Hematopoietic stem cells: concepts, definitions, and the new reality. Blood. 2015;125:2605-2613. [PMID: 25762175 DOI: 10.1182/blood-2014-12-570200]

Quantifying Drug-Induced Bone Marrow Toxicity Using a Novel Haematopoiesis Systems Pharmacology Model

Haematological toxicity associated with cancer therapeutics is monitored by changes in blood cell count, and their primary effect is on proliferative progenitors in the bone marrow. Using observations in rat bone marrow and blood, we characterize a mathematical model that comprises cell proliferation and differentiation of the full haematopoietic phylogeny, with interacting feedback loops between lineages in homeostasis as well as following carboplatin exposure. We accurately predicted the temporal dynamics of several mature cell types related to carboplatin-induced bone marrow toxicity and identified novel insights into haematopoiesis. Our model confirms a significant degree of plasticity within bone marrow cells, with the number and type of both early progenitors and circulating cells affecting cell balance, via feedback mechanisms, through fate decisions of the multipotent progenitors. We also demonstrated cross-species translation of our predictions to patients, applying the same core model structure and considering differences in drug-dependent and physiology-dependent parameters.

Applications of single cell RNA sequencing to research of stem cells

Stem cells (SCs) with their self-renewal and pluripotent differentiation potential, show great promise for therapeutic applications to some refractory diseases such as stroke, Parkinsonism, myocardial infarction, and diabetes. Furthermore, as seed cells in tissue engineering, SCs have been applied widely to tissue and organ regeneration. However, previous studies have shown that SCs are heterogeneous and consist of many cell subpopulations. Owing to this heterogeneity of cell states, gene expression is highly diverse between cells even within a single tissue, making precise identification and analysis of biological properties difficult, which hinders their further research and applications. Therefore, a defined understanding of the heterogeneity is a key to research of SCs. Traditional ensemble-based sequencing approaches, such as microarrays, reflect an average of expression levels across a large population, which overlook unique biological behaviors of individual cells, conceal cell-to-cell variations, and cannot understand the heterogeneity of SCs radically. The development of high throughput single cell RNA sequencing (scRNA-seq) has provided a new research tool in biology, ranging from identification of novel cell types and exploration of cell markers to the analysis of gene expression and predicating developmental trajectories. scRNA-seq has profoundly changed our understanding of a series of biological phenomena. Currently, it has been used in research of SCs in many fields, particularly for the research of heterogeneity and cell subpopulations in early embryonic development. In this review, we focus on the scRNA-seq technique and its applications to research of SCs.

Potential therapeutic application of mesenchymal stem cells in ophthalmology

At present a wide variety of methods have been proposed to treat eye disorders, drug therapies are most commonly used. It should be noted that effective treatment modalities especially for degeneration of the retina and optic nerve are lacking. In the last few years stem cell transplantation has been proposed as an alternative method. The opportunities that stem cells provide within clinical use are almost unlimited. These cells are presently applied to treat various traumatic and degenerative disorders due to their unique biologic properties. Stem cells have high proliferative capabilities and are a self-maintained population of cells capable of differentiating into different cell types. Thus, they are represent a very primary stage of a cell lineage. Their ability to differentiate into different pathways provides animals with great plasticity in the renewal of somatic cells in postnatal ontogenesis. Pre-clinical and clinical ophthalmology studies where mesenchymal stem cells are applied and various methods of their administration are discussed herein. In addition the safety and efficacy of using bone marrow- and adipose tissue-derived mesenchymal stem cells have been discussed.

IRF2 is a master regulator of human keratinocyte stem cell fate

Resident adult epithelial stem cells maintain tissue homeostasis by balancing self-renewal and differentiation. The stem cell potential of human epidermal keratinocytes is retained in vitro but lost over time suggesting extrinsic and intrinsic regulation. Transcription factor-controlled regulatory circuitries govern cell identity, are sufficient to induce pluripotency and transdifferentiate cells. We investigate whether transcriptional circuitry also governs phenotypic changes within a given cell type by comparing human primary keratinocytes with intrinsically high versus low stem cell potential. Using integrated chromatin and transcriptional profiling, we implicate IRF2 as antagonistic to stemness and show that it binds and regulates active cis-regulatory elements at interferon response and antigen presentation genes. CRISPR-KD of IRF2 in keratinocytes with low stem cell potential increases self-renewal, migration and epidermis formation. These data demonstrate that transcription factor regulatory circuitries, in addition to maintaining cell identity, control plasticity within cell types and offer potential for therapeutic modulation of cell function.

Epidermal homeostasis requires long term stem cell function. Here, the authors apply transcriptional circuitry analysis based on integrated epigenomic profiling of primary human keratinocytes with high and low stem cell function to identify IRF2 as a negative regulator of stemness.

Molecular heterogeneity unravelled by single-cell transcriptomics in patients with essential thrombocythaemia

Significant phenotypic heterogeneity exists in patients with all subtypes of myeloproliferative neoplasms (MPN), including essential thrombocythaemia (ET). Single-cell RNA sequencing (scRNA-Seq) holds the promise of unravelling the biology of MPN at an unprecedented level of resolution. Herein we employed this approach to dissect the transcriptomes in the CD34⁺ cells from the peripheral blood of seven previously untreated ET patients and one healthy adult. The mutational profiles in these patients were as follows: JAK2 V617F in two, CALR in three (one type I and two type II) and triple-negative (TN) in two. Our results reveal substantial heterogeneity within this enrolled cohort of patients. Activation of JAK/STAT signalling was recognized in discrepant progenitor lineages among different samples. Significantly disparate molecular profiling was identified in the comparison between ET patients and the control, between patients with different driver mutations (JAK2 V617F and CALR exon 9 indel), and even between patients harbouring the same driver. Intra-individual clonal diversity was also found in the CD34⁺ progenitor population of a patient, possibly indicating the presence of multiple clones in this case. Estimation of subpopulation size based on cellular immunophenotyping suggested differentiation bias in all analysed samples. Furthermore, combining the transcriptomic information with data from targeted sequencing enabled us to unravel key somatic mutations that are molecularly relevant. To conclude, we demonstrated that scRNA-Seq extended our knowledge of clonal diversity and inter-individual heterogeneity in patients with ET. The obtained information could potentially leapfrog our efforts in the elucidation of the pathogenesis of the disease.

Assessment of Short-Term Engraftment Potential of Ex Vivo Expanded Hematopoietic Stem Cells Using Normal Fetal Mouse in Utero Transplantation Model

OBJECTIVE

Ex vivo expansion is a promising strategy to overcome the low number of human umbilical cord blood hematopoietic stem cells (hUCB-HSCs). Although based on the obtained results in unnatural physiological condition of irradiated genetically immune-deficient mouse models, there has always been concern that the expanded cells have less engraftment potential. The purpose of this study was to investigate effect of common ex vivo expansion method on engraftment potential of hUCB-mononuclear cells (MNCs), using normal fetal mouse, as a model with more similarity to human physiological conditions.

MATERIALS AND METHODS

In this experimental study, briefly, isolated hUCB-MNCs were cultured in common expansion medium containing stem cell factor, Flt3 ligand and thrombopoietin. The unexpanded and expanded cells were transplanted to the fetal mice on gestational days of 11.5-13.5. After administration of human hematopoiesis growth factors (hHGFs), presence of human CD45+ cells, in the peripheral blood of recipients, was assessed at various time points after transplantation.

RESULTS

The expanded MNCs showed 32-fold increase in the expression of CD34+38- phenotype and about 3-fold higher clonogenic potential as compared to the uncultured cells. Four weeks after transplantation, 73% (19/26) of expanded-cell recipients and 35% (7/20) of unexpanded-cell recipients were found to be successfully engrafted with human CD45+ cells. The engraftment level of expanded MNCs was significantly (1.8-fold) higher than unexpanded cells. After hHGFs administration, the level was increased to 3.2, 3.8 and 2.6-fold at respectively 8, 12, and 16 weeks of post transplantation. The increased expression of CXCR4 protein in expanded MNCs is a likely explanation for the present findings.

CONCLUSION

The presented data showed that expanded MNCs compared to unexpended cells are capable of more rapid and higher short-term engraftment in normal fetal mouse. It could also be suggested that in utero transplantation (IUT) of normal fetal mice could be an appropriate substitute for NOD/SCID mice in xenotransplantation studies.

Primary myelofibrosis marrow-derived CD14+/CD34- monocytes induce myelofibrosis-like phenotype in immunodeficient mice and give rise to megakaryocytes

To confirm that neoplastic monocyte-derived collagen- and fibronectin-producing fibrocytes induce bone marrow (BM) fibrosis in primary myelofibrosis (PMF), we injected PMF BM-derived fibrocyte-precursor CD14⁺/CD34^- monocytes into the tail vein of NOD-SCID-γ (NSG) mice. PMF BM-derived CD14⁺/CD34^- monocytes engrafted and induced a PMF-like phenotype with splenomegaly, myeloid hyperplasia with clusters of atypical megakaryocytes, persistence of the JAK2^V617F mutation, and BM and spleen fibrosis. As control we used normal human BM-derived CD14⁺/CD34^- monocytes. These monocytes also engrafted and gave rise to normal megakaryocytes that, like PMF CD14⁺/CD34^--derived megakaryocytes, expressed HLA-ABC and human CD42b antigens. Using 2 clonogenic assays we confirmed that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte colony-forming cells, suggesting that a subpopulation BM monocytes harbors megakaryocyte progenitor capacity. Taken together, our data suggest that PMF monocytes induce myelofibrosis-like phenotype in immunodeficient mice and that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte progenitor cells.

A Prospective Analysis of Human Leukemogenesis

Decades of lack of progress in treating many fatal malignancies of the blood-forming system is commanding interest in new approaches. Targeting early events in the leukemogenic process has long been recognized as likely to offer the information required for these diseases. Analysis of the representation of different mutations in the leukemic cells from individual patients offers a retrospective method to infer their sequence of acquisition and associated subclonal dynamics. An alternative, prospective approach is to exploit strategies for recreating human leukemia de novo using defined genetic methods. This concept is not new, but has been historically difficult to realize. A brief review of our experience in generating insights into the properties and regulation of primitive normal human hematopoietic cells serves as a reminder of how this has enabled our recent advances in developing this approach using both primary sources of chronic myeloid leukemic cells and normal cord blood cells as targets.

JAK2 V617F -Mediated Clonal Hematopoiesis Accelerates Pathological Remodeling in Murine Heart Failure

Janus kinase 2 (valine to phenylalanine at residue 617) (JAK2 ^V617F ) mutations lead to myeloproliferative neoplasms associated with elevated myeloid, erythroid, and megakaryocytic cells. Alternatively these same mutations can lead to the condition of clonal hematopoiesis with no impact on blood cell counts. Here, a model of myeloid-restricted JAK2 ^V617F expression from lineage-negative bone marrow cells was developed and evaluated. This model displayed greater cardiac inflammation and dysfunction following permanent left anterior descending artery ligation and transverse aortic constriction. These data suggest that JAK2 ^V617F mutations arising in myeloid progenitor cells may contribute to cardiovascular disease by promoting the proinflammatory properties of circulating myeloid cells.

Mycobacterium tuberculosis-Infected Hematopoietic Stem and Progenitor Cells Unable to Express Inducible Nitric Oxide Synthase Propagate Tuberculosis in Mice

Persistence of Mycobacterium tuberculosis within human bone marrow stem cells has been identified as a potential bacterial niche during latent tuberculosis. Using a murine model of tuberculosis, we show here that bone marrow stem and progenitor cells containing M. tuberculosis propagated tuberculosis when transferred to naive mice, given that both transferred cells and recipient mice were unable to express inducible nitric oxide synthase, which mediates killing of intracellular bacteria via nitric oxide. Our findings suggest that bone marrow stem and progenitor cells containing M. tuberculosis propagate hallmarks of disease if nitric oxide-mediated killing of bacteria is defective.

The MarrowMiner: A Novel Minimally Invasive and Effective Device for the Harvest of Bone Marrow

Bone marrow (BM) is a rich source of hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), and other important stem/progenitor cells. It is the traditional source of cells used in hematopoietic cell transplantation, which is a proven curative treatment for many blood and immune diseases. BM-derived cells have also been shown to have other diverse clinical uses and are increasingly being used in orthopedic medicine, regenerative medicine, and gene therapy applications. Traditional methods for harvesting BM are crude, tedious, time-consuming, and expensive, requiring multiple bone punctures under general anesthesia with serial small-volume aspirates often diluted with peripheral blood. The MarrowMiner (MM) is a novel device designed for rapid and minimally invasive BM harvest. Here we show the safety and efficacy of the MM in both preclinical and clinical settings. In a large-animal porcine model, the MM enabled effective BM collection with similar total nucleated cell collection and increased colony formation compared with standard methods. The MM was subsequently evaluated in a clinical study showing effective and complication-free anterior and posterior BM collection of 20 patients under only local anesthesia or light sedation. Increased total nucleated and mononucleated cell collection was achieved with the MM compared with standard methods in the same patients. Importantly, stem cell content was high with trends toward increased HSC, MSC, and endothelial progenitor cells with similar T cell content. Given the MM is a novel device approved by the US Food and Drug Administration, enabling safe, effective, and minimally invasive harvest of BM, we anticipate rapid adoption for various applications.

Developmental programming of adult haematopoiesis system

The Barker hypothesis of 'foetal origin of adult diseases' has led to emphasize the concept of 'developmental programming', based on the crucial role of epigenetic factors. Accordingly, it has been demonstrated that parental adversity (before conception and during pregnancy) and foetal factors (i.e., hypoxia, malnutrition and placental insufficiency) permanently modify the physiological systems of the progeny, predisposing them to premature ageing and chronic disease during adulthood. Thus, an altered functionality of the endocrine, immune, nervous and cardiovascular systems is observed in the progeny. However, it remains to be understood whether the haematopoietic system itself also represents a portrait of foetal programming. Here, we provide evidence, reporting and discussing related theories, and results of studies described in the literature. In addition, we have outlined our opinions and suggest how it is possible to intervene to correct foetal mal-programming. Some pro-health interventions and recommendations are proposed, with the hope of guarantee the health of future generations and trying to combat the continuous increase in age-related diseases in human populations.

The cell of origin and the leukemia stem cell in acute myeloid leukemia

There is experimental and observational evidence that the cells of the leukemic clone in acute myeloid leukemia (AML) have different phenotypes even though they share the same somatic mutations. The organization of the malignant clone in AML has many similarities to normal hematopoiesis, with leukemia stem cells (LSCs) that sustain leukemia and give rise to more differentiated cells. LSCs, similar to normal hematopoietic stem cells (HSCs), are those cells that are able to give rise to a new leukemic clone when transplanted into a recipient. The cell of origin of leukemia (COL) is defined as the normal cell that is able to transform into a leukemia cell. Current evidence suggests that the COL is distinct from the LSC. Here, we will review the current knowledge about LSCs and the COL in AML.

Biological implications of clonal hematopoiesis

Adult hematological malignancies, such as acute myeloid leukemia, are thought to arise through the gradual acquisition of oncogenic mutations within long-lived hematopoietic stem cells (HSCs). Genomic analysis of peripheral blood DNA has recently identified leukemia-associated genetic mutations within otherwise healthy individuals, an observation that is strongly associated with age. These genetic mutations are often found at high frequency, suggesting dominance of a mutant HSC clone. Expansion of clones carrying other mutations not associated with leukemia or larger chromosomal deletions was also observed. This clinical observation has been termed clonal hematopoiesis, a condition associated with increased risk of both hematological malignancy and cardiovascular disease. Here, we discuss the identification of clonal hematopoiesis and its implications on human health, based on the May 2019 International Society for Experimental Hematology New Investigator Committee Webinar.

Five Active Components Compatibility of Astragali Radix and Angelicae Sinensis Radix Protect Hematopoietic Function Against Cyclophosphamide-Induced Injury in Mice and t-BHP-Induced Injury in HSCs

Although the compatibility of Astragali Radix (AR) and Angelicae Sinensis Radix (ASR) has favorable effect on promoting hematopoiesis in traditional Chinese medicine (TCM), the main active components and pharmacological mechanism are unknown. We investigated the five active components and its mechanisms in vitro and in vivo. Five active components of Astragalus glycosides (AST), Formononetin (FRM), Ferulic acid (FRA), Calycosin (CAL), and Calycosin-7-glucoside (CLG), which could be absorbed in intestinal tract, were detected in this study. The peripheral blood, hematopoietic growth factors (HGFs), and hematopoietic progenitor cells (HPCs) colony were observed to evaluate the effect of these five active components promoting hematopoiesis. Furthermore, hematopoietic stem cell (HSC) proliferation, aging, cycle, and related proteins were detected to explore the mechanism of these five components promoting HSC proliferation. i) The in vivo experiments showed that the combination of the five active components could remarkably increase the number of RBCs, WBCs, PLTs, and content of Hb in peripheral blood and the area of bone marrow hematopoietic tissue, as well as thrombopoietin (TPO), erythropoietin (EPO), granulocyte-macrophage colony stimulating factor (GM-CSF), and colony of CFU-GM, CFU-MK, CFU-E, and BFU-E in serum. Each of these five components promoted the recovery of RBCs and Hb, and increased TPO, CFU-MK, and CFU-E. All components except for AST increased the CFU-GM. FRA increased the number of WBCs, the area of bone marrow hematopoietic tissue, and BFU-E. FRA and AST promoted PLT recovery. FRA and CAL improved the content of GM-CSF. FRA, CAL, and CLG improved the content of EPO. ii) The in vitro experiments showed that FRA, FRM, and AST significantly promoted cell proliferation, reduced the positive rate and G0/G1 cells, and increased G2/M + S cells and the expression of cyclin D1 and CDK4 proteins in aging HSCs. Furthermore, the combination of five components had the best effect. Taken together, the five active components of AST, FRM, FRA, CAL, and CLG were the main pharmacodynamic substances of the AR-ASR compatibility, which promoted hematopoiesis. The combination of them had a synergistic effect. The mechanism of promoting hematopoiesis may be relevant to regulating cyclin-related proteins, promoting cell cycle transformation, and promoting HSC proliferation.

Hedgehog pathway inhibition as a therapeutic target in acute myeloid leukemia

Introduction: The Hedgehog (HH) pathway constitutes a collection of signaling molecules which critically influence embryogenesis. In adults, however, the HH pathway remains integral to the proliferation, maintenance, and apoptosis of adult stem cells including hematopoietic stem cells. Areas covered: We discuss the current understanding of the HH pathway as it relates to normal hematopoiesis, the pathology of acute myeloid leukemia (AML), the rationale for and data from combination therapies including HH pathway inhibitors, and ultimately the prospects that might offer promise in targeting this pathway in AML. Expert opinion: Efforts to target the HH pathway have been focused on impeding this disposition and restoring chemosensitivity to conventional myeloid neoplasm therapies. The year 2018 saw the first approval of a HH pathway inhibitor (glasdegib) for AML, though for an older population and in combination with an uncommonly-used therapy. Several other clinical trials with agents targeting modulators of HH signaling in AML and MDS are underway. Further study and understanding of the interplay between the numerous aspects of HH signaling and how it relates to the augmented survival of AML will provide a more reliable substrate for therapeutic strategies in patients with this poor-risk disease.

Imaging and spatial analysis of hematopoietic stem cell niches

Hematopoietic stem cells (HSCs) have been long proposed to reside in defined anatomical locations within bone marrow (BM) tissues in direct contact or close proximity to nurturing cell types. Imaging techniques that allow the simultaneous mapping of HSCs and interacting cell types have been central to the discovery of basic principles of these so-called HSC niches. Despite major progress in the field, a quantitative and comprehensive model of the cellular and molecular components that define these specialized microenvironments is lacking to date, and uncertainties remain on the preferential localization of HSCs in the context of complex BM tissue landscapes. Recent technological breakthroughs currently allow for the quantitative spatial analysis of BM cellular components with extraordinary precision. Here, we critically discuss essential technical aspects related to imaging approaches, image processing tools, and spatial statistics, which constitute the three basic elements of rigorous quantitative spatial analyses of HSC niches in the BM microenvironment.

Spermatogonial stem cells

Spermatogonial stem cells (SSCs) are the most primitive spermatogonia in the testis and have an essential role to maintain highly productive spermatogenesis by self-renewal and continuous generation of daughter spermatogonia that differentiate into spermatozoa, transmitting genetic information to the next generation. Since the 1950s, many experimental methods, including histology, immunostaining, whole-mount analyses, and pulse-chase labeling, had been used in attempts to identify SSCs, but without success. In 1994, a spermatogonial transplantation method was reported that established a quantitative functional assay to identify SSCs by evaluating their ability to both self-renew and differentiate to spermatozoa. The system was originally developed using mice and subsequently extended to nonrodents, including domestic animals and humans. Availability of the functional assay for SSCs has made it possible to develop culture systems for their ex vivo expansion, which dramatically advanced germ cell biology and allowed medical and agricultural applications. In coming years, SSCs will be increasingly used to understand their regulation, as well as in germline modification, including gene correction, enhancement of male fertility, and conversion of somatic cells to biologically competent male germline cells.

A comprehensive single cell transcriptional landscape of human hematopoietic progenitors

Hematopoietic Stem/Progenitor cells (HSPCs) are endowed with the role of maintaining a diverse pool of blood cells throughout the human life. Despite recent efforts, the nature of the early cell fate decisions remains contentious. Using single-cell RNA-Seq, we show that existing approaches to stratify bone marrow CD34+ cells reveal a hierarchically-structured transcriptional landscape of hematopoietic differentiation. Still, this landscape misses important early fate decisions. We here provide a broader transcriptional profiling of bone marrow lineage negative hematopoietic progenitors that recovers a key missing branchpoint into basophils and expands our understanding of the underlying structure of early adult human haematopoiesis. We also show that this map has strong similarities in topology and gene expression to that found in mouse. Finally, we identify the sialomucin CD164, as a reliable marker for the earliest branches of HSPCs specification and we showed how its use can foster the design of alternative transplantation cell products.

Long-term ex vivo haematopoietic-stem-cell expansion allows nonconditioned transplantation

Multipotent self-renewing haematopoietic stem cells (HSCs) regenerate the adult blood system after transplantation¹, which is a curative therapy for numerous diseases including immunodeficiencies and leukaemias². Although substantial effort has been applied to identifying HSC maintenance factors through the characterization of the in vivo bone-marrow HSC microenvironment or niche^3-5, stable ex vivo HSC expansion has previously been unattainable^6,7. Here we describe the development of a defined, albumin-free culture system that supports the long-term ex vivo expansion of functional mouse HSCs. We used a systematic optimization approach, and found that high levels of thrombopoietin synergize with low levels of stem-cell factor and fibronectin to sustain HSC self-renewal. Serum albumin has long been recognized as a major source of biological contaminants in HSC cultures⁸; we identify polyvinyl alcohol as a functionally superior replacement for serum albumin that is compatible with good manufacturing practice. These conditions afford between 236- and 899-fold expansions of functional HSCs over 1 month, although analysis of clonally derived cultures suggests that there is considerable heterogeneity in the self-renewal capacity of HSCs ex vivo. Using this system, HSC cultures that are derived from only 50 cells robustly engraft in recipient mice without the normal requirement for toxic pre-conditioning (for example, radiation), which may be relevant for HSC transplantation in humans. These findings therefore have important implications for both basic HSC research and clinical haematology.

BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were linked to genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Targeting the Spleen as an Alternative Site for Hematopoiesis

Bone marrow is the main site for hematopoiesis in adults. It acts as a niche for hematopoietic stem cells (HSCs) and contains non-hematopoietic cells that contribute to stem cell dormancy, quiescence, self-renewal, and differentiation. HSC also exist in resting spleen of several species, although their contribution to hematopoiesis under steady-state conditions is unknown. The spleen can however undergo extramedullary hematopoiesis (EMH) triggered by physiological stress or disease. With the loss of bone marrow niches in aging and disease, the spleen as an alternative tissue site for hematopoiesis is an important consideration for future therapy, particularly during HSC transplantation. In terms of harnessing the spleen as a site for hematopoiesis, here the remarkable regenerative capacity of the spleen is considered with a view to forming additional or ectopic spleen tissue through cell engraftment. Studies in mice indicate the potential for such grafts to support the influx of hematopoietic cells leading to the development of normal spleen architecture. An important goal will be the formation of functional ectopic spleen tissue as an aid to hematopoietic recovery following clinical treatments that impact bone marrow. For example, expansion or replacement of niches could be considered where myeloablation ahead of HSC transplantation compromises treatment outcomes.

Human adult HSCs can be discriminated from lineage-committed HPCs by the expression of endomucin

EMCN is a novel marker of human HSCs. EMCN is a more specific marker of HSCs than CD34 as it can discriminate HSCs from lineage-committed HPCs.

New insights into hematopoietic differentiation landscapes from single-cell RNA sequencing

Single-cell transcriptomics has recently emerged as a powerful tool to analyze cellular heterogeneity, discover new cell types, and infer putative differentiation routes. The technique has been rapidly embraced by the hematopoiesis research community, and like other technologies before, single-cell molecular profiling is widely expected to make important contributions to our understanding of the hematopoietic hierarchy. Much of this new interpretation relies on inference of the transcriptomic landscape as a representation of existing cellular states and associated transitions among them. Here we review how this model allows, under certain assumptions, charting of time-resolved differentiation trajectories with unparalleled resolution and how the landscape of multipotent cells may be rather devoid of discrete structures, challenging our preconceptions about stem and progenitor cell types and their organization. Finally, we highlight how promising technological advances may convert static differentiation landscapes into a dynamic cell flux model and thus provide a more holistic understanding of normal hematopoiesis and blood disorders.

Enhancing human cord blood hematopoietic stem cell engraftment by targeting nuclear hormone receptors

PURPOSE OF REVIEW

Allogeneic hematopoietic cell transplantation (HCT) is a life-saving therapy for hematological and nonhematological diseases. Cord blood is a source of transplantable hematopoietic stem cells (HSCs), but limited numbers of HSCs in single cord blood units, which may cause delayed neutrophil, platelet, and immune cell reconstitution, is a major problem for efficient transplantation. Ex-vivo expansion and enhanced homing of cord blood HSC may overcome this disadvantage and improve its long-term engraftment. Here, we discuss the role of nuclear hormone receptors signaling in human cord blood HSC engraftment.

RECENT FINDINGS

Antagonizing retinoid acid receptor (RAR) signaling promotes human HSC expansion and increases myeloid cell production. Cord blood CD34 cells expanded by SR1 promotes efficient myeloid recovery after transplantation compared with control groups, and leads to successful engraftment. Short-term treatment of glucocorticoids enhances homing and long-term engraftment of human HSCs and HPCs in NSG mice. Peroxisome proliferator-activated receptor-γ (PPARγ) antagonism expands human HSCs and HPCs by preventing differentiation and enhancing glucose metabolism. These findings demonstrate that nuclear hormone receptor signaling components might be promising targets for improving human cord blood HCT.

SUMMARY

Better understanding of molecular mechanisms underlying human HSC expansion and homing mediated by nuclear hormone receptor signaling pathways will facilitate enhanced HCT efficacy.

Iron and iron-dependent reactive oxygen species in the regulation of macrophages and fibroblasts in non-healing chronic wounds

Chronic wounds pose a stern challenge to health care systems with growing incidence especially in the aged population. In the presence of increased iron concentrations, recruitment of monocytes from the circulation and activation towards ROS and RNS releasing M1 macrophages together with the persistence of senescent fibroblasts at the wound site are significantly enhanced. This unrestrained activation of pro-inflammatory macrophages and senescent fibroblasts has increasingly been acknowledged as main driver causing non-healing wounds. In a metaphor, macrophages act like stage directors of wound healing, resident fibroblasts constitute main actors and increased iron concentrations are decisive parts of the libretto, and - if dysregulated - are responsible for the development of non-healing wounds. This review will focus on recent cellular and molecular findings from chronic venous leg ulcers and diabetic non-healing wounds both constituting the most common pathologies often resulting in limb amputations of patients. This not only causes tremendous suffering and loss of life quality, but is also associated with an increase in mortality and a major socio-economic burden. Despite recent advances, the underlying molecular mechanisms are not completely understood. Overwhelming evidence shows that reactive oxygen species and the transition metal and trace element iron at pathological concentrations are crucially involved in a complex interplay between cells of different histogenetic origin and their extracellular niche environment. This interplay depends on a variety of cellular, non-cellular biochemical and cell biological mechanisms. Here, we will highlight recent progress in the field of iron-dependent regulation of macrophages and fibroblasts and related pathologies linked to non-healing chronic wounds.

Chasing Mavericks: The quest for defining developmental waves of hematopoiesis

Hematopoiesis is the process by which mature blood and immune cells are produced from hematopoietic stem and progenitor cells (HSCs and HSPCs). The last several decades of research have shed light on the origin of HSCs, as well as the heterogeneous pools of fetal progenitors that contribute to lifelong hematopoiesis. The overarching concept that hematopoiesis occurs in dynamic, overlapping waves throughout development, with each wave contributing to both continuous and developmentally limited cell types, has been solidified over the years. However, recent advances in our ability to track the production of hematopoietic cells in vivo have challenged several long-held dogmas on the origin and persistence of distinct hematopoietic cell types. In this review, we highlight emerging concepts in hematopoietic development and identify unanswered questions.

High-fat diet disturbs lipid raft/TGF-β signaling-mediated maintenance of hematopoietic stem cells in mouse bone marrow

Despite recent in vivo data demonstrating that high-fat diet (HFD)-induced obesity leads to major perturbations in murine hematopoietic stem cells (HSC), the direct role of a HFD is not yet completely understood. Here, we investigate the direct impact of a short-term HFD on HSC and hematopoiesis in C57BL/6J mice compared with standard diet-fed mice. We detect a loss of half of the most primitive HSC in the bone marrow (BM) cells of HFD-fed mice, which exhibit lower hematopoietic reconstitution potential after transplantation. Impaired maintenance of HSC is due to reduced dormancy after HFD feeding. We discover that a HFD disrupts the TGF-β receptor within lipid rafts, associated to impaired Smad2/3-dependent TGF-β signaling, as the main molecular mechanism of action. Finally, injecting HFD-fed mice with recombinant TGF-β1 avoids the loss of HSC and alteration of the BM’s ability to recover, underscoring the fact that a HFD affects TGF-β signaling on HSC.

High fat diets (HFD) are thought to perturb murine hematopoiesis as a result of obesity. Here the authors find that short-term HFD reduces hematopoietic stem cells (HSC), disrupts lipid rafts and TGF-β1 signalling. Injecting HFD-fed mice with recombinant TGF-β1 can rescue HSC loss.

The Impact of the Cellular Origin in Acute Myeloid Leukemia: Learning From Mouse Models

Acute myeloid leukemia (AML) is a genetically heterogeneous disease driven by a limited number of cooperating mutations. There is a long-standing debate as to whether AML driver mutations occur in hematopoietic stem or in more committed progenitor cells. Here, we review how different mouse models, despite their inherent limitations, have functionally demonstrated that cellular origin plays a critical role in the biology of the disease, influencing clinical outcome. AML driven by potent oncogenes such as mixed lineage leukemia fusions often seem to emerge from committed myeloid progenitors whereas AML without any major cytogenetic abnormalities seem to develop from a combination of preleukemic initiating events arising in the hematopoietic stem cell pool. More refined mouse models may serve as experimental platforms to identify and validate novel targeted therapeutic strategies.

Machine-Learning Approach for Modeling Myelosuppression Attributed to Nimustine Hydrochloride

PURPOSE

A major adverse effect arising from nimustine hydrochloride (ACNU) therapy for brain tumors is myelosuppression. Because its timing and severity vary among individual patients, the ACNU dose level has been adjusted in an empiric manner at individual medical facilities. To our knowledge, ours is the first study to develop a machine-learning approach to estimate myelosuppression through analysis of patient factors before treatment and attempts to clarify the relationship between myelosuppression and hematopoietic stem cells from daily clinical data. Adverse effect prediction will allow ACNU dose adjustment for patients predicted to have decreases in blood cell counts and will enable focused follow-up of patients undergoing chemoradiotherapy.

PATIENTS AND METHODS

Patients were newly pathologically diagnosed with WHO grade 2 or 3 tumors and were treated with ACNU-based chemoradiotherapy. For detailed analysis of the timing and intensity of adverse effects in patients, we developed a data-weighted support vector machine (SVM) based on adverse event criteria (nadir-weighted SVM [NwSVM]). To evaluate the estimation accuracy of blood cell count dynamics, the determination coefficient ( r²) between real and estimated data was calculated by three regression methods: polynomial, SVM, and NwSVM.

RESULTS

Only the NwSVM-based regression enabled estimation of the dynamics of all blood cell types with high accuracy (mean r² = 0.81). The mean timing of nadir arrival estimated using this regression was 35 days for platelets, 41 days for RBCs, 52 days for lymphocytes, 57 days for WBCs, and 62 days for neutrophils.

CONCLUSION

The NwSVM can be used to predict myelosuppression and clearly depicts nadir timing differences between platelets and other blood cells.

Hematopoietic Stem and Progenitor Cells (HSPCs)

Hematopoietic stem/progenitor cells (HSPCs) isolated from bone marrow have been successfully employed for 50 years in hematological transplantations. Currently, these cells are more frequently isolated from mobilized peripheral blood or umbilical cord blood. In this chapter, we overview several topics related to these cells including their phenotype, methods for isolation, and in vitro and in vivo assays to evaluate their proliferative potential. The successful clinical application of HSPCs is widely understood to have helped establish the rationale for the development of stem cell therapies and regenerative medicine.

Assessment of Young and Aged Hematopoietic Stem Cell Activity by Competitive Serial Transplantation Assays

Healthy hematopoietic stem cells (HSCs) are capable to self-renew and reconstitute the complete hematopoietic system. Upon aging, there is an increased incidence of blood-related diseases. Age-related phenotypes have been widely studied by bone marrow transplantation experiments, where reconstitution of the transplanted cells is a direct measure of HSC activity. In this protocol we describe a competitive bone marrow transplantation assay to functionally test young and old HSCs.

A Unique Nonsaccharide Mimetic of Heparin Hexasaccharide Inhibits Colon Cancer Stem Cells via p38 MAP Kinase Activation

Targeting of cancer stem cells (CSC) is expected to be a paradigm-shifting approach for the treatment of cancers. Cell surface proteoglycans bearing sulfated glycosaminoglycan (GAG) chains are known to play a critical role in the regulation of stem cell fate. Here, we show for the first time that G2.2, a sulfated nonsaccharide GAG mimetic (NSGM) of heparin hexasaccharide, selectively inhibits colonic CSCs in vivo G2.2-reduced CSCs (CD133+/CXCR4+, Dual hi) induced HT-29 and HCT 116 colon xenografts' growth in a dose-dependent fashion. G2.2 also significantly delayed the growth of colon xenograft further enriched in CSCs following oxaliplatin and 5-fluorouracil treatment compared with vehicle-treated xenograft controls. In fact, G2.2 robustly inhibited CSCs' abundance (measured by levels of CSC markers, e.g., CD133, DCMLK1, LGR5, and LRIG1) and self-renewal (quaternary spheroids) in colon cancer xenografts. Intriguingly, G2.2 selectively induced apoptosis in the Dual hi CSCs in vivo eluding to its CSC targeting effects. More importantly, G2.2 displayed none to minimal toxicity as observed through morphologic and biochemical studies of vital organ functions, blood coagulation profile, and ex vivo analyses of normal intestinal (and bone marrow) progenitor cell growth. Through extensive in vitro, in vivo, and ex vivo mechanistic studies, we showed that G2.2's inhibition of CSC self-renewal was mediated through activation of p38α, uncovering important signaling that can be targeted to deplete CSCs selectively while minimizing host toxicity. Hence, G2.2 represents a first-in-class (NSGM) anticancer agent to reduce colorectal CSCs.

Colony Formation: An Assay of Hematopoietic Progenitor Cells

The colony-forming cell (CFC) assay is used to study the proliferation and differentiation pattern of each input hematopoietic progenitors by their ability to form colonies in a semisolid medium. The resulting colonies are consisting of more differentiated cells, and the number and the morphology of the colonies provide preliminary information about the ability of progenitors to differentiate and proliferate. To allow colonies to grow to a size which facilitates accurate counting and identification, about 14 days of culture is sufficient. In certain situations also shorter periods may be used.

Immune and metabolic shifts during neonatal development reprogram liver identity and function

BACKGROUND & AIMS

The liver is the main hematopoietic site in embryos, becoming a crucial organ in both immunity and metabolism in adults. However, how the liver adapts both the immune system and enzymatic profile to challenges in the postnatal period remains elusive. We aimed to identify the mechanisms underlying this adaptation.

METHODS

We analyzed liver samples from mice on day 0 after birth until adulthood. Human biopsies from newborns and adults were also examined. Liver immune cells were phenotyped using mass cytometry (CyTOF) and expression of several genes belonging to immune and metabolic pathways were measured. Mortality rate, bacteremia and hepatic bacterial retention after E. coli challenge were analyzed using intravital and in vitro approaches. In a set of experiments, mice were prematurely weaned and the impact on gene expression of metabolic pathways was evaluated.

RESULTS

Human and mouse newborns have a sharply different hepatic cellular composition and arrangement compared to adults. We also found that myeloid cells and immature B cells primarily compose the neonatal hepatic immune system. Although neonatal mice were more susceptible to infections, a rapid evolution to an efficient immune response was observed. Concomitantly, newborns displayed a reduction of several macronutrient metabolic functions and the normal expression level of enzymes belonging to lipid and carbohydrate metabolism was reached around the weaning period. Interestingly, early weaning profoundly disturbed the expression of several hepatic metabolic pathways, providing novel insights into how dietary schemes affect the metabolic maturation of the liver.

CONCLUSION

In newborns, the immune and metabolic profiles of the liver are dramatically different to those of the adult liver, which can be explained by the differences in the liver cell repertoire and phenotype. Also, dietary and antigen cues may be crucial to guide liver development during the postnatal phase.

LAY SUMMARY

Newborns face major challenges in the extra-uterine life. In fact, organs need to modify their cellular composition and gene expression profile in order to adapt to changes in both microbiota and diet throughout life. The liver is interposed between the gastrointestinal system and the systemic circulation, being the destination of all macronutrients and microbial products from the gut. Therefore, it is expected that delicately balanced mechanisms govern the transformation of a neonatal liver to a key organ in adults.

Heterogeneity in myeloproliferative neoplasms: Causes and consequences

Myeloproliferative neoplasms (MPNs) are haematopoietic stem cell-derived clonal disorders characterised by proliferation of some or all myeloid lineages, depending on the subtype. MPNs are classically categorized into three disease subgroups; essential thrombocythaemia (ET), polycythaemia vera (PV) and primary myelofibrosis (PMF). The majority (>85%) of patients carry a disease-initiating or driver mutation, the most prevalent occurring in the janus kinase 2 gene (JAK2 V617F), followed by calreticulin (CALR) and myeloproliferative leukaemia virus (MPL) genes. Although these diseases are characterised by shared clinical, pathological and molecular features, one of the most challenging aspects of these disorders is the diverse clinical features which occur in each disease type, with marked variability in risks of disease complications and progression to leukaemia. A remarkable aspect of MPN biology is that the JAK2 V617F mutation, often occurring in the absence of additional mutations, generates a spectrum of phenotypes from asymptomatic ET through to aggressive MF, associated with a poor outcome. The mechanisms promoting MPN heterogeneity remain incompletely understood, but contributing factors are broad and include patient characteristics (gender, age, comorbidities and environmental exposures), additional somatic mutations, target disease-initiating cell, bone marrow microenvironment and germline genetic associations. In this review, we will address these in detail and discuss their role in heterogeneity of MPN disease phenotypes. Tailoring patient management according to the multiple different factors that influence disease phenotype may prove to be the most effective approach to modify the natural history of the disease and ultimately improve outcomes for patients.

Adipose Stem Cell Translational Applications: From Bench-to-Bedside

During the last five years, there has been a significantly increasing interest in adult adipose stem cells (ASCs) as a suitable tool for translational medicine applications. The abundant and renewable source of ASCs and the relatively simple procedure for cell isolation are only some of the reasons for this success. Here, we document the advances in the biology and in the innovative biotechnological applications of ASCs. We discuss how the multipotential property boosts ASCs toward mesenchymal and non-mesenchymal differentiation cell lineages and how their character is maintained even if they are combined with gene delivery systems and/or biomaterials, both in vitro and in vivo.

The in vitro growth of a cord blood-derived cell population enriched for CD34+ cells is influenced by its cell cycle status and treatment with hydroxyurea

OBJECTIVE

Cell cycle plays a fundamental role in the physiology of hematopoietic stem and progenitor cells. In the present study we used a negative selection system to obtain an immature cell population-enriched for cord blood-derived CD34⁺ cells-and we determined its proliferation, expansion and differentiation patterns as a function of the cell cycle status. The effects of hydroxyurea (HU) were also assessed.

RESULTS

As compared with cells in synthesis (S)/Gap2 (G2)/mitosis (M), cells in quiescent state (G0)/Gap1 (G1) showed a higher proliferation potential in vitro. At culture onset, G0, G1 and S/G2/M cells corresponded with 63%, 33% and 4%, respectively. Treatment with HU before culture resulted in an increase in the proportion of cells in G1 with a concomitant decrease in S/G2/M cells, without affecting the proportion of cells in G0. After 3 days of culture in the presence of recombinant cytokines, the vast majority of the cells (90%) were in G1, and by day 8, G0, G1 and S/G2/M cells corresponded with 18%, 67% and 15%, respectively. HU also induced an increase in colony-forming cell (CFC) frequency, in the proliferation and expansion capacities of cultured cells under myeloid conditions, and favored the development of the erythroid lineage.

CONCLUSION

Our results show that the in vitro proliferation, expansion and differentiation potentials of immature hematopoietic cells are determined, at least in part, by their cell cycle status and that the cell cycle modifier HU significantly influences the growth of human hematopoietic cells. These results are of potential relevance for the development of ex vivo expansion protocols.

Kinetics of adult hematopoietic stem cell differentiation in vivo

The process whereby hematopoietic stem cells (HSCs) generate different blood cell types in the steady-state is poorly understood. Upadhaya et al. used inducible lineage tracing to characterize the earliest steps of adult HSC differentiation in vivo.

Adult hematopoiesis has been studied in terms of progenitor differentiation potentials, whereas its kinetics in vivo is poorly understood. We combined inducible lineage tracing of endogenous adult hematopoietic stem cells (HSCs) with flow cytometry and single-cell RNA sequencing to characterize early steps of hematopoietic differentiation in the steady-state. Labeled cells, comprising primarily long-term HSCs and some short-term HSCs, produced megakaryocytic lineage progeny within 1 wk in a process that required only two to three cell divisions. Erythroid and myeloid progeny emerged simultaneously by 2 wk and included a progenitor population with expression features of both lineages. Myeloid progenitors at this stage showed diversification into granulocytic, monocytic, and dendritic cell types, and rare intermediate cell states could be detected. In contrast, lymphoid differentiation was virtually absent within the first 3 wk of tracing. These results show that continuous differentiation of HSCs rapidly produces major hematopoietic lineages and cell types and reveal fundamental kinetic differences between megakaryocytic, erythroid, myeloid, and lymphoid differentiation.

Understanding Hematological Toxicities Using Mathematical Modeling

Balancing antitumor efficacy with toxicity is a significant challenge, and drug-induced myelosuppression is a common dose-limiting toxicity of cancer treatments. Mathematical modeling has proven to be a powerful ally in this field, scaling results from animal models to humans, and designing optimized treatment regimens. Here we outline existing mathematical approaches for studying bone marrow toxicity, identify gaps in current understanding, and make future recommendations to advance this vital field of safety research further.

Infection perturbs Bach2- and Bach1-dependent erythroid lineage 'choice' to cause anemia

Elucidation of how the differentiation of hematopoietic stem and progenitor cells (HSPCs) is reconfigured in response to the environment is critical for understanding the biology and disorder of hematopoiesis. Here we found that the transcription factors (TFs) Bach2 and Bach1 promoted erythropoiesis by regulating heme metabolism in committed erythroid cells to sustain erythroblast maturation and by reinforcing erythroid commitment at the erythro-myeloid bifurcation step. Bach TFs repressed expression of the gene encoding the transcription factor C/EBPβ, as well as that of its target genes encoding molecules important for myelopoiesis and inflammation; they achieved the latter by binding to their regulatory regions also bound by C/EBPβ. Lipopolysaccharide diminished the expression of Bach TFs in progenitor cells and promoted myeloid differentiation. Overexpression of Bach2 in HSPCs promoted erythroid development and inhibited myelopoiesis. Knockdown of BACH1 or BACH2 in human CD34⁺ HSPCs impaired erythroid differentiation in vitro. Thus, Bach TFs accelerate erythroid commitment by suppressing the myeloid program at steady state. Anemia of inflammation and myelodysplastic syndrome might involve reduced activity of Bach TFs.

Targeting the Extracellular Signal-Regulated Kinase 5 Pathway to Suppress Human Chronic Myeloid Leukemia Stem Cells

Tyrosine kinase inhibitors (TKi) are effective against chronic myeloid leukemia (CML), but their inefficacy on leukemia stem cells (LSCs) may lead to relapse. To identify new druggable targets alternative to BCR/ABL, we investigated the role of the MEK5/ERK5 pathway in LSC maintenance in low oxygen, a feature of bone marrow stem cell niches. We found that MEK5/ERK5 pathway inhibition reduced the growth of CML patient-derived cells and cell lines in vitro and the number of leukemic cells in vivo. Treatment in vitro of primary CML cells with MEK5/ERK5 inhibitors, but not TKi, strikingly reduced culture repopulation ability (CRA), serial colony formation ability, long-term culture-initiating cells (LTC-ICs), and CD26-expressing cells. Importantly, MEK5/ERK5 inhibition was effective on CML cells regardless of the presence or absence of imatinib, and did not reduce CRA or LTC-ICs of normal CD34+ cells. Thus, targeting MEK/ERK5 may represent an innovative therapeutic approach to suppress CML progenitor/stem cells.

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ERK5 is constitutively active in chronic myeloid leukemia (CML) cells

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ERK5 pathway inhibition reduces the growth of CML cells in vitro and in vivo

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ERK5 pathway inhibition strikingly reduces CML progenitor/stem cell maintenance

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The combination of ERK5i with imatinib reduces the expression of stem cell proteins