UM171 induces a homeostatic inflammatory-detoxification response supporting human HSC self-renewal

Further biological characterization of small molecules UM171 and SR1: In vitro effects on three hematopoietic cell populations from human cord blood

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.

Deciphering the effect of UM171 on human hematopoietic progenitor cell fate through clonal analysis

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.

Advances in hematopoietic stem cells ex vivo expansion associated with bone marrow niche

Hematopoietic stem cells (HSCs) are an ideal source for the treatment of many hematological diseases and malignancies, as well as diseases of other systems, because of their two important features, self-renewal and multipotential differentiation, which have the ability to rebuild the blood system and immune system of the body. However, so far, the insufficient number of available HSCs, whether from bone marrow (BM), mobilized peripheral blood or umbilical cord blood, is still the main restricting factor for the clinical application. Therefore, strategies to expand HSCs numbers and maintain HSCs functions through ex vivo culture are urgently required. In this review, we outline the basic biology characteristics of HSCs, and focus on the regulatory factors in BM niche affecting the functions of HSCs. Then, we introduce several representative strategies used for HSCs from these three sources ex vivo expansion associated with BM niche. These findings have deepened our understanding of the mechanisms by which HSCs balance self-renewal and differentiation and provided a theoretical basis for the efficient clinical HSCs expansion.

Robust Expansion of Hematopoietic Stem Cells Ex Vivo Using Small Molecule Cocktails

The insufficient number of hematopoietic stem cells (HSCs) poses a significant challenge for successful hematopoietic stem cell transplantation and gene-based therapies. To address this issue, ex vivo expansion of HSCs has been developed, improving engraftment and reducing morbidity risks in hematological disorders. Small molecules, known as stem cell agonists (SCAs), have been utilized to promote HSC expansion and have been implemented in clinical trials. While most HSC expansion protocols focus on the single use of SCAs, we describe a protocol using an optimized small molecule cocktail (SMC), X2A, to robustly enhance HSC yield. This protocol is applicable to human CD34+ hematopoietic stem and progenitor cells (HSPCs) derived from both umbilical cord blood and peripheral blood. In addition to the ex vivo HSC expansion protocol, we detail the CD34+ HSPC isolation technique and flow cytometry methods to characterize HSPC sub-populations from cell cultures. This culture protocol serves as a robust tool for pre-clinical studies in HSPCs and provides a foundation for further modifications to meet specific research needs.

KBTBD4-mediated reduction of MYC is critical for hematopoietic stem cell expansion upon UM171 treatment

ABSTRACT

Ex vivo expansion of hematopoietic stem cells (HSCs) is gaining importance for cell and gene therapy, and requires a shift from dormancy state to activation and cycling. However, abnormal or excessive HSC activation results in reduced self-renewal ability and increased propensity for myeloid-biased differentiation. We now report that activation of the E3 ligase complex CRL3KBTBD4 by UM171 not only induces epigenetic changes through CoREST1 degradation but also controls chromatin-bound master regulator of cell cycle entry and proliferative metabolism (MYC) levels to prevent excessive activation and maintain lympho-myeloid potential of expanded populations. Furthermore, reconstitution activity and multipotency of UM171-treated HSCs are specifically compromised when MYC levels are experimentally increased despite degradation of CoREST1.

Effects of different concentrations of nicotinamide on hematopoietic stem cells cultured in vitro

BACKGROUND

In vitro expansion to increase numbers of hematopoietic stem cells (HSCs) in cord blood could improve clinical efficacy of this vital resource. Nicotinamide (NAM) can promote HSC expansion ex vivo, but its effect on hematopoietic stem and progenitor cells (HSPCs, CD34+CD38) and functional subtypes of HSCs - short-term repopulating HSCs (ST-HSCs, CD34+CD38CD45RACD49f+) and long-term repopulating HSCs (LT-HSCs, CD34+CD38CD45RACD49f+CD90+) is not yet known. As a sirtuin 1 (SIRT1) inhibitor, NAM participates in regulating cell adhesion, polarity, migration, proliferation, and differentiation. However, SIRT1 exhibits dual effects by promoting or inhibiting differentiation in different tissues or cells. We propose that the concentration of NAM may influence proliferation, differentiation, and SIRT1 signaling of HSCs.

AIM

To evaluate the effects and underlying mechanisms of action of different concentrations of NAM on HSC proliferation and differentiation.

METHODS

CD34+ cells were purified from umbilical cord blood using MacsCD34 beads, and cultured for 10-12 d in a serum-free medium supplemented with cytokines, with different concentrations of NAM added according to experimental requirements. Flow cytometry was used to detect phenotype, cell cycle distribution, and apoptosis of the cultured cells. Real-time polymerase chain reaction was used to detect the transcription levels of target genes encoding stemness-related factors, chemokines, components of hypoxia pathways, and antioxidant enzymes. Dichloro-dihydro-fluorescein diacetate probes were used to evaluate intracellular production of reactive oxygen species (ROS). Determination of the effect of different culture conditions on the balance of cytokine by cytometric bead array.

RESULTS

Compared with the control group, the proportion and expansion folds of HSPCs (CD34+CD38) incubated with 5 mmol/L or 10 mmol/L NAM were significantly increased (all P < 0.05). The ST-HSCs ratio and fold expansion of the 5 mmol/L NAM group were significantly higher than those of the control and 10 mmol/L NAM groups (all P < 0.001), whereas the LT-HSCs ratio and fold expansion of the 10 mmol/L NAM group were significantly higher than those of the other two groups (all P < 0.05). When the NAM concentration was > 10 mmol/L, cell viability significantly decreased. In addition, compared with the 5 mmol/L NAM group, the proportion of apoptotic cells in the 10 mmol/L NAM group increased and the proportion of cells in S and G2 phase decreased. Compared with the 5 mmol/L NAM group, the HSCs incubated with 10 mmol/L NAM exhibited significantly inhibited SIRT1 expression, increased intracellular ROS content, and downregulated expression of genes encoding antioxidant enzymes (superoxide dismutase 1, peroxiredoxin 1).

CONCLUSION

Low concentrations (5 mmol/L) of NAM can better regulate the balance between proliferation and differentiation, thereby promoting expansion of HSCs. These findings allow adjustment of NAM concentrations according to expansion needs.

AA2P-mediated DNA demethylation synergizes with stem cell agonists to promote expansion of hematopoietic stem cells

Small molecules have enabled expansion of hematopoietic stem and progenitor cells (HSPCs), but limited knowledge is available on whether these agonists can act synergistically. In this work, we identify a stem cell agonist in AA2P and optimize a series of stem cell agonist cocktails (SCACs) to help promote robust expansion of human HSPCs. We find that SCACs provide strong growth-promoting activities while promoting retention and function of immature HSPC. We show that AA2P-mediated HSPC expansion is driven through DNA demethylation leading to enhanced expression of AXL and GAS6. Further, we demonstrate that GAS6 enhances the serial engraftment activity of HSPCs and show that the GAS6/AXL pathway is critical for robust HSPC expansion.

An interactive resource of molecular signalling in the developing human haematopoietic stem cell niche

The emergence of definitive human haematopoietic stem cells (HSCs) from Carnegie Stage (CS) 14 to CS17 in the aorta-gonad-mesonephros (AGM) region is a tightly regulated process. Previously, we conducted spatial transcriptomic analysis of the human AGM region at the end of this period (CS16/CS17) and identified secreted factors involved in HSC development. Here, we extend our analysis to investigate the progression of dorso-ventral polarised signalling around the dorsal aorta over the entire period of HSC emergence. Our results reveal a dramatic increase in ventral signalling complexity from the CS13-CS14 transition, coinciding with the first appearance of definitive HSCs. We further observe stage-specific changes in signalling up to CS17, which may underpin the step-wise maturation of HSCs described in the mouse model. The data-rich resource is also presented in an online interface enabling in silico analysis of molecular interactions between spatially defined domains of the AGM region. This resource will be of particular interest for researchers studying mechanisms underlying human HSC development as well as those developing in vitro methods for the generation of clinically relevant HSCs from pluripotent stem cells.

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

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

APEX1 Nuclease and Redox Functions are Both Essential for Adult Mouse Hematopoietic Stem and Progenitor Cells

Self-renewal and differentiation of hematopoietic stem and progenitor cells (HSPCs) are carefully controlled by extrinsic and intrinsic factors, to ensure the lifelong process of hematopoiesis. Apurinic/apyrimidinic endonuclease 1 (APEX1) is a multifunctional protein implicated in DNA repair and transcriptional regulation. Although previous studies have emphasized the necessity of studying APEX1 in a lineage-specific context and its role in progenitor differentiation, no studies have assessed the role of APEX1, nor its two enzymatic domains, in supporting adult HSPC function. In this study, we demonstrated that complete loss of APEX1 from murine bone marrow HSPCs (induced by CRISPR/Cas9) caused severe hematopoietic failure following transplantation, as well as a HSPC expansion defect in culture conditions maintaining in vivo HSC functionality. Using specific inhibitors against either the nuclease or redox domains of APEX1 in combination with single cell transcriptomics (CITE-seq), we found that both APEX1 nuclease and redox domains are regulating mouse HSPCs, but through distinct underlying transcriptional changes. Inhibition of the APEX1 nuclease function resulted in loss of HSPCs accompanied by early activation of differentiation programs and enhanced lineage commitment. By contrast, inhibition of the APEX1 redox function significantly downregulated interferon-stimulated genes and regulons in expanding HSPCs and their progeny, resulting in dysfunctional megakaryocyte-biased HSPCs, as well as loss of monocytes and lymphoid progenitor cells. In conclusion, we demonstrate that APEX1 is a key regulator for adult regenerative hematopoiesis, and that the APEX1 nuclease and redox domains differently impact proliferating HSPCs.

CD14+/CD31+ monocytes expanded by UM171 correct hemophilia A in zebrafish upon lentiviral gene transfer of factor VIII

Emerging gene therapy clinical trials test the correction of hemophilia A (HA) by replacing factor VIII (FVIII) in autologous hematopoietic stem cells (HSCs). Although it is known that platelets, monocyte/macrophages, and mesenchymal stromal cells can secrete transgenic FVIII, a systematic examination of blood lineages as extrahepatic sources of FVIII, to our knowledge, has not yet been performed. In this study, we sought to provide a comprehensive map of native and lentivirus-based transgenic FVIII production from HSC stage to mature blood cells, through a flow cytometry analysis. In addition, we generated a model of transient HA in zebrafish based on antisense RNA, to assess the corrective potential of the FVIII-transduced HSCs. We discovered that FVIII production begins at the CD34+ progenitor stage after cytokine stimulation in culture. Among all mature white blood cells, monocytes are the largest producers of native FVIII and can maintain protein overexpression during differentiation from HSCs when transduced by a FVIII lentiviral vector. Moreover, the addition of the HSC self-renewal agonist UM171 to CD34+ cells during transduction expanded a subpopulation of CD14+/CD31+ monocytes with excellent ability to carry the FVIII transgene, allowing the correction of HA phenotype in zebrafish. Finally, the HA zebrafish model showed that f8 RNA is predominantly localized in the hematopoietic system at the larval stage, which indicates a potential contributory role of FVIII in hematopoiesis that warrants further investigation. We believe that this study may be of broad interest to hematologists and researchers striving to advance knowledge and permanent treatments for patients with HA.

RNAi screen identifies MTA1 as an epigenetic modifier of differentiation commitment in human HSPCs

The molecular mechanisms regulating key fate decisions of hematopoietic stem cells (HSCs) remain incompletely understood. Here, we targeted global shRNA libraries to primary human hematopoietic stem and progenitor cells (HSPCs) to screen for modifiers of self-renewal and differentiation, and identified metastasis-associated 1 (MTA1) as a negative regulator of human HSPC propagation in vitro. Knockdown of MTA1 by independent shRNAs in primary human cord blood (CB) HSPCs led to a cell expansion during culture and a relative accumulation of immature CD34⁺CD90⁺ cells with perturbed in vitro differentiation potential. Transplantation experiments in immunodeficient mice showed a significant reduction of human chimerism in both blood and bone marrow from HSPCs with knockdown of MTA1, possibly due to reduced maturation of blood cells. We further show that MTA1 associates with the nucleosome remodeling deacetylase (NuRD) complex in human HSPCs, and upon knockdown of MTA1 we observed an increase in H3K27Ac marks coupled with a downregulation of genes linked to differentiation towards the erythroid lineage. Altogether, our findings identify MTA1 as a novel regulator of human HSPCs in vitro and in vivo with critical functions for differentiation commitment.

LSD1 Inhibition Enhances the Immunogenicity of Mesenchymal Stromal Cells by Eliciting a dsRNA Stress Response

Mesenchymal stromal cells (MSCs) are commonly known for their immune-suppressive abilities. However, our group provided evidence that it is possible to convert MSCs into potent antigen presenting cells (APCs) using either genetic engineering or pharmacological means. Given the capacity of UM171a to trigger APC-like function in MSCs, and the recent finding that this drug may modulate the epigenome by inhibiting the lysine-specific demethylase 1 (LSD1), we explored whether the direct pharmacological inhibition of LSD1 could instill APC-like functions in MSCs akin to UM171a. The treatment of MSCs with the LSD1 inhibitor tranylcypromine (TC) elicits a double-stranded (ds)RNA stress response along with its associated responsive elements, including pattern recognition receptors (PRRs), Type-I interferon (IFN), and IFN-stimulated genes (ISGs). The net outcome culminates in the enhanced expression of H2-K^b, and an increased stability of the cell surface peptide: MHCI complexes. As a result, TC-treated MSCs stimulate CD8 T-cell activation efficiently, and elicit potent anti-tumoral responses against the EG.7 T-cell lymphoma in the context of prophylactic vaccination. Altogether, our findings reveal a new pharmacological protocol whereby targeting LSD1 in MSCs elicits APC-like capabilities that could be easily exploited in the design of future MSC-based anti-cancer vaccines.

New Insights into Hematopoietic Stem Cell Expansion to Stimulate Repopulation of the Adult Blood System for Transplantation

Successful engraftment of hematopoietic stem cells (HSCs) and progenitor cells (HSPCs) may be considered as a basis for the repopulation of the blood cells after transplantation in adults. Therefore, in vivo and ex vivo expansion of HSCs holds great promise for clinical applications. In this review, the mechanisms of HSC expansion will be discussed, considering the previous studies and works of literature. This is aimed to identify the signaling pathways that regulate HSC expansion and improve the application of engraftment in disease management. The following aspects will be included: (i) Stimulation of HSCs growth in vivo through gene regulation and cytokines activation; (ii) direct or indirect induction of HSC expansion by regulating signaling pathways; (iii) addition to assisting cells to help in the proliferation of HSCs; (iv) changing of living environment in the HSCs cultures via adjusting components and forms of cultures; (v) enhancement of HSC expansion by incorporating substances, such as extracellular vesicles (EVs), UM171, among others. In this review, recent new findings that provide us with new insights into HSC expansion methods have been summarized. Furthermore, these findings will also provide more possibilities for the development of some novel strategies for expanding and engrafting HSCs applied for treatments of some hematopoietic disorders.

Decoding Human Hematopoietic Stem Cell Self-Renewal

Purpose of Review

Hematopoietic stem cells (HSCs) maintain blood and immune cell homeostasis by balancing quiescence, self-renewal, and differentiation. HSCs can be used in lifesaving transplantation treatments to create a healthy hematopoietic system in patients suffering from malignant or inherited blood diseases. However, lack of matching bone marrow donors, and the low quantity of HSCs in a single cord blood graft, are limitations for successful transplantation. The enormous regenerative potential of HSCs has raised the hope that HSC self-renewal could be recapitulated in culture to achieve robust expansion of HSCs for therapeutic use. Yet, when HSCs are cultured ex vivo their function becomes compromised, limiting successful expansion.

Recent Findings

After decades of efforts to expand human HSCs ex vivo that resulted in minimal increase in transplantable units, recent studies have helped define culture conditions that can increase functional HSCs. These studies have provided new insights into how HSC stemness can be controlled from the nucleus by transcriptional, posttranscriptional and epigenetic regulators, or by improving the HSC microenvironment using 3D scaffolds, niche cells, or signaling molecules that mimic specific aspects of human HSC niche. Recent studies have also highlighted the importance of mitigating culture induced cellular stress and balancing mitochondrial, endoplasmic reticulum, and lysosomal functions. These discoveries have provided better markers for functional human HSCs and new insights into how HSC self-renewal and engraftment ability may be controlled ex vivo.

Summary

Uncovering the mechanisms that control the human HSC self-renewal process may help improve the ex vivo expansion of HSCs for clinical purposes.

UM171A-induced ROS promote antigen cross-presentation of immunogenic peptides by bone marrow-derived mesenchymal stromal cells

BACKGROUND

Mesenchymal stromal cells (MSCs) have been extensively used in the clinic due to their exquisite tissue repair capacity. However, they also hold promise in the field of cellular vaccination as they can behave as conditional antigen presenting cells in response to interferon (IFN)-gamma treatment under a specific treatment regimen. This suggests that the immune function of MSCs can be pharmacologically modulated. Given the capacity of the agonist pyrimido-indole derivative UM171a to trigger the expression of various antigen presentation-related genes in human hematopoietic progenitor cells, we explored the potential use of UM171a as a means to pharmacologically instill and/or promote antigen presentation by MSCs.

METHODS

Besides completing a series of flow-cytometry-based phenotypic analyses, several functional antigen presentation assays were conducted using the SIINFEKL-specific T-cell clone B3Z. Anti-oxidants and electron transport chain inhibitors were also used to decipher UM171a's mode of action in MSCs. Finally, the potency of UM171a-treated MSCs was evaluated in the context of therapeutic vaccination using immunocompetent C57BL/6 mice with pre-established syngeneic EG.7T-cell lymphoma.

RESULTS

Treatment of MSCs with UM171a triggered potent increase in H2-Kb cell surface levels along with the acquisition of antigen cross-presentation abilities. Mechanistically, such effects occurred in response to UM171a-mediated production of mitochondrial-derived reactive oxygen species as their neutralization using anti-oxidants or Antimycin-A mitigated MSCs' ability to cross-present antigens. Processing and presentation of the immunogenic ovalbumin-derived SIINFEKL peptide was caused by de novo expression of the Psmb8 gene in response to UM171a-triggered oxidative stress. When evaluated for their anti-tumoral properties in the context of therapeutic vaccination, UM171a-treated MSC administration to immunocompetent mice with pre-established T-cell lymphoma controlled tumor growth resulting in 40% survival without the need of additional supportive therapy and/or standard-of-care.

CONCLUSIONS

Altogether, our findings reveal a new immune-related function for UM171a and clearly allude to a direct link between UM171a-mediated ROS induction and antigen cross-presentation by MSCs. The fact that UM171a treatment modulates MSCs to become antigen-presenting cells without the use of IFN-gamma opens-up a new line of investigation to search for additional agents capable of converting immune-suppressive MSCs to a cellular tool easily adaptable to vaccination.

Hematopoietic stem cell gene editing and expansion: State-of-the-art technologies and recent applications

Hematopoietic stem cell transplantation (HSCT) is a curative therapy for a range of hematological diseases, from leukemias to immunodeficiencies and anemias. The aim in using HSCT is to replace a patient's dysfunctional blood system with a functional one by transplanting healthy hematopoietic stem cells (HSCs). HSCs may be collected from a healthy donor (for allogeneic HSCT) or from the patient for genetic correction (for autologous HSCT gene therapies). Despite the curative potential of HSCT, several hurdles to its wider and safer use remain, including how to efficiently genetically correct HSCs and how to increase donor HSC numbers to improve the donor pool. In recent years, the development of state-of-the-art technologies, such as Cas9-AAV6 technologies and identification of the small molecule HSC agonist UM171, have accelerated progress in HSC gene editing and expansion. These translational research efforts were the focus of the Spring 2021 International Society for Experimental Hematology (ISEH) webinar. Here we present a summary and discussion of the implications of these new approaches to improve HSC-based therapy.

'Off-the-Shelf' Immunotherapy: Manufacture of CD8+ T Cells Derived from Hematopoietic Stem Cells

Cellular immunotherapy is revolutionizing cancer treatment. However, autologous transplants are complex, costly, and limited by the number and quality of T cells that can be isolated from and expanded for re-infusion into each patient. This paper demonstrates a stromal support cell-free in vitro method for the differentiation of T cells from umbilical cord blood hematopoietic stem cells (HSCs). For each single HSC cell input, approximately 5 × 104 T cells were created with an initial five days of HSC expansion and subsequent T cell differentiation over 49 days. When the induced in vitro differentiated T cells were activated by cytokines and anti-CD3/CD28 beads, CD8+ T cell receptor (TCR) γδ+ T cells were preferentially generated and elicited cytotoxic function against ovarian cancer cells in vitro. This process of inducing de novo functional T cells offers a possible strategy to increase T cell yields, simplify manufacturing, and reduce costs with application potential for conversion into chimeric antigen receptor (CAR)-T cells for cancer immunotherapy and for allogeneic transplantation to restore immune competence.

Asymmetric organelle inheritance predicts human blood stem cell fate

Understanding human hematopoietic stem cell fate control is important for their improved therapeutic manipulation. Asymmetric cell division, the asymmetric inheritance of factors during division instructing future daughter cell fates, was recently described in mouse blood stem cells. In human blood stem cells, the possible existence of asymmetric cell division remained unclear due to technical challenges in its direct observation. Here, we use long-term quantitative single-cell imaging to show that lysosomes and active mitochondria are asymmetrically inherited in human blood stem cells and that their inheritance is a coordinated, non-random process. Furthermore, multiple additional organelles, including autophagosomes, mitophagosomes, autolysosomes and recycling endosomes show preferential asymmetric co-segregation with lysosomes. Importantly, asymmetric lysosomal inheritance predicts future asymmetric daughter cell cycle length, differentiation and stem cell marker expression, while asymmetric inheritance of active mitochondria correlates with daughter metabolic activity. Hence, human hematopoietic stem cell fates are regulated by asymmetric cell division, with both mechanistic evolutionary conservation and differences to the mouse system.

Development of β-globin gene correction in human hematopoietic stem cells as a potential durable treatment for sickle cell disease

Sickle cell disease (SCD) is the most common serious monogenic disease with 300,000 births annually worldwide. SCD is an autosomal recessive disease resulting from a single point mutation in codon six of the β-globin gene (HBB). Ex vivo β-globin gene correction in autologous patient-derived hematopoietic stem and progenitor cells (HSPCs) may potentially provide a curative treatment for SCD. We previously developed a CRISPR-Cas9 gene targeting strategy that uses high-fidelity Cas9 precomplexed with chemically modified guide RNAs to induce recombinant adeno-associated virus serotype 6 (rAAV6)-mediated HBB gene correction of the SCD-causing mutation in HSPCs. Here, we demonstrate the preclinical feasibility, efficacy, and toxicology of HBB gene correction in plerixafor-mobilized CD34⁺ cells from healthy and SCD patient donors (gcHBB-SCD). We achieved up to 60% HBB allelic correction in clinical-scale gcHBB-SCD manufacturing. After transplant into immunodeficient NSG mice, 20% gene correction was achieved with multilineage engraftment. The long-term safety, tumorigenicity, and toxicology study demonstrated no evidence of abnormal hematopoiesis, genotoxicity, or tumorigenicity from the engrafted gcHBB-SCD drug product. Together, these preclinical data support the safety, efficacy, and reproducibility of this gene correction strategy for initiation of a phase 1/2 clinical trial in patients with SCD.

Analyzing signaling activity and function in hematopoietic cells

Cells constantly sense their environment, allowing the adaption of cell behavior to changing needs. Fine-tuned responses to complex inputs are computed by signaling pathways, which are wired in complex connected networks. Their activity is highly context-dependent, dynamic, and heterogeneous even between closely related individual cells. Despite lots of progress, our understanding of the precise implementation, relevance, and possible manipulation of cellular signaling in health and disease therefore remains limited. Here, we discuss the requirements, potential, and limitations of the different current technologies for the analysis of hematopoietic stem and progenitor cell signaling and its effect on cell fates.

Answered and Unanswered Questions in Early-Stage Viral Vector Transduction Biology and Innate Primary Cell Toxicity for Ex-Vivo Gene Editing

Adeno-associated virus is a highly efficient DNA delivery vehicle for genome editing strategies that employ CRISPR/Cas9 and a DNA donor for homology-directed repair. Many groups have used this strategy in development of therapies for blood and immune disorders such as sickle-cell anemia and severe-combined immunodeficiency. However, recent events have called into question the immunogenicity of AAV as a gene therapy vector and the safety profile dictated by the immune response to this vector. The target cells dictating this response and the molecular mechanisms dictating cellular response to AAV are poorly understood. Here, we will investigate the current known AAV capsid and genome interactions with cellular proteins during early stage vector transduction and how these interactions may influence innate cellular responses. We will discuss the current understanding of innate immune activation and DNA damage response to AAV, and the limitations of what is currently known. In particular, we will focus on pathway differences in cell line verses primary cells, with a focus on hematopoietic stem and progenitor cells (HSPCs) in the context of ex-vivo gene editing, and what we can learn from HSPC infection by other parvoviruses. Finally, we will discuss how innate immune and DNA damage response pathway activation in these highly sensitive stem cell populations may impact long-term engraftment and clinical outcomes as these gene-editing strategies move towards the clinic, with the aim to propose pathways relevant for improved hematopoietic stem cell survival and long-term engraftment after AAV-mediated genome editing.

UM171 Preserves Epigenetic Marks that Are Reduced in Ex Vivo Culture of Human HSCs via Potentiation of the CLR3-KBTBD4 Complex

Human hematopoietic stem cells (HSCs) exhibit attrition of their self-renewal capacity when cultured ex vivo, a process that is partially reversed upon treatment with epigenetic modifiers, most notably inhibitors of histone deacetylases (HDACs) or lysine-specific demethylase LSD1. A recent study showed that the human HSC self-renewal agonist UM171 modulates the CoREST complex, leading to LSD1 degradation, whose inhibition mimics the activity of UM171. The mechanism underlying the UM171-mediated loss of CoREST function remains undetermined. We now report that UM171 potentiates the activity of a CULLIN3-E3 ubiquitin ligase (CRL3) complex whose target specificity is dictated by the poorly characterized Kelch/BTB domain protein KBTBD4. CRL3^KBTBD4 targets components of the LSD1/RCOR1 corepressor complex for proteasomal degradation, hence re-establishing H3K4me2 and H3K27ac epigenetic marks, which are rapidly decreased upon ex vivo culture of human HSCs.

Lysine-specific demethylase 1A restricts ex vivo propagation of human HSCs and is a target of UM171

Culture conditions in which hematopoietic stem cells (HSCs) can be expanded for clinical benefit are highly sought after. Here, we report that inhibition of the epigenetic regulator lysine-specific histone demethylase 1A (LSD1) induces a rapid expansion of human cord blood-derived CD34+ cells and promotes in vitro propagation of long-term repopulating HSCs by preventing differentiation. The phenotype and molecular characteristics of cells treated with LSD1 inhibitors were highly similar to cells treated with UM171, an agent promoting expansion of HSCs through undefined mechanisms and currently being tested in clinical trials. Strikingly, we found that LSD1, as well as other members of the LSD1-containing chromatin remodeling complex CoREST, is rapidly polyubiquitinated and degraded upon UM171 treatment. CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 depletion of the CoREST core member, RCOR1, resulted in expansion of CD34+ cells similar to LSD1 inhibition and UM171. Taken together, LSD1 and CoREST restrict HSC expansion and are principal targets of UM171, forming a mechanistic basis for the HSC-promoting activity of UM171.

Continuous NF-κB pathway inhibition promotes expansion of human phenotypical hematopoietic stem/progenitor cells through metabolism regulation

Hematopoietic stem/progenitor cells (HSPCs) ex vivo expansion is critical in facilitating their widespread clinical application. NF-κB pathway is implicated in the energy homeostasis and metabolic adaptation. To explore the effect of NF-κB pathway on the ex vivo HSPC expansion and metabolism, the 50 nM-1 μM inhibitor of NF-κB pathway TPCA-1 was used to expand cord blood derived CD34⁺ cells in serum-free culture. The expansion folds, function, mitochondrial profile and metabolism of HSPCs were determined. After 10 days of culture with 100 nM TPCA-1, the expansion of total cells， CD34⁺CD38^- cells， and CD34⁺CD38^-CD45RA^-CD90⁺CD49f⁺ cells were significantly increased compared to the cytokine priming alone. Notably, TPCA-1 treatment generated ~ 2-fold greater percentage of CD34⁺EPCR⁺ and CD34⁺CD38^-CD45RA^-CD90⁺CD49f⁺ cells compared to cytokine only conditions. Moreover, TPCA-1 expanded CD34⁺ cells displayed enhanced serial colonies forming potential and secondary expansion capability. NF-κB inhibition increased the expression of self-renewal related genes, while downregulated the expression of mitochondrial biogenesis regulator (Pgc1α) and mitochondrial chaperones and proteases (ClpP, Hsp10, Hsp60). Mitochondrial mass and membrane potential were markedly decreased with TPCA-1 treatment, leading to the reduced mitochondrial reactive oxygen species (ROS) level in HSPCs. NF-κB inhibition displayed augmented glycolysis rate with compromising mitochondrial metabolism. This study demonstrated that NF-κB pathway inhibition improved glycolysis and limited ROS production that promoted the ex vivo expansion and maintenance of functional HSPCs.

In vivo and ex vivo haematopoietic stem cell expansion

PURPOSE OF REVIEW

Haematopoietic stem cells (HSCs) are characterized by two key features: self-renewal ability and multilineage differentiation potential. Through these cellular activities, HSCs sustain blood and immune system homeostasis throughout life and can also reconstitute the entire haematopoietic system within a bone marrow ablated recipient. This approach of HSC transplantation is used clinically as a curative treatment option for numerous haematological diseases, both malignant and nonmalignant.

RECENT FINDINGS

Elucidation of the mechanism of HSC expansion represents a major focus within haematology. Here, we review the recent progress towards understanding HSC expansion in vivo and ex vivo, including a discussion of recent clonal transplantation assays and the development of novel ex vivo culture systems.

SUMMARY

Recent findings provide exciting promise for improving the safety and efficacy of current HSC-based therapies as well as for the development of new therapeutic paradigms.

Ex Vivo Analysis of Primary Tumor Specimens for Evaluation of Cancer Therapeutics

The use of ex vivo drug sensitivity testing to predict drug activity in individual patients has been actively explored for almost 50 years without delivering a generally useful predictive capability. However, extended failure should not be an indicator of futility. This is especially true in cancer research where ultimate success is often preceded by less successful attempts. For example, both immune- and genetic-based targeted therapies for cancer underwent numerous failed attempts before biological understanding, improved targets, and optimized drug development matured to facilitate an arsenal of transformational drugs. Similarly, the concept of directly assessing drug sensitivity of primary tumor biopsies-and the use of this information to help direct therapeutic approaches-has a long history with a definitive learning curve. In this review, we will survey the history of ex vivo testing as well as the current state of the art for this field. We will present an update on methodologies and approaches, describe the use of these technologies to test cutting-edge drug classes, and describe an increasingly nuanced understanding of tumor types and models for which this strategy is most likely to succeed. We will consider the relative strengths and weaknesses of predicting drug activity across the broad biological context of cancer patients and tumor types. This will include an analysis of the potential for ex vivo drug sensitivity testing to accurately predict drug activity within each of the biological hallmarks of cancer pathogenesis.

Activation of the receptor tyrosine kinase RET improves long-term hematopoietic stem cell outgrowth and potency

Expansion of human hematopoietic stem cells (HSCs) is a rapidly advancing field showing great promise for clinical applications. Recent evidence has implicated the nervous system and glial family ligands (GFLs) as potential drivers of hematopoietic survival and self-renewal in the bone marrow niche; how to apply this process to HSC maintenance and expansion has yet to be explored. We show a role for the GFL receptor, RET, at the cell surface of HSCs in mediating sustained cellular growth, resistance to stress, and improved cell survival throughout in vitro expansion. HSCs treated with the key RET ligand/coreceptor complex, glial-derived neurotrophic factor and its coreceptor, exhibit improved progenitor function at primary transplantation and improved long-term HSC function at secondary transplantation. Finally, we show that RET drives a multifaceted intracellular signaling pathway, including key signaling intermediates protein kinase B, extracellular signal-regulated kinase 1/2, NF-κB, and p53, responsible for a wide range of cellular and genetic responses that improve cell growth and survival under culture conditions.

Stabilizing hematopoietic stem cells in vitro

Hematopoietic stem cells (HSCs) can regenerate all lineages of the adult blood and immune systems long-term following transplantation via a combination of self-renewal and multipotent differentiation. HSCs are therefore an important cell type in both basic research and in the clinic, where HSC transplantation is a curative therapy for a range of diseases. However, as a rare bone marrow cell population, the characterization and collection of HSCs can often be challenging. This has led to a large search for in vitro culture conditions that support the growth of functional HSCs and the in vitro stabilization of the HSC state represents a major goal in the field. Here, we review recent progress towards stabilizing HSCs in vitro.

Haematopoietic stem cell self-renewal in vivo and ex vivo

The self-renewal capacity of multipotent haematopoietic stem cells (HSCs) supports blood system homeostasis throughout life and underlies the curative capacity of clinical HSC transplantation therapies. However, despite extensive characterization of the HSC state in the adult bone marrow and embryonic fetal liver, the mechanism of HSC self-renewal has remained elusive. This Review presents our current understanding of HSC self-renewal in vivo and ex vivo, and discusses important advances in ex vivo HSC expansion that are providing new biological insights and offering new therapeutic opportunities.

UM171 promotes expansion of autologous peripheral blood hematopoietic stem cells from poorly mobilizing lymphoma patients

BACKGROUND

Autologous hematopoietic stem cell transplantation is an effective therapeutic strategy for lymphoma patients. However, some patients have to give up receiving transplantation because of failing to obtain sufficient CD34⁺ cells yields. Therefore, we ex vivo expanded HSCs of lymphoma patients using UM171 to solve the problem of HSCs deficiency.

METHODS

Mobilized peripheral blood-derived CD34⁺ cells from lymphoma patients were cultured for 10 days with or without UM171. The fold of cell expansion and the immunophenotype of expanded cells were assessed by flow cytometry. RNA-seq experiment was performed to identify the mechanism by which UM171 promoted HSCs expansion.

RESULTS

UM171 treatment increased the proportion of CD34⁺ (68.97 ± 6.91%), CD34⁺ CD38^- cells (44.10 ± 9.20%) and CD34⁺CD38^-CD45RA^-CD90⁺ LT-HSCs (3.05 ± 2.08%) compared to vehicle treatment (36.08 ± 11.14%, 18.30 ± 9.49% and 0.56 ± 0.45%, respectively). UM171 treatment led to an 85.08-fold increase in LT-HSC numbers relative to initial cells. Importantly, UM171 promoted expansion of LT-HSCs achieved 138.57-fold in patients with poor mobilization. RNA-seq data showed that UM171 upregulated expression of HSC-, mast cell-specific genes and non-canonical Wnt signaling related genes, and inhibited genes expression of erythroid, megakaryocyte and inflammatory mediated chemokine.

CONCLUSIONS

Our study shows that UM171 can efficiently promote ex vivo expansion of HSCs from lymphoma patients, especially for poorly mobilizing patients. In terms of mechanism, UM171 upregulate HSC-specific genes expression and suppress erythroid and megakaryocytic differentiation, as well as activate non-classical Wnt signaling.