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

Advances in ex vivo expansion of hematopoietic stem and progenitor cells for clinical applications

As caretakers of the hematopoietic system, hematopoietic stem cells assure a lifelong supply of differentiated populations that are responsible for critical bodily functions, including oxygen transport, immunological protection and coagulation. Due to the far-reaching influence of the hematopoietic system, hematological disorders typically have a significant impact on the lives of individuals, even becoming fatal. Hematopoietic cell transplantation was the first effective therapeutic avenue to treat such hematological diseases. Since then, key use and manipulation of hematopoietic stem cells for treatments has been aspired to fully take advantage of such an important cell population. Limited knowledge on hematopoietic stem cell behavior has motivated in-depth research into their biology. Efforts were able to uncover their native environment and characteristics during development and adult stages. Several signaling pathways at a cellular level have been mapped, providing insight into their machinery. Important dynamics of hematopoietic stem cell maintenance were begun to be understood with improved comprehension of their metabolism and progressive aging. These advances have provided a solid platform for the development of innovative strategies for the manipulation of hematopoietic stem cells. Specifically, expansion of the hematopoietic stem cell pool has triggered immense interest, gaining momentum. A wide range of approaches have sprouted, leading to a variety of expansion systems, from simpler small molecule-based strategies to complex biomimetic scaffolds. The recent approval of Omisirge, the first expanded hematopoietic stem and progenitor cell product, whose expansion platform is one of the earliest, is predictive of further successes that might arise soon. In order to guarantee the quality of these ex vivo manipulated cells, robust assays that measure cell function or potency need to be developed. Whether targeting hematopoietic engraftment, immunological differentiation potential or malignancy clearance, hematopoietic stem cells and their derivatives need efficient scaling of their therapeutic potency. In this review, we comprehensively view hematopoietic stem cells as therapeutic assets, going from fundamental to translational.

Rebuilding and rebooting immunity with stem cells

Advances in modern medicine have enabled a rapid increase in lifespan and, consequently, have highlighted the immune system as a key driver of age-related disease. Immune regeneration therapies present exciting strategies to address age-related diseases by rebooting the host's primary lymphoid tissues or rebuilding the immune system directly via biomaterials or artificial tissue. Here, we identify important, unanswered questions regarding the safety and feasibility of these therapies. Further, we identify key design parameters that should be primary considerations guiding technology design, including timing of application, interaction with the host immune system, and functional characterization of the target patient population.

Generating human bone marrow organoids for disease modeling and drug discovery

The bone marrow supports and regulates hematopoiesis, responding to physiological requirements for blood cell production over ontogeny and during pathological challenges. Interactions between hematopoietic cells and niche components are challenging to study mechanistically in the human context, but are important to delineate in order to explore the pathobiology of blood and bone marrow disorders. Organoids are proving transformative in many research settings, but an accurate human bone marrow model incorporating multiple hematopoietic and stromal elements has been lacking. This protocol describes a method to generate three-dimensional, multilineage bone marrow organoids from human induced pluripotent stem cells (hiPSCs), detailing the steps for the directed differentiation of hiPSCs using a series of cytokine cocktails and hydrogel embedding. Over 18 days of differentiation, hiPSCs yield the key lineages that are present in central myelopoietic bone marrow, organized in a well-vascularized architecture that resembles native hematopoietic tissues. This presents a robust, in vitro system that can model healthy and perturbed hematopoiesis in a scalable three-dimensional microenvironment. Bone marrow organoids also support the growth of immortalized cell lines and primary cells from healthy donors and patients with myeloid and lymphoid cancers, including cell types that are poorly viable in standard culture systems. Moreover, we discuss assays for the characterization of organoids, including interrogation of pathogenic remodeling using recombinant TGF-ß treatment, and methods for organoid engraftment with exogenous cells. This protocol can be readily adapted to specific experimental requirements, can be easily implemented by users with tissue culture experience and does not require access to specialist equipment.

Fetal liver macrophages contribute to the hematopoietic stem cell niche by controlling granulopoiesis

During embryogenesis, the fetal liver becomes the main hematopoietic organ, where stem and progenitor cells as well as immature and mature immune cells form an intricate cellular network. Hematopoietic stem cells (HSCs) reside in a specialized niche, which is essential for their proliferation and differentiation. However, the cellular and molecular determinants contributing to this fetal HSC niche remain largely unknown. Macrophages are the first differentiated hematopoietic cells found in the developing liver, where they are important for fetal erythropoiesis by promoting erythrocyte maturation and phagocytosing expelled nuclei. Yet, whether macrophages play a role in fetal hematopoiesis beyond serving as a niche for maturing erythroblasts remains elusive. Here, we investigate the heterogeneity of macrophage populations in the murine fetal liver to define their specific roles during hematopoiesis. Using a single-cell omics approach combined with spatial proteomics and genetic fate-mapping models, we found that fetal liver macrophages cluster into distinct yolk sac-derived subpopulations and that long-term HSCs are interacting preferentially with one of the macrophage subpopulations. Fetal livers lacking macrophages show a delay in erythropoiesis and have an increased number of granulocytes, which can be attributed to transcriptional reprogramming and altered differentiation potential of long-term HSCs. Together, our data provide a detailed map of fetal liver macrophage subpopulations and implicate macrophages as part of the fetal HSC niche.

Improving hematopoietic differentiation from human induced pluripotent stem cells by the modulation of Hippo signaling with a diarylheptanoid derivative

BACKGROUND

The diarylheptanoid ASPP 049 has improved the quality of adult hematopoietic stem cell (HSC) expansion ex vivo through long-term reconstitution in animal models. However, its effect on hematopoietic regeneration from human induced pluripotent stem cells (hiPSCs) is unknown.

METHOD

We utilized a defined cocktail of cytokines without serum or feeder followed by the supplementation of ASPP 049 to produce hematopoietic stem/progenitor cells (HSPCs). Flow cytometry and trypan blue exclusion analysis were used to identify nonadherent and adherent cells. Nonadherent cells were harvested to investigate the effect of ASPP 049 on multipotency using LTC-IC and CFU assays. Subsequently, the mechanism of action was explored through transcriptomic profiles, which were validated by qRT-PCR, immunoblotting, and immunofluorescence analysis.

RESULT

The supplementation of ASPP 049 increased the number of phenotypically defined primitive HSPCs (CD34+CD45+CD90+) two-fold relative to seeded hiPSC colonies, indicating enhanced HSC derivation from hiPSCs. Under ASPP 049-supplemented conditions, we observed elevated HSPC niches, including CD144+CD73- hemogenic- and CD144+CD73+ vascular-endothelial progenitors, during HSC differentiation. Moreover, harvested ASPP 049-treated cells exhibited improved self-renewal and a significantly larger proportion of different blood cell colonies with unbiased lineages, indicating enhanced HSC stemness properties. Transcriptomics and KEGG analysis of sorted CD34+CD45+ cells-related mRNA profiles revealed that the Hippo signaling pathway is the most significant in responding to WWTR1/TAZ, which correlates with the validation of the protein expression. Interestingly, ASPP 049-supplemented HSPCs upregulated 11 genes similarly to umbilical cord blood-derived HSPCs.

CONCLUSION

These findings suggest that ASPP 049 can improve HSC-generating protocols with proliferative potentials, self-renewal ability, unbiased differentiation, and a definable mechanism of action for the clinical perspective of hematopoietic regenerative medicine.

Engineered T cells from induced pluripotent stem cells: from research towards clinical implementation

Induced pluripotent stem cell (iPSC)-derived T (iT) cells represent a groundbreaking frontier in adoptive cell therapies with engineered T cells, poised to overcome pivotal limitations associated with conventional manufacturing methods. iPSCs offer an off-the-shelf source of therapeutic T cells with the potential for infinite expansion and straightforward genetic manipulation to ensure hypo-immunogenicity and introduce specific therapeutic functions, such as antigen specificity through a chimeric antigen receptor (CAR). Importantly, genetic engineering of iPSC offers the benefit of generating fully modified clonal lines that are amenable to rigorous safety assessments. Critical to harnessing the potential of iT cells is the development of a robust and clinically compatible production process. Current protocols for genetic engineering as well as differentiation protocols designed to mirror human hematopoiesis and T cell development, vary in efficiency and often contain non-compliant components, thereby rendering them unsuitable for clinical implementation. This comprehensive review centers on the remarkable progress made over the last decade in generating functional engineered T cells from iPSCs. Emphasis is placed on alignment with good manufacturing practice (GMP) standards, scalability, safety measures and quality controls, which constitute the fundamental prerequisites for clinical application. In conclusion, the focus on iPSC as a source promises standardized, scalable, clinically relevant, and potentially safer production of engineered T cells. This groundbreaking approach holds the potential to extend hope to a broader spectrum of patients and diseases, leading in a new era in adoptive T cell therapy.

Cellular and animal models for the investigation of β-thalassemia

β-Thalassemia is a genetic form of anemia due to mutations in the β-globin gene, that leads to ineffective and extramedullary erythropoiesis, abnormal red blood cells and secondary iron-overload. The severity of the disease ranges from mild to lethal anemia based on the residual levels of globins production. Despite being a monogenic disorder, the pathophysiology of β-thalassemia is multifactorial, with different players contributing to the severity of anemia and secondary complications. As a result, the identification of effective therapeutic strategies is complex, and the treatment of patients is still suboptimal. For these reasons, several models have been developed in the last decades to provide experimental tools for the study of the disease, including erythroid cell lines, cultures of primary erythroid cells and transgenic animals. Years of research enabled the optimization of these models and led to decipher the mechanisms responsible for globins deregulation and ineffective erythropoiesis in thalassemia, to unravel the role of iron homeostasis in the disease and to identify and validate novel therapeutic targets and agents. Examples of successful outcomes of these analyses include iron restricting agents, currently tested in the clinics, several gene therapy vectors, one of which was recently approved for the treatment of most severe patients, and a promising gene editing strategy, that has been shown to be effective in a clinical trial. This review provides an overview of the available models, discusses pros and cons, and the key findings obtained from their study.

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.

Engineered hematopoietic and immune cells derived from human pluripotent stem cells

For the past decade, significant advances have been achieved in human hematopoietic stem cell (HSC) transplantation for treating various blood diseases and cancers. However, challenges remain with the quality control, amount, and cost of HSCs and HSC-derived immune cells. The advent of human pluripotent stem cells (hPSCs) may transform HSC transplantation and cancer immunotherapy by providing a cost-effective and scalable cell source for fundamental studies and translational applications. In this review, we discuss the current developments in the field of stem cell engineering for hematopoietic stem and progenitor cell (HSPC) differentiation and further differentiation of HSPCs into functional immune cells. The key advances in stem cell engineering include the generation of HSPCs from hPSCs, genetic modification of hPSCs, and hPSC-derived HSPCs for improved function, further differentiation of HPSCs into functional immune cells, and applications of cell culture platforms for hematopoietic cell manufacturing. Current challenges impeding the translation of hPSC-HSPCs and immune cells as well as further directions to address these challenges are also discussed.

Understanding blood development and leukemia using sequencing-based technologies and human cell systems

Our current understanding of human hematopoiesis has undergone significant transformation throughout the years, challenging conventional views. The evolution of high-throughput technologies has enabled the accumulation of diverse data types, offering new avenues for investigating key regulatory processes in blood cell production and disease. In this review, we will explore the opportunities presented by these advancements for unraveling the molecular mechanisms underlying normal and abnormal hematopoiesis. Specifically, we will focus on the importance of enhancer-associated regulatory networks and highlight the crucial role of enhancer-derived transcription regulation. Additionally, we will discuss the unprecedented power of single-cell methods and the progression in using in vitro human blood differentiation system, in particular induced pluripotent stem cell models, in dissecting hematopoietic processes. Furthermore, we will explore the potential of ever more nuanced patient profiling to allow precision medicine approaches. Ultimately, we advocate for a multiparameter, regulatory network-based approach for providing a more holistic understanding of normal hematopoiesis and blood disorders.

Unravelling human hematopoietic progenitor cell diversity through association with intrinsic regulatory factors

Hematopoietic stem and progenitor cell (HSPC) transplantation is an essential therapy for hematological conditions, but finer definitions of human HSPC subsets with associated function could enable better tuning of grafts and more routine, lower-risk application. To deeply phenotype HSPCs, following a screen of 328 antigens, we quantified 41 surface proteins and functional regulators on millions of CD34+ and CD34- cells, spanning four primary human hematopoietic tissues: bone marrow, mobilized peripheral blood, cord blood, and fetal liver. We propose more granular definitions of HSPC subsets and provide new, detailed differentiation trajectories of erythroid and myeloid lineages. These aspects of our revised human hematopoietic model were validated with corresponding epigenetic analysis and in vitro clonal differentiation assays. Overall, we demonstrate the utility of using molecular regulators as surrogates for cellular identity and functional potential, providing a framework for description, prospective isolation, and cross-tissue comparison of HSPCs in humans.

Induced pluripotent and CD34+ stem cell derived myeloid cells display differential responses to particle and dust mite exposure

Myeloid cells form an essential component of initial responses to environmental hazards and toxic exposures. The ability to model these responses in vitro is central to efforts tasked with identifying hazardous materials and understanding mechanisms of injury and disease. Induced pluripotent stem cell (iPSC) derived cells have been suggested as alternatives to more established primary cell testing systems for these purposes. iPSC derived macrophage and dendritic like cells were compared to CD34+ haematopoietic stem cell derived populations using transcriptomic analysis. Using single cell sequencing-based characterisation of iPSC derived myeloid cells, we identified transitional, mature and M2 like macrophages as well as dendritic like antigen presenting cells and fibrocytes. Direct transcriptomic comparisons between iPSC and CD34+ cell derived populations revealed higher expression of myeloid differentiation genes such as MNDA, CSF1R and CSF2RB in CD34+ cells, while iPSC populations had higher fibroblastic and proliferative markers. Exposure of differentiated macrophage populations to nanoparticle alone or in combination with dust mite, resulted in differential gene expression on combination only, with responses markedly absent in iPSC compared to CD34+ derived cells. The lack of responsiveness in iPSC derived cells may be attributable to lower levels of dust mite component receptors CD14, TLR4, CLEC7A and CD36. In summary, iPSC derived myeloid cells display typical characteristics of immune cells but may lack a fully mature phenotype to adequately respond to environmental exposures.

The differentiation of human induced pluripotent stem cells into hematopoietic stem cells on 3D bone scaffold in a dynamic culture system

Hematopoietic stem cell transplantation is used for cell-based therapy for many hematological disorders. However, difficulty in finding proper donors has limited this source of stem cells. For clinical application, the generation of these cells from induced pluripotent stem cells (iPSs) is a fascinating and endless source. One of the experimental methods to generate HSCs from iPSs is the mimicking of the hematopoietic niche. In the current study, as the first phase of differentiation, embryoid bodies were formed from iPSs. They were then cultured in different dynamic conditions in order to determine the appropriate settings for their differentiation into HSCs. The dynamic culture was composed of DBM Scaffold with or without growth factor. After ten days, the specific HSC markers (CD34, CD133, CD31 and CD45) were assessed using flow-cytometry. Our findings demonstrated that the dynamic conditions were significantly suitable than static ones. In addition, in 3D scaffold and dynamic system the expression of CXCR4, as a homing marker, was increased. These results suggest that the 3D culture bioreactor with DBM scaffold could provide a new approach for differentiation of iPSs into HSCs. Moreover, this system could provide maximum mimicry of bone marrow niche.

Wnt regulation of hematopoietic stem cell development and disease

Hematopoietic stem cells (HSCs) are multipotent stem cells that give rise to all cells of the blood and most immune cells. Due to their capacity for unlimited self-renewal, long-term HSCs replenish the blood and immune cells of an organism throughout its life. HSC development, maintenance, and differentiation are all tightly regulated by cell signaling pathways, including the Wnt pathway. Wnt signaling is initiated extracellularly by secreted ligands which bind to cell surface receptors and give rise to several different downstream signaling cascades. These are classically categorized either β-catenin dependent (BCD) or β-catenin independent (BCI) signaling, depending on their reliance on the β-catenin transcriptional activator. HSC development, homeostasis, and differentiation is influenced by both BCD and BCI, with a high degree of sensitivity to the timing and dosage of Wnt signaling. Importantly, dysregulated Wnt signals can result in hematological malignancies such as leukemia, lymphoma, and myeloma. Here, we review how Wnt signaling impacts HSCs during development and in disease.

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.

Generation of CD34+CD43+ Hematopoietic Progenitors to Induce Thymocytes from Human Pluripotent Stem Cells

Immunotherapy using primary T cells has revolutionized medical care in some pathologies in recent years, but limitations associated to challenging cell genome edition, insufficient cell number production, the use of only autologous cells, and the lack of product standardization have limited its clinical use. The alternative use of T cells generated in vitro from human pluripotent stem cells (hPSCs) offers great advantages by providing a self-renewing source of T cells that can be readily genetically modified and facilitate the use of standardized universal off-the-shelf allogeneic cell products and rapid clinical access. However, despite their potential, a better understanding of the feasibility and functionality of T cells differentiated from hPSCs is necessary before moving into clinical settings. In this study, we generated human-induced pluripotent stem cells from T cells (T-iPSCs), allowing for the preservation of already recombined TCR, with the same properties as human embryonic stem cells (hESCs). Based on these cells, we differentiated, with high efficiency, hematopoietic progenitor stem cells (HPSCs) capable of self-renewal and differentiation into any cell blood type, in addition to DN3a thymic progenitors from several T-iPSC lines. In order to better comprehend the differentiation, we analyzed the transcriptomic profiles of the different cell types and demonstrated that HPSCs differentiated from hiPSCs had very similar profiles to cord blood hematopoietic stem cells (HSCs). Furthermore, differentiated T-cell progenitors had a similar profile to thymocytes at the DN3a stage of thymic lymphopoiesis. Therefore, utilizing this approach, we were able to regenerate precursors of therapeutic human T cells in order to potentially treat a wide range of diseases.

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.

Immunological barriers to haematopoietic stem cell gene therapy

Cell and gene therapies using haematopoietic stem cells (HSCs) epitomize the transformative potential of regenerative medicine. Recent clinical successes for gene therapies involving autologous HSC transplantation (HSCT) demonstrate the potential of genetic engineering in this stem cell type for curing disease. With recent advances in CRISPR gene-editing technologies, methodologies for the ex vivo expansion of HSCs and non-genotoxic conditioning protocols, the range of clinical indications for HSC-based gene therapies is expected to significantly expand. However, substantial immunological challenges need to be overcome. These include pre-existing immunity to gene-therapy reagents, immune responses to neoantigens introduced into HSCs by genetic engineering, and unique challenges associated with next-generation and off-the-shelf HSC products. By synthesizing these factors in this Review, we hope to encourage more research to address the immunological issues associated with current and next-generation HSC-based gene therapies to help realize the full potential of this field.

HOX genes in stem cells: Maintaining cellular identity and regulation of differentiation

Stem cells display a unique cell type within the body that has the capacity to self-renew and differentiate into specialized cell types. Compared to pluripotent stem cells, adult stem cells (ASC) such as mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) exhibit restricted differentiation capabilities that are limited to cell types typically found in the tissue of origin, which implicates that there must be a certain code or priming determined by the tissue of origin. HOX genes, a subset of homeobox genes encoding transcription factors that are generally repressed in undifferentiated pluripotent stem cells, emerged here as master regulators of cell identity and cell fate during embryogenesis, and in maintaining this positional identity throughout life as well as specifying various regional properties of respective tissues. Concurrently, intricate molecular circuits regulated by diverse stem cell-typical signaling pathways, balance stem cell maintenance, proliferation and differentiation. However, it still needs to be unraveled how stem cell-related signaling pathways establish and regulate ASC-specific HOX expression pattern with different temporal-spatial topography, known as the HOX code. This comprehensive review therefore summarizes the current knowledge of specific ASC-related HOX expression patterns and how these were integrated into stem cell-related signaling pathways. Understanding the mechanism of HOX gene regulation in stem cells may provide new ways to manipulate stem cell fate and function leading to improved and new approaches in the field of regenerative medicine.

Correction of Fanconi Anemia Mutations Using Digital Genome Engineering

Fanconi anemia (FA) is a rare genetic disease in which genes essential for DNA repair are mutated. Both the interstrand crosslink (ICL) and double-strand break (DSB) repair pathways are disrupted in FA, leading to patient bone marrow failure (BMF) and cancer predisposition. The only curative therapy for the hematological manifestations of FA is an allogeneic hematopoietic cell transplant (HCT); however, many (>70%) patients lack a suitable human leukocyte antigen (HLA)-matched donor, often resulting in increased rates of graft-versus-host disease (GvHD) and, potentially, the exacerbation of cancer risk. Successful engraftment of gene-corrected autologous hematopoietic stem cells (HSC) circumvents the need for an allogeneic HCT and has been achieved in other genetic diseases using targeted nucleases to induce site specific DSBs and the correction of mutated genes through homology-directed repair (HDR). However, this process is extremely inefficient in FA cells, as they are inherently deficient in DNA repair. Here, we demonstrate the correction of FANCA mutations in primary patient cells using ‘digital’ genome editing with the cytosine and adenine base editors (BEs). These Cas9-based tools allow for C:G > T:A or A:T > C:G base transitions without the induction of a toxic DSB or the need for a DNA donor molecule. These genetic corrections or conservative codon substitution strategies lead to phenotypic rescue as illustrated by a resistance to the alkylating crosslinking agent Mitomycin C (MMC). Further, FANCA protein expression was restored, and an intact FA pathway was demonstrated by downstream FANCD2 monoubiquitination induction. This BE digital correction strategy will enable the use of gene-corrected FA patient hematopoietic stem and progenitor cells (HSPCs) for autologous HCT, obviating the risks associated with allogeneic HCT and DSB induction during autologous HSC gene therapy.

The altered expression of homing factors in CD34+ hematopoietic stem cells following G-CSF injection and its effects on transplantation quality in ALL patients

Hematopoietic stem cells (HSCs) transplantation is considered a suitable treatment for malignant or nonmalignant hematological diseases. This study aims to investigate the HSCs homing factors in bone marrow (BM) donors of acute lymphoblastic leukemia (ALL) patients following granulocyte colony-stimulating factor (G-CSF) injection, as well as the G-CSF effects on BM transplantation quality in these patients. To mobilize HSCs into peripheral blood, G-CSF was used for ALL patient's BM donors. For HSCs counting, CD34+ cells were evaluated in analogous and autologous donors using flow cytometry. The expression of stem cell homing factors in CD34+ cells and peripheral blood mononuclear cells (PBMCs) were investigated using a real-time polymerase chain reaction. Finally, hematological factors after BM transplantation in ALL patients were assessed. According to our results, after G-CSF injection, the level of CD34+ HSCs was statistically increased. Besides, autologous donors showed a higher level of CD34+ cells compared to analogous donors before and after G-CSF injection. Additionally, a higher number of CD34+ HSCs was achieved in the autologous samples following G-CSF injection. Furthermore, after G-CSF injection, the expression of matrix metalloproteinase (MMP)-2, MMP-9 was increased; while, stromal cell-derived factor 1, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 expression were decreased. Moreover, the expression of C-X-C chemokine receptor type 4, lymphocyte function-associated antigen 1, and very late antigen-4 in CD34+ cells and PBMCs were decreased. BM transplantation on Day 90 also caused an increased level of white blood cells, red blood cells, and platelets as compared to the first day; however, no statistical differences were observed in hemoglobin level. In conclusion, G-CSF by altering the expression of HSCs homing factors in ALL donors improves BM transplantation quality in ALL patients.

Hypoxia drives hematopoiesis with the enhancement of T lineage through eliciting arterial specification of hematopoietic endothelial progenitors from hESC

Background

Hematopoietic stem cells are able to self-renew and differentiate into all blood cell lineages. Hematopoietic stem cell transplantation is a mainstay of life-saving therapy for hematopoietic malignancies and hypoproliferative disorders. In vitro hematopoietic differentiation of human pluripotent stem cells (hPSCs) is a promising approach for modeling hematopoietic development and cell replacement therapies. Although using hPSCs to derive hematopoietic progenitor cells has achieved some successes in the past, differentiation from hPSCs to produce all hematopoietic cells which can provide robust long-term multilineage engraftment is still very difficult. Here, we reported a novel culture system for hematopoietic differentiation from human embryonic stem cells (hESCs) with optimal cytokines combinations under hypoxia condition.

Methods

In vitro production of T lineage hematopoietic stem/progenitor cells from hESCs by using hypoxia differentiation system, the effects and the potential mechanism of hypoxia promoting T lineage hematopoiesis were investigated by RT-qPCR validation, cell cycle assay and flow cytometry analysis.

Results

Using our differentiation system, almost 80% CD45⁺ cells generated from hESCs were hematopoietic cells and particularly could be further induced into CD3⁺TCRαβ⁺ T cells in vitro. We detected more CD34⁺CD144⁺ hematopoietic endothelial progenitors (HEPs) induced from hESCs than those in normoxia conditions, and the early HEPs-related gene DLL4 was upregulated by enhancing the hypoxia signaling via potential HIF-1α/NOTCH1/DLL4 axis to enhance arterial feature, thus drove T lineage during the hematopoiesis. Strikingly, hematopoietic cells generated in our system exhibited the potential for all multilineage reconstruction including lymphoid, myeloid and erythroid lineages in vivo by transplantation assay.

Conclusion

Our results demonstrated that hypoxia plays an important role in T lineage hematopoiesis by promoting the expression of arterial endothelial gene DLL4 and upregulation of NOTCH1 through the activation of the HIF-1α signaling pathway. These results provide a significant approach for in vitro and in vivo production of fully functional hematopoietic stem/progenitor cells from hESCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02967-0.

Leukemic Stem Cell: A Mini-Review on Clinical Perspectives

Hematopoietic stem cells (HSCs) are known for their ability to proliferate and self-renew, thus being responsible for sustaining the hematopoietic system and residing in the bone marrow (BM). Leukemic stem cells (LSCs) are recognized by their stemness features such as drug resistance, self-renewal, and undifferentiated state. LSCs are also present in BM, being found in only 0.1%, approximately. This makes their identification and even their differentiation difficult since, despite the mutations, they are cells that still have many similarities with HSCs. Although the common characteristics, LSCs are heterogeneous cells and have different phenotypic characteristics, genetic mutations, and metabolic alterations. This whole set of alterations enables the cell to initiate the process of carcinogenesis, in addition to conferring drug resistance and providing relapses. The study of LSCs has been evolving and its application can help patients, where through its count as a biomarker, it can indicate a prognostic factor and reveal treatment results. The selection of a target to LSC therapy is fundamental. Ideally, the target chosen should be highly expressed by LSCs, highly selective, absence of expression on other cells, in particular HSC, and preferentially expressed by high numbers of patients. In view of the large number of similarities between LSCs and HSCs, it is not surprising that current treatment approaches are limited. In this mini review we seek to describe the immunophenotypic characteristics and mechanisms of resistance presented by LSCs, also approaching possible alternatives for the treatment of patients.

Dendritic cell differentiation from human induced pluripotent stem cells: challenges and progress

Dendritic cells (DCs) are the major antigen-presenting cells of the immune system responsible for initiating and coordinating immune responses. These abilities provide potential for several clinical applications, such as the development of immunogenic vaccines. However, difficulty in obtaining DCs from conventional sources, such as bone marrow (BM), peripheral blood (PBMC), and cord blood (CB), is a significantly hinders routine application. The use of human induced pluripotent stem cells (hiPSCs) is a valuable alternative for generating sufficient numbers of DCs to be used in basic and pre-clinical studies. Despite the many challenges that must be overcome to achieve an efficient protocol for obtaining the major DC types from hiPSCs, recent progress has been made. Here we review the current state of developing DCs from hiPSCs, as well as the key elements required to enable the routine use of hiPSC-derived DCs in pre-clinical and clinical assays.

Hematopoietic Cells from Pluripotent Stem Cells: Hope and Promise for the Treatment of Inherited Blood Disorders

Inherited blood disorders comprise a large spectrum of diseases due to germline mutations in genes with key function in the hematopoietic system; they include immunodeficiencies, anemia or metabolic diseases. For most of them the only curative treatment is bone marrow transplantation, a procedure associated to severe complications; other therapies include red blood cell and platelet transfusions, which are dependent on donor availability. An alternative option is gene therapy, in which the wild-type form of the mutated gene is delivered into autologous hematopoietic stem cells using viral vectors. A more recent therapeutic perspective is gene correction through CRISPR/Cas9-mediated gene editing, that overcomes safety concerns due to insertional mutagenesis and allows correction of base substitutions in large size genes difficult to incorporate into vectors. However, applying this technique to genomic disorders caused by large gene deletions is challenging. Chromosomal transplantation has been proposed as a solution, using a universal source of wild-type chromosomes as donor, and induced pluripotent stem cells (iPSCs) as acceptor. One of the obstacles to be addressed for translating PSC research into clinical practice is the still unsatisfactory differentiation into transplantable hematopoietic stem or mature cells. We provide an overview of the recent progresses in this field and discuss challenges and potential of iPSC-based therapies for the treatment of inherited blood disorders.

Stem Cell-Based Disease Models for Inborn Errors of Immunity

The intrinsic capacity of human hematopoietic stem cells (hHSCs) to reconstitute myeloid and lymphoid lineages combined with their self-renewal capacity hold enormous promises for gene therapy as a viable treatment option for a number of immune-mediated diseases, most prominently for inborn errors of immunity (IEI). The current development of such therapies relies on disease models, both in vitro and in vivo, which allow the study of human pathophysiology in great detail. Here, we discuss the current challenges with regards to developmental origin, heterogeneity and the subsequent implications for disease modeling. We review models based on induced pluripotent stem cell technology and those relaying on use of adult hHSCs. We critically review the advantages and limitations of current models for IEI both in vitro and in vivo. We conclude that existing and future stem cell-based models are necessary tools for developing next generation therapies for IEI.

The Future of Gene Therapy for Transfusion-Dependent Beta-Thalassemia: The Power of the Lentiviral Vector for Genetically Modified Hematopoietic Stem Cells

β-thalassemia, a disease that results from defects in β-globin synthesis, leads to an imbalance of β- and α-globin chains and an excess of α chains. Defective erythroid maturation, ineffective erythropoiesis, and shortened red blood cell survival are commonly observed in most β-thalassemia patients. In severe cases, blood transfusion is considered as a mainstay therapy; however, regular blood transfusions result in chronic iron overload with life-threatening complications, e.g., endocrine dysfunction, cardiomyopathy, liver disease, and ultimately premature death. Therefore, transplantation of healthy hematopoietic stem cells (HSCs) is considered an alternative treatment. Patients with a compatible human leukocyte antigen (HLA) matched donor can be cured by allogeneic HSC transplantation. However, some recipients faced a high risk of morbidity/mortality due to graft versus host disease or graft failure, while a majority of patients do not have such HLA match-related donors. Currently, the infusion of autologous HSCs modified with a lentiviral vector expressing the β-globin gene into the erythroid progenitors of the patient is a promising approach to completely cure β-thalassemia. Here, we discuss a history of β-thalassemia treatments and limitations, in particular the development of β-globin lentiviral vectors, with emphasis on clinical applications and future perspectives in a new era of medicine.

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.

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.

Mapping Human Pluripotent Stem Cell-derived Erythroid Differentiation by Single-cell Transcriptome Analysis

There is an imbalance between the supply and demand of functional red blood cells (RBCs) in clinical applications. This imbalance can be addressed by regenerating RBCs using several in vitro methods. Induced pluripotent stem cells (iPSCs) can handle the low supply of cord blood and the ethical issues in embryonic stem cell research and provide a promising strategy to eliminate immune rejection. However, no complete single-cell level differentiation pathway exists for the iPSC-derived RBC differentiation system. In this study, we used iPSC line BC1 to establish a RBCs regeneration system. The 10× genomics single-cell transcriptome platform was used to map the cell lineage and differentiation trajectories on day 14 of the regeneration system. We observed that iPSCs differentiation was not synchronized during embryoid body (EB) culture. The cells (day 14) mainly consisted of mesodermal and various blood cells, similar to the yolk sac hematopoiesis. We identified six cell classifications and characterized the regulatory transcription factors (TFs) networks and cell-cell contacts underlying the system. iPSCs undergo two transformations during the differentiation trajectory, accompanied by the dynamic expression of cell adhesion molecules and estrogen-responsive genes. We identified different stages of erythroid cells, such as burst-forming unit erythroid (BFU-E) and orthochromatic erythroblasts (ortho-E), and found that the regulation of TFs (e.g., TFDP1 and FOXO3) is erythroid-stage specific. Immune erythroid cells were identified in our system. This study provides systematic theoretical guidance for optimizing the iPSCs-derived RBCs differentiation system, and this system is a useful model for simulating in vivo hematopoietic development and differentiation.

Therapy Development by Genome Editing of Hematopoietic Stem Cells

Accessibility of hematopoietic stem cells (HSCs) for the manipulation and repopulation of the blood and immune systems has placed them at the forefront of cell and gene therapy development. Recent advances in genome-editing tools, in particular for clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) and CRISPR/Cas-derived editing systems, have transformed the gene therapy landscape. Their versatility and the ability to edit genomic sequences and facilitate gene disruption, correction or insertion, have broadened the spectrum of potential gene therapy targets and accelerated the development of potential curative therapies for many rare diseases treatable by transplantation or modification of HSCs. Ongoing developments seek to address efficiency and precision of HSC modification, tolerability of treatment and the distribution and affordability of corresponding therapies. Here, we give an overview of recent progress in the field of HSC genome editing as treatment for inherited disorders and summarize the most significant findings from corresponding preclinical and clinical studies. With emphasis on HSC-based therapies, we also discuss technical hurdles that need to be overcome en route to clinical translation of genome editing and indicate advances that may facilitate routine application beyond the most common disorders.

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.

A Benchmark Side-by-Side Comparison of Two Well-Established Protocols for in vitro Hematopoietic Differentiation From Human Pluripotent Stem Cells

The generation of transplantable hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) remains challenging. Current differentiation protocols from hPSCs generate mostly hematopoietic progenitors of the primitive HSC-independent program, and it remains unclear what is the best combination of cytokines and hematopoietic growth factors (HGFs) for obtaining functional hematopoietic cells in vitro. Here, we have used the AND1 and H9 hESC lines and the H9:dual-reporter RUNX1C-GFP-SOX17-Cherry to compare the hematopoietic differentiation in vitro based on the treatment of embryoid bodies (EBs) with the ventral mesoderm inducer BMP4 plus HGFs in the absence (protocol 1) or presence (protocol 2) of stage-specific activation of Wnt/β-catenin and inhibition of Activin/Nodal. Despite a slight trend in favor of protocol 1, no statistically significant differences were observed between protocols at any time point analyzed throughout EB development regarding the frequency of hemogenic endothelial (HE) precursors; CD43+ CD45−, CD45+, and CD45 + CD34 + hematopoietic derivatives; or the output of clonogenic progenitors. Similarly, the kinetics of emergence throughout EB development of both SOX17 + HE and RUNX1C + definitive hematopoiesis was very similar for both protocols. The expression of the early master mesendodermal transcription factors Brachyury, MIXL1, and KDR revealed similar gene expression kinetics prior to the emergence of RUNX1C + definitive hematopoiesis for both protocols. Collectively, the simpler protocol 1 is, at least, as efficient as protocol 2, suggesting that supplementation with additional morphogens/HGFs and modulation of Activin/Nodal and Wnt/β-catenin pathways seem dispensable for in vitro hematopoietic differentiation of hPSCs.

The Therapeutic Potential of Hematopoietic Stem Cells in Bone Regeneration

The repair process of bone fractures is a complex biological mechanism requiring the recruitment and in situ functionality of stem/stromal cells from the bone marrow (BM). BM mesenchymal stem/stromal cells have been widely explored in multiple bone tissue engineering applications, whereas the use of hematopoietic stem cells (HSCs) has been poorly investigated in this context. A reasonable explanation is the fact that the role of HSCs and their combined effect with other elements of the hematopoietic niches in the bone-healing process is still elusive. Therefore, in this review we intend to highlight the influence of HSCs in the bone repair process, mainly through the promotion of osteogenesis and angiogenesis at the bone injury site. For that, we briefly describe the main biological characteristics of HSCs, as well as their hematopoietic niches, while reviewing the biomimetic engineered BM niche models. Moreover, we also highlighted the role of HSCs in translational in vivo transplantation or implantation as promoters of bone tissue repair.

In situ delivery of iPSC-derived dendritic cells with local radiotherapy generates systemic antitumor immunity and potentiates PD-L1 blockade in preclinical poorly immunogenic tumor models

BACKGROUND

Dendritic cells (DCs) are a promising therapeutic target in cancer immunotherapy given their ability to prime antigen-specific T cells, and initiate antitumor immune response. A major obstacle for DC-based immunotherapy is the difficulty to obtain a sufficient number of functional DCs. Theoretically, this limitation can be overcome by using induced pluripotent stem cells (iPSCs); however, therapeutic strategies to engage iPSC-derived DCs (iPSC-DCs) into cancer immunotherapy remain to be elucidated. Accumulating evidence showing that induction of tumor-residing DCs enhances immunomodulatory effect of radiotherapy (RT) prompted us to investigate antitumor efficacy of combining intratumoral administration of iPSC-DCs with local RT.

METHODS

Mouse iPSCs were differentiated to iPSC-DCs on OP9 stromal cells expressing the notch ligand delta-like 1 in the presence of granulocyte macrophage colony-stimulating factor. Phenotype and the capacities of iPSC-DCs to traffic tumor-draining lymph nodes (TdLNs) and prime antigen-specific T cells were evaluated by flow cytometry and imaging flow cytometry. Antitumor efficacy of intratumoral injection of iPSC-DCs and RT was tested in syngeneic orthotopic mouse tumor models resistant to anti-PD-1 ligand 1 (PD-L1) therapy.

RESULTS

Mouse iPSC-DCs phenotypically resembled conventional type 2 DCs, and had a capacity to promote activation, proliferation and effector differentiation of antigen-specific CD8+ T cells in the presence of the cognate antigen in vitro. Combination of in situ administration of iPSC-DCs and RT facilitated the priming of tumor-specific CD8+ T cells, and synergistically delayed the growth of not only the treated tumor but also the distant non-irradiated tumors. Mechanistically, RT enhanced trafficking of intratumorally injected iPSC-DCs to the TdLN, upregulated CD40 expression, and increased the frequency of DC/CD8+ T cell aggregates. Phenotypic analysis of tumor-infiltrating CD8+ T cells and myeloid cells revealed an increase of stem-like Slamf6+ TIM3- CD8+ T cells and PD-L1 expression in tumor-associated macrophages and DCs. Consequently, combined therapy rendered poorly immunogenic tumors responsive to anti-PD-L1 therapy along with the development of tumor-specific immunological memory.

CONCLUSIONS

Our findings illustrate the translational potential of iPSC-DCs, and identify the therapeutic efficacy of a combinatorial platform to engage them for overcoming resistance to anti-PD-L1 therapy in poorly immunogenic tumors.

Cord blood beyond transplantation: can we use the experience to advance all cell therapies?

Unrelated cord blood (CB) units, already manufactured, fully tested and stored, are high-quality products for haematopoietic stem cell transplantation and cell therapies, as well as an optimal starting material for cell expansion, cell engineering or cell re-programming technologies. CB banks have been pioneers in the development and implementation of Current Good Manufacturing Practices for cell-therapy products. Sharing their technological and regulatory experience will help advance all cell therapies, CB-derived or not, particularly as they transition from autologous, individually manufactured products to stored, 'off-the shelf' treatments. Such strategies will allow broader patient access and wide product utilisation.

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.