Bone marrow niches in haematological malignancies

Recent advancement in the spatial immuno-oncology

Recent advancements in spatial transcriptomics and spatial proteomics enabled the high-throughput profiling of single or multi-cell types and cell states with spatial information. They transformed our understanding of the higher-order architectures and paired cell-cell interactions within a tumor microenvironment (TME). Within less than a decade, this rapidly emerging field has discovered much crucial fundamental knowledge and significantly improved clinical diagnosis in the field of immuno-oncology. This review summarizes the conceptual frameworks to understand spatial omics data and highlights the updated knowledge of spatial immuno-oncology.

The prognostic value of the platelet-to-lymphocyte ratio in multiple myeloma patients treated with a bortezomib-based regimen

Multiple myeloma (MM) is the second most common hematological malignancy. Previous studies have validated the prognostic significance of the platelet-to-lymphocyte ratio (PLR) in patients with certain solid tumors. However, the relationship between the PLR and prognosis in myeloma patients has not been clearly demonstrated. In our study, we included 122 newly diagnosed MM patients who were treated with bortezomib-based chemotherapy. These patients were divided into low-PLR and high-PLR groups based on their initial PLR values. We compared the clinical characteristics between the two groups and utilized restricted cubic splines (RCSs) in the regression model to estimate the nonlinear relationship between the initial PLR and overall survival (OS) in MM patients. The results showed that patients in the low-PLR group had significantly worse OS (P = 0.00031) and progression-free survival (PFS) (P < 0.0001) compared to those in the high-PLR group. Furthermore, within the higher-risk MM group, a low PLR was also associated with worse OS (P = 0.0037) and PFS (P = 0.0048). Therefore, a low PLR was identified as an independent predictor of poor OS in MM patients. The RCS curves further confirmed a significant nonlinear relationship between the PLR and OS in patients with MM. The PLR may serve as a significant independent prognostic indicator for MM patients undergoing bortezomib-based chemotherapy, and there exists a crucial nonlinear relationship between the PLR and OS in these patients.

In Vitro 3D Models of Haematological Malignancies: Current Trends and the Road Ahead?

Haematological malignancies comprise a diverse group of life-threatening systemic diseases, including leukaemia, lymphoma, and multiple myeloma. Currently available therapies, including chemotherapy, immunotherapy, and CAR-T cells, are often associated with important side effects and with the development of drug resistance and, consequently, disease relapse. In the last decades, it was largely demonstrated that the tumor microenvironment significantly affects cancer cell proliferation and tumor response to treatment. The development of biomimetic, in vitro models may promote the investigation of the interactions between cancer cells and the tumor microenvironment and may help to better understand the mechanisms leading to drug resistance. Although advanced in vitro models have been largely explored in the field of solid tumors, due to the complex nature of the blood cancer tumor microenvironment, the mimicking of haematological malignancies mostly relies on simpler systems, often limited to two-dimensional cell culture, which intrinsically excludes the microenvironmental niche, or to ethically debated animal models. This review aims at reporting an updated overview of state-of-the-art hematological malignancies 3D in vitro models, emphasizing the key features and limitations of existing systems to inspire further research in this underexplored field.

The role of the haematopoietic stem cell niche in development and ageing

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.

Detection and Characterization of Clonal Hematopoiesis

Clonal hematopoiesis (CH) is the age-related expansion of hematopoietic stem cell clones resulting from the acquisition of somatic point mutations or mosaic chromosomal alterations (mCAs). It is linked to adverse systemic effects, including hematologic malignancies, cardiovascular diseases, metabolic disorders, as well as liver and kidney ailments, ultimately contributing to elevated overall mortality.Given its diverse biological and clinical implications, the identification of clonal hematopoiesis holds significance in various contexts. While traditionally centered on mutations associated with myeloid malignancies, stem/progenitor cell involvement has been documented for various lymphoid malignancies, including T-cell lymphoma, chronic lymphocytic leukemia (CLL), and follicular lymphoma (FL). Lymphoid CH (L-CH) involves a broader spectrum of genes and occurs at a lower prevalence, resulting in reduced mutation prevalences per gene. This characteristic poses challenges for efficient CH detection.The major strategies to identify CH are whole exome sequencing (WES), whole genome sequencing (WGS), or targeted sequencing. Targeted sequencing allows for much higher sequencing depth compared to WES and WGS because of the focus on genes known to be associated with CH and therefore allows detecting potential variants at low frequencies with high precision. Here, we describe an error-corrected targeted sequencing approach for detection of CH in bone marrow (BM) or peripheral blood (PB) samples, which we have successfully established and used in various cohorts. This protocol includes the process of DNA isolation from PB and BM samples, library preparation with molecular tags including quality control steps and computational analysis including variant filtering.

Bone Marrow Endothelial Progenitor Cells remodelling facilitates normal hematopoiesis during Acute Myeloid Leukemia Complete Remission

Although acute myeloid leukemia (AML) affects hematopoietic stem cell (HSC)-supportive microenvironment, it is largely unknown whether leukemia-modified bone marrow (BM) microenvironment can be remodeled to support normal hematopoiesis after complete remission (CR). As a key element of BM microenvironment, endothelial progenitor cells (EPCs) provide a feasible way to investigate BM microenvironment remodeling. Here, we find reduced and dysfunctional BM EPCs in AML patients, characterized by impaired angiogenesis and high ROS levels, could be partially remodeled after CR and improved by N-acetyl-L-cysteine (NAC). Importantly, HSC-supporting ability of BM EPCs is partially recovered, whereas leukemia-supporting ability is decreased in CR patients. Mechanistically, the transcriptome characteristics of leukemia-modified BM EPCs return to near-normal after CR. In a classic AML mouse and chemotherapy model, BM vasculature and normal hematopoiesis are reversed after CR. In summary, we provide further insights into how leukemia-modified BM microenvironment can be remodeled to support normal hematopoiesis after CR, which can be further improved by NAC.

TIM-3 marks measurable residual leukemic stem cells responsible for relapse after allogeneic stem cell transplantation

In this study, we investigated the measurable residual leukemic stem cell (MR-LSC) population after allogeneic stem cell transplantation (allo-SCT) for high-risk acute myeloid leukemia (AML), utilizing T-cell immunoglobulin mucin-3 (TIM-3) expression as a functional marker of AML leukemic stem cells (LSCs). Analysis of the CD34+CD38- fraction of bone marrow cells immediately after achievement of engraftment revealed the presence of both TIM-3+LSCs and TIM-3- donor hematopoietic stem cells (HSCs) at varying ratios. Genetic analysis confirmed that TIM-3+ cells harbored patient-specific mutations identical to those found in AML clones, whereas TIM-3- cells did not, indicating that TIM-3+CD34+CD38- cells represent residual AML LSCs. In 92 allo-SCT occasions involving 83 AML patients, we enumerated the frequencies of TIM-3+LSCs immediately after achieving hematologic complete remission with complete donor cell chimerism. Notably, only 22.2% of patients who achieved a TIM-3+MR-LSClow status (<60%) experienced relapse, with a median event-free survival (EFS) of 1581 days (median follow-up duration was 2177 days among event-free survivors). Conversely, 87.5% of patients with TIM-3+MR-LSCint/high (≥60%) relapsed, with a median EFS of 140.5 days. Furthermore, MR-LSC status emerged as a significant independent risk factor for relapse (hazard ratio, 8.56; p < 0.0001), surpassing the impact of patient disease status prior to allo-SCT, including failure to achieve complete remission (hazard ratio, 1.98; p = 0.048). These findings suggest that evaluating TIM-3+ MR-LSCs immediately after engraftment, which reflects the competitive reconstitution of residual TIM-3+ LSCs and donor HSCs, may be valuable for predicting outcomes in AML patients undergoing allo-SCT.

Erythrocyte-Based Biomimetic MOFs as a Triple Epigenetic Regulator for Enhancing Anti-Leukemia Immunity

While therapeutic strategies targeting epigenetic dysregulation hold promise for leukemia, epigenetic drugs face several limitations, including low utilization rates, the emergence of resistance, and off-target effects. The hypoxic microenvironment in leukemia further impairs drug sensitivity. Here, we synthesized an MOF-based erythrocyte biomimetic nanoplatform to enhance immune responses against leukemia by targeting three epigenetic modifications. UiO-66-NH2 was loaded with two epigenetic drugs, along with oxygen-rich erythrocytes (red blood cells, RBCs). MA272@MOF@RBC suppressed hypoxia-induced factor (HIF-1α) and its downstream oncogenes, thereby enhancing the efficacy of the epigenetic drugs. The drugs inhibited the growth of leukemia cells by targeting DNA and histone methylation while enhancing m6A-RNA methylation. MA272@MOF@RBC activated cytotoxic and memory T cells by increasing the antigenicity of leukemia cells. MA272@MOF@RBC also demonstrated immunotherapeutic effects on solid tumors. This was the first study to report the synthesis of triple epigenetic regulatory biomimetic MOFs with significant clinical potential for tumor immunotherapy.

Pharmacokinetic Positron Emission Tomography Imaging of an Optimized CD38-Targeted 68Ga-Labeled Peptide in Multiple Myeloma: A Pilot Study

Multiple myeloma (MM) is an incurable disease characterized by its clinical and prognostic heterogeneity. Despite conventional chemotherapy and autologous hematopoietic stem cell transplantation, the management of relapsed and refractory MM disease poses significant challenges, both medically and socioeconomically. CD38, highly expressed on the surface of MM cells, serves as a distinct tumor biological target in MM. Peptides offer advantages over antibodies, enabling precise tumor imaging and facilitating early tumor diagnosis and dynamic immunotherapy monitoring. In this study, we developed PF381, a CD38-targeted peptide, and investigated its role in diagnosis, biodistribution, and dosimetry through 68Ga-labeling for preclinical evaluation in tumor-bearing models. We screened a microchip-based combinatorial chemistry peptide library to obtain the amino acid sequence of PF381. Affinity for human CD38 was evaluated by SPRi. PF381 was conjugated with DOTA for radiolabeling with 68Ga, and the complex was characterized by HPLC. PET imaging was performed in murine tumor models after the administration of [68Ga]Ga-DOTA-PF381. Biodistribution analysis compared CD38-positive H929 and CD38-negative U266 tumors, and human radiation dosimetry was estimated. Tumor sections were stained for CD38 expression. SPRi showed that PF381 had a high affinity for CD38 with a KD of 2.49 × 10-8 M. HPLC measured a radiolabeling efficiency of 78.45 ± 7.91% for [68Ga]Ga-DOTA-PF381, with >98% radiochemical purity. PET imaging revealed rapid and persistent accumulation of radioactivity in CD38-positive H929 tumors, contrasting with negligible uptake in CD38-negative U266 tumors. Biodistribution confirmed higher uptake in H929 tumors (0.75 ± 0.03%ID/g) vs U266 (0.26 ± 0.08%ID/g, P < 0.001). The kidney received the highest radiation dose (3.57 × 10-02 mSv/MBq), with an effective dose of 1.41 × 10-02 mSv/MBq. Immunofluorescence imaging supported PET and biodistribution findings. We developed a novel peptide targeting CD38 and proved that 68Ga-labeled PF381 had rapid targeting and good tumor penetration capabilities. Therefore, 68Ga-labeled PF381 could achieve high sensitivity in vivo imaging for CD38-positive hematological malignancies.

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.

Adult skull bone marrow is an expanding and resilient haematopoietic reservoir

The bone marrow microenvironment is a critical regulator of haematopoietic stem cell self-renewal and fate1. Although it is appreciated that ageing, chronic inflammation and other insults compromise bone marrow function and thereby negatively affect haematopoiesis2, it is not known whether different bone compartments exhibit distinct microenvironmental properties and functional resilience. Here we use imaging, pharmacological approaches and mouse genetics to uncover specialized properties of bone marrow in adult and ageing skull. Specifically, we show that the skull bone marrow undergoes lifelong expansion involving vascular growth, which results in an increasing contribution to total haematopoietic output. Furthermore, skull is largely protected against major hallmarks of ageing, including upregulation of pro-inflammatory cytokines, adipogenesis and loss of vascular integrity. Conspicuous rapid and dynamic changes to the skull vasculature and bone marrow are induced by physiological alterations, namely pregnancy, but also pathological challenges, such as stroke and experimental chronic myeloid leukaemia. These responses are highly distinct from femur, the most extensively studied bone marrow compartment. We propose that skull harbours a protected and dynamically expanding bone marrow microenvironment, which is relevant for experimental studies and, potentially, for clinical treatments in humans.

Molecular and cellular mechanisms of chemoresistance in paediatric pre-B cell acute lymphoblastic leukaemia

Paediatric patients with relapsed B cell acute lymphoblastic leukaemia (B-ALL) have poor prognosis, as relapse-causing clones are often refractory to common chemotherapeutics. While the molecular mechanisms leading to chemoresistance are varied, significant evidence suggests interactions between B-ALL blasts and cells within the bone marrow microenvironment modulate chemotherapy sensitivity. Importantly, bone marrow mesenchymal stem cells (BM-MSCs) and BM adipocytes are known to support B-ALL cells through multiple distinct molecular mechanisms. This review discusses the contribution of integrin-mediated B-ALL/BM-MSC signalling and asparagine supplementation in B-ALL chemoresistance. In addition, the role of adipocytes in sequestering anthracyclines and generating a BM niche favourable for B-ALL survival is explored. Furthermore, this review discusses the role of BM-MSCs and adipocytes in promoting a quiescent and chemoresistant B-ALL phenotype. Novel treatments which target these mechanisms are discussed herein, and are needed to improve dismal outcomes in patients with relapsed/refractory disease.

ID1 and ID3 functions in the modulation of the tumour immune microenvironment in adult patients with B-cell acute lymphoblastic leukaemia

Introduction

B-cell acute lymphoblastic leukemia (B-ALL) in adults often presents a poor prognosis. ID1 and ID3 genes have been identified as predictors of poor response in Colombian adult B-ALL patients, contributing to cancer development. In various cancer models, these genes have been associated with immune regulatory populations within the tumor immune microenvironment (TIME). B-ALL progression alters immune cell composition and the bone marrow (BM) microenvironment, impacting disease progression and therapy response. This study investigates the relationship between ID1 and ID3 expression, TIME dynamics, and immune evasion mechanisms in adult B-ALL patients.

Methods

This exploratory study analysed BM samples from 10 B-ALL adult patients diagnosed at the National Cancer Institute of Colombia. First, RT-qPCR was used to assess ID1 and ID3 expression in BM tumour cells. Flow cytometry characterised immune populations in the TIME. RNA-seq evaluated immune genes associatedwith B-ALL immune response, while xCell and CytoSig analysed TIME cell profiles and cytokines. Pathway analysis, gene ontology, and differential gene expression (DEGs) were examined, with functional enrichment analysis performed using KEGG ontology.

Results

Patients were divided into two groups based on ID1 and ID3 expression, namely basal and overexpression. A total of 94 differentially expressed genes were identified between these groups, with top overexpressed genes associated with neutrophil pathways. Gene set enrichment analysis revealed increased expression of genes associated with neutrophil degranulation, immune response-related neutrophil activation, and neutrophil-mediated immunity. These findings correlated with xCell data. Overexpression group showed significant differences in neutrophils, monocytes and CD4+ naive T cells compared to basal group patients. Microenvironment and immune scores were also significantly different, consistent with the flow cytometry results. Elevated cytokine levels associated with neutrophil activation supported these findings. Validation was performed using the Therapeutically Applicable Research to Generate Effective Treatments (TARGET) TCGA B-ALL cohorts.

Discussion

These findings highlight significant differences in ID1 and ID3 expression levels and their impact on TIME populations, particularly neutrophil-related pathways. The results suggest a potential role for ID1 and ID3 in immune evasion in adult B-ALL, mediated through neutrophil activation and immune regulation.

Inhibition of TGF-β signaling in bone marrow endothelial cells promotes hematopoietic recovery in acute myeloid leukemia patients

Although it is an effective treatment for acute myeloid leukemia (AML), chemotherapy leads to myelosuppression and poor hematopoietic reconstruction. Hematopoiesis is regulated by bone marrow (BM) endothelial cells (ECs), and BM ECs are dysfunctional in acute leukemia patients with poor hematopoietic reconstitution after allogenic hematopoietic stem cell transplantation. Thus, it is crucial to explore the underlying mechanism of EC impairment and establish strategies for targeted therapy. TGF-β signaling was found to be upregulated in ECs from AML patients in complete remission (CR ECs) and led to CR EC damage. Administration of a TGF-β inhibitor rescued the dysfunction of ECs caused by TGF-β1 expression in vitro, especially their hematopoiesis-supporting ability. Moreover, inhibition of TGF-β expression repaired the BM EC damage triggered by chemotherapy in both AML patients in vitro and in an AML-CR murine model, and restored normal hematopoiesis without promoting AML progression. Mechanistically, our data reveal alterations in the transcriptomic pattern of damaged BM ECs, accompanied by the overexpression of downstream molecules TGF-βR1, pSmad2/3, and functional genes related to adhesion, angiogenesis suppression and pro-apoptosis. Collectively, our findings reveal for the first time that the activation of TGF-β signaling leads to BM EC dysfunction and poor hematopoietic reconstitution. Targeting TGF-β represents a potential therapeutic strategy to promote multilineage hematopoiesis, thereby benefiting more cancer patients who suffer from myelosuppression after chemotherapy.

Exploitation of the fibrinolytic system by B-cell acute lymphoblastic leukemia and its therapeutic targeting

Fibrinolysis influences the mobilization of hematopoietic stem cells from their bone marrow microenvironment (BMM). Here we show that activation of plasmin, a key fibrinolytic agent, by annexin A2 (ANXA2) distinctly impacts progression of BCR-ABL1+ B-cell acute lymphoblastic leukemia (B-ALL) via modulation of the extracellular matrix (ECM) in the BMM. The dense ECM in a BMM with decreased plasmin activity entraps insulin-like growth factor (IGF) 1 and reduces mTORC2-dependent signaling and proliferation of B-ALL cells. Conversely, B-ALL conditions the BMM to induce hepatic generation of plasminogen, the plasmin precursor. Treatment with ε-aminocaproic acid (EACA), which inhibits plasmin activation, reduces tumor burden and prolongs survival, including in xenogeneic models via increased fibronectin in the BMM. Human data confirm that IGF1 and fibronectin staining in trephine biopsies are correlated. Our studies suggest that fibrinolysis-mediated ECM remodeling and subsequent growth factor release influence B-ALL progression and inhibition of this process by EACA may be beneficial as adjunct therapy.

Co-delivery of protopanaxatriol/icariin into niche cells restores bone marrow niches to rejuvenate HSCs for chemotherapy-induced myelosuppression

BACKGROUND

Up to 80 % of chemotherapeutic drugs induce myelosuppression in patients. Chemotherapy not only impairs of hematopoietic stem cells (HSCs) but also damages bone marrow niches (vascular and endosteal). Current treatments for myelosuppression overlook these chemotherapy-induced damages to bone marrow niches and the critical role of niche restoration on hematopoietic regeneration. Ginsenoside protopanaxatriol (PPT) protects vascular endothelium from injury, while icariin (ICA) promotes osteogenic differentiation. The combination of PPT and ICA aims to restore damaged vascular and endosteal niches, thus rejuvenating HSCs for treating myelosuppression.

PURPOSE

This study aims to develop effective, bone marrow niche-directed PPT/ICA therapies for treating chemotherapy-induced myelosuppression.

METHODS

3D cell spheroids were used to investigate the effects of PPT/ICA on cell-cell interactions in vascular niches, osteogenesis, and extracellular matrix (ECM) secretion in endosteal niches. In vitro mimic niche models were designed to access the drug combination's efficacy in rejuvenating and mobilizing in HSCs within bone marrow niches. The delivery capability of PPT/ICA to key niche cell types (mesenchymal stromal cells (MSCs), endothelial cells (ECs), and osteoblasts (OBs)) via nanocarriers has been determined. DSS6 peptide-modified nanoparticles (DSS6-NPs) were prepared for specific co-delivery of PPT/ICA into key niche cell populations in vivo.

RESULTS

PPT can prevent vascular niche injury by restoring vascular EC cell-cell adhesion and the intercellular interactions between ECs and MSCs in 5-fluorouracil (5-FU)-damaged cell spheroids. ICA repaired 5-FU-damaged endosteal niches by promoting osteogenesis and ECM secretion. The combination of PPT and ICA restores key HSC niche factor gene expressions, normalizing HSC differentiation and mobilization. The in vitro cellular uptake efficiency of nanocarriers in a mimic niche is positively correlated with their in vivo delivery into bone marrow niche cells. DSS6-NPs greatly enhance the delivery of PPT/ICA into MSCs and OBs within bone marrow niches. Co-loading of PPT/ICA into DSS6-NPs effectively repairs damaged bone marrow niches and promotes HSC rejuvenation in vivo.

CONCLUSION

The combination of PPT and ICA effectively prevents injury to the vascular and endosteal niches, thereby promoting hematopoietic regeneration in the bone marrow. This study provides novel niche-directed PPT/ICA therapies for managing chemotherapy-induced myelosuppression.

RNA-loaded nanoparticles for the treatment of hematological cancers

Hematological cancers encompass a diverse group of malignancies affecting the blood, bone marrow, lymph nodes, and spleen. These disorders present unique challenges due to their complex etiology and varied clinical manifestations. Despite significant advancements in understanding and treating hematological malignancies, innovative therapeutic approaches are continually sought to enhance patient outcomes. This review highlights the application of RNA nanoparticles (RNA-NPs) in the treatment of hematological cancers. We delve into detailed discussions on in vitro and preclinical studies involving RNA-NPs for adult patients, as well as the application of RNA-NPs in pediatric hematological cancer. The review also addresses ongoing clinical trials involving RNA-NPs and explores the emerging field of CAR-T therapy engineered by RNA-NPs. Finally, we discuss the challenges still faced in translating RNA-NP research to clinics.

A View of Myeloid Transformation through the Hallmarks of Cancer

The development of myeloid malignancies is influenced by a range of cell-intrinsic and cell-extrinsic factors, which can be conceptualized using the hallmarks of cancer. Although many facets of myeloid transformation are similar to those in solid tumors, there are also notable differences. Unlike solid tumors, hematologic malignancies typically exhibit fewer genetic mutations, which have been well characterized. However, understanding the cell-extrinsic factors contributing to myeloid malignancies can be challenging due to the complex interactions in the hematopoietic microenvironment. Researchers need to focus on these intricate factors to prevent the early onset of myeloid transformation and develop appropriate interventions. Significance: Myeloid malignancies are common in the elderly, and acute myeloid leukemia has an adverse prognosis in older patients. Investigating cell-extrinsic factors influencing myeloid malignancies is crucial to developing approaches for preventing or halting disease progression and predicting clinical outcomes in patients with advanced disease. Whereas successful intervention may require targeting various mechanisms, understanding the contribution of each cell-extrinsic factor will help prioritize clinical targets.

Etiological Spectrum of Bone Marrow Biopsy in Patients With Pancytopenia

Background Pancytopenia is defined as a decrease in all three hematologic cell lines. The condition is not a disease in itself but a common pathway caused by various etiologies that can be infectious, autoimmune, genetic, nutritional, and/or malignant. Determining the cause of pancytopenia is a challenge and is key in determining the proper treatment regimen and estimating prognosis. Objective The aim of this study was to evaluate the etiological spectrum of pancytopenia in patients who underwent bone marrow biopsy at a tertiary care hospital. Methodology This study was conducted at the Internal Medicine and Gastroenterology Departments of Lady Reading Hospital, Peshawar, Pakistan, from January 1, 2023, to December 31, 2023. A total of 120 patients with pancytopenia aged 12 to 60 years who underwent bone marrow biopsy were enrolled. Data on age, gender, clinical presentations, and bone marrow biopsy findings were observed. Results The mean age was 34.97 years. Males were more frequently affected, 74 (61.7%), than females, 46 (38.3%). Pallor, 86 (71.7%), and weakness, 66 (55.0%), were the most frequent presentations of pancytopenia. The etiological spectrum showed that megaloblastic anemia was present in 48 (40%) of the cases, followed by infection-related changes in 20 (16.7%) and aplastic anemia in 20 (16.7%). Conclusion Megaloblastic anemia emerged as the leading cause of pancytopenia in our study, followed by aplastic anemia and infection-related changes.

Met-Flow analyses of the metabolic heterogeneity associated with different stages of cord blood-derived hematopoietic cell differentiation

Background

The differentiation of hematopoietic cells is significantly affected by cell metabolic activity. However, despite increasing interest in this field, there has been no comprehensive investigation of the metabolic functions of human hematopoietic cells during specific phases of differentiation. Thus, this study was conducted to develop a method for comparing hematopoietic cell lineage differentiation based on the metabolic functions of the cell. The metabolic activity of human umbilical cord-derived hematopoietic cells was examined during various phases of differentiation, specifically, hematopoietic stem cells (HSCs), hematopoietic progenitor cells, and differentiated blood cells. This approach was used to develop comprehensive metabolic maps corresponding to the different stages.

Results

HSCs were found to have robust fatty acid (FA) synthesis, FA oxidation, pentose phosphate pathway (PPP) activity, and glucose uptake, shown by their significantly higher expression of ACAC, CPT1A, G6PD, and GLUT1 as compared to differentiated pluripotent progenitor cells, common myeloid progenitors, megakaryocyte erythroid progenitors, lympho-myeloid primed progenitors, and granulocyte-macrophage progenitor cell populations. In monocytic differentiation, higher levels of ACAC, ASS1, ATP5A, CPT1A, G6PD, GLUT1, IDH2, PRDX2, and HK1 protein expression were evident in classical and intermediate monocytes relative to non-classical monocytes, consistent with high anabolic and catabolic levels. Compared with myelocytes and mature cells, the meta-myelocyte and pro-myelocyte populations of granulocytes show significantly elevated levels of ACAC, ASS1, ATP5A, CPT1A, G6PD, IDH2, PRDX2, and HK. In contrast to naïve and regulatory B cells, pro-B cells had higher levels of oxidative phosphorylation, while regulatory B cells showed greater PPP activity, glucose uptake, and tricarboxylic acid cycle activity. The analyses of T cells also indicated significantly higher ACAC, ASS1, ATP5A, CPT1A, G6PD, GLUT1, IDH2, PRDX2, and HK1 expression levels in CD4+ populations compared with CD8+ populations.

Conclusions

The results provide comprehensive analytical methods and reference values for future systematic studies into the metabolic functions of various cord blood-derived hematopoietic cell populations in different pathological or physiological conditions. These findings could also contribute to research on the connection between cellular metabolism and cancer or aging.

Construction and validation of a prognostic model of angiogenesis-related genes in multiple myeloma

BACKGROUND

Angiogenesis is associated with tumour growth, infiltration, and metastasis. This study aimed to detect the mechanisms of angiogenesis-related genes (ARGs) in multiple myeloma (MM) and to construct a new prognostic model.

METHODS

MM research foundation (MMRF)-CoMMpass cohort, GSE47552, GSE57317, and ARGs were sourced from public databases. Differentially expressed genes (DEGs) in the tumour and control cohorts in GSE47552 were determined through differential expression analysis and were enriched with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Weighted gene coexpression network analysis (WGCNA) was applied to derive modules linked to the ARG scores and obtain module genes in GSE47552. Differentially expressed ARGs (DE-ARGs) were selected for subsequent analyses by overlapping DEGs and module genes. Furthermore, prognostic genes were selected using univariate Cox and least absolute shrinkage and selection operator (LASSO) regression analyses. Depending on the prognostic genes, a risk model was constructed, and risk scores were determined. Moreover, MM samples from MMRF-CoMMpass were sorted into high- and low-risk teams on account of the median risk score. Additionally, correlations among clinical characteristics, gene set variation analysis (GSVA), gene set enrichment analysis (GSEA), immune analysis, immunotherapy predictions and the mRNA‒miRNA‒lncRNA network were carried out.

RESULTS

A total of 898 DEGs, 211 module genes, 24 DE-ARGs and three prognostic genes (AKAP12, C11orf80 and EMP1) were selected for this study. Enrichment analysis revealed that the DEGs were related to 86 GO terms, such as 'cytoplasmic translation', and 41 KEGG pathways, such as 'small cell lung cancer'. A prognostic gene-based risk model was created in MMRF-CoMMpass and confirmed with the GSE57317 dataset. Moreover, a nomogram was established on the basis of independent prognostic factors that have proven to be good predictors. In addition, the immune cell infiltration results suggested that memory B cells were enriched in the high-risk group and that immature B cells were enriched in the low-risk group. Finally, the mRNA‒miRNA‒lncRNA network demonstrated that hsa-miR-508-5p was tightly associated with EMP1 and AKAP12. RT‒qPCR was used to validate the expression of the genes associated with prognosis.

CONCLUSION

A new prognostic model of MM associated with ARGs was created and validated, providing a new perspective for exploring the connection between ARGs and MM.

Differential inflammatory conditioning of the bone marrow by acute myeloid leukemia and its impact on progression

ABSTRACT

Inflammation promotes solid tumor progression, but how regulatory mechanisms of inflammation may affect leukemia is less well studied. Using annexin A5 (ANXA5), a calcium-binding protein known for apoptosis, which we discovered to be differentially expressed in the bone marrow microenvironment (BMM) of mice with acute myeloid (AML) vs chronic myeloid leukemia, as a model system, we unravel here a circuit in which AML-derived tumor necrosis factor α (TNF-α) dose-dependently reduces ANXA5 in the BMM. This creates an inflammatory BMM via elevated levels of prostaglandin E2 (PGE2). Via binding to its EP4 receptor, PGE2 increases β-catenin and hypoxia-inducible factor 1α signaling in AML cells, thereby accelerating PGE2-sensitive AML. Human trephine biopsies may show lower ANXA5 expression and higher PGE2 expression in AML than other hematologic malignancies. Furthermore, syngeneic and xenogeneic transplantation models suggest a survival benefit after treatment with the inhibitor of prostaglandin-endoperoxide synthase 2 (cyclooxygenase 2 [COX2]), celecoxib, plus cytarabine in those AML types highly sensitive to PGE2 compared with cytarabine alone. Taken together, TNF-α/ANXA5/NF-κB/COX2/PGE2-mediated inflammation influences AML course in a highly differential and circular manner, and patients with AML with "inflammatory AML" may benefit from antiphlogistic agents as adjunct therapy.

The evolving hematopoietic niche during development

Mammalian hematopoietic stem cells (HSCs) emerge from the hemogenic endothelium in the major embryonic arteries. HSCs undergo a complex journey first migrating to the fetal liver (FL) and from there to the fetal bone marrow (FBM), where they mostly remain during adult life. In this process, a pool of adult HSCs is produced, which sustains lifelong hematopoiesis. Multiple cellular components support HSC maturation and expansion and modulate their response to environmental and developmental cues. While the adult HSC niche has been extensively studied over the last two decades, the niches present in the major embryonic arteries, FL, FBM and perinatal bone marrow (BM) are poorly described. Recent investigations highlight important differences among FL, FBM and adult BM niches and emphasize the important role that inflammation, microbiota and hormonal factors play regulating HSCs and their niches. We provide a review on our current understanding of these important cellular microenvironments across ontogeny. We mainly focused on mice, as the most widely used research model, and, when possible, include relevant insights from other vertebrates including birds, zebrafish, and human. Developing a comprehensive picture on these processes is critical to understand the earliest origins of childhood leukemia and to achieve multiple goals in regenerative medicine, such as mimicking HSC development in vitro to produce HSCs for broad transplantation purposes in leukemia, following chemotherapy, bone marrow failure, and in HSC-based gene therapy.

Applications of 18F-Fluorodesoxyglucose PET Imaging in Leukemia

The main finding that 18F-FDG PET imaging can reveal in patients with leukemias is the presence of bone marrow (BM) infiltration in both acute or chronic forms. This ability can influence and guide the use of BM biopsy but also assess to therapy response. Additionally 18F-FDG PET imaging has been reported as particularly useful for the diagnosis of leukemias in patients with non specific symptoms. In the case of acute leukemias it revealed also a role for the evaluation of extramedullary forms while in the case of chronic forms a role for the assessment of Richter transformation has been reported.

27-Hydroxycholesterol Negatively Affects the Function of Bone Marrow Endothelial Cells in the Bone Marrow

Hematopoietic stem cells (HSCs) reside in specific microenvironments that facilitate their regulation through both internal mechanisms and external cues. Bone marrow endothelial cells (BMECs), which are found in one of these microenvironments, play a vital role in controlling the self-renewal and differentiation of HSCs during hematological stress. We previously showed that 27-hydroxycholesterol (27HC) administration of exogenous 27HC negatively affected the population of HSCs and progenitor cells by increasing the reactive oxygen species levels in the bone marrow. However, the effect of 27HC on BMECs is unclear. To determine the function of 27HC in BMECs, we employed magnetic-activated cell sorting to isolate CD31+ BMECs and CD31- cells. We demonstrated the effect of 27HC on CD31+ BMECs and HSCs. Treatment with exogenous 27HC led to a decrease in the number of BMECs and reduced the expression of adhesion molecules that are crucial for maintaining HSCs. Our results demonstrate that BMECs are sensitively affected by 27HC and are crucial for HSC survival.

Protocol for in vitro co-culture, proliferation, and cell cycle analyses of patient-derived leukemia cells

Leukemia niche impacts quiescence; however, culturing patient-derived samples ex vivo is technically challenging. Here, we present a protocol for in vitro co-culture of patient-derived xenograft acute lymphoblastic leukemia (PDX-ALL) cells with human mesenchymal stem cells (MSCs). We describe steps for labeling PDX-ALL cells with CellTrace Violet dye to demonstrate MSC-primed PDX-ALL cycling. We then detail procedures to identify MSC-primed G0/quiescent PDX-ALL cells via Hoechst-33342/Pyronin Y live cell cycle analysis. For complete details on the use and execution of this protocol, please refer to Pal et al.1,2.

CCL17, CCL22 and their receptor CCR4 in hematologic malignancies

Hematological malignancies (HM) are common malignant tumors with high morbidity and mortality rates, and are malignant diseases that seriously affect human health, with chemotherapy prone to recurrence and toxic side effects. Therefore, the development of precise, effective, and safe targeted therapeutic agents has become a hotspot in the current research of antitumor technology. More and more studies have shown that the interaction of C-C chemokine ligand 17 (CCL17) and C-C chemokine ligand 22 (CCL22) with the receptor C-C chemokine receptor type 4 (CCR4) promotes the immune escape of tumors and is closely related to the occurrence, development, and prognosis of hematological tumors. In this regard, we present a review on the expression and role of the CCL17/CCL22-CCR4 axis in HM, including lymphoma, leukemia, and multiple myeloma, with the aim of providing latest ideas and directions for the diagnosis and treatment of HM. In addition, we discuss the role and related mechanisms of HM therapeutic agents targeting the CCL17/CCL22-CCR4 axis and the potential of humanized anti-CCR4 antibodies for the treatment of HM.

miR-4716-3p and the target AKT2 Gene/rs2304186 SNP are associated with blood cancer pathogenesis in Pakistani population

AKT2 is crucial for cancer cells' invasion, metastasis, and survival. It is a possible downstream gene target of cancer glycolysis-related microRNAs. The study investigated the role of miRNA-4716-3p, rs2304186, and the AKT2 gene in blood cancer pathogenesis. RT-qPCR was used to analyze AKT2 gene mRNA and miRNA-4716-3p expression in 200 blood cancer samples and 200 healthy controls. Furthermore, Tetra-ARMS PCR was used to examine the rs2304186 AKT2 SNP in 300 patients and 290 control samples. miRNA-4716-3p was shown to be significantly downregulated (p = 0.0294), whereas mRNA expression of the AKT2 gene was found to be significantly upregulated (p = 0.0034) in blood cancer patients compared to healthy individuals. miRNA-4716-3p downregulation (p = 0.0466) was more pronounced, while AKT2 upregulation was non-significant (p = 0.1661) in untreated patients compared to chemotherapy-treated patients. Blood cancer risk was significantly associated with the rs2304186 GT genotype (p = 0.0432), TT genotype (p = 0.0502), and mutant allele (T) frequency (p = 0.0008). Polymorphism rs2304186 was associated with an increased risk of blood cancer in dominant (p = 0.0011), recessive (p = 0.0502), and additive (p = 0.0008) genetic models. The results suggested that the rs2304186 and the deregulated expression of miRNA-4716-3p and AKT2 gene at the mRNA level may significantly increase the incidence of blood cancer, particularly in the Pakistani population. Therefore, these may function as suitable biomarkers for blood cancer diagnosis and prognosis. Additional, larger-scale investigations may be required to affirm these results.

In vivo monitoring of leukemia-niche interactions in a zebrafish xenograft model

Acute lymphoblastic leukemia (ALL) is the most common type of malignancy in children. ALL prognosis after initial diagnosis is generally good; however, patients suffering from relapse have a poor outcome. The tumor microenvironment is recognized as an important contributor to relapse, yet the cell-cell interactions involved are complex and difficult to study in traditional experimental models. In the present study, we established an innovative larval zebrafish xenotransplantation model, that allows the analysis of leukemic cells (LCs) within an orthotopic niche using time-lapse microscopic and flow cytometric approaches. LCs homed, engrafted and proliferated within the hematopoietic niche at the time of transplant, the caudal hematopoietic tissue (CHT). A specific dissemination pattern of LCs within the CHT was recorded, as they extravasated over time and formed clusters close to the dorsal aorta. Interactions of LCs with macrophages and endothelial cells could be quantitatively characterized. This zebrafish model will allow the quantitative analysis of LCs in a functional and complex microenvironment, to study mechanisms of niche mediated leukemogenesis, leukemia maintenance and relapse development.

Bone marrow niches for hematopoietic stem cells

Hematopoietic stem cells (HSCs) are the cornerstone of the hematopoietic system. HSCs sustain the continuous generation of mature blood derivatives while self-renewing to preserve a relatively constant pool of progenitors throughout life. Yet, long-term maintenance of functional HSCs exclusively takes place in association with their native tissue microenvironment of the bone marrow (BM). HSCs have been long proposed to reside in fixed and identifiable anatomical units found in the complex BM tissue landscape, which control their identity and fate in a deterministic manner. In the last decades, tremendous progress has been made in the dissection of the cellular and molecular fabric of the BM, the structural organization governing tissue function, and the plethora of interactions established by HSCs. Nonetheless, a holistic model of the mechanisms controlling HSC regulation in their niche is lacking to date. Here, we provide an overview of our current understanding of BM anatomy, HSC localization, and crosstalk within local cellular neighborhoods in murine and human tissues, and highlight fundamental open questions on how HSCs functionally integrate in the BM microenvironment.

Plasma Proteomic Signature Predicts Myeloid Neoplasm Risk

PURPOSE

Clonal hematopoiesis (CH) is thought to be the origin of myeloid neoplasms (MN). Yet, our understanding of the mechanisms driving CH progression to MN and clinical risk prediction of MN remains limited. The human proteome reflects complex interactions between genetic and epigenetic regulation of biological systems. We hypothesized that the plasma proteome might predict MN risk and inform our understanding of the mechanisms promoting MN development.

EXPERIMENTAL DESIGN

We jointly characterized CH and plasma proteomic profiles of 46,237 individuals in the UK Biobank at baseline study entry. During 500,036 person-years of follow-up, 115 individuals developed MN. Cox proportional hazard regression was used to test for an association between plasma protein levels and MN risk.

RESULTS

We identified 115 proteins associated with MN risk, of which 30% (N = 34) were also associated with CH. These were enriched for known regulators of the innate and adaptive immune system. Plasma proteomics improved the prediction of MN risk (AUC = 0.85; P = 5×10-9) beyond clinical factors and CH (AUC = 0.80). In an independent group (N = 381,485), we used inherited polygenic risk scores (PRS) for plasma protein levels to validate the relevance of these proteins toMNdevelopment. PRS analyses suggest that most MN-associated proteins we identified are not directly causally linked toMN risk, but rather represent downstream markers of pathways regulating the progression of CH to MN.

CONCLUSIONS

These data highlight the role of immune cell regulation in the progression of CH to MN and the promise of leveraging multi-omic characterization of CH to improveMN risk stratification. See related commentary by Bhalgat and Taylor, p. 3095.

MiR-223-3p in Cancer Development and Cancer Drug Resistance: Same Coin, Different Faces

MicroRNAs (miRNAs) are mighty post-transcriptional regulators in cell physiology and pathophysiology. In this review, we focus on the role of miR-223-3p (henceforth miR-223) in various cancer types. MiR-223 has established roles in hematopoiesis, inflammation, and most cancers, where it can act as either an oncogenic or oncosuppressive miRNA, depending on specific molecular landscapes. MiR-223 has also been linked to either the sensitivity or resistance of cancer cells to treatments in a context-dependent way. Through this detailed review, we highlight that for some cancers (i.e., breast, non-small cell lung carcinoma, and glioblastoma), the oncosuppressive role of miR-223 is consistently reported in the literature, while for others (i.e., colorectal, ovarian, and pancreatic cancers, and acute lymphocytic leukemia), an oncogenic role prevails. In prostate cancer and other hematological malignancies, although an oncosuppressive role is frequently described, there is less of a consensus. Intriguingly, NLRP3 and FBXW7 are consistently identified as miR-223 targets when the miRNA acts as an oncosuppressor or an oncogene, respectively, in different cancers. Our review also describes that miR-223 was increased in biological fluids or their extracellular vesicles in most of the cancers analyzed, as compared to healthy or lower-risk conditions, confirming the potential application of this miRNA as a diagnostic and prognostic biomarker in the clinic.

Effects of chain lengths and backbone chirality on the bone-targeting ability of poly(glutamic acid)s

Anionic synthetic polypeptides are promising candidates as standalone bone-targeting drug carriers. Nevertheless, the structure-property relationship of the bone-targeting ability of polypeptides remains largely unexplored. Herein we report the optimization of the in vitro and in vivo bone-targeting ability of poly(glutamic acid)s (PGAs) by altering their chain lengths and backbone chirality. PGA 100-mers exhibited higher hydroxyapatite affinity in vitro, but their rapid macrophage clearance limited their targeting ability. Shorter PGA was therefore favored in terms of in vivo bone targeting. Meanwhile, the backbone chirality showed less significant impact on the in vitro and in vivo targeting behavior. This study highlights the modulation of structural parameters on the bone-targeting performance of anionic polypeptides, shedding light on the future design of polypeptide-based carriers.

Synergistic Enhancement of Chemotherapy-Induced Cell Death and Antitumor Efficacy against Tumoral T-Cell Lymphoblasts by IMMUNEPOTENT CRP

T-cell malignancies, including T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL), present significant challenges to treatment due to their aggressive nature and chemoresistance. Chemotherapies remain a mainstay for their management, but the aggressiveness of these cancers and their associated toxicities pose limitations. Immunepotent CRP (ICRP), a bovine dialyzable leukocyte extract, has shown promise in inducing cytotoxicity against various cancer types, including hematological cancers. In this study, we investigated the combined effect of ICRP with a panel of chemotherapies on cell line models of T-ALL and T-LBL (CEM and L5178Y-R cells, respectively) and its impact on immune system cells (peripheral blood mononuclear cells, splenic and bone marrow cells). Our findings demonstrate that combining ICRP with chemotherapies enhances cytotoxicity against tumoral T-cell lymphoblasts. ICRP + Cyclophosphamide (CTX) cytotoxicity is induced through a caspase-, reactive oxygen species (ROS)-, and calcium-dependent mechanism involving the loss of mitochondrial membrane potential, an increase in ROS production, and caspase activation. Low doses of ICRP in combination with CTX spare non-tumoral immune cells, overcome the bone marrow-induced resistance to CTX cell death, and improves the CTX antitumor effect in vivo in syngeneic Balb/c mice challenged with L5178Y-R. This led to a reduction in tumor volume and a decrease in Ki-67 proliferation marker expression and the granulocyte/lymphocyte ratio. These results set the basis for further research into the clinical application of ICRP in combination with chemotherapeutic regimens for improving outcomes in T-cell malignancies.

LILRB4 regulates multiple myeloma development through STAT3-PFKFB1 pathway

Although multiple myeloma (MM) responds well to immunotherapeutic treatment, certain portions of MM are still unresponsive or relapse after immunotherapy. Other immune molecules are needed for the immunotherapy of MM. Here, we revealed that leukocyte immunoglobulin-like receptor B4 (LILRB4) was highly expressed in multiple myeloma cell lines and patient samples and that the expression of LILRB4 was adversely correlated with the overall survival of MM patients. Knockdown of LILRB4 efficiently delayed the growth of MM cells both in vitro and in vivo. Mechanistically, IKZF1 transactivated LILRB4 expression to trigger the downstream of STAT3-PFKFB1 pathways to support MM cell proliferation. Blockade of LILRB4 signaling by blocking antibodies can effectively inhibit MM progression. Our data show that targeting LILRB4 is potentially an additional therapeutic strategy for the immunotherapeutic treatment of MM.

Hematopoietic stem and progenitor cell membrane-coated vesicles for bone marrow-targeted leukaemia drug delivery

Leukemia is a kind of hematological malignancy originating from bone marrow, which provides essential signals for initiation, progression, and recurrence of leukemia. However, how to specifically deliver drugs to the bone marrow remains elusive. Here, we develop biomimetic vesicles by infusing hematopoietic stem and progenitor cell (HSPC) membrane with liposomes (HSPC liposomes), which migrate to the bone marrow of leukemic mice via hyaluronic acid-CD44 axis. Moreover, the biomimetic vesicles exhibit superior binding affinity to leukemia cells through intercellular cell adhesion molecule-1 (ICAM-1)/integrin β2 (ITGB2) interaction. Further experiments validate that the vesicles carrying chemotherapy drug cytarabine (Ara-C@HSPC-Lipo) markedly inhibit proliferation, induce apoptosis and differentiation of leukemia cells, and decrease number of leukemia stem cells. Mechanically, RNA-seq reveals that Ara-C@HSPC-Lipo treatment induces apoptosis and differentiation and inhibits the oncogenic pathways. Finally, we verify that HSPC liposomes are safe in mice. This study provides a method for targeting bone marrow and treating leukemia.

Hem1 inborn errors of immunity: waving goodbye to coordinated immunity in mice and humans

Inborn errors of immunity (IEI) are a group of diseases in humans that typically present as increased susceptibility to infections, autoimmunity, hyperinflammation, allergy, and in some cases malignancy. Among newly identified genes linked to IEIs include 3 independent reports of 9 individuals from 7 independent kindreds with severe primary immunodeficiency disease (PID) and autoimmunity due to loss-of-function mutations in the NCKAP1L gene encoding Hematopoietic protein 1 (HEM1). HEM1 is a hematopoietic cell specific component of the WASp family verprolin homologous (WAVE) regulatory complex (WRC), which acts downstream of multiple immune receptors to stimulate actin nucleation and polymerization of filamentous actin (F-actin). The polymerization and branching of F-actin is critical for creating force-generating cytoskeletal structures which drive most active cellular processes including migration, adhesion, immune synapse formation, and phagocytosis. Branched actin networks at the cell cortex have also been implicated in acting as a barrier to regulate inappropriate vesicle (e.g. cytokine) secretion and spontaneous antigen receptor crosslinking. Given the importance of the actin cytoskeleton in most or all hematopoietic cells, it is not surprising that HEM1 deficient children present with a complex clinical picture that involves overlapping features of immunodeficiency and autoimmunity. In this review, we will provide an overview of what is known about the molecular and cellular functions of HEM1 and the WRC in immune and other cells. We will describe the common clinicopathological features and immunophenotypes of HEM1 deficiency in humans and provide detailed comparative descriptions of what has been learned about Hem1 disruption using constitutive and immune cell-specific mouse knockout models. Finally, we discuss future perspectives and important areas for investigation regarding HEM1 and the WRC.

Generating human bone marrow organoids for disease modeling and drug discovery

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

Building bones for blood and beyond: the growing field of bone marrow niche model development

The bone marrow (BM) niche is a complex microenvironment that provides the signals required for regulation of hematopoietic stem cells (HSCs) and the process of hematopoiesis they are responsible for. Bioengineered models of the BM niche incorporate various elements of the in vivo BM microenvironment, including cellular components, soluble factors, a three-dimensional environment, mechanical stimulation of included cells, and perfusion. Recent advances in the bioengineering field have resulted in a spate of new models that shed light on BM function and are approaching precise imitation of the BM niche. These models promise to improve our understanding of the in vivo microenvironment in health and disease. They also aim to serve as platforms for HSC manipulation or as preclinical models for screening novel therapies for BM-associated disorders and diseases.

The Paradox of Ribosomal Insufficiency Coupled with Increased Cancer: Shifting the Perspective from the Cancer Cell to the Microenvironment

Ribosomopathies are defined as inherited diseases in which ribosomal factors are mutated. In general, they present multiorgan symptoms. In spite of the fact that in cellular models, ribosomal insufficiency leads to a reduced rate of oncogenic transformation, patients affected by ribosomopathies present a paradoxical increase in cancer incidence. Several hypotheses that explain this paradox have been formulated, mostly on the assumption that altered ribosomes in a stem cell induce compensatory changes that lead to a cancer cell. For instance, the lack of a specific ribosomal protein can lead to the generation of an abnormal ribosome, an oncoribosome, that itself leads to altered translation and increased tumorigenesis. Alternatively, the presence of ribosomal stress may induce compensatory proliferation that in turns selects the loss of tumor suppressors such as p53. However, modern views on cancer have shifted the focus from the cancer cell to the tumor microenvironment. In particular, it is evident that human lymphocytes are able to eliminate mutant cells and contribute to the maintenance of cancer-free tissues. Indeed, many tumors develop in conditions of reduced immune surveillance. In this review, we summarize the current evidence and attempt to explain cancer and ribosomopathies from the perspective of the microenvironment.

Dual role of signaling pathways in myeloma requires cell type-specific targeting of ligand-receptor interactions

ABSTRACT

Although most patients with multiple myeloma respond to treatment initially, therapy resistance develops almost invariably, and only a subset of patients show durable responses to immunomodulatory therapies. Although the immune microenvironment has been extensively studied in patients with myeloma, its composition is currently not used as prognostic markers in clinical routine. We hypothesized that the outcome of immune signaling pathway engagement can be highly variable, depending on which 2 cellular populations participate in this interaction. This would have important prognostic and therapeutic implications, suggesting that it is crucial for immune pathways to be targeted in a specific cellular context. To test this hypothesis, we investigated a cohort of 25 patients with newly diagnosed multiple myeloma. We examined the complex regulatory networks within the immune compartment and their impact on disease progression. Analysis of immune cell composition and expression profiles revealed significant differences in the B-cell compartment associated with treatment response. Transcriptional states in patients with short time to progression demonstrated an enrichment of pathways promoting B-cell differentiation and inflammatory responses, which may indicate immune dysfunction. Importantly, the analysis of molecular interactions within the immune microenvironment highlights the dual role of signaling pathways, which can either be associated with good or poor prognosis depending on the cell types involved. Our findings therefore argue that therapeutic strategies targeting ligand-receptor interactions should take into consideration the composition of the microenvironment and the specific cell types involved in molecular interactions.

Hematopoietic Stem Cells and Their Niche in Bone Marrow

Extensive research has explored the functional correlation between stem cells and progenitor cells, particularly in blood. Hematopoietic stem cells (HSCs) can self-renew and regenerate tissues within the bone marrow, while stromal cells regulate tissue function. Recent studies have validated the role of mammalian stem cells within specific environments, providing initial empirical proof of this functional phenomenon. The interaction between bone and blood has always been vital to the function of the human body. It was initially proposed that during evolution, mammalian stem cells formed a complex relationship with the surrounding microenvironment, known as the niche. Researchers are currently debating the significance of molecular-level data to identify individual stromal cell types due to incomplete stromal cell mapping. Obtaining these data can help determine the specific activities of HSCs in bone marrow. This review summarizes key topics from previous studies on HSCs and their environment, discussing current and developing concepts related to HSCs and their niche in the bone marrow.

Mapping the cellular biogeography of human bone marrow niches using single-cell transcriptomics and proteomic imaging

Non-hematopoietic cells are essential contributors to hematopoiesis. However, heterogeneity and spatial organization of these cells in human bone marrow remain largely uncharacterized. We used single-cell RNA sequencing (scRNA-seq) to profile 29,325 non-hematopoietic cells and discovered nine transcriptionally distinct subtypes. We simultaneously profiled 53,417 hematopoietic cells and predicted their interactions with non-hematopoietic subsets. We employed co-detection by indexing (CODEX) to spatially profile over 1.2 million cells. We integrated scRNA-seq and CODEX data to link predicted cellular signaling with spatial proximity. Our analysis revealed a hyperoxygenated arterio-endosteal neighborhood for early myelopoiesis, and an adipocytic localization for early hematopoietic stem and progenitor cells (HSPCs). We used our CODEX atlas to annotate new images and uncovered mesenchymal stromal cell (MSC) expansion and spatial neighborhoods co-enriched for leukemic blasts and MSCs in acute myeloid leukemia (AML) patient samples. This spatially resolved, multiomic atlas of human bone marrow provides a reference for investigation of cellular interactions that drive hematopoiesis.

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

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

The critical role of the bone marrow stromal microenvironment for the development of drug screening platforms in leukemia

Extensive research over the past 50 years has resulted in significant improvements in survival for patients diagnosed with leukemia. Despite this, a subgroup of patients harboring high-risk genetic alterations still suffer from poor outcomes. There is a desperate need for new treatments to improve survival, yet consistent failure exists in the translation of in vitro drug development to clinical application. Preclinical screening conventionally utilizes tumor cell monocultures to assess drug activity; however, emerging research has acknowledged the vital role of the tumor microenvironment in treatment resistance and disease relapse. Current co-culture drug screening methods frequently employ fibroblasts as the designated stromal cell component. Alternative stromal cell types that are known to contribute to chemoresistance are often absent in preclinical evaluations of drug efficacy. This review highlights mechanisms of chemoresistance by a range of different stromal constituents present in the bone marrow microenvironment. Utilizing an array of stromal cell types at the early stages of drug screening may enhance the translation of in vitro drug development to clinical use. Ultimately, we highlight the need to consider the bone marrow microenvironment in drug screening platforms for leukemia to develop superior therapies for the treatment of high-risk patients with poor prognostic outcomes.

Chronic myeloid leukaemia: Biology and therapy

Chronic myeloid leukaemia (CML) is caused by BCR::ABL1. Tyrosine kinase-inhibitors (TKIs) are the initial therapy. Several organizations have reported milestones to evaluate response to initial TKI-therapy and suggest when a change of TKI should be considered. Achieving treatment-free remission (TFR) is increasingly recognized as the optimal therapy goal. Which TKI is the best initial therapy for which persons and what depth and duration of molecular remission is needed to achieve TFR are controversial. In this review we discuss these issues and suggest future research directions.

EV-mediated intercellular communication in acute myeloid leukemia: Transport of genetic materials in the bone marrow microenvironment

Acute myeloid leukemia (AML) is a common hematological cancer. Cancer cells exchange information with the surrounding microenvironment, which can be transmitted by extracellular vesicles (EVs). In recent years, the genetic materials transported by EVs have attracted attention due to their important roles in different pathological processes. EV-derived ncRNAs (EV-ncRNAs) regulate physiological functions and maintain homeostasis, mainly including microRNAs, long noncoding RNAs, and circular RNAs. However, the mechanism of involvement and potential clinical application of EV-ncRNAs in AML have not been reported. Given the unique importance of the bone marrow microenvironment (BMME) for AML, a greater understanding of the communication between leukemic cells and the BMME is needed to improve the prognosis of patients and reduce the incidence of recurrence. Additionally, studies on leukemic EV-ncRNA transport guide the design of new diagnostic and therapeutic tools for AML. This review systematically describes intercellular communication in the BMME of AML and emphasizes the role of EVs. More importantly, we focus on the information transmission of EV-ncRNAs in the BMME to explore their clinical application as potential biomarkers and therapeutic targets.

Hematopoietic Clonal Evolution Goes Spatial

SUMMARY

The spatial distribution of cells carrying clonal hematopoiesis mutations in the bone marrow and the potential role of interactions with the microenvironment are largely unknown. This study takes clonal evolution to the spatial level by describing a novel technique examining the spatial location of mutated clones in the bone marrow and the first evidence that mutated hematopoietic clones are spatially constrained and have heterogenous locations within millimeters of distance. See related article by Young et al., p. 153 (10).