate decisions and manipulate cells to optimize expansion of HSCs in vitro. Here, we review the plethora of HSC expansion protocols that have been proposed and indicate the current state of the art for their clinical application.

NK cells direct the perspective approaches to cancer immunotherapy

Natural killer (NK) cells are innate immune cells with cytotoxic potentials to kill cancerous cells in several mechanisms, which could be implied for cancer therapy. While potent, their antitumor activities specially for solid tumors impaired by inadequate tumor infiltration, suppressive tumor microenvironment, cancer-associated stroma cells, and tumor-supportive immune cells. Therefore, manipulating or reprogramming these barriers by prospective strategies might improve current immunotherapies in the clinic or introduce novel NK-based immunotherapies. NK-based immunotherapy could be developed in monotherapy or in combination with other therapeutic regimens such as oncolytic virus therapy and immune checkpoint blockade, as presented in this review.

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.

Current status of producing autologous hematopoietic stem cells

Hematopoietic stem cells (HSCs) transplantation is an established therapy for many diseases of the hematopoietic system, for example aplastic anemia, acute myeloid leukemia and acute lymphoblastic leukemia. With the development of the HSCs research, HSCs provide an attractive method for treating hereditary blood disorders and immunotherapy of cancer by introducing gene modification. Compared with allogenic HSCs transplantation, using autologous HSCs or HSCs from induced pluripotent stem cells (iPSCs) would eliminate the probability of alloimmunization and transfusion-transmitted infectious diseases. The methods for obtaining autologous HSCs include amplifying patients' HSCs or inducing patients' somatic cells to HSCs (graph abstract). However, the biggest problem is inducing HSCs to proliferate in vitro and maintaining their stemness at the same time. Although many tests have been made to transform iPSCs to HSCs, the artificially generated HSCs still have substantial disparity compared with physiological HSCs. This review summarized the application status and obstacles to implantation of autologous HSCs and iPSC-derived HSCs. Meanwhile, we summarized the latest research progress in HSCs amplification and iPSCs reprogramming methods, which will help to solve the problems mentioned above.

Acute Lymphoblastic Leukemia Developing in a Patient with 46, XY Pure Gonadal Dysgenesis (Swyer Syndrome) with Malignant Gonadal Germ Cell Tumor: A Case Report and Literature Review

A female phenotype with strip-like gonads, 46, XY pure gonadal dysgenesis (PGD) has a high tendency to develop into gonadal germ cell tumors. We described one patient with 46, XY PGD, who had a gonadal mixed germ cell tumor (GCT) and acute lymphoblastic leukemia (ALL). This is a unique case because two malignancies developed and relapsed in one person with chromosome abnormality, and the patient is the youngest reported so far. There is an association between her GCT and ALL, as the two malignancies may share a common clonal origin and the NRAS mutation likely plays a role in tumor genesis. We organized MDT to formulate a suitable plan of treatment. We completed the surgery and full cycles of chemotherapy for GCT and controlled ALL by chemotherapy and bone marrow transplantation. However, unfortunately, the young life finally ended following a rare transplant rejection. We concluded that ALL likely shares common clonal origin with GCT and that gene mutations may play a role in neoplasia, which requires further exploration. In the face of such complex conditions, we need to balance the treatment of both diseases to prolong survival and improve the patients' quality of life.

Using Pluripotent Stem Cells to Understand Normal and Leukemic Hematopoietic Development

Several decades have passed since the generation of the first embryonic stem cell (ESC) lines both in mice and in humans. Since then, stem cell biologists have tried to understand their potential biological and clinical uses for their implementation in regenerative medicine. The hematopoietic field was a pioneer in establishing the potential use for the development of blood cell products and clinical applications; however, early expectations have been truncated by the difficulty in generating bonafide hematopoietic stem cells (HSCs). Despite some progress in understanding the origin of HSCs during embryonic development, the reproduction of this process in vitro is still not possible, but the knowledge acquired in the embryo is slowly being implemented for mouse and human pluripotent stem cells (PSCs). In contrast, ESC-derived hematopoietic cells may recapitulate some leukemic transformation processes when exposed to oncogenic drivers. This would be especially useful to model prenatal leukemia development or other leukemia-predisposing syndromes, which are difficult to study. In this review, we will review the state of the art of the use of PSCs as a model for hematopoietic and leukemia development.

Challenges in Cell Fate Acquisition to Scid-Repopulating Activity from Hemogenic Endothelium of hiPSCs Derived from AML Patients Using Forced Transcription Factor Expression

The generation of human hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) represents a major goal in regenerative medicine and is believed would follow principles of early development. HSCs arise from a type of endothelial cell called a “hemogenic endothelium” (HE), and human HSCs are experimentally detected by transplantation into SCID or other immune-deficient mouse recipients, termed SCID-Repopulating Cells (SRC). Recently, SRCs were detected by forced expression of seven transcription factors (TF) (ERG, HOXA5, HOXA9, HOXA10, LCOR, RUNX1, and SPI1) in hPSC-derived HE, suggesting these factors are deficient in hPSC differentiation to HEs required to generate HSCs. Here we derived PECAM-1-, Flk-1-, and VE-cadherin-positive endothelial cells that also lack CD45 expression (PFV^CD45−) which are solely responsible for hematopoietic output from iPSC lines reprogrammed from AML patients. Using HEs derived from AML patient iPSCs devoid of somatic leukemic aberrations, we sought to generate putative SRCs by the forced expression of 7TFs to model autologous HSC transplantation. The expression of 7TFs in hPSC-derived HE cells from an enhanced hematopoietic progenitor capacity was present in vitro, but failed to acquire SRC activity in vivo. Our findings emphasize the benefits of forced TF expression, along with the continued challenges in developing HSCs for autologous-based therapies from hPSC sources.

Proof-of-Concept of a Novel Cell Separation Technology Using Magnetic Agarose-Based Beads

The safety of the cells used for Advanced Therapy Medicinal Products is crucial for patients. Reliable methods for the cell purification are very important for the commercialization of those new therapies. With the large production scale envisioned for commercialization, the cell isolation methods need to be efficient, robust, operationally simple and generic while ensuring cell biological functionality and safety. In this study, we used high magnetized magnetic agarose-based beads conjugated with protein A to develop a new method for cell separation. A high separation efficiency of 91% yield and consistent isolation performances were demonstrated using population mixtures of human mesenchymal stem cells and HER2+ SKBR3 cells (80:20, 70:30 and 30:70). Additionally, high robustness against mechanical stress and minimal unspecific binding obtained with the protein A base conjugated magnetic beads were significant advantages in comparison with the same magnetic microparticles where the antibodies were covalently conjugated. This study provided insights on features of large high magnetized microparticles, which is promising for the large-scale application of cell purification.

Evaluation of the Effects of Exposure to Power-Frequency Magnetic Fields on the Differentiation of Hematopoietic Stem/Progenitor Cells Using Human-Induced Pluripotent Stem Cells

The causal association between exposure to power‐frequency magnetic fields (MFs) and childhood leukemia has been under discussion. Although evidence from experimental studies is required for a conclusion to be reached, only a few studies have focused on the effects of MF exposure on the human hematopoietic system directly related to leukemogenesis. Here, we established an in vitro protocol to simulate the differentiation of human mesodermal cells to hematopoietic stem progenitor cells (HSPCs) using human‐induced pluripotent stem cells. Furthermore, we introduced MF in the protocol to study the effects of exposure. After a continuous exposure to 0–300 mT of 50‐Hz MFs during the differentiation process, the efficiency of differentiation of mesodermal cells into HSPCs was analyzed in a single‐blinded manner. The percentage of emerged HSPCs from mesodermal cells in groups exposed to 50‐Hz MFs indicated a lack of significant changes compared with those in the sham‐exposed group. These results suggest that exposure to 50‐Hz MFs up to 300 mT does not affect the differentiation of human mesodermal cells to HSPCs, which may be involved in the initial process of leukemogenesis. © 2022 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.

Immunomagnetic microfluidic integrated system for potency-based multiple separation of heterogeneous stem cells with high throughput capabilities

Multipotent adult stem cells (MASCs) derived from Pluripotent stem cells (PSCs) have found widespread use in various applications, including regenerative therapy and drug screening. For these applications, highly pluripotent PSCs need to be selectively separated from those that show low pluripotency for reusage of PSCs, and MASCs need to be collected for further application. Herein, we developed immunomagnetic microfluidic integrated system (IM-MIS) for separation of stem cells depending on potency level. In this system, each stem cell was multiple-separated in microfluidics chip by magnetophoretic mobility of magnetic-activated cells based on the combination of two sizes of magnetic nanoparticles and two different antibodies. Magnetic particles had a difference in the degree of magnetization, and antibodies recognized potency-related surface markers. IM-MIS showed superior cell separation performance than FACS with high throughput (49.5%) in a short time (<15 min) isolate 1 × 10⁷ cells, and higher purity (92.1%) than MACS. IM-MIS had a cell viability of 89.1%, suggesting that IM-MIS had no effect on cell viability during isolation. Furthermore, IM-MIS did not affect the key characteristics of stem cells including its differentiation potency, phenotype, genotype, and karyotype. IM-MIS may offer a new platform for the development of multi-separation systems for diverse stem cell applications.

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.

Hematopoietic Stem Cells and Regeneration

Hematopoietic stem cell (HSC) regeneration is the remarkable process by which extremely rare, normally inactive cells of the bone marrow can replace an entire organ if called to do so by injury or harnessed by transplantation. HSC research is arguably the first quantitative single-cell science and the foundation of adult stem cell biology. Bone marrow transplant is the oldest and most refined technique of regenerative medicine. Here we review the intertwined history of the discovery of HSCs and bone marrow transplant, the molecular and cellular mechanisms of HSC self-renewal, and the use of HSCs and their derivatives for cell therapy.

Single-Cell Approaches to Deconvolute the Development of HSCs

Hematopoietic stem cells (HSCs) play a core role in blood development. The ability to efficiently produce HSCs from various pluripotent stem cell sources is the Holy Grail in the hematology field. However, in vitro or in vivo HSC production remains low, which may be attributable to the lack of understanding of hematopoiesis. Here, we review the recent progress in this area and introduce advanced technologies, such as single-cell RNA-seq, spatial transcriptomics, and molecular barcoding, which may help to acquire missing information about HSC generation. We finally discuss unresolved questions, the answers to which may be conducive to HSC production, providing a promising path toward HSC-based immunotherapies.

Industrially Compatible Transfusable iPSC-Derived RBCs: Progress, Challenges and Prospective Solutions

Amidst the global shortfalls in blood supply, storage limitations of donor blood and the availability of potential blood substitutes for transfusion applications, society has pivoted towards in vitro generation of red blood cells (RBCs) as a means to solve these issues. Many conventional research studies over the past few decades have found success in differentiating hematopoietic stem and progenitor cells (HSPCs) from cord blood, adult bone marrow and peripheral blood sources. More recently, techniques that involve immortalization of erythroblast sources have also gained traction in tackling this problem. However, the RBCs generated from human induced pluripotent stem cells (hiPSCs) still remain as the most favorable solution due to many of its added advantages. In this review, we focus on the breakthroughs for high-density cultures of hiPSC-derived RBCs, and highlight the major challenges and prospective solutions throughout the whole process of erythropoiesis for hiPSC-derived RBCs. Furthermore, we elaborate on the recent advances and techniques used to achieve cost-effective, high-density cultures of GMP-compliant RBCs, and on their relevant novel applications after downstream processing and purification.

Induced Pluripotent Stem Cells to Model Juvenile Myelomonocytic Leukemia: New Perspectives for Preclinical Research

Juvenile myelomonocytic leukemia (JMML) is a malignant myeloproliferative disorder arising in infants and young children. The origin of this neoplasm is attributed to an early deregulation of the Ras signaling pathway in multipotent hematopoietic stem/progenitor cells. Since JMML is notoriously refractory to conventional cytostatic therapy, allogeneic hematopoietic stem cell transplantation remains the mainstay of curative therapy for most cases. However, alternative therapeutic approaches with small epigenetic molecules have recently entered the stage and show surprising efficacy at least in specific subsets of patients. Hence, the establishment of preclinical models to test novel agents is a priority. Induced pluripotent stem cells (IPSCs) offer an opportunity to imitate JMML ex vivo, after attempts to generate immortalized cell lines from primary JMML material have largely failed in the past. Several research groups have previously generated patient-derived JMML IPSCs and successfully differentiated these into myeloid cells with extensive phenotypic similarities to primary JMML cells. With infinite self-renewal and the capability to differentiate into multiple cell types, JMML IPSCs are a promising resource to advance the development of treatment modalities targeting specific vulnerabilities. This review discusses current reprogramming techniques for JMML stem/progenitor cells, related clinical applications, and the challenges involved.

Specific Blood Cells Derived from Pluripotent Stem Cells: An Emerging Field with Great Potential in Clinical Cell Therapy

Widely known for self-renewal and multilineage differentiation, stem cells can be differentiated into all specialized tissues and cells in the body. In the past few years, a number of researchers have focused on deriving hematopoietic stem cells (HSCs) from pluripotent stem cells (PSCs) as alternative sources for clinic. Existing findings demonstrated that it is feasible to obtain HSCs and certain mature blood lineages from PSCs, except for several issues to be addressed. This short review outlines the technologies used for hematopoietic differentiation in recent years. In addition, the therapeutic value of PSCs as a potential source of various blood cells is also discussed as well as its challenges and directions in future clinical applications.

Progress in the production of haematopoietic stem and progenitor cells from human pluripotent stem cells

Cell therapies are currently used to treat many haematological diseases. These treatments range from the long-term reconstitution of the entire haematopoietic system using the most potent haematopoietic stem cells (HSCs) to the short-term rescue with mature functional end cells such as oxygen-carrying red blood cells and cells of the immune system that can fight infection and repair tissue. Limitations in supply and the risk of transmitting infection has prompted the design of protocols to produce some of these cell types from human pluripotent stem cells (hPSCs). Although it has proven challenging to generate the most potent HSCs directly from hPSCs, significant progress has been made in the development of differentiation protocols that can successfully produce haematopoietic progenitor cells and most of the mature cell lineages. We review the key steps used in the production of haematopoietic stem and progenitor cells (HSPCs) from hPSCs and the cell surface markers and reporter strategies that have been used to define specific transitions. Most studies have relied on the use of known markers that define HSPC production in vivo but more recently single cell RNA sequencing has allowed a less biased approach to their characterisation. Transcriptional profiling has identified new markers for naïve and committed hPSC-derived HSPC populations and trajectory analyses has provided novel insights into their lineage potential. Direct comparison of in vitro- and in vivo-derived RNA single cell sequencing datasets has highlights similarities and differences between the two systems and this deeper understanding will be key to the design and the tracking of improved and more efficient differentiation protocols.

Myogenic Cell Transplantation in Genetic and Acquired Diseases of Skeletal Muscle

This article will review myogenic cell transplantation for congenital and acquired diseases of skeletal muscle. There are already a number of excellent reviews on this topic, but they are mostly focused on a specific disease, muscular dystrophies and in particular Duchenne Muscular Dystrophy. There are also recent reviews on cell transplantation for inflammatory myopathies, volumetric muscle loss (VML) (this usually with biomaterials), sarcopenia and sphincter incontinence, mainly urinary but also fecal. We believe it would be useful at this stage, to compare the same strategy as adopted in all these different diseases, in order to outline similarities and differences in cell source, pre-clinical models, administration route, and outcome measures. This in turn may help to understand which common or disease-specific problems have so far limited clinical success of cell transplantation in this area, especially when compared to other fields, such as epithelial cell transplantation. We also hope that this may be useful to people outside the field to get a comprehensive view in a single review. As for any cell transplantation procedure, the choice between autologous and heterologous cells is dictated by a number of criteria, such as cell availability, possibility of in vitro expansion to reach the number required, need for genetic correction for many but not necessarily all muscular dystrophies, and immune reaction, mainly to a heterologous, even if HLA-matched cells and, to a minor extent, to the therapeutic gene product, a possible antigen for the patient. Finally, induced pluripotent stem cell derivatives, that have entered clinical experimentation for other diseases, may in the future offer a bank of immune-privileged cells, available for all patients and after a genetic correction for muscular dystrophies and other myopathies.

To Better Generate Organoids, What Can We Learn From Teratomas?

The genomic profile of animal models is not completely matched with the genomic profile of humans, and 2D cultures do not represent the cellular heterogeneity and tissue architecture found in tissues of their origin. Derived from 3D culture systems, organoids establish a crucial bridge between 2D cell cultures and in vivo animal models. Organoids have wide and promising applications in developmental research, disease modeling, drug screening, precision therapy, and regenerative medicine. However, current organoids represent only single or partial components of a tissue, which lack blood vessels, native microenvironment, communication with near tissues, and a continuous dorsal-ventral axis within 3D culture systems. Although efforts have been made to solve these problems, unfortunately, there is no ideal method. Teratoma, which has been frequently studied in pathological conditions, was recently discovered as a new in vivo model for developmental studies. In contrast to organoids, teratomas have vascularized 3D structures and regions of complex tissue-like organization. Studies have demonstrated that teratomas can be used to mimic multilineage human development, enrich specific somatic progenitor/stem cells, and even generate brain organoids. These results provide unique opportunities to promote our understanding of the vascularization and maturation of organoids. In this review, we first summarize the basic characteristics, applications, and limitations of both organoids and teratomas and further discuss the possibility that in vivo teratoma systems can be used to promote the vascularization and maturation of organoids within an in vitro 3D culture system.

Cell and Gene Therapy for Anemia: Hematopoietic Stem Cells and Gene Editing

Hereditary anemia has various manifestations, such as sickle cell disease (SCD), Fanconi anemia, glucose-6-phosphate dehydrogenase deficiency (G6PDD), and thalassemia. The available management strategies for these disorders are still unsatisfactory and do not eliminate the main causes. As genetic aberrations are the main causes of all forms of hereditary anemia, the optimal approach involves repairing the defective gene, possibly through the transplantation of normal hematopoietic stem cells (HSCs) from a normal matching donor or through gene therapy approaches (either in vivo or ex vivo) to correct the patient’s HSCs. To clearly illustrate the importance of cell and gene therapy in hereditary anemia, this paper provides a review of the genetic aberration, epidemiology, clinical features, current management, and cell and gene therapy endeavors related to SCD, thalassemia, Fanconi anemia, and G6PDD. Moreover, we expound the future research direction of HSC derivation from induced pluripotent stem cells (iPSCs), strategies to edit HSCs, gene therapy risk mitigation, and their clinical perspectives. In conclusion, gene-corrected hematopoietic stem cell transplantation has promising outcomes for SCD, Fanconi anemia, and thalassemia, and it may overcome the limitation of the source of allogenic bone marrow transplantation.

Cisplatin induces differentiation in teratomas derived from pluripotent stem cells

Introduction

Currently, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can be induced to differentiate at the cellular level but not to form mature tissues or organs suitable for transplantation. ESCs/iPSCs form immature teratomas after injection into immunodeficient mice. In humans, immature teratomas often transform into fully differentiated mature teratomas after administration of anticancer agents.

Methods

We first investigated the ability of cisplatin to induce changes in mouse ESCs/iPSCs in vitro. Next, we designed experiments to analyze ESC/iPSC-derived immature teratoma tissue in vivo after treatment of cisplatin. Groups of six mice carrying ESC- or iPSC-derived teratomas were given either low or high dose intraperitoneal injection of cisplatin, while the control group received saline for 4 weeks.

Results

Treatment of ESC/iPSC cultures with cisplatin for 3 days caused a dose-related decrease in cell numbers without inducing any morphological changes to the cells. ESC/iPSC-derived teratomas showed lower growth rates with a significantly higher mature components ratio in a concentration dependent manner after cisplatin treatment (P < 0.05); however, immunohistochemical analyses demonstrated a significantly reduced PCNA labelling index and an increase in an apoptosis marker on immature neural components (P < 0.05) along with emergence of h-Caldesmon⁺ mature smooth muscle cells in treated mice. Moreover, newly differentiated components not found in the control group, such as mature adipose tissue, cartilage, and pancreas, as well as striated muscle, salivary glands, gastric mucosa with fundic glands, and hair follicles emerged. The identities of these components were confirmed by immunostaining for specific markers.

Conclusions

Cisplatin has the ability to reduce immature components in ESC/iPSC-derived teratomas, presumably through apoptosis, and also to induce them to differentiate.

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Transformation of immature to mature teratoma after chemotherapy was verified.

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Mice bearing ESC/iPSC-derived immature teratomas were used.

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Mice were treated with intraperitoneal injection of cisplatin for 4 weeks.

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Newly differentiated structures were found only in the tumors of treated mice.

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Cisplatin can induce differentiation in ESC/iPSC-derived immature teratomas.

Genetically edited CD34+ cells derived from human iPS cells in vivo but not in vitro engraft and differentiate into HIV-resistant cells

Genetic editing of induced pluripotent stem (iPS) cells represents a promising avenue for an HIV cure. However, certain challenges remain before bringing this approach to the clinic. Among them, in vivo engraftment of cells genetically edited in vitro needs to be achieved. In this study, CD34+ cells derived in vitro from iPS cells genetically modified to carry the CCR5Δ32 mutant alleles did not engraft in humanized immunodeficient mice. However, the CD34+ cells isolated from teratomas generated in vivo from these genetically edited iPS cells engrafted in all experiments. These CD34+ cells also gave rise to peripheral blood mononuclear cells in the mice that, when inoculated with HIV in cell culture, were resistant to HIV R5-tropic isolates. This study indicates that teratomas can provide an environment that can help evaluate the engraftment potential of CD34+ cells derived from the genetically modified iPS cells in vitro. The results further confirm the possibility of using genetically engineered iPS cells to derive engraftable hematopoietic stem cells resistant to HIV as an approach toward an HIV cure.

Running the full human developmental clock in interspecies chimeras using alternative human stem cells with expanded embryonic potential

Human pluripotent stem cells (hPSCs) can generate specialized cell lineages that have great potential for regenerative therapies and disease modeling. However, the developmental stage of the lineages generated from conventional hPSC cultures in vitro are embryonic in phenotype, and may not possess the cellular maturity necessary for corrective regenerative function in vivo in adult recipients. Here, we present the scientific evidence for how adult human tissues could generate human–animal interspecific chimeras to solve this problem. First, we review the phenotypes of the embryonic lineages differentiated from conventional hPSC in vitro and through organoid technologies and compare their functional relevance to the tissues generated during normal human in utero fetal and adult development. We hypothesize that the developmental incongruence of embryo-stage hPSC-differentiated cells transplanted into a recipient adult host niche is an important mechanism ultimately limiting their utility in cell therapies and adult disease modeling. We propose that this developmental obstacle can be overcome with optimized interspecies chimeras that permit the generation of adult-staged, patient-specific whole organs within animal hosts with human-compatible gestational time-frames. We suggest that achieving this goal may ultimately have to await the derivation of alternative, primitive totipotent-like stem cells with improved embryonic chimera capacities. We review the scientific challenges of deriving alternative human stem cell states with expanded embryonic potential, outline a path forward for conducting this emerging research with appropriate ethical and regulatory oversight, and defend the case of why current federal funding restrictions on this important category of biomedical research should be liberalized.

Modulation of APLNR Signaling Is Required during the Development and Maintenance of the Hematopoietic System

Apelin receptor (APLNR/AGTRLl1/APJ) marks a transient cell population during the differentiation of hematopoietic stem and progenitor cells (HSPCs) from pluripotent stem cells, but its function during the production and maintenance of hematopoietic stem cells is not clear. We generated an Aplnr-tdTomato reporter mouse embryonic stem cell (mESC) line and showed that HSPCs are generated exclusively from mesodermal cells that express Aplnr-tdTomato. HSPC production from mESCs was impaired when Aplnr was deleted, implying that this pathway is required for their production. To address the role of APLNR signaling in HSPC maintenance, we added APELIN ligands to ex vivo AGM cultures. Activation of the APLNR pathway in this system impaired the generation of long-term reconstituting HSPCs and appeared to drive myeloid differentiation. Our data suggest that the APLNR signaling is required for the generation of cells that give rise to HSCs, but that its subsequent downregulation is required for their maintenance.

The hemogenic endothelium: a critical source for the generation of PSC-derived hematopoietic stem and progenitor cells

In vitro generation of hematopoietic cells and especially hematopoietic stem cells (HSCs) from human pluripotent stem cells (PSCs) are subject to intensive research in recent decades, as these cells hold great potential for regenerative medicine and autologous cell replacement therapies. Despite many attempts, in vitro, de novo generation of bona fide HSCs remains challenging, and we are still far away from their clinical use, due to insufficient functionality and quantity of the produced HSCs. The challenges of generating PSC-derived HSCs are already apparent in early stages of hemato-endothelial specification with the limitation of recapitulating complex, dynamic processes of embryonic hematopoietic ontogeny in vitro. Further, these current shortcomings imply the incompleteness of our understanding of human ontogenetic processes from embryonic mesoderm over an intermediate, specialized hemogenic endothelium (HE) to their immediate progeny, the HSCs. In this review, we examine the recent investigations of hemato-endothelial ontogeny and recently reported progress for the conversion of PSCs and other promising somatic cell types towards HSCs with the focus on the crucial and inevitable role of the HE to achieve the long-standing goal—to generate therapeutically applicable PSC-derived HSCs in vitro.

Generation and manipulation of human iPSC-derived platelets

The discovery of iPSCs has led to the ex vivo production of differentiated cells for regenerative medicine. In the case of transfusion products, the derivation of platelets from iPSCs is expected to complement our current blood-donor supplied transfusion system through donor-independent production with complete pathogen-free assurance. This derivation can also overcome alloimmune platelet transfusion refractoriness by resulting in autologous, HLA-homologous or HLA-deficient products. Several developments were necessary to produce a massive number of platelets required for a single transfusion. First, expandable megakaryocytes were established from iPSCs through transgene expression. Second, a turbulent-type bioreactor with improved platelet yield and quality was developed. Third, novel drugs that enabled efficient feeder cell-free conditions were developed. Fourth, the platelet-containing suspension was purified and resuspended in an appropriate buffer. Finally, the platelet product needed to be assured for competency and safety including non-tumorigenicity through in vitro and in vivo preclinical tests. Based on these advancements, a clinical trial has started. The generation of human iPSC-derived platelets could evolve transfusion medicine to the next stage and assure a ubiquitous, safe supply of platelet products. Further, considering the feasibility of gene manipulations in iPSCs, other platelet products may bring forth novel therapeutic measures.

Studying leukemia stem cell properties and vulnerabilities with human iPSCs

The reprogramming of cancer cells into induced pluripotent stem cells (iPSCs) can capture entire cancer genomes, and thus create genetically faithful models of human cancers. By providing stringent genetically clonal conditions, iPSC modeling can also unveil non-genetic sources of cancer heterogeneity and provide a unique opportunity to study them separately from genetic sources, as we recently showed in an iPSC-based model of acute myeloid leukemia (AML). Genetically clonal iPSCs, derived from a patient with AML, reproduce, upon hematopoietic differentiation, phenotypic and functional heterogeneity with all the hallmarks of a leukemia stem cell (LSC) hierarchy. Here we discuss the lessons that can be learned about the LSC state, its plasticity, stability and genetic and epigenetic determinants from iPSC modeling. We also discuss the practical and translational implications of exploiting AML-iPSCs to prospectively isolate large numbers of iLSCs for large-scale experiments, such as screens, and for discovery of new therapeutic targets specific to AML LSCs.

Defining the Teratoma as a Model for Multi-lineage Human Development

We propose that the teratoma, a recognized standard for validating pluripotency in stem cells, could be a promising platform for studying human developmental processes. Performing single-cell RNA sequencing (RNA-seq) of 179,632 cells across 23 teratomas from 4 cell lines, we found that teratomas reproducibly contain approximately 20 cell types across all 3 germ layers, that inter-teratoma cell type heterogeneity is comparable with organoid systems, and teratoma gut and brain cell types correspond well to similar fetal cell types. Furthermore, cellular barcoding confirmed that injected stem cells robustly engraft and contribute to all lineages. Using pooled CRISPR-Cas9 knockout screens, we showed that teratomas can enable simultaneous assaying of the effects of genetic perturbations across all germ layers. Additionally, we demonstrated that teratomas can be sculpted molecularly via microRNA (miRNA)-regulated suicide gene expression to enrich for specific tissues. Taken together, teratomas are a promising platform for modeling multi-lineage development, pan-tissue functional genetic screening, and tissue engineering.

Definitive hematopoietic stem/progenitor cells from human embryonic stem cells through serum/feeder-free organoid-induced differentiation

Background

Ex vivo production of hematopoietic stem/precursor cells (HSPCs) represents a promising versatile approach for blood disorders.

Methods

To derive definitive HSPCs from human embryonic stem cells (ESCs), we differentiated mesodermally specified embryoid bodies (EBs) on gelatin-coated plates in serum/feeder-free conditions.

Results

Seven-day EB maturation followed by an 8-day differentiation period on OP9 cells provided the highest number of definitive (CD34+ CD235a−, 69%, p < 0.01) and lowest number of primitive (CD34− CD235a+, 1.55%, p < 0.01) precursor cells along with the highest colony-forming units (149.8 ± 11.6, p < 0.01) in feeder-free conditions. Maximal HSPC fraction (CD34+ CD38− CD45RA− CD49f+ CD90+) was 7.6–8.9% after 10 days of hematopoietic differentiation with 14.5% adult β-globin expression following RBC differentiation. Myeloid and erythroid colonies were restricted strictly to the CD34+ CD43+ fraction (370.5 ± 65.7, p < 0.001), while the CD34− CD43+ fraction produced only a small number of colonies (21.6 ± 11.9). In addition, we differentiated the CD34+ CD43+ cells towards T-lymphocytes using the OP9/DLL1 co-culture system demonstrating double-positive T cells (CD4+ CD8+) with CD3+ expression displaying a broad T cell receptor (TCR) repertoire. Confocal imaging of organoid-like structures revealed a close association of CD31+ cells with CD34+ and CD43+ cells, suggesting a potential emergence of HSPCs through endothelial to hematopoietic transition. Furthermore, fluorescently labeled organoids exhibited the emergence of spherical non-attached cells from rare progenitors at the border of the organoid center.

Conclusions

In summary, definitive HSPCs can be derived from ESCs through a dynamic cellular process from an organoid-like structure, where erythroid progeny are capable of producing adult hemoglobin and lymphoid progeny shows a diverse TCR repertoire.

Multifaceted Actions of GFI1 and GFI1B in Hematopoietic Stem Cell Self-Renewal and Lineage Commitment

Growth factor independence 1 (GFI1) and the closely related protein GFI1B are small nuclear proteins that act as DNA binding transcriptional repressors. Both recognize the same consensus DNA binding motif via their C-terminal zinc finger domains and regulate the expression of their target genes by recruiting chromatin modifiers such as histone deacetylases (HDACs) and demethylases (LSD1) by using an N-terminal SNAG domain that comprises only 20 amino acids. The only region that is different between both proteins is the region that separates the zinc finger domains and the SNAG domain. Both proteins are co-expressed in hematopoietic stem cells (HSCs) and, to some extent, in multipotent progenitors (MPPs), but expression is specified as soon as early progenitors and show signs of lineage bias. While expression of GFI1 is maintained in lymphoid primed multipotent progenitors (LMPPs) that have the potential to differentiate into both myeloid and lymphoid cells, GFI1B expression is no longer detectable in these cells. By contrast, GFI1 expression is lost in megakaryocyte precursors (MKPs) and in megakaryocyte-erythrocyte progenitors (MEPs), which maintain a high level of GFI1B expression. Consequently, GFI1 drives myeloid and lymphoid differentiation and GFI1B drives the development of megakaryocytes, platelets, and erythrocytes. How such complementary cell type- and lineage-specific functions of GFI1 and GFI1B are maintained is still an unresolved question in particular since they share an almost identical structure and very similar biochemical modes of actions. The cell type-specific accessibility of GFI1/1B binding sites may explain the fact that very similar transcription factors can be responsible for very different transcriptional programming. An additional explanation comes from recent data showing that both proteins may have additional non-transcriptional functions. GFI1 interacts with a number of proteins involved in DNA repair and lack of GFI1 renders HSCs highly susceptible to DNA damage-induced death and restricts their proliferation. In contrast, GFI1B binds to proteins of the beta-catenin/Wnt signaling pathway and lack of GFI1B leads to an expansion of HSCs and MKPs, illustrating the different impact that GFI1 or GFI1B has on HSCs. In addition, GFI1 and GFI1B are required for endothelial cells to become the first blood cells during early murine development and are among those transcription factors needed to convert adult endothelial cells or fibroblasts into HSCs. This role of GFI1 and GFI1B bears high significance for the ongoing effort to generate hematopoietic stem and progenitor cells de novo for the autologous treatment of blood disorders such as leukemia and lymphoma.

Using Eukaryotic Expression Systems to Generate Human α1,3-Fucosyltransferases That Effectively Create Selectin-Binding Glycans on Stem Cells

Recruitment of circulating cells toward target sites is primarily dependent on selectin/ligand adhesive interactions. Glycosyltransferases are involved in the creation of selectin ligands on proteins and lipids. α1,3-Fucosylation is imperative for the creation of selectin ligands, and a number of fucosyltransferases (FTs) can modify terminal lactosamines on cells to create these ligands. One FT, fucosyltransferase VI (FTVI), adds a fucose in an α1,3 configuration to N-acetylglucosamine to generate sialyl Lewis X (sLe^x) epitopes on proteins of live cells and enhances their ability to bind E-selectin. Although a number of recombinant human FTVIs have been purified, apart from limited commercial enzymes, they were not characterized for their activity on live cells. Here we focused on establishing a robust method for producing FTVI that is active on living cells (hematopoietic cells and mesenchymal stromal cells). To this end, we used two expression systems, Bombyx mori (silkworm) and Pichia pastoris (yeast), to produce significant amounts of N-terminally tagged FTVI and demonstrated that these enzymes have superior activity when compared to currently available commercial enzymes that are produced from various expression systems. Overall, we outline a scheme for obtaining large amounts of highly active FTVI that can be used for the application of FTVI in enhancing the engraftment of cells lacking the sLe^x epitopes.

Activated HoxB4-induced hematopoietic stem cells from murine pluripotent stem cells via long-term programming

Hematopoietic stem cells (HSCs) are multipotent cells that form the entire blood system and have the potential to cure several pathogenic conditions directly or indirectly arising from defects within the HSC compartment. Pluripotent stem cells (PSCs) or induced pluripotent stem cells (iPSCs) can give rise to all embryonic cell types; however, efficient in vitro differentiation of HSCs from PSCs remains challenging. HoxB4 is a key regulator orchestrating the differentiation of PSCs into all cells types across the mesodermal lineage, including HSCs. Moreover, the ectopic expression of HoxB4 enhances the in vitro generation and expansion of HSCs. However, several aspects of HoxB4 biology including its regulatory functions are not fully understood. Here, we describe the role of HoxB4 in indirectly inhibiting the emergence of mature CD45⁺ HSCs from iPSCs in vitro. Forced activation of HoxB4 permitted long-term maintenance of functional hematopoietic stem and progenitor cells (HSPCs), which efficiently reconstituted hematopoiesis upon transplantation. Our method enables an easy and scalable in vitro platform for the generation of HSCs from iPSCs, which will ultimately lead to a better understanding of HSC biology and facilitate preparation of the roadma for producing an unrestricted supply of HSCs for several curative therapies.

Hematopoietic stem cells from pluripotent stem cells: Clinical potential, challenges, and future perspectives

The generation of hematopoietic stem cells (HSCs) from induced pluripotent stem cells (iPSCs) is an active and promising area of research; however, generating engraftable HSCs remains a major obstacle. Ex vivo HSC derivation from renewable sources such as iPSCs offers an experimental tool for studying developmental hematopoiesis, disease modeling, and drug discovery, and yields tremendous therapeutic potential for malignant and nonmalignant hematological disorders. Although initial attempts mostly recapitulated yolk sac primitive/definitive hematopoiesis with inability to engraft, recent advances suggest the feasibility of engraftable HSC derivation from iPSCs utilizing ectopic transcription factor expression. Strategic development for de novo HSC generation includes further investigations of HSC ontogeny, and elucidation of critical signaling pathways, epigenetic modulations, HSC and iPSC microenvironment, and cell‐cell interactions that contribute to stem cell biology and function.

Footprint-free gene mutation correction in induced pluripotent stem cell (iPSC) derived from recessive dystrophic epidermolysis bullosa (RDEB) using the CRISPR/Cas9 and piggyBac transposon system

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a monogenic skin blistering disorder caused by mutations in the type VII collagen gene. A combination of biological technologies, including induced pluripotent stem cells (iPSCs) and several gene-editing tools, allows us to develop gene and cell therapies for such inherited diseases. However, the methodologies for gene and cell therapies must be continuously innovated for safe clinical use.

OBJECTIVE

In this study, we used the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology to correct the pathogenic mutation in RDEB-specific iPSCs, and the piggyBac transposon system so that no residual gene fragments remained in the genome of iPSCs after correcting the mutation.

METHODS

For homologous recombination (HR)-based gene editing using CRISPR/Cas9, we designed guide RNA and template DNA including homologous sequences with drug-mediated selection cassette flanked by inverted repeat sequences of the transposon. HR reaction using CRISPR/Cas9 was induced in RDEB-specific iPSCs, and mutation-corrected iPSCs (MC-iPSCs) was obtained. Consequently, the selection cassette in the genome of MC-iPSCs was removed by transposase expression.

RESULTS

After CRISPR/Cas9-induced gene editing, we confirmed that the pathogenic mutation in RDEB-specific iPSCs was properly corrected. In addition, MC-iPSCs had no genetic footprint after removing the selection cassette by transposon system, and maintained their "stemness". When differentiating MC-iPSCs into keratinocytes, the expression of type VII collagen was restored.

CONCLUSIONS

Our study demonstrated one of the safer approaches to establish gene and cell therapies for skin hereditary disorders for future clinical use.