Biology and relevance of human acute myeloid leukemia stem cells. Blood. 2017;129:1577-1585. [PMID: 28159741 DOI: 10.1182/blood-2016-10-696054]

Targeting Cancer Stemness in the Clinic: From Hype to Hope

Tumors are composed of non-homogeneous cell populations exhibiting varying degrees of genetic and functional heterogeneity. Cancer stem cells (CSCs) are capable of sustaining tumors by manipulating genetic and non-genetic factors to metastasize, resist treatment, and maintain the tumor microenvironment. Understanding the key traits and mechanisms of CSC survival provides opportunities to improve patient outcomes via improved prognostic models and therapeutics. Here, we review the clinical significance of CSCs and results of potential CSC-targeting therapies in various cancers. We discuss barriers to translating cues from pre-clinical models into clinical applications and propose new strategies for rational design of future anti-CSC trials.

Hif-1α Deletion May Lead to Adverse Treatment Effect in a Mouse Model of MLL-AF9-Driven AML

Relapse of acute myeloid leukemia (AML) remains a significant clinical challenge due to limited therapeutic options and poor prognosis. Leukemic stem cells (LSCs) are the cellular units responsible for relapse in AML, and strategies that target LSCs are thus critical. One proposed potential strategy to this end is to break the quiescent state of LSCs, thereby sensitizing LSCs to conventional cytostatics. The hypoxia-inducible factor (HIF) pathway is a main driver of cellular quiescence and a potential therapeutic target, with precedence from both solid cancers and leukemias. Here, we used a conditional knockout Hif-1α mouse model together with a standard chemotherapy regimen to evaluate LSC targeting in AML. Contrary to expectation, our studies revealed that Hif-1α-deleted-leukemias displayed a faster disease progression after chemotherapy. Our studies thereby challenge the general notion of cancer stem cell sensitization by inhibition of the HIF pathway, and warrant caution when applying HIF inhibition in combination with chemotherapy in AML.

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Deletion of Hif-1α accelerates the progression of chemotherapy-treated MLL-AF9-AML

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Deletion of Hif-1α does not decrease LSC frequency after chemotherapy

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Chemotherapy targets more mature cells indicated by transcriptional analysis

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Hif-1α deletion affects few transcriptional pathways in AML cells

Targeting cell-bound MUC1 on myelomonocytic, monocytic leukemias and phenotypically defined leukemic stem cells with anti-SEA module antibodies

Cell surface molecules aberrantly expressed or overexpressed by myeloid leukemic cells represent potential disease-specific therapeutic targets for antibodies. MUC1 is a polymorphic glycoprotein, the cleavage of which yields two unequal chains: a large extracellular α subunit containing a tandem repeat array bound in a strong noncovalent interaction to a smaller β subunit containing the transmembrane and cytoplasmic domains. Because the α-chain can be released from the cell-bound domains of MUC1, agents directed against the α-chain will not effectively target MUC1⁺ cells. The MUC1 SEA (a highly conserved protein module so called from its initial identification in a sea urchin sperm protein, in enterokinase, and in agrin) domain formed by the binding of the α and β chains  represents a stable structure fixed to the cell surface at all times. DMB-5F3, a partially humanized murine anti-MUC1 SEA domain monoclonal antibody, was used to examine MUC1 expression in acute myeloid leukemia (AML) and was found to bind acute myelomonocytic and monocytic leukemia (AML-M4 and AML-M5) cell lines. We also examined monocytic neoplasms freshly obtained from patients including chronic myelomonocytic leukemia and juvenile myelomonocytic leukemia, which were found to uniformly express MUC1. CD34⁺/lin^-/CD38^- or CD38⁺ presumed leukemic stem cell populations from CD34⁺ AML and CD34^-CD38^- or CD38⁺ populations from CD34^- AML were also found to express MUC1, although at low percentages. Based on these studies, we generated an anti-MUC1 immunotoxin to directly gauge the cytotoxic efficacy of targeting AML-bound MUC1. Using single-chain DMB-5F3 fused to recombinant gelonin toxin, the degree of AML cytotoxicity was found to correlate with MUC1 expression. Our data support the use of an anti-MUC1 SEA module-drug conjugates to selectively target and inhibit MUC1-expressing myelomonocytic leukemic cells.

Hematopoietic Stem Cells: Normal Versus Malignant

SIGNIFICANCE

The long-term hematopoietic stem cell (LT-HSC) demonstrates characteristics of self-renewal and the ability to manage expansion of the hematopoietic compartment while maintaining the capacity for differentiation into hematopoietic stem/progenitor cell (HSPC) and terminal subpopulations. Deregulation of the HSPC redox environment results in loss of signaling that normally controls HSPC fate, leading to a loss of HSPC function and exhaustion. The characteristics of HSPC exhaustion via redox stress closely mirror phenotypic traits of hematopoietic malignancies and the leukemic stem cell (LSC). These facets elucidate the HSC/LSC redox environment as a druggable target and a growing area of cancer research. Recent Advances: Although myelosuppression and exhaustion of the hematopoietic niche are detrimental side effects of classical chemotherapies, new agents that modify the HSPC/LSC redox environment have demonstrated the potential for protection of normal HSPC function while inducing cytotoxicity within malignant populations.

CRITICAL ISSUES

New therapies must preserve, or only slightly disturb normal HSPC redox balance and function, while simultaneously altering the malignant cellular redox state. The cascade nature of redox damage makes this a critical and delicate line for the development of a redox-based therapeutic index.

FUTURE DIRECTIONS

Recent evidence demonstrates the potential for redox-based therapies to impact metabolic and epigenetic factors that could contribute to initial LSC transformation. This is balanced by the development of therapies that protect HSPC function. This pushes toward therapies that may alter the HSC/LSC redox state but lead to initiation cell fate signaling lost in malignant transformation while protecting normal HSPC function. Antioxid. Redox Signal.

Prognostic and therapeutic role of CLEC12A in acute myeloid leukemia

CLEC12A has recently been identified as an antigen, expressed on leukemic stem cells and leukemic blasts. Given the fact that this expression profile seems stable throughout diagnosis, treatment and relapse on leukemic blasts and leukemic stem cells, CLEC12A can be considered a highly potent and reliable marker for the detection of measurable residual disease and therefore applicable for risk stratification and prognostication in AML. Low CLEC12A expression on leukemic blasts seems to be independently associated with lower likelihood of achieving complete remission after 1 cycle of induction chemotherapy, shorter event free survival, as well as overall survival, indicating potential prognostic properties of CLEC12A expression itself. Lack of expression on the normal hematopoietic stem and progenitor cells, in contrast to CD123 and CD33, might result in less toxicity regarding cytopenias, making CLEC12A an interesting target for innovating immunotherapies, including monoclonal and bispecific antibodies, antibody-drug conjugates and CAR-T cells therapy.

Synthesis and biological evaluation of dithiocarbamate esters of parthenolide as potential anti-acute myelogenous leukaemia agents

A series of dithiocarbamate esters of parthenolide (PTL) was designed, synthesised, and evaluated for their anti- acute myelogenous leukaemia (AML) activities. The most promising compound 7l showed greatly improved potency against AML progenitor cell line KG1a with IC₅₀ value of 0.7 μM, and the efficacy was 8.7-folds comparing to that of PTL (IC₅₀ = 6.1 μM). Compound 7l induced apoptosis of total primary human AML cells and leukaemia stem cell (LSCs) of primary AML cells while sparing normal cells. Furthermore, 7l suppressed the colony formation of primary human leukaemia cells. Moreover, compound 12, the salt form of 7l, prolonged the lifespan of mice in two patient-derived xenograft models and had no observable toxicity. The preliminary molecular mechanism study revealed that 7l-mediated apoptosis is associated with mitogen-activated protein kinase signal pathway. On the basis of these investigations, we propose that 12 might be a promising drug candidate for ultimate discovery of anti-LSCs drug.

The Ins and Outs of Autophagy and Metabolism in Hematopoietic and Leukemic Stem Cells: Food for Thought

Discovered over fifty years ago, autophagy is a double-edged blade. On one hand, it regulates cellular energy sources by "cannibalization" of its own cellular components, feeding on proteins and other unused cytoplasmic factors. On the other, it is a recycling process that removes dangerous waste from the cytoplasm keeping the cell clean and healthy. Failure of the autophagic machinery is translated in dysfunction of the immune response, in aging, and in the progression of pathologies such as Parkinson disease, diabetes, and cancer. Further investigation identified autophagy with a protective role in specific types of cancer, whereas in other cases it can promote tumorigenesis. Evidence shows that treatment with chemotherapeutics can upregulate autophagy in order to maintain a stable intracellular environment promoting drug resistance and cell survival. Leukemia, a blood derived cancer, represents one of the malignancies in which autophagy is responsible for drug treatment failure. Inhibition of autophagy is becoming a strategic target for leukemic stem cell (LSC) eradication. Interestingly, the latest findings demonstrate that LSCs show higher levels of mitochondrial metabolism compared to normal stem cells. With this review, we aim to explore the links between autophagy and metabolism in the hematopoietic system, with special focus on primitive LSCs.

Identification of Chemotherapy-Induced Leukemic-Regenerating Cells Reveals a Transient Vulnerability of Human AML Recurrence

Despite successful remission induction, recurrence of acute myeloid leukemia (AML) remains a clinical obstacle thought to be caused by the retention of dormant leukemic stem cells (LSCs). Using chemotherapy-treated AML xenografts and patient samples, we have modeled patient remission and relapse kinetics to reveal that LSCs are effectively depleted via cell-cycle recruitment, leaving the origins of relapse unclear. Post-chemotherapy, in vivo characterization at the onset of disease relapse revealed a unique molecular state of leukemic-regenerating cells (LRCs) responsible for disease re-growth. LRCs are transient, can only be detected in vivo, and are molecularly distinct from therapy-naive LSCs. We demonstrate that LRC features can be used as markers of relapse and are therapeutically targetable to prevent disease recurrence.

Dual-targeting triplebody 33-16-123 (SPM-2) mediates effective redirected lysis of primary blasts from patients with a broad range of AML subtypes in combination with natural killer cells

A number of agents designed for immunotherapy of Acute Myeloid Leukemia (AML) are in preclinical and early clinical development. Most of them target a single antigen on the surface of AML cells. Here we describe the development and key biological properties of a tri-specific agent, the dual-targeting triplebody SPM-2, with binding sites for target antigens CD33 and CD123, and for CD16 to engage NK cells as cytolytic effectors. Primary blasts of nearly all AML patients carry at least one of these target antigens and the pair is particularly promising for the elimination of blasts and leukemia stem cells (LSCs) from a majority of AML patients by dual-targeting agents. The cytolytic activity of NK cells mediated by SPM-2 was analyzed in vitro for primary leukemic cells from 29 patients with a broad range of AML-subtypes. Blasts from all 29 patients, including patients with genomic alterations associated with an unfavorable genetic subtype, were lysed at nanomolar concentrations of SPM-2. Maximum susceptibility was observed for cells with a combined density of CD33 and CD123 above 10,000 copies/cell. Cell populations enriched for AML-LSCs (CD34pos and CD34pos CD38neg cells) from 2 AML patients carried an increased combined antigen density and were lysed at correspondingly lower concentrations of SPM-2 than unsorted blasts. These initial findings raise the expectation that SPM-2 may also be capable of eliminating AML-LSCs and thus of prolonging survival. In the future, patients with a broad range of AML subtypes may benefit from treatment with SPM-2.

Murine models based on acute myeloid leukemia-initiating stem cells xenografting

Acute myeloid leukemia (AML) is an aggressive malignant disease defined by abnormal expansion of myeloid blasts. Despite recent advances in understanding AML pathogenesis and identifying their molecular subtypes based on somatic mutations, AML is still characterized by poor outcomes, with a 5-year survival rate of only 30%-40%, the majority of the patients dying due to AML relapse. Leukemia stem cells (LSC) are considered to be at the root of chemotherapeutic resistance and AML relapse. Although numerous studies have tried to better characterize LSCs in terms of surface and molecular markers, a specific marker of LSC has not been found, and still the most universally accepted phenotypic signature remains the surface antigens CD34+CD38- that is shared with normal hematopoietic stem cells. Animal models provides the means to investigate the factors responsible for leukemic transformation, the intrinsic differences between secondary post-myeloproliferative neoplasm AML and de novo AML, especially the signaling pathways involved in inflammation and hematopoiesis. However, AML proved to be one of the hematological malignancies that is difficult to engraft even in the most immunodeficient mice strains, and numerous ongoing attempts are focused to develop "humanized mice" that can support the engraftment of LSC. This present review is aiming to introduce the field of AML pathogenesis and the concept of LSC, to present the current knowledge on leukemic blasts surface markers and recent attempts to develop best AML animal models.

Pin1 inhibition exerts potent activity against acute myeloid leukemia through blocking multiple cancer-driving pathways

Background

The increasing genomic complexity of acute myeloid leukemia (AML), the most common form of acute leukemia, poses a major challenge to its therapy. To identify potent therapeutic targets with the ability to block multiple cancer-driving pathways is thus imperative. The unique peptidyl-prolyl cis-trans isomerase Pin1 has been reported to promote tumorigenesis through upregulation of numerous cancer-driving pathways. Although Pin1 is a key drug target for treating acute promyelocytic leukemia (APL) caused by a fusion oncogene, much less is known about the role of Pin1 in other heterogeneous leukemia.

Methods

The mRNA and protein levels of Pin1 were detected in samples from de novo leukemia patients and healthy controls using real-time quantitative RT-PCR (qRT-PCR) and western blot. The establishment of the lentiviral stable-expressed short hairpin RNA (shRNA) system and the tetracycline-inducible shRNA system for targeting Pin1 were used to analyze the biological function of Pin1 in AML cells. The expression of cancer-related Pin1 downstream oncoproteins in shPin1 (Pin1 knockdown) and Pin1 inhibitor all-trans retinoic acid (ATRA) treated leukemia cells were examined by western blot, followed by evaluating the effects of genetic and chemical inhibition of Pin1 in leukemia cells on transformed phenotype, including cell proliferation and colony formation ability, using trypan blue, cell counting assay, and colony formation assay in vitro, as well as the tumorigenesis ability using in vivo xenograft mouse models.

Results

First, we found that the expression of Pin1 mRNA and protein was significantly increased in both de novo leukemia clinical samples and multiple leukemia cell lines, compared with healthy controls. Furthermore, genetic or chemical inhibition of Pin1 in human multiple leukemia cell lines potently inhibited multiple Pin1 substrate oncoproteins and effectively suppressed leukemia cell proliferation and colony formation ability in cell culture models in vitro. Moreover, tetracycline-inducible Pin1 knockdown and slow-releasing ATRA potently inhibited tumorigenicity of U937 and HL-60 leukemia cells in xenograft mouse models.

Conclusions

We demonstrate that Pin1 is highly overexpressed in human AML and is a promising therapeutic target to block multiple cancer-driving pathways in AML.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0611-7) contains supplementary material, which is available to authorized users.

Transforming growth factor β1-mediated functional inhibition of mesenchymal stromal cells in myelodysplastic syndromes and acute myeloid leukemia

Mesenchymal stromal cells are involved in the pathogenesis of myelodysplastic syndromes and acute myeloid leukemia, but the underlying mechanisms are incompletely understood. To further characterize the pathological phenotype we performed RNA sequencing of mesenchymal stromal cells from patients with myelodysplastic syndromes and acute myeloid leukemia and found a specific molecular signature of genes commonly deregulated in these disorders. Pathway analysis showed a strong enrichment of genes related to osteogenesis, senescence, inflammation and inhibitory cytokines, thereby reflecting the structural and functional deficits of mesenchymal stromal cells in myelodysplastic syndromes and acute myeloid leukemia on a molecular level. Further analysis identified transforming growth factor β1 as the most probable extrinsic trigger factor for this altered gene expression. Following exposure to transforming growth factor β1, healthy mesenchymal stromal cells developed functional deficits and adopted a phenotype reminiscent of that observed in patient-derived stromal cells. These suppressive effects of transforming growth factor β1 on stromal cell functionality were abrogated by SD-208, an established inhibitor of transforming growth factor β receptor signaling. Blockade of transforming growth factor β signaling by SD-208 also restored the osteogenic differentiation capacity of patient-derived stromal cells, thus confirming the role of transforming growth factor β1 in the bone marrow microenvironment of patients with myelodysplastic syndromes and acute myeloid leukemia. Our findings establish transforming growth factor β1 as a relevant trigger causing functional inhibition of mesenchymal stromal cells in myelodysplastic syndromes and acute myeloid leukemia and identify SD-208 as a candidate to revert these effects.

Cell Density-Dependent Cytological Stage Profile and Its Application for a Screen of Cytostatic Agents Active Toward Leukemic Stem Cells

Proliferation and expansion of leukemia is driven by leukemic stem cells (LSCs). Multidrug resistance (MDR) of LSCs is one of the main reasons of failure and relapses in acute myeloid leukemia (AML) treatment. In this study, we show that maintaining HL-60 at low cell culture density or applying a 240-day treatment with anthrapyridazone (BS-121) increased the percentage of primitive cells, which include LSCs determining the overall stage profile. This change manifested in morphology, expression of both cell surface markers and redox-state proteins, as well as mitochondrial potential. Moreover, four sublines were generated, each with unique and characteristic stage profile and cytostatic sensitivity. Cell density-induced culture alterations (affecting stage profiles) were exploited in a screen of anthrapyridazones. Among the compound tested, C-123 was the most potent against primitive cell stages while generating relatively low amounts of reactive oxygen species (ROS). Furthermore, it had low toxicity in vivo and weakly affected blood morphology of healthy mice. The cell density-dependent stage profiles could be utilized in preliminary drug screens for activity against LSCs or in construction of patient-specific platforms to find drugs effective in case of AML relapse (drug extrapolation). The correlation between ROS generation in differentiated cells and toxic effect observed in HL-60 has a potential application in myelotoxicity predictions. The discovered properties of C-123 indicate its potential application in AML treatment, specifically in conditioned myeloablation preceding allogeneic transplantation and/or ex vivo treatment preceding autologous transplantation.

Decreased SCIN expression, associated with promoter methylation, is a valuable predictor for prognosis in acute myeloid leukemia

The present study was aimed to investigate SCIN expression as well as promoter methylation and further explore their clinical relevance in acute myeloid leukemia (AML) patients. Real-time quantitative PCR was carried out to detect the expression level of SCIN in 119 AML patients and 37 healthy controls. Real-time quantitative methylation-specific PCR and bisulfite sequencing PCR were carried out to detect SCIN promoter methylation levels in 103 AML patients and 29 controls. As compared with controls, the level of SCIN transcript was significantly down-regulated in AML patients (P = 0.001), and the level of methylated SCIN promoter was significantly higher in AML patients (P = 0.001). Moreover, the level of promoter methylation was weakly negatively correlated with SCIN expression in AML patients (R = -0.265, P = 0.027). Demethylation of SCIN promoter by 5-aza-2'-deoxycytidine could restore its expression in leukemic cell line THP1. The age of SCIN^low patients was significantly higher and C/EBPA mutation was significantly less than SCIN^high patients (P = 0.039 and 0.038, respectively). Moreover, the rate of complete remission (CR) of SCIN^low patients was significantly lower than SCIN^high patients (P = 0.009). Kaplan-Meier analysis showed that low SCIN expression was associated with shorter overall survival (P = 0.036). Cox regression analysis demonstrated low SCIN expression was an independent poor prognostic factor (P = 0.047). Furthermore, SCIN expression was restored in those patients who achieved CR after induction therapy (P = 0.003). These findings indicate that decreased SCIN expression associated with its promoter methylation is a valuable biomarker for predicting adverse prognosis in AML patients.

Targeting Leukemia Stem Cells in the Bone Marrow Niche

Abstract: The bone marrow (BM) niche encompasses multiple cells of mesenchymal and hematopoietic origin and represents a unique microenvironment that is poised to maintain hematopoietic stem cells. In addition to its role as a primary lymphoid organ through the support of lymphoid development, the BM hosts various mature lymphoid cell types, including naïve T cells, memory T cells and plasma cells, as well as mature myeloid elements such as monocyte/macrophages and neutrophils, all of which are crucially important to control leukemia initiation and progression. The BM niche provides an attractive milieu for tumor cell colonization given its ability to provide signals which accelerate tumor cell proliferation and facilitate tumor cell survival. Cancer stem cells (CSCs) share phenotypic and functional features with normal counterparts from the tissue of origin of the tumor and can self-renew, differentiate and initiate tumor formation. CSCs possess a distinct immunological profile compared with the bulk population of tumor cells and have evolved complex strategies to suppress immune responses through multiple mechanisms, including the release of soluble factors and the over-expression of molecules implicated in cancer immune evasion. This chapter discusses the latest advancements in understanding of the immunological BM niche and highlights current and future immunotherapeutic strategies to target leukemia CSCs and overcome therapeutic resistance in the clinic.

Single cell analysis of normal and leukemic hematopoiesis

The hematopoietic system is well established as a paradigm for the study of cellular hierarchies, their disruption in disease and therapeutic use in regenerative medicine. Traditional approaches to study hematopoiesis involve purification of cell populations based on a small number of surface markers. However, such population-based analysis obscures underlying heterogeneity contained within any phenotypically defined cell population. This heterogeneity can only be resolved through single cell analysis. Recent advances in single cell techniques allow analysis of the genome, transcriptome, epigenome and proteome in single cells at an unprecedented scale. The application of these new single cell methods to investigate the hematopoietic system has led to paradigm shifts in our understanding of cellular heterogeneity in hematopoiesis and how this is disrupted in disease. In this review, we summarize how single cell techniques have been applied to the analysis of hematopoietic stem/progenitor cells in normal and malignant hematopoiesis, with a particular focus on recent advances in single-cell genomics, including how these might be utilized for clinical application.

Targeting murine leukemic stem cells by antibody functionalized mesoporous silica nanoparticles

Acute leukemia is initiated and maintained by leukemia stem cells (LSCs) and therefore there is great interest to develop innovative therapeutic approaches which target LSCs. Here we show that mesoporous silica nanoparticles (MSNs) functionalized with succinic anhydride, tagged with an anti-B220 antibody and loaded with the anthracycline daunorubicin are efficiently incorporated into murine B220-positive AML LSCs and preferentially kill these cells in comparison to B220-negative AML LSCs in vitro. Furthermore, short – term treatment of the AML LSCs with these MSNs before transplant significantly delayed leukemia development in recipient mice. These data demonstrate that targeting of AML LSCs can be improved by using functionalized and antigen directed MSNs as carriers for anti-leukemic drugs.

Gemtuzumab ozogamicin for acute myeloid leukemia

On 1 September 2017, the US Food and Drug Administration (FDA) approved gemtuzumab ozogamicin (GO) for the treatment of adults with newly diagnosed CD33⁺ acute myeloid leukemia and for patients aged ≥2 years with CD33⁺ acute myeloid leukemia who have experienced a relapse or who have not responded to initial treatment. This signals a new chapter in the long and unusual story of GO, which was the first antibody-drug conjugate approved for human use by the FDA.

The potential of targeting Sin3B and its associated complexes for cancer therapy

INTRODUCTION

Sin3B serves as a scaffold for chromatin-modifying complexes that repress gene transcription to regulate distinct biological processes. Sin3B-containing complexes are critical for cell cycle withdrawal, and abrogation of Sin3B-dependent cell cycle exit impacts tumor progression. Areas covered: In this review, we discuss the biochemical characteristics of Sin3B-containing complexes and explore how these complexes regulate gene transcription. We focus on how Sin3B-containing complexes, through the association of the Rb family of proteins, repress the expression of E2F target genes during quiescence, differentiation, and senescence. Finally, we speculate on the potential benefits of the inhibition of Sin3B-containing complexes for the treatment of cancer. Expert opinion: Further identification and characterization of specific Sin3B-containing complexes provide a unique opportunity to prevent the pro-tumorigenic effects of the senescence-associated secretory phenotype, and to abrogate cancer stem cell quiescence and the associated resistance to therapy.

Emerging therapies for acute myeloid leukemia: translating biology into the clinic

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a poor outcome; overall survival is approximately 35% at two years and some subgroups have a less than 5% two-year survival. Recently, significant improvements have been made in our understanding of AML biology and genetics. These fundamental discoveries are now being translated into new therapies for this disease. This review will discuss recent advances in AML biology and the emerging treatments that are arising from biological studies. Specifically, we will consider new therapies that target molecular mutations in AML and dysregulated pathways such as apoptosis and mitochondrial metabolism. We will also discuss recent advances in immune and cellular therapy for AML.

The microenvironment in human myeloid malignancies: emerging concepts and therapeutic implications

Similar to their healthy counterpart, malignant hematopoietic stem cells in myeloid malignancies, such as myeloproliferative neoplasms, myelodysplastic syndromes, and acute myeloid leukemia, reside in a highly complex and dynamic cellular microenvironment in the bone marrow. This environment provides key regulatory signals for and tightly controls cardinal features of hematopoietic stem cells (HSCs), including self-renewal, quiescence, differentiation, and migration. These features are essential to maintaining cellular homeostasis and blood regeneration throughout life. A large number of studies have extensively addressed the composition of the bone marrow niche in mouse models, as well as the cellular and molecular communication modalities at play under both normal and pathogenic situations. Although instrumental to interrogating the complex composition of the HSC niche and dissecting the niche remodeling processes that appear to actively contribute to leukemogenesis, these models may not fully recapitulate the human system due to immunophenotypic, architectural, and functional inter-species variability. This review summarizes several aspects related to the human hematopoietic niche: (1) its anatomical structure, composition, and function in normal hematopoiesis; (2) its alteration and functional relevance in the context of chronic and acute myeloid malignancies; (3) age-related niche changes and their suspected impact on hematopoiesis; (4) ongoing efforts to develop new models to study niche-leukemic cell interaction in human myeloid malignancies; and finally, (5) how the knowledge gained into leukemic stem cell (LSC) niche dependencies might be exploited to devise novel therapeutic strategies that aim at disrupting essential niche-LSC interactions or improve the regenerative ability of the disease-associated hematopoietic niche.