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Embryonic hematopoietic cells develop in the fetal liver (FL), surrounded by diverse non-hematopoietic stromal cells. However, the spatial organization and cytokine production patterns of the stroma during FL development remain poorly understood. Here, we characterized and mapped the hematopoietic and stromal cell populations at early (E12.5-14.5) FL stages, revealing that while hepatoblasts were the primary source of hematopoietic growth factors, other stromal cells-including mesenchymal, mesothelial, and endothelial cells-also contributed to this signaling network. Using a dedicated image analysis pipeline, we quantified cell distances to tissue structures and defined neighbor relationships, uncovering that different hematopoietic progenitors exhibit distinct preferences for neighboring stromal cells and show developmental changes in spatial distribution. Notably, our data suggest that the sub-mesothelium region plays a prominent role in early fetal hematopoiesis. This approach offers a valuable tool for studying complex cellular interactions in biological systems, providing new insights into hematopoietic niche organization during development., (© 2025 Mesquita Peixoto et al.)

Mesenchymal stromal cells (MSCs) isolated from tissues such as bone marrow, cord, cord blood, etc., are frequently used as feeder layers to expand hematopoietic stem/ progenitor cells (HSCs/HSPCs) in vitro. They are also co-infused with the HSCs to improve the efficacy of transplantation. However, the MSCs sourced from non-hematopoietic tissues could have suboptimal hematopoiesis-supportive ability. Likewise, the functionality of the MSCs is known to decline after continuous in vitro culture - an unavoidable manipulation to get clinically relevant cell numbers. Hence, it may be necessary to boost the hematopoiesis-supportive ability of the long-term cultured MSCs so that they can, in turn, be used to prime the HSCs before their clinical applications. Here, I show that priming human bone marrow-derived MSCs (BMSCs) with appropriately selected signaling modifiers and integrin-activating bioactive peptides boosts their hematopoiesis-supportive ability, as seen by the formation of a significantly higher number of colonies from the bone marrow-derived mononuclear cells (MNCs) and extensive proliferation of CD34 + HSCS briefly interacted with them. Priming the BMSCs with signaling modifiers is a cost-effective and time-efficient process as synthesizing these small molecule compounds is relatively inexpensive - an advantage in clinical settings. The approach of briefly interacting the donor HSCs/HSPCs with the primed BMSCs just before their infusion into the recipients' bodies could save the cost of long-term ex vivo expansion of HSCs. This concept could also find applications in other regenerative medicine protocols after identifying suitable pharmacological modulators that have the desired effects on the target cells., Competing Interests: Declaration of Competing Interest The author declares no conflict of interest., (Copyright © 2025 Elsevier Ltd. All rights reserved.)

Apheresis is essential to conducting hematopoietic cell transplantation and genetically engineered cellular therapy procedures. Many patients and donors require central venous catheter (CVC) access for apheresis due to lack of adequate peripheral venous access. CVC placement has risks of associated complications and requires additional institutional resources and expertise. We present a single institutional experience with 78 patients, who underwent a total of 87 apheresis procedures after placement of a midline catheter. This included 49 individuals who collected cells for immune effector cell therapy. Apheresis through midline catheter was successful in 81 out of 87 procedures. There were no midline catheter associated thromboses or infections. Six patients required placement of a backup CVC and were able to undergo apheresis without delay. Our experience shows that use of midline catheter for apheresis is feasible and generalizable to most populations requiring cellular therapy, with the potential to decrease utilization of limited healthcare resources., (© 2025 Wiley Periodicals LLC.)

The ubiquitination or SUMOylation of hematopoietic-related factors plays pivotal roles in hematopoiesis. RNF111, known as a ubiquitin ligase, is a newly discovered SUMO-targeted ubiquitin ligase involved in multiple signaling pathways mediated by transforming growth factor (TGF)-β family members. However, its role in hematopoiesis remains unclear. Herein, a heritable Rnf111 mutant zebrafish line was generated by CRISPR/Cas9-mediated genome editing. Impairment of hematopoietic stem and progenitor cells (HSPC) of definitive hematopoiesis was found in Rnf111-deficient mutants. Ablation of Rnf111 resulted in decreased phosphorylation of Smad2/3 in HSPC. Definitive endoderm 2 inducer (IDE2), which specifically activates TGF-β signaling and downstream Smad2 phosphorylation, could restore definitive hematopoiesis in Rnf111-deficient embryos. Further molecular mechanism studies revealed that Gcsfr/NO signaling was an important target pathway of Smad2/3 involved in Rnf111-mediated HSPC development. In conclusion, our study demonstrated that Rnf111 contributes to the development of HSPC by maintaining Smad2/3 phosphorylation and activation of the Gcsfr/NO signaling pathway.

Bone marrow mesenchymal stem cells (MSCs) serve a pivotal role in the hematopoietic niche. The present study collected bone marrow samples from individuals across various age groups to investigate the biological characteristics of MSCs. By modifying the bone marrow microenvironment through co‑culture techniques, changes in the stemness of MSCs were examined. An in vitro hematopoietic co‑culture system was established to simulate the impact of MSCs on hematopoietic stem cells. The results demonstrated that the mode of cell‑to‑cell contact among stem cells is more influential in shaping bone marrow function compared with the effects of aging on these stem cells. Transcriptomic analysis revealed that MSCs serve as essential mediators, with their growth variations being both a consequence and a cause of changes in the bone marrow microenvironment. Furthermore, the decline in hematopoietic function observed in the elderly is a manifestation of this phenomenon. Data from the present study suggest that targeting MSCs is essential for enhancing bone marrow function and improving the outcomes of bone marrow transplantation.

Small molecules UM171 and SR1 have already been taken into clinically-oriented protocols for the ex vivo expansion of hematopoietic stem (HSCs) and progenitor (HPCs) cells. In order to gain further insight into their biology, in the present study we have assessed their effects, both individually and in combination, on the in vitro long-term proliferation and expansion of HSCs and HPCs contained within three different cord blood-derived cell populations: MNCs (CD34 + cells = 0.8 %), LIN - cells (CD34 + cells = 41 %), and CD34 + cells (CD34 + cells >98 %). Our results show that when added to cultures in the absence of recombinant stimulatory cytokines, neither molecule had any effect. In contrast, when added in the presence of hematopoietic cytokines, UM171 and SR1 had significant stimulatory effects on cell proliferation and expansion in cultures of LIN - and CD34 + cells. No significant effects were observed in cultures of MNCs. The effects of both molecules were more pronounced in cultures with the highest proportion of CD34 + cells, and the greatest effects were observed when both molecules were added in combination. In the absence of small molecules, cell numbers reached a peak by days 25-30, and then declined; whereas in the presence of UM171 or/and SR1 cell numbers were sustained up to day 45 of culture. Our results indicate that besides CD34 + cells, LIN - cells could also be used as input cells in clinically-oriented expansion protocols, and that using both molecules simultaneously would be a better approach than using only one of them., Competing Interests: Declaration of competing interest All three authors declare that they have no potential conflict of interests of any kind., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The present knowledge on hematopoietic stem and progenitor cell (HSPC) biology and aging is based largely on studies in mouse models. Although mouse models are invaluable, they are not without limitations for defining how physical properties of HSPCs and their niche change with age. The bone marrow (BM) niche is a complex, interactive environment with multiple cell types. The structure and organization of the BM niche, especially the extracellular matrix (ECM), change with age. Provided with recent advances in quantitative analytical techniques and in vitro niche models, we have developed novel tools to quantitatively assess the impact of specific biochemical and physical cues on homing, adhesion, and migration of HSPCs. Recent developments in in vitro niche models have also provided new insights into the interactions between HSPCs and their niche, particularly the role of matrix stiffness. Further research is needed to integrate physical biomarkers into comprehensive mathematical models of age-dependent HSPC-niche interactions. The key is to use mouse models in conjunction with direct analyses in in vitro niche models to achieve a more comprehensive understanding of age-dependent alterations in niche function and regulation., Competing Interests: Conflict of Interest Disclosure The authors do not have any conflicts of interest to declare in relation to this work., (Copyright © 2024 International Society for Experimental Hematology. Published by Elsevier Inc. All rights reserved.)

Stem cells are special cells with the distinctive capability to self-renew, forming a new pool of undifferentiated stem cells. They are also able to differentiate into lineage-specific cell types that are specialized and matured. Thus, stem cells are considered as the building blocks of tissues and organs in which they reside. Among the many types of stem cells, hematopoietic stem cells (HSCs) are the most studied adult stem cells and are considered as a promising source of cells for applications in the clinical and basic sciences. Historically, research on HSCs was initiated in the 1940s, where in a groundbreaking experiment, intravenously injected bone marrow (BM) cells prevented the death of irradiated mice by restoring blood cell production. Since then, HSCs have been studied and utilized in medical therapies and research for over several decades. Over time, more sophisticated tools have been developed to evaluate the behaviour of specifically purified subsets of hematopoietic cells that have the capacity to produce blood cells. One of the established tools is the colony-forming units (CFUs) assay. This assay facilitates the identification, enumeration, and analysis of colonies formed by differentiated hematopoietic stem and progenitor cells (HSPCs) from myeloid, erythroid and lymphoid lineages. Hence, the CFUs assay is a fundamental in vitro platform that allows functional studies on the lineage potential of an individual HSPCs. The outcomes of such studies are crucial in providing critical insights into hematopoiesis. In this review, we explore the fundamental discoveries concerning the CFUs assay by covering the following aspects: (i) the historical overview of the CFUs assay for the study of clonal hematopoiesis involving multilineage potential of HSPCs, (ii) its use in various experimental models comprising humans, mice/rodents, zebrafish and induced pluripotent stem cells (iPSCs) and (iii) research gaps and future direction concerning the role of CFUs assay in clinical and basic sciences. Overall, the CFUs assay confers a transformative platform for a better understanding of HSPCs biology in governing hematopoiesis., Competing Interests: The authors declare there are no competing interests., (©2025 Yusoff et al.)

Definitive hematopoietic stem and progenitor cells (HSPCs) arise from a small number of hemogenic endothelial cells (HECs) within the developing embryo. Understanding the origin and ontogeny of HSPCs is of considerable interest and potential therapeutic value. It has been proposed that the murine placenta contains HECs that differentiate into HSPCs. However, during human gestation HSPCs arise in the aorta considerably earlier than when they can first be detected in the placenta, suggesting that the placenta may primarily serve as a niche. We found that the Runx1 transcription factor, which is required to generate HSPCs from HECs, is not expressed by mouse placental ECs. To definitively determine whether the mouse placenta is a site of HSPC emergence, we performed lineage tracing experiments with a Hoxa13Cre allele that specifically labels ECs in the placenta and umbilical cord (UC), but not in the yolk sac or embryo. Immunostaining revealed Hoxa13Cre lineage-traced HECs and HSPCs in the UC, a known site of HECs, but not the placenta. Consistent with these findings, ECs harvested from the E10.5 aorta and UC, but not the placenta, gave rise to hematopoietic cells ex vivo, while colony forming assays using E14.5 fetal liver revealed only 2% of HSPCs arose from Hoxa13-expressing precursors. In contrast, the pan-EC Cdh5-CreERT2 allele labeled most HSPCs in the mouse placenta. Lastly, we found that RUNX1 and other HEC genes were not expressed in first-trimester human placenta villous ECs, suggesting that human placenta is not hemogenic. Our findings demonstrate that the placenta functions as a site for expansion of HSPCs that arise within the embryo proper and is not a primary site of HSPC emergence., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2025 Chen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Abstract: Adult hematopoietic stem cells (HSCs) are responsible for the lifelong production of blood and immune cells, a process regulated by extracellular cues, including cytokines. Many cytokines signal through the conserved Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in which tyrosine-phosphorylated STATs (pSTATs) function as transcription factors. STAT5 is a pivotal downstream mediator of several cytokines known to regulate hematopoiesis, but its function in the HSC compartment remains poorly understood. In this study, we show that STAT5-deficient HSCs exhibit an unusual phenotype, including reduced multilineage repopulation and self-renewal, combined with reduced exit from quiescence and increased differentiation. This was driven not only by the loss of canonical pSTAT5 signaling, but also by the loss of distinct transcriptional functions mediated by STAT5 that lack canonical tyrosine phosphorylation (uSTAT5). Consistent with this concept, expression of an unphosphorylatable STAT5 mutant constrained wild-type HSC differentiation, promoted their maintenance, and upregulated transcriptional programs associated with quiescence and stemness. The JAK1/2 inhibitor, ruxolitinib, which increased the uSTAT5:pSTAT5 ratio, had similar effects on murine HSC function; it constrained HSC differentiation and proliferation, promoted HSC maintenance, and upregulated transcriptional programs associated with stemness. Ruxolitinib also enhanced serial replating of normal human hematopoietic stem and progenitor cells (HSPCs), calreticulin-mutant murine HSCs, and HSPCs obtained from patients with myelofibrosis. Our results therefore reveal a previously unrecognized interplay between pSTAT5 and uSTAT5 in the control of HSC function and highlight JAK inhibition as a potential strategy for enhancing HSC function during ex vivo culture. Increased levels of uSTAT5 may also contribute to the failure of JAK inhibitors to eradicate myeloproliferative neoplasms., (© 2024 by The American Society of Hematology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

To identify the differences between aged and young human hematopoiesis, we performed a direct comparison of aged and young human hematopoietic stem and progenitor cells (HSPCs). Alterations in transcriptome profiles upon aging between humans and mice were then compared. Human specimens consist of CD34+ cells from bone marrow, and mouse specimens of hematopoietic stem cells (HSCs; Lin- Kit+ Sca1+ CD150+). Single-cell transcriptomic studies, functional clustering, and developmental trajectory analyses were performed. A significant increase in multipotent progenitor 2A (MPP2A) cluster is found in the early HSC trajectory in old human subjects. This cluster is enriched in senescence signatures (increased telomere attrition, DNA damage, activation of P53 pathway). In mouse models, the accumulation of an analogous subset was confirmed in the aged LT-HSC population. Elimination of this subset has been shown to rejuvenate hematopoiesis in mice. A significant activation of the P53-P21WAF1/CIP1 pathway was found in the MPP2A population in humans. In contrast, the senescent HSCs in mice are characterized by activation of the p16Ink4a pathway. Aging in the human HSC compartment is mainly caused by the clonal evolution and accumulation of a senescent cell cluster. A population with a similar senescence signature in the aged LT-HSCs was confirmed in the murine aging model. Clearance of this senescent population with senotherapy in humans is feasible and potentially beneficial.

Inflammation is a dynamic process which importantly involves migration of immune cells. Understanding the onset, acute phase and resolution of inflammation is greatly facilitated by their in vivo imaging. However, immune cells are sensitive, difficult to genetically manipulate and prone to changes in response to contact, hindering the application of well-established cell labeling methods. We generated the first reported SNAP-tag expressing conditionally immortalized early hematopoietic progenitor cells (ER-HoxB8) and synthesized benzylguanine (BG) analogs with bioorthogonal groups for SNAP-tag mediated cell surface labeling. Comparative investigation of SNAP-tag positive HeLa cells, ER-HoxB8 progenitor cells and ER-HoxB8-derived macrophages as well as neutrophiles revealed remarkable differences in labeling depending on the bioorthogonal group and fluorescent reporter used. HeLa cells and ER-HoxB8 progenitor cells were efficiently labeled with BG analogs bearing an azide and a dioxolan-fused trans -cyclooctene (dTCO). When we differentiated ER-HoxB8 cells into macrophages, labeling was less bright due to lower SNAP-tag expression and only the tetrazine ligation of dTCO proved suitable for cell-type specific labeling. These results show that exploring different reactions and bioorthogonal groups is important to address the challenge of labeling differentiated immune cells. Combining the SNAP-tag with click chemistry provides a modular approach for cell-specific labeling and the combination of SNAP-tag and dTCO presents an improved system for labeling ER-HoxB8-derived macrophages.

Human hematopoietic stem cells (HSCs) have traditionally been viewed as self-renewing, multipotent cells with enormous potential in sustaining essential steady state blood and immune cell production throughout life. Indeed, around 86% (10 11 -10 12 ) of new cells generated daily in a healthy young human adult are of hematopoietic origin. Therapeutically, human HSCs have contributed to over 1.5 million hematopoietic cell transplants (HCTs) globally, making this the most successful regenerative therapy to date. We will commence this review by briefly highlighting selected key achievements (from 1868 to the end of the 20th century) that have contributed to this accomplishment. Much of our knowledge of hematopoiesis is based on small animal models that, despite their enormous importance, do not always recapitulate human hematopoiesis. Given this, we will critically review the progress and challenges faced in identifying adult human HSCs and tracing their lineage differentiation trajectories, referring to murine studies as needed. Moving forward and given that human hematopoiesis is dynamic and can readily adjust to a variety of stressors, we will then discuss recent research advances contributing to understanding (i) which HSPCs maintain daily steady state human hematopoiesis, (ii) where these are located, and (iii) which mechanisms come into play when homeostatic hematopoiesis switches to stress-induced or emergency hematopoiesis.

Hematopoietic stem cells (HSCs) are crucial for maintaining hematopoietic homeostasis and are localized within distinct bone marrow (BM) niches. While BM niches are often considered similar across different skeletal sites, we discovered that the alveolar BM (al-BM) in the mandible harbors the highest frequency of immunophenotypic HSCs in nine different skeletal sites. Transplantation assays revealed significantly increased engraftment from al-BM compared to femur, tibia, or pelvis BM, likely due to a higher proportion of alveolar HSCs. Moreover, hematopoietic progenitor cells (c-Kit + Sca-1 + Lin - ) in al-BM exhibited increased quiescence and reduced apoptosis, indicating superior maintenance and survival characteristics. We also observed an enrichment of mesenchymal stromal cells and skeletal stem cells in al-BM, suggesting a more supportive microenvironment. These findings indicate that al-BM provides a unique microenvironment conducive to higher frequency of HSCs, offering new insights into site-specific hematopoiesis., Competing Interests: Declaration of interests H.N. is a co-founder, member of the scientific advisory board, and shareholder of Megakaryon Corp., and Century Therapeutics, Inc., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Abstract: Current efforts in translational studies in hematology often rely on immunodeficient mouse models for engrafting patient-derived hematopoietic stem and progenitor cells (HSPCs), yet these models often face challenges in effectively engrafting cells from patients with various diseases, such as myelodysplastic syndromes (MDSs). In this study, we developed an induced pluripotent stem cell (iPSC)-derived human bone marrow organoid model that closely replicates the bone marrow microenvironment, facilitating the engraftment of HSPCs derived from patients with MDS, thereby mirroring the patients' distinct disease characteristics. Specifically, using advanced microscopy, we verified the development of a complex 3-dimensional network of endothelial, stromal, and hematopoietic cells within organoids, resembling the autonomous human marrow microenvironment. Furthermore, we showed that HSPCs derived from the donor bone marrow of normal individuals or patients with MDS can migrate to and proliferate within the organoid vascular niche while maintaining self-renewal and original genetic profiles. Within the organoids, the differentiation patterns of MDS HSPCs were significantly distinct from those of multilineage hematopoiesis in normal HSPCs, which can be correlated with the clinical manifestations of the disease. These findings underscore the significance of the organoid model in studying human hematopoiesis and the pathophysiology of hematologic diseases, thereby offering new avenues for personalized medicine and therapeutic interventions., (© 2024 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Erythropoiesis, a remarkably dynamic and efficient process responsible for generating the daily quota of red blood cells (approximately 280 ± 20 billion cells per day), is crucial for maintaining individual health. Any disruption in this pathway can have significant consequences, leading to health issues. According to the World Health Organization, an estimated 25% of the global population presents symptoms of anemia. This protocol describes how to generate human erythroid cells both in vitro using hematopoietic stem and progenitor cells (HSPCs) from sources such as umbilical cord blood (UCB) or blood taken from healthy donors and ex vivo with HSPCs isolated from patients' bone marrow. Using genetic approach, genes of interest can be modulated in HSPCs, and their impact on erythropoiesis can be monitored at various stages of the differentiation process. This method allows for the screening of compounds perturbing, enhancing, or rescuing the capacity of HSPCs to differentiate into mature erythroid cells and to investigate the role of genes of interest during the erythroid differentiation process.

Populations of very small embryonic-like stem cells (VSELs) (CD34+lin-CD45- and CD133+lin-CD45-), circulating in the peripheral blood of adults in small numbers, have been identified in several human tissues and together with the populations of hematopoietic stem cells (HSCs) (CD34+lin-CD45+) and CD133+lin-CD45+constitute a pool of cells with self-renewal and pluripotent stem cell characteristics. Using advanced cell staining and sorting strategies, we isolated populations of VSELs and HSCs for bulk RNA-Seq analysis to compare the transcriptomic profiles of both cell populations. Libraries were prepared from an extremely small number of cells; however, their good quality was preserved, and they met the criteria for sequencing. We present here a step-by-step NGS protocol for sequencing VSELs and HSC with a description of troubleshooting during library preparation and sequencing., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2025 Jarczak et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nuclear receptors regulate hematopoietic stem cells (HSCs) and peripheral immune cells in mice and humans. The nuclear orphan receptor NR2F6 (EAR-2) has been shown to control murine hematopoiesis. Still, detailed analysis of the distinct stem cell, myeloid, and lymphoid progenitors in the bone marrow in a genetic loss of function model remains pending. In this study, we found that adult germline Nr2f6 -deficient mice contained increased percentages of total long-term and short-term HSCs, as well as a subpopulation within the lineage-biased multipotent progenitor (MPP3) cells. The loss of NR2F6 thus led to an increase in the percentage of LSK + cells. Following the differentiation from the common myeloid progenitors (CMP), the granulocyte-monocyte progenitors (GMP) were decreased, while monocyte-dendritic progenitors (MDP) were increased in Nr2f6 -deficient bone marrow. Within the pre-conventional dendritic progenitors (pre-cDCs), the subpopulation of pre-cDC2s was reduced in the bone marrow of Nr2f6 -deficient mice. We did not observe differences in the development of common lymphoid progenitor populations. Our findings contrast previous studies but underscore the role of NR2F6 in regulating gene expression levels during mouse bone marrow hematopoiesis and myelopoiesis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2025 Woelk, Narasimhan, Pfeifhofer-Obermair, Schraml and Hermann-Kleiter.)

Prime Editing can rewrite genes in living cells by allowing point mutations, deletions, or insertion of small DNA sequences with high precision. However, its safe and efficient delivery into human stem cells remains a technical challenge. In this report, we engineer Nanoscribes, virus-like particles that encapsidate ribonucleoprotein complexes of the Prime Editing system and allow their delivery into recipient cells. We identify key features that unlock the potential of Nanoscribes, including the use of multiple fusogens, the improvement of pegRNAs structures, their encoding by a Pol II system and the optimization of Prime-Editors. Nanoscribes edit HEK293T with an efficiency of 68% at the HEK3 locus with increased fidelity over DNA-transfection and support pegRNA-multiplexing. Importantly, Nanoscribes permit editing of myoblasts, hiPSCs and hiPSCs-derived hematopoietic stem cells with an editing efficiency up to 25%. Nanoscribes is an asset for development of next generation genome editing approaches using VLPs., Competing Interests: Competing interests: T.H., P.E.M. and T.O. are inventors of two patents owned by Inserm Transfert EP N° EP24305987.0 and EP 24305808.8 protecting the molecular designs of constructs of the final Nanoscribes system. Patent application numbers are pending. The remaining authors declare no competing interests., (© 2025. The Author(s).)

Niches are often found in specific positions in tissues relative to the stem cells they support. Consistency of niche position suggests that placement is important for niche function. However, the complexity of most niches has precluded a thorough understanding of how their proper placement is established. To address this, we investigated the formation of a genetically tractable niche, the Drosophila Posterior Signaling Center (PSC), the assembly of which had not been previously explored. This niche controls hematopoietic progenitors of the lymph gland (LG). PSC cells were previously shown to be specified laterally in the embryo, but ultimately reside dorsally, at the LG posterior. Here, using live-imaging, we show that PSC cells migrate as a tight collective and associate with multiple tissues during their trajectory to the LG posterior. We find that Slit emanating from two extrinsic sources, visceral mesoderm and cardioblasts, is required for the PSC to remain a collective, and for its attachment to cardioblasts during migration. Without proper Slit-Robo signaling, PSC cells disperse, form aberrant contacts, and ultimately fail to reach their stereotypical position near progenitors. Our work characterizes a novel example of niche formation and identifies an extrinsic signaling relay that controls precise niche positioning., Competing Interests: KN, KL, LA, SD No competing interests declared, (© 2024, Nelson et al.)

Abstract: Ascorbate (vitamin C) limits hematopoietic stem cell (HSC) function and suppresses leukemia development, partly by promoting the function of the Tet2 tumor suppressor. In humans, ascorbate is obtained from the diet, whereas in mice, it is synthesized in the liver. In this study, we show that deletion of the Slc23a2 ascorbate transporter from hematopoietic cells depleted ascorbate to undetectable levels in HSCs and multipotent hematopoietic progenitors (MPPs) without altering the plasma ascorbate levels. Slc23a2 deficiency increased HSC reconstituting potential and self-renewal potential upon transplantation into irradiated mice. Slc23a2 deficiency also increased the reconstituting and self-renewal potentials of MPPs, conferring the ability to reconstitute irradiated mice long term. Slc23a2-deficient HSCs and MPPs divided much less frequently than control HSCs and MPPs. Increased self-renewal and reconstituting potential were observed particularly in quiescent Slc23a2-deficient HSCs and MPPs. The effect of Slc23a2 deficiency on MPP self-renewal was not mediated by reduced Tet2 function. Ascorbate thus regulates quiescence and restricts self-renewal potential in HSCs and MPPs such that ascorbate deficiency confers MPPs with long-term self-renewal potential., (© 2025 American Society of Hematology. Published by Elsevier Inc. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Ex vivo expansion of hematopoietic stem cells (HSC) requires the maintenance of a stemness state while cells are proliferating. This can be achieved via exposure to UM171 which leads to the degradation of chromatin modifiers and prevents the loss of key epigenetic marks. However, the chromatin landscape varies across populations within the hematopoietic system and the effect of UM171 on self-renewal and differentiation potential of different hematopoietic progenitor cells is less characterized. To address this, we use the CellTag barcoding approach to track the fate of individual stem and progenitor cells during in vitro expansion. We show that, in addition to its HSC self-renewing property, UM171 specifically modulates cell fate of a precursor common to erythroid, megakaryocytic, and mast cells in favor of self-renewal and a mast-bias differentiation trajectory. This differentiation bias can be driven by pro-inflammatory signaling pathways that are activated downstream of UM171 and results in an abundant mast cell population that can be transplanted as part of the graft to populate mice tissues in xenotransplantation studies., Competing Interests: Competing interests: Except for G.S., the authors declare no competing interests. G.S. is co-founder of ExCellThera, a small biotech which owns an exclusive license to UM171., (© 2024. The Author(s).)

The Innate Lymphoid Cells (ILCs) are a family of innate immune cells composed by the Natural Killer (NK) cells and the helper ILCs (hILCs) (ILC1, ILC2, ILC3), both developing from a common ILC precursor (ILCP) derived from hematopoietic stem cells (HSCs). A correct ILC reconstitution is crucial, particularly in patients receiving HSC transplantation (HSCT), the only therapeutic option for many adult and pediatric high-risk hematological malignancies. Indeed, mainly thanks to their cytotoxic activity, NK cells have a strong Graft-versus-Leukemia (GvL) effect. On the other hand, hILCs, that are mainly tissue resident, are involved in tissue repair and homeostasis, Graft-versus-Host Disease (GvHD) prevention and immune response to infections. Unlike NK cell development, hILC-poiesis is still poorly characterized in humans. Here, we provide a protocol for the in vitro ILC differentiation from healthy donor peripheral blood-derived CD34 + HSCs. This could represent a useful model to dissect the molecular mechanisms by which the distinct ILC subsets are generated from ILCP leading to the development of novel strategies to improve the HSCT clinical outcome., (Copyright © 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

Hematopoietic cell transplantation (HCT) is an important therapy for many hematological malignancies as well as some non-malignant diseases. Post-transplant hematopoiesis is affected by multiple factors, and the mechanisms of delayed post-transplant hematopoiesis remain poorly understood. Patients undergoing HCT often suffer from significantly reduced food intake due to complications induced by preconditioning treatments. Here, we used a dietary restriction (DR) mouse model to study the effect of post-transplant dietary reduction on hematopoiesis and hematopoietic stem cells (HSCs). We found that post-transplant DR significantly inhibited both lymphopoiesis and myelopoiesis in the primary recipient mice. However, when bone marrow cells (BMCs) from the primary recipient mice were serially transplanted into secondary and tertiary recipient mice, the HSCs derived from the primary recipient mice, which were exposed to post-transplant DR, exhibited a much higher reconstitution capacity. Transplantation experiments with purified HSCs showed that post-transplant DR greatly inhibited hematopoietic stem cell (HSC) expansion. Additionally, post-transplant DR reshaped the gut microbiotas of the recipient mice, which inhibited inflammatory responses and thus may have contributed to maintaining HSC function. Our findings may have important implications for clinical work because reduced food intake and problems with digestion and absorption are common in patients undergoing HCT., Competing Interests: Declarations. Ethics Approval: The Animal Experimental Ethical Inspection of Nanchang Royo Biotech Co., Ltd. (RYEI20170513-1) approved all mouse experiments. Consent for Publication: This manuscript has been approved by all authors and is solely the work of the authors named. Consent for Participate: Not applicable. Conflict of Interest: The authors have no conflicts of interest to declare., (© 2024. The Author(s).)

Fasting regimens have shown profound impact on pro-longevity and tissue regeneration in diverse species. Physiological events can induce a regenerative response in adult stem cells. However, little is known about signaling and activation of adult stem cells which are modulated by fasting. This study analyzed the presence of hematopoietic stem/progenitor cells (HSPCs) and their circulation in the peripheral blood (PB) of healthy male adults practicing Ramadan fasting. Ten healthy male volunteers were enrolled in this prospective observational study. PB samples were collected twice daily on days 0, 10, 20, and 30 of Ramadan fasting (RF). Populations of stem cells and serum soluble factors were analyzed by flow cytometry. As a response to RF, we report an increase in the average absolute count of circulating of HSPCs, defined as LIN - CD45 - and LIN - CD45 + cell subsets expressing the stem markers, CD34 and CD133. Changes in the number of HSPCs subsets reflected changes in the peripheral concentration of chemoattractant soluble factors during fasting. A chemotaxis assay showed a migratory property of HSPCs towards plasma, collected at D30 of fasting that contained a higher concentration of SCF and G-CSF. The relationship between RF and an increase in the number of circulating HSPCs in part, describes a regenerative response to the physiological changes during fasting and may open opportunities to define the role of dietary intervention in the stem cell therapy.

Hematopoiesis is the process that generates the cells of the blood and immune system from hematopoietic stem and progenitor cells (HSPCs) and represents the system with the most rapid cell turnover in a mammalian organism. HSPC differentiation trajectories, their underlying molecular mechanisms, and their dysfunctions in hematologic disorders are the focal research questions of experimental hematology. While HSPC transplantations in murine models are the traditional tool in this research field, recent advances in genome editing and next generation sequencing resulted in the development of many fundamentally new approaches for the analyses of mammalian hematopoiesis in situ and at single cell resolution. The current review will cover many recent developments in this field in murine models, from the bulk lineage tracing studies of HSPC differentiation to the barcoding of individual HSPCs with Cre-recombinase, Sleeping Beauty transposase, or CRISPR/Cas9 tools, to map hematopoietic cell fates, together with their transcriptional and epigenetic states. We also address studies of the clonal dynamics of human hematopoiesis, from the tracing of HSPC clonal behaviours based on viral integration sites in gene therapy patients to the recent analyses of unperturbed human hematopoiesis based on naturally accrued mutations in either nuclear or mitochondrial genomes. Such studies are revolutionizing our understanding of HSPC biology and hematopoiesis both under homeostatic conditions and in the response to various forms of physiological stress, reveal the mechanisms responsible for the decline of hematopoietic function with age, and in the future may advance the understanding and management of the diverse disorders of hematopoiesis., Competing Interests: Declarations. Ethical Approval: Not applicable. Consent for Publication: All authors provide their consent for publication. Consent to Participate: Not applicable. Competing Interests: Authors declare that there are no conflicts of interest., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The maintenance of genomic integrity in rapidly proliferating cells is a substantial challenge during embryonic development 1-3 . Although numerous cell-intrinsic mechanisms have been revealed 4-7 , little is known about genome-protective effects and influences of developmental tissue microenvironments on tissue-forming cells. Here we show that fetal liver hepatocytes provide protection to haematopoietic stem and progenitor cell (HSPC) genomes. Lineage tracing and depletion in mice demonstrated that delayed hepatocyte development in early fetal livers increased the chromosomal instability of newly colonizing HSPCs. In addition, HSPCs developed tolerance to genotoxins in hepatocyte-conditioned medium, suggesting that hepatocytes protect the HSPC genome in a paracrine manner. Proteomic analyses demonstrated the enrichment of fetuin-A in hepatocyte-conditioned medium but not in early fetal livers. Fetuin-A activates a Toll-like receptor pathway to prevent pathogenic R-loop accumulation in HSPCs undergoing DNA replication and gene transcription in the fetal liver. Numerous haematopoietic regulatory genes frequently involved in leukaemogenic mutations are associated with R-loop-enriched regions. In Fetua-knockout mice, HSPCs showed increased genome instability and susceptibility to malignancy induction. Moreover, low concentrations of fetuin-A correlated with the oncogenesis of childhood leukaemia. Therefore, we uncover a mechanism operating in developmental tissues that offers tissue-forming cell genome protection and is implicated in developmental-related diseases., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Aging is a process accompanied by functional decline in tissues and organs with great social and medical consequences. Developing effective anti-aging strategies is of great significance. In this study, we demonstrated that transplantation of young hematopoietic stem cells (HSCs) into old mice can mitigate aging phenotypes, underscoring the crucial role of HSCs in the aging process. Through comprehensive molecular and functional analyses, we identified a subset of HSCs in aged mice that exhibit "younger" molecular profiles and functions, marked by low levels of CD150 expression. Mechanistically, CD150 low HSCs from old mice but not their CD150 high counterparts can effectively differentiate into downstream lineage cells. Notably, transplantation of old CD150 low HSCs attenuates aging phenotypes and prolongs lifespan of elderly mice compared to those transplanted with unselected or CD150 high HSCs. Importantly, reducing the dysfunctional CD150 high HSCs can alleviate aging phenotypes in old recipient mice. Thus, our study demonstrates the presence of "younger" HSCs in old mice, and that aging-associated functional decline can be mitigated by reducing dysfunctional HSCs., Competing Interests: Competing interests: The authors declare the following competing financial interests: Y.Z. and Y.W. are the inventors of a patent related to the work presented in this manuscript. The patent number is 63472759 and the title is: “Compositions and Methods for Assessing, Treating, or Reducing Aging-Related Functional Decline”, which was filed on June 13, 2023., (© 2024. The Author(s).)

The liver-derived circulating in peripheral blood and intrinsic cell-expressed complement known as complosome orchestrate the trafficking of hematopoietic stem/progenitor cells (HSPCs) both during pharmacological mobilization and homing/engraftment after transplantation. Our previous research demonstrated that C3 deficient mice are easy mobilizers, and their HSPCs engraft properly in normal mice. In contrast, C5 deficiency correlates with poor mobilization and defects in HSPCs' homing and engraftment. The trafficking of HSPCs during mobilization and homing/engraftment follows the sterile inflammation cues in the BM microenvironment caused by stress induced by pro-mobilizing drugs or myeloablative conditioning for transplantation. Therefore, to explain deficiencies in HSPC trafficking between C3-KO and C5-KO mice, we evaluated the responsiveness of C3 and C5 deficient cells to low oxidative stress. As reported, oxidative stress in BM is mediated by the activation of purinergic signaling, which is triggered by the elevated level of extracellular adenosine triphosphate (eATP) and by the activation of the complement cascade (ComC). In the current work, we noticed that BM lineage negative cells (lin - ) isolated from C3-KO mice display several mitochondrial defects reflected by an impaired ability to adapt to oxidative stress. In contrast, C5-KO-derived BM cells show a high level of adaptation to this challenge. To support this data, C3-KO BM lin - cells were highly responsive to eATP stimulation, which correlates with enhanced levels of reactive oxygen species (ROS) generation and more efficient activation of intracellular Nlrp3 inflammasome. We conclude that the enhanced sensitivity of C3-KO mice cells to oxidative stress and better activation of the Nox2-ROS-Nlrp3 inflammasome signaling axis explains the molecular level differences in trafficking between C3- and C5-deficient HSPCs., Competing Interests: Declarations. Ethical Approval: All studies were conducted according to the European Act on Protecting Animals for Scientific or Educational Purposes and the Animal Care and Use Committee guidelines of the Warsaw Medical University (Warsaw, Poland). Competing Interests: None identified., (© 2024. The Author(s).)

Background: The advent of autologous gene modified cell therapies to treat monogenic disorders has been a major step forward for the field of hematopoietic stem cell transplantation (HCT) and cellular therapies. The need for disease-specific conditioning to enable these products to provide a potential cure has required extrapolation from experience in myeloablative and non-myeloablative HCT for these disorders., Methods: In this manuscript, we review the current datasets and clinical experience using different conditioning regimens for autologous gene therapies in hemoglobinopathies, metabolic and lysosomal disorders, inborn errors of immunity (IEI) and bone marrow failure (BMF) syndromes., Results: The disease specific and unique conditioning requirements of each disorder are considered in order to achieve maximal benefit while minimizing associated toxicities., Conclusions: Standardized recommendations based on these data are made for each set of disorders to harmonize treatment. Future directions and the possibility of non-genotoxic conditioning regimens for autologous gene therapies are also discussed. Ethical Statement: The authors followed all relevant ethical considerations in writing this manuscript., Competing Interests: Declaration of Competing Interest Joseph Oved received consulting fees and/or honoraria from Emendo Bio, Turn.Bio, Grifols, Ensoma, Sobi and Amgen. He receives research support from Sobi and is the site PI for the Jasper SCID trial (NCT02963064). Akshay Sharma has received consultant fee from Spotlight Therapeutics, Medexus Inc., Vertex Pharmaceuticals, BioLineRx, Sangamo Therapeutics and Editas Medicine. He is a medical monitor for RCI BMT CSIDE clinical trial for which receives financial compensation. He has also received research funding from CRISPR Therapeutics and honoraria from Vindico Medical Education. Dr Sharma is the St. Jude Children's Research Hospital site principal investigator of clinical trials for genome editing of sickle cell disease sponsored by Vertex Pharmaceuticals/CRISPR Therapeutics (NCT03745287), Novartis Pharmaceuticals (NCT04443907) and Beam Therapeutics (NCT05456880). The industry sponsors provide funding for the clinical trial, which includes salary support paid to Dr Sharma's institution. Dr Sharma has no direct financial interest in these therapies. Amy E DeZern participated in advisory boards and/or had a consultancy with and received honoraria from Celgene/BMS, Agios, Novartis, Appellis and Gilead. AED served on clinical trial committees or DSMB for Novartis, Abbvie, Kura, Geron, Servier, Keros, Shuattuck labs and Celgene/BMS. SEP receives support for the conduct of clinical trials through Boston Children's Hospital from AlloVir, Atara, and Jasper Therapeutics. Honoraria from Pierre Fabre, and Regeneron. Consulting for Century, CellEvolve and VOR. Carmem Bonfim consults for Zodiac, Amgen and Novartis. Duncan Purtill receives honoraris (to Fiona Stanley Hospital and not the author) from Novartis, Gilead, BMS-Celgene and Jazz Pharmaceuticals. Sandeep Soni is employed by CRSPR Therapeutics AG. Jaap Jan Boelens consults for Advanced Clinical, Sanofi, Sobi, Immusoft, SmartImmune and Merck and receives research funding from Sanofi. Allistair Abraham served on the safety monitoring committee for Sangamo Therapeutics and has no financial interest in the development of gene therapies. Remaining authors have no conflicts of interest., (Copyright © 2024 International Society for Cell & Gene Therapy. All rights reserved.)

Stem cells are subject to continuous regulation to ensure that the correct balance between stem cell differentiation and self-renewal is maintained. The dynamic and ongoing nature of stem cell regulation, as well as the complex signaling microenvironment in which stem cells are typically found, means that studying them in their endogenous environment in real time has multiple advantages over static fixed-sample approaches. We recently described a method for long-term, ex-vivo, live imaging of the blood progenitors in the Drosophila larval hematopoietic organ, the Lymph Gland (LG). This methodology has allowed us to analyze multiple aspects of fly hematopoiesis, in real time, in a manner that could not be carried out previously. Here, we describe novel insights derived from our quantitative live imaging approach. These insights include: the identification of extensive filopodia in the progenitors and description of their morphology and dynamics; visualization and quantitative analysis of JAK/STAT signaling in progenitors by the simultaneous tracking of thousands of vesicles containing internalized Domeless receptors; quantitative analysis of the location, morphology, and dynamics of mitochondria in blood progenitors; long-term tracking of patterns of cell division and migration of mature blood cell in the LG; long-term tracking of multiple cell behaviors in the distal committed progenitors; analysis of Ca 2+ signaling of blood progenitors in the secondary lobes of the LG. Together, these observations illustrate the power of imaging fly hematopoiesis in real time and identify many previously undescribed processes and behaviors in the LG that are likely to play important roles in the regulation of progenitor differentiation and self-renewal., Competing Interests: Declaration of competing interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Introduction: Megakaryocytes are classified into several subtypes including LSP1-positive immune-skewed, MYLK4-positive hematopoietic stem cell (HSC)-regulating, and BMAL1-positive platelet-producing megakaryocytes. Podoplanin (PDPN)-expressing stromal cells generate a microenvironment that promotes megakaryopoiesis in the bone marrow. In this context, PDPN interacts with C-type lectin-like receptor-2 (CLEC-2) on megakaryocyte progenitors, which induces megakaryocyte proliferation. However, the megakaryocyte subtypes developed by the regulation of the PDPN/CLEC-2 axis have not yet been elucidated., Materials and Methods: We established an immortalized bone marrow PDPN-expressing stromal cell line and a PDPN-knockout line (PDPN WT and KO feeder cells, respectively). Bone marrow hematopoietic progenitors were committed to megakaryocytes in co-culture with PDPN WT or KO feeder cells. The number and ploidy of megakaryocytes, resultant platelets, and the polarization of megakaryocyte subtypes were investigated., Results: The number of megakaryocytes was significantly increased in the co-culture with PDPN WT feeder cells compared to that with PDPN KO feeder cells. The megakaryocytes on the PDPN WT and KO feeders showed their main ploidy at 16 N∼32 N and 8 N∼16 N, respectively. The number of platelets was decreased in the co-culture with the PDPN WT feeder compared to that in the co-culture with the PDPN KO feeder. For each megakaryocyte subtype, the percentage of MYLK4-positive megakaryocytes significantly increased and the percentage of BMAL1-positive megakaryocytes significantly decreased when co-cultured with the PDPN WT feeder. These results were also confirmed in the co-culture of CLEC-2 conditional KO megakaryocytes with PDPN WT feeder cells., Conclusion: The PDPN/CLEC-2 axis modulates megakaryocyte subtype differentiation, with a predominance of HSC-regulating megakaryocytes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Platelets are an essential component of hemorrhage control and management, and engineering platelets to express therapeutic proteins could expand their use as a cell therapy. Genetically engineered platelets can be achieved by modifying the platelet precursor cells, megakaryocytes (MKs). Current strategies include transfecting MK progenitors ex vivo with viral vectors harboring lineage-driven transgenes and inducing the production of in vitro modified platelets. The use of viruses, however, poses challenges in clinical implementation, and no methods currently exist to genetically modify MKs with nonviral techniques. Lipid nanoparticles (LNPs) are a nonviral delivery system that could enable a facile strategy to modify MKs with a variety of nucleic acid payloads., Objectives: To investigate whether LNPs can transfect cultured hematopoietic stem/progenitor cell-derived MKs to express exogenous proteins and induce functional changes., Methods: MK and MK progenitors differentiated from cord blood-derived hematopoietic stem/progenitor cells were treated with LNP formulations containing messenger RNA and resembling the clinically approved LNP formulations. Transfection efficiency was assessed through flow cytometry by expression of enhanced green fluorescent protein. Functional changes to the MKs were assessed through rotational thromboelastometry by expression of exogenous coagulation factor (F)VII, a representative physiologically relevant protein., Results: LNPs enabled transfection efficiencies of 99% in MKs and did not impair MK maturation, viability, and morphology. MKs engineered to express exogenous FVII decreased clotting time in FVII-deficient plasma following clot initiation., Conclusion: This approach provides an easy-to-use modular platform to genetically modify MK and MK progenitors, which can be potentially extended to producing genetically modified cultured platelets., Competing Interests: Declaration of competing interests P.R.C. and C.J.K. are cofounders of and hold equity in NanoVation Therapeutics Inc. P.R.C. and C.J.K. are cofounders of and hold equity in SeraGene Therapeutics Inc. C.J.K. is a cofounder of and holds equity in CoMotion Drug Delivery Systems Inc. P.R.C. is a cofounder of and holds equity in Acuitas Therapeutics. P.W.Z. is a cofounder of and holds equity in Notch Therapeutics. P.W.Z. is the Canada Research Chair in Stem Cell Engineering. J.L., C.S., P.R.C., and C.J.K. have submitted intellectual property on RNA-LNP. A.P., B.N.H., H.H.H., A.H., L.J.F., and D.D. have no conflicts of interest to declare., (Copyright © 2024 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Blood production depends on rare haematopoietic stem cells (HSCs) and haematopoietic stem and progenitor cells (HSPCs) that ultimately take up residence in the bone marrow during development. HSPCs and HSCs are subject to extrinsic regulation by the bone marrow microenvironment, or niche. Studying the interactions between HSCs and their niche is critical for improving ex vivo culturing conditions and genetic manipulation of HSCs, which is pivotal for improving autologous HSC therapies and transplantations. Additionally, understanding how the complex molecular network in the bone marrow is altered during ageing is paramount for developing novel therapeutics for ageing-related haematopoietic disorders. HSCs are unique amongst stem and progenitor cell pools in that they engage with multiple physically distinct niches during their ontogeny. HSCs are specified from haemogenic endothelium in the aorta, migrate to the fetal liver and, ultimately, colonize their final niche in the bone marrow. Recent studies employing single-cell transcriptomics and microscopy have identified novel cellular interactions that govern HSC specification and engagement with their niches throughout ontogeny. New lineage-tracing models and microscopy tools have raised questions about the numbers of HSCs specified, as well as the functional consequences of HSCs interacting with each developmental niche. Advances have also been made in understanding how these niches are modified and perturbed during ageing, and the role of these altered interactions in haematopoietic diseases. In this Review, we discuss these new findings and highlight the questions that remain to be explored., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. Springer Nature Limited.)

To ensure the preservation of functional hematopoietic stem cells (HSC) and committed progenitor cells (HPC) at + 4 °C in ex vivo expanded cord blood cell products during worldwide transportation and subsequent infusion-without the need for washing and cell concentration-we developed a conservation medium called Stabilizer of Expanded Cells (SEC), composed exclusively of injectable pharmacological products. The in vivo engraftment assay in immunodeficient mice was used to detect primitive HSCs before and after preservation at + 4 °C. In some experiments, a complex phenotype based on CD34, CD38, and CD133 expression was utilized for this purpose. Committed progenitors (CFU-GM, BFU-E, and CFU-Mix) were detected using methylcellulose culture colony-forming assays. Additionally, in some cases, the energetic metabolism (mitochondrial respiration) was evaluated using Seahorse technology. SEC was able to preserve the functionality of HSCs and HPCs in ex vivo expanded cell populations at + 4 °C for at least 48 h. Furthermore, SEC is also effective in fully preserving HSCs and HPCs in cytapheresis products for at least 72 h. Additionally, SEC enabled the full preservation of HSCs and HPCs for 72 h in freshly collected cord blood, maintaining a normal metabolic profile of CD34 + cells. The SEC medium exhibits a positive effect on the maintenance of both HSCs and HPCs at + 4 °C, regardless of their source. Therefore, SEC can be applied in cell therapy protocols based on HSCs and HPCs with a significant advantage: the product does not need to be washed and concentrated before injection into the patient., Competing Interests: Declarations. Ethics Approval: Human cells and animal experiments were involved in this study. The use of the cells for the purpose of scientific research in our laboratory was approved by Ministry of Education and Research of French Republic in compliance with regulatory procedures that apply (DC 2013-1998, DC 2018-3143 and DC 2019-3713). Concerning the animal studies, upon a favorable opinion of the Bordeaux Ethics Committee for animal experimentation, this project was authorized by the French National Ministry of the High Education and Research (APAFIS#13468-2018020914295792v4). Consent to Participate: Not applicable in terms of clinical trial. The informed consent for the experimental use cells destined to be discarded was obtained systematically in context of the file for above-mentioned approvals of Ministry of Education and Research. Consent for Publication: All authors are aware of the manuscript content and did not present any objection concerning the publication of the manuscript. Competing Interests: The SEC medium was patented by ZI, JC, LR, EA (FR 1558409; EP 16777718.4; US 15/580,699; CA 2,986,267). The cord blood collection procedure utilizing a special kit and HP02 medium was patented by B. Delorme and ZI under the title “Method for Preserving Placental Blood” (WO 2014/057220A1, International Publication Number). EA is currently employed by Institute Genethon (Evry, France). The authors (ZI, JC, LR, EA) declare no other commercial, proprietary, or financial interests in the products or companies discussed in this article. PD has been excluded from the list of patent inventors and declares no conflicts of interest., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Mammalian blood cells originate from specialized 'hemogenic' endothelial (HE) cells in major arteries. During the endothelial-to-hematopoietic transition (EHT), nascent hematopoietic stem cells (HSCs) bud from the arterial endothelial wall and enter circulation, destined to colonize the fetal liver before ultimately migrating to the bone marrow. Mechanisms and processes that facilitate EHT and the release of nascent HSCs are incompletely understood, but may involve signaling from neighboring vascular endothelial cells, stromal support cells, circulating pre-formed hematopoietic cells, and/or systemic factors secreted by distal organs. We used single cell RNA sequencing analysis from human embryonic cells to identify relevant signaling pathways that support nascent HSC release. In addition to intercellular and secreted signaling modalities that have been previously functionally validated to support EHT and/or developmental hematopoiesis in model systems, we identify several novel modalities with plausible mechanisms to support EHT and HSC release. Our findings paint a portrait of the complex inter-regulated signals from the local niche, circulating hematopoietic/inflammatory cells, and distal fetal liver that support hematopoiesis.

Hematopoietic stem cells (HSCs) have the ability to self-renew, differentiate into various blood cell types, and reside in the bone marrow (BM) niche. Estrogen-related receptor α (ERRα) is an orphan nuclear receptor that has a role in mitochondrial biogenesis and metabolic regulation. Previous research has shown that ERRα contributes to the development of acute myeloid leukemia (AML) by acting as a key regulator of mitochondrial processes, though its role in HSC regulation remains mostly unknown. Flow cytometric analysis determined the population of the hematopoietic stem and progenitor cells (HSPC) using Errα knockout (KO) and conditional KO (cKO) mice. Furthermore, we investigated reconstitution with BM transplantation assay. Here, the ablation of Errα in the BM demonstrated that the production of mature blood cells, lineage distribution within hematopoietic organs, and frequencies of the HSPC populations were similar to those of controls. In addition, the ablation of Errα did not perturb HSC function under the stress of transplantation. Collectively, ERRα is not necessary for the control of HSPC populations, as well as for the maintenance of HSC characteristics and functions within the BM., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Abtract: During the transition from embryonic to adult life, the sites of hematopoiesis undergo dynamic shifts across various tissues. In adults, although bone marrow (BM) becomes the primary site for definitive hematopoiesis, the establishment of the BM niche for accommodating hematopoietic stem cells (HSCs) remains incompletely understood. Here, we reveal that perinatal BM mesenchymal stem cells (BMSCs) exhibit highly activated insulin-like growth factor 1 receptor (IGF1R) signaling compared with adult BMSCs (aBMSCs). Deletion of Igf1r in perinatal BMSCs (pBMSCs) hinders the transition of HSCs from the fetal liver to the BM in perinatal mice and disrupts hematopoiesis in adult individuals. Conversely, the deletion of Igf1r in aBMSCs, adipocytes, osteoblasts, or endothelial cells does not affect HSCs in the BM. Mechanistically, IGF1R signaling activates the transcription factor nuclear factor of activated T cells c1 in pBMSCs, which upregulates CXCL12 and other niche factors for HSC retention. Overall, IGF1R signaling in pBMSCs regulates the development of the BM niche for hematopoiesis., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

Dual-double stem cell therapy, which integrates mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs), represents a cutting-edge approach in regenerative medicine, particularly for conditions such as ovarian decline, premature ovarian insufficiency (POI), and induced ovarian failure. This therapy leverages the unique properties of MSCs and HSCs, enhancing tissue repair, immune modulation, and overall regenerative outcomes. MSCs, known for their ability to differentiate into various cell types, provide a supportive microenvironment and secrete bioactive molecules that promote angiogenesis and reduce inflammation. HSCs, crucial for hematopoiesis and immune function, further enhance this environment by supporting hematopoietic processes and immune regulation. Clinical evidence increasingly supports the effectiveness of stem cell therapy in ovarian regeneration. Studies have demonstrated improved folliculogenesis, normalization of hormone profiles, and successful pregnancies in patients with POI. Furthermore, recent clinical trials in various medical fields underline the superior potential of dual-double therapy compared to monotherapies involving MSCs or HSCs alone, enhancing tissue repair and functional outcomes. However, despite these benefits, the therapy presents risks that require careful consideration. For autologous MSC therapy involving expanded cell populations, risks include tumorigenic potential, with evidence of sarcoma formation in certain cases of cultured MSCs. In contrast, autologous non-expanded MSC and HSC therapies may be limited by low cell yields, potentially compromising therapeutic efficacy. Additionally, non-expanded HSC therapy poses risks of insufficient cell numbers for successful engraftment and delayed immune reconstitution. These considerations underscore the importance of quality control and rigorous screening to optimize safety and efficacy. This article explores the mechanisms of action, clinical applications, and potential complications of dual-double stem cell therapy, underscoring the need for continued research and optimized protocols to enhance safety and outcomes in ovarian insufficiency and related conditions, offering new hope for affected women.

The H3K9me3-specific histone methyltransferase SETDB1 is critical for proper regulation of developmental processes, but the underlying mechanisms are only partially understood. Here, we show that deletion of Setdb1 in mouse fetal liver hematopoietic stem and progenitor cells (HSPCs) results in compromised stem cell function, enhanced myeloerythroid differentiation, and impaired lymphoid development. Notably, Setdb1 -deficient HSPCs exhibit reduced quiescence and increased proliferation, accompanied by the acquisition of a lineage-biased transcriptional program. In Setdb1 -deficient HSPCs, we identify genomic regions that are characterized by loss of H3K9me3 and increased chromatin accessibility, suggesting enhanced transcription factor (TF) activity. Interestingly, hematopoietic TFs like PU.1 bind these cryptic enhancers in wild-type HSPCs, despite the H3K9me3 status. Thus, our data indicate that SETDB1 restricts activation of nonphysiological TF binding sites which helps to ensure proper maintenance and differentiation of fetal liver HSPCs., Competing Interests: Competing interests statement:The authors declare no competing interest.

Hematopoietic stem cells (HSCs) reside in a milieu that supports their functions, differentiation, and survival. This niche consists of several types of cells, including mesenchymal stem/stromal cells, endothelial cells, osteoblasts, megakaryocytes, macrophages, adipocytes, lymphoid cells, and nerve fibers. The interactions between these cells and HSCs have a role in HSC fate. Several studies have focused on identification of the biological and cellular mechanisms contributing to the establishment of this niche. However, the exact mechanisms of the interaction between HSCs and the bone marrow niche have not been elucidated yet. Unraveling these mechanisms would help in the design of effective methods for maintenance and multiplication of HSCs in clinical settings, in addition to establishment of novel therapies for hematopoietic diseases. The current review summarizes the effects of the niche cells on HSC function and underlying mechanisms of interplay between HSCs and their niche., Competing Interests: Declarations. Conflict of interest: The authors declare no competing interests. Ethical approval and consent to participate: Not applicable. Consent for publication: Not applicable., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Alternative polyadenylation (APA) is an essential post-transcriptional process that produces mature mRNA isoforms by regulating the usage of polyadenylation sites (PASs). APA is involved in lymphocyte activation; however, its role throughout the entire differentiation trajectory remains elusive. Here, we analyzed single-cell 3'-end transcriptome data from healthy subjects to construct a dynamic-APA landscape from hematopoietic stem and progenitor cells (HSPCs) to terminally differentiated lymphocytes. This analysis covered 19973 cells of 12 clusters from five lineages (B cells, CD4+ T cells, CD8+ T cells, natural killer cells, and plasmacytoid dendritic cells). A total of 2364 genes exhibited differential 3'-untranslated region (3'UTR) PAS usage, and 3021 genes displayed differential intronic cleavage during lymphoid differentiation. We observed a global trend of 3'UTR shortening during lymphoid differentiation. Nevertheless, specific events of both 3'UTR shortening and lengthening were also identified within each cluster. The APA patterns delineated three differentiation stages: HSPCs, precursor cells, and mature cells. Moreover, we demonstrated that the conversion of naïve T cells to memory T cells was accompanied by dynamic APA in transcription factor-encoding genes (TCF7 and NFATC2IP), immune function-related genes (BCL2, CD5, CD28, GOLT1B, and TMEM59), and protein ubiquitination-related genes (UBE2G1, YPEL5, and SUMO3). These findings expand our understanding of the underlying molecular mechanisms of APA and facilitate studies on the regulatory role of APA in lymphoid hematopoiesis., (© The Author(s) (2024). Published by Oxford University Press on behalf of Journal of Molecular Cell Biology, CEMCS, CAS.)

A combination of hematopoietic stem cell (HSC)- and endothelial cell (EC)-lineage-tracing mouse models enables us to determine blood cell origins. We present a protocol to induce cell labeling in vivo and to trace labeled hematopoietic cells to segregate their origins. We describe the steps for harvesting various hematopoietic tissues, antibody staining, and analyzing the Tomato+ percentages within each immune cell population. We also show how to estimate HSC- and EC-derived percentages of the target cell populations. For complete details on the use and execution of this protocol, please refer to Kobayashi et al. 1 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Clonal hematopoiesis involves the clonal expansion of hematopoietic cells, potentially progressing into hematological malignancies. Here, we present a protocol for the development and characterization of two mouse models designed to simulate clonal hematopoiesis and acute myeloid leukemia. We describe steps for model generation, monitoring clonal expansion, harvesting, fixation, and staining of bone marrow and spleen tissues. We specifically focus on the visualization and analysis of p53 mutant clonal expansions, providing a comprehensive protocol for studying these phenomena in mouse models. For complete details on the use and execution of this protocol, please refer to Pourebrahim et al. 1 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Hematopoietic stem cells (HSCs), essential for lifelong blood cell regeneration, are clinically utilized to treat various hematological disorders. These cells originate in the aorta-gonad-mesonephros region, expand in the fetal liver, and mature in the bone marrow. Chemotaxis, involving gradient sensing, polarization, and migration, directs HSCs and is crucial for their homing and mobilization. The molecular regulation of HSC chemotaxis involves chemokines, chemokine receptors, signaling pathways, and cytoskeletal proteins. Recent advances in understanding these regulatory mechanisms have deepened insights into HSC development and hematopoiesis, offering new avenues for therapeutic innovations. Strategies including glucocorticoid receptor activation, modulation of histone acetylation, stimulation of nitric oxide signaling, and interference with m6A RNA modification have shown potential in enhancing CXCR4 expression, thereby improving the chemotactic response and homing capabilities of human HSCs. This review synthesizes current knowledge on the molecular regulation of human HSC chemotaxis and its implications for health and disease., (© 2024 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.)

Background: The challenge of expanding haematopoietic stem/progenitor cells (HSPCs) in vitro has limited their clinical application. Human hair follicle mesenchymal stem cells (hHFMSCs) can be reprogrammed to generate intermediate stem cells by transducing OCT4 (hHFMSCs OCT4 ) and pre-inducing with FLT3LG/SCF, and differentiated into erythrocytes. These intermediate cells exhibit gene expression patterns similar to pre-HSCs, making them promising for artificial haematopoiesis. However, further investigation is required to elucidate the in vitro proliferation ability and mechanism underlying the self-renewal of pre-HSCs derived from hHFMSCs., Methods: hHFMSCs OCT4 were pre-treated with FLT3LG and SCF cytokines, followed by characterization and isolation of the floating cell subsets for erythroid differentiation through stimulation with hematopoietic cytokines and nutritional factors. Cell adhesion was assessed through disassociation and adhesion assays. OCT4 expression levels were measured using immunofluorescence staining, RT-qPCR, and Western blotting. RNA sequencing and Gene Ontology (GO) enrichment analysis were then conducted to identify proliferation-related biological processes. Proliferative capacity was evaluated through CCK-8, colony formation assays, Ki67 index, and cell cycle analysis. Cytoskeleton was observed through Wright‒Giemsa, Coomassie brilliant blue, and phalloidin staining. Expression of adherens junction (AJ) core members was confirmed through RT‒qPCR, Western blotting, and immunofluorescence staining before and after ZO-1 knockdown. A regulatory network was constructed to determine relationships among cytoskeleton, proliferation, and the AJ pathway. Student's t tests (GraphPad Prism 8.0.2) were used for group comparisons. The results were considered significant at P < 0.05., Results: Pre-treatment of hHFMSCs OCT4 with FLT3LG and SCF leads to the emergence of floating cell subsets exhibiting small, globoid morphology, suspended above adherent cells, forming colonies, and displaying minimal expression of CD45. Excessive OCT4 expression weakens adhesion in floating hHFMSCs OCT4 . Floating cells moderately enhanced proliferation and undergo cytoskeleton remodelling, with increased contraction and aggregation of F-actin near the nucleus. The upregulation of ZO-1 could impact the expressions of F-actin, E-cadherin, and β-catenin genes, as well as the nuclear positioning of β-catenin, leading to variations in the cytoskeleton and cell cycle. Finally, a regulatory network revealed that the AJ pathway cored with ZO-1 critically bridges cytoskeletal remodelling and haematopoiesis-related proliferation in a β-catenin-dependent manner., Conclusions: ZO-1 improved the self-renewal of pre-HSCs from OCT4-overexpressing hHFMSCs by remodeling the cytoskeleton via the ZO-1-regulated AJ pathway, suggesting floating hHFMSCs OCT4 as the promising seed cells for artificial hematopoiesis., Competing Interests: Declarations. Ethics approval and consent to participate: Informed consent was obtained from the donors to isolated hHFMSCs for research use. All experiments were approved by the Medical Ethics Committee of Qingdao Municipal Hospital. Title of the approved project: OCT4 facilitates the transdifferentiation of human hair follicle stem cells into erythrocytes by remodeling the cytoskeleton. Name of the institutional approval committee or unit: Medical Ethics Committee/IRB of Qingdao Municipal Hospital. Approval number: 2024-KY-077, Date of approval: Oct 16, 2024. Consent for publication: Informed consent was obtained from the donors to isolated hHFMSCs for research use. All authors have reviewed the manuscript and approved the publication. Competing interests: The authors declare that they have no competing interests., (© 2024. The Author(s).)

T cells develop from hematopoietic progenitors in the thymus and protect against pathogens and cancer. However, the emergence of human T cell-competent blood progenitors and their subsequent specification to the T lineage have been challenging to capture in real time. Here, we leveraged a pluripotent stem cell differentiation system to understand the transcriptional dynamics and cell fate restriction events that underlie this critical developmental process. Time-resolved single-cell RNA sequencing revealed that downregulation of the multipotent hematopoietic program, upregulation of >90 lineage-associated transcription factors, and cell-cycle exit all occur within a highly coordinated developmental window. Gene-regulatory network inference uncovered a role for YBX1 in T lineage specification. We mapped the differentiation cell fate hierarchy using transcribed lineage barcoding and discovered that mast and myeloid potential bifurcate from each other early in hematopoiesis, upstream of T lineage restriction. Our systems-level analyses provide a quantitative, time-resolved model of human T cell fate specification. A record of this paper's transparent peer review process is included in the supplemental information., Competing Interests: Declaration of interests Y.S.M., P.W.Z., and J.M.E. are named inventors on patents for T cell differentiation technology. P.W.Z. is a cofounder of Notch Therapeutics. P.W.Z. and Y.S.M. are co-founders of Apiary Therapeutics. P.W.Z., Y.S.M., and J.M.E. consult for cell therapy companies., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Over the last decades, significant progress has been made in studying agonistic and antagonistic hematopoietic peptides. The main disadvantage of this class of peptides is their low stability with noninvasive administration methods, which limits the widespread use of hematopoiesis-regulated peptide drugs in medical practice. The aim of this work is to study novel peptidomimetics with hematopoietic activity sustained in invasive and oral administration. The activity of the leading compound cyclopeptide Cyclo-[Glu(Ile)-Glu(Trp)] (CP-88) was compared to that of the pharmaceutical preparation Stemokin in stimulating the population of committed colony-forming cells in intact and irradiated mice. CP-88 peptide increases the relative number of CD34+ cells in the blood and bone marrow, leading to expanded hematopoietic stem cells. CP-88 peptide, applied 48 h before bone marrow extraction, stimulates the population of committed colony-forming cells in the normal bone marrow by 33-37% above the normal level. In recipient mice injected with irradiated bone marrow, this peptide was restored practically to normal levels of colony-forming cells in a wide range of doses at intraperitoneal and oral administration. The toxicological results conclude that in humans, considering interspecies extrapolation, the CP-88 peptide can be practically safe with a single and course administration in doses of up to 100 μg/kg. The results of this investigation underscore the significant potential of CP-88 peptide as a hematopoiesis-regulated drug and instill optimism for its future application in medical practice.

Hematopoietic stem cells (HSCs) develop from hemogenic endothelial cells (HECs) during mouse embryogenesis. Understanding the signaling molecules required for HSC development is crucial for the in vitro derivation of HSCs. We previously induced HSCs from embryonic HECs, isolated at embryonic day 10.5 (E10.5), in serum-free culture conditions with stem cell factor, thrombopoietin, and an endothelial feeder layer. Here, we aimed to elucidate signal requirements for inducing HSCs from earlier-stage HECs. Single-cell RNA sequencing (RNA-seq) analysis detected bone morphogenetic protein (BMP) signaling activation in E9.5 HECs. Adding BMP4 to the culture conditions led to the induction of HSCs from E9.5 HECs. Furthermore, isolating BMP4 receptor-expressing HECs from E9.5 embryos enriched progenitors with HSC-forming ability. This study identified BMP4 as an essential factor promoting the differentiation of early HECs into HSCs, opening up new possibilities for the in vitro derivation of HSCs., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Innate immune cells can develop a long-lasting hyperresponsive phenotype, termed trained immunity, mediated by epigenetic and metabolic reprogramming. In mice, exposure to Bacille Calmette-Guérin (BCG), β-glucan, or Western diet induces trained immunity by reprogramming hematopoietic progenitor cells (HPCs), through interleukin-1β (IL-1β) signaling in the bone marrow (BM). We investigated whether IL-1β induces trained immunity in primary human BM-derived HPCs in vitro. We exposed human BM-derived HPCs to IL-1β for 4 h. HPCs were expanded and differentiated into monocytes followed by functional and transcriptomic characterization. IL-1β-exposed HPCs showed higher granulocyte-macrophage colony-forming units. The monocyte offspring produced more tumor necrosis factor (TNF) and IL-1β after restimulation with lipopolysaccharide (LPS) and Pam3Cys and is metabolically more active. Transcriptomic analysis showed upregulation of key atherogenic and inflammatory pathways. In conclusion, brief exposure of human BM-derived HPCs to IL-1β in vitro induces a trained immunity phenotype., Competing Interests: Declaration of interests M.G.N. and L.A.B.J. are scientific founders of TTxD and Lemba TX. M.G.N. is scientific founder of Biotrip. W.H.C.R. is a consultant for Stryker for educational purposes only., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)