Experimental hematology最新文献

{"title":"3270 – UNDERSTANDING THE CELLULAR AND MOLECULAR CONSEQUENCES OF DISRUPTED TWIN PHOSPHOTYROSINE SIGNALING IN BCR-ABL-DRIVEN LEUKEMIA.","authors":"Sian Evans, Nuo Cheng, George Giotopoulus, Cécile K. Lopez, Luis Milan-Barea, Michael Hemann, Michael B. Yaffe, Brian Huntly, Pau Creixell","doi":"10.1016/j.exphem.2026.105592","DOIUrl":"10.1016/j.exphem.2026.105592","url":null,"abstract":"<div><div>Chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (ALL) are driven by expression of Breakpoint cluster region-Abelson (BCR-ABL), an oncogenic fusion protein that promotes aberrant myeloid expansion at the expense of normal hematopoiesis. Recent studies have shown that ABL kinase preferentially phosphorylates motifs containing a phosphotyrosine (pTyr) directly upstream of its target phospho-acceptor tyrosine. Previous work from our laboratory has identified the molecular determinant driving this pTyr-recognition and engineered mutants (BCR-ABL R328A and BCR-ABL R328M) that disrupt recognition of pTyr, preventing twin phosphotyrosine (pTyr-pTyr) signaling. Unexpectedly, these pTyr-recognition mutants accelerate myeloproliferative disease in vivo compared with BCR-ABL wild-type (WT), suggesting an important but unexplored role for pTyr-pTyr signaling in leukemogenesis. Here, we investigated the cellular and molecular consequences of disrupting BCR-ABL pTyr-pTyr signaling and their impact on leukemia development. Using the pTyr-deficient mutants, we showed that loss of pTyr-pTyr signaling alters BCR-ABL-induced differentiation dynamics and preserves a greater number of ckit+ hematopoietic progenitors. This is accompanied by enhanced serial replating capacity of transduced LSK cells and distinct transcriptional changes. Together, these findings revealed a previously uncharacterized signaling arm of BCR-ABL that may restrict leukemic progenitor self-renewal.</div></div><div>Chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (ALL) are driven by expression of Breakpoint cluster region-Abelson (BCR-ABL), an oncogenic fusion protein that promotes aberrant myeloid expansion at the expense of normal hematopoiesis. Recent studies have shown that ABL kinase preferentially phosphorylates motifs containing a phosphotyrosine (pTyr) directly upstream of its target phospho-acceptor tyrosine. Previous work from our laboratory has identified the molecular determinant driving this pTyr-recognition and engineered mutants (BCR-ABL R328A and BCR-ABL R328M) that disrupt recognition of pTyr, preventing twin phosphotyrosine (pTyr-pTyr) signaling. Unexpectedly, these pTyr-recognition mutants accelerate myeloproliferative disease in vivo compared with BCR-ABL wild-type (WT), suggesting an important but unexplored role for pTyr-pTyr signaling in leukemogenesis. Here, we investigated the cellular and molecular consequences of disrupting BCR-ABL pTyr-pTyr signaling and their impact on leukemia development. Using the pTyr-deficient mutants, we showed that loss of pTyr-pTyr signaling alters BCR-ABL-induced differentiation dynamics and preserves a greater number of ckit+ hematopoietic progenitors. This is accompanied by enhanced serial replating capacity of transduced LSK cells and distinct transcriptional changes. Together, these findings revealed a previously uncharacterized signaling arm of BCR-ABL ","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105592"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2004 – CLONALLY RESOLVED DYNAMICS OF HUMAN HEMATOPOIETIC IN VITRO DIFFERENTIATION ACROSS ONTOGENY","authors":"Júlia Viladevall, Emily Calderbank-May, Myriam Haltalli, Qi Liu, Shirom Chabra, Iwo Kucinksi, Nieves Garcia-Gisbert, Nicola Wilson, Bertie Göttgens, Elisa Laurenti","doi":"10.1016/j.exphem.2026.105532","DOIUrl":"10.1016/j.exphem.2026.105532","url":null,"abstract":"<div><div>Hematopoiesis encompasses the dynamic process of hematopoietic stem and progenitor cell (HSPC) differentiation into mature blood lineages. The relative composition of HSPCs and mature blood cells differs in human fetal liver (FL), fetal bone marrow (FBM), and umbilical cord blood (CB), but how differentiation dynamics vary across these tissues is poorly studied.</div><div>We report a single-cell, time- and clonally resolved atlas of human FL, FBM and CB HSPC differentiation into eight blood lineages in vitro. Our dataset includes 500,000 cells and 45,000 barcoded clones. We identified cellular behaviors based on lineage and total differentiative output using CLADES, a NeuralODE-based framework.</div><div>Across all tissues, multilineage clones, particularly originating from single hematopoietic stem cell (HSC) and megakaryocytic-erythroid–mast cell progenitor (MEMP) compartments, exhibited the highest total differentiative output over 17 days. HSPC maturation trajectories differed between tissues, especially toward granulocytes: FBM produced more eosinophils (Eo), CB more basophils (Baso), and FL more mast cells (MC). High MC production in FL was driven by (1) coexisting MC-producing differentiative behaviors and (2) a subset of high MC-producing MEMPs marked by high HLA-DR expression. Last, we defined fate-based signatures of Eo, Baso, and MC progenitors, which can identify early lineage specification in independent scRNA-seq datasets of HSPCs.</div><div>Collectively, this study reports the largest clonally resolved dataset of human HSPC differentiation, providing powerful “ground truth” for fate prediction algorithms and studies of altered HSPC function in disease. Moreover, we uncover previously unknown lineage biases in fetal tissues and quantitively distinct population dynamics not predicted by snapshot transcriptomics.</div></div><div>Hematopoiesis encompasses the dynamic process of hematopoietic stem and progenitor cell (HSPC) differentiation into mature blood lineages. The relative composition of HSPCs and mature blood cells differs in human fetal liver (FL), fetal bone marrow (FBM), and umbilical cord blood (CB), but how differentiation dynamics vary across these tissues is poorly studied.</div><div>We report a single-cell, time- and clonally resolved atlas of human FL, FBM and CB HSPC differentiation into eight blood lineages in vitro. Our dataset includes 500,000 cells and 45,000 barcoded clones. We identified cellular behaviors based on lineage and total differentiative output using CLADES, a NeuralODE-based framework.</div><div>Across all tissues, multilineage clones, particularly originating from single hematopoietic stem cell (HSC) and megakaryocytic-erythroid–mast cell progenitor (MEMP) compartments, exhibited the highest total differentiative output over 17 days. HSPC maturation trajectories differed between tissues, especially toward granulocytes: FBM produced more eosinophils (Eo), CB more basophils (Baso), and FL mor","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105532"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3274 – DEVELOPMENTAL PROGRAMMING OF HEMATOPOIETIC STEM CELL DORMANCY THROUGH EVASION OF NOTCH SIGNALING","authors":"Patricia Herrero Molinero, Eric Cantón, María Maqueda, Cristina Ruiz-Herguido, Arnau Iglesias, Jessica González, Brandon Hadland, Lluís Espinosa, Anna Bigas","doi":"10.1016/j.exphem.2026.105878","DOIUrl":"10.1016/j.exphem.2026.105878","url":null,"abstract":"<div><div>Dormant hematopoietic stem cells (HSCs) are deeply quiescent, metabolically restrained cells that sustain lifelong hematopoiesis, yet when and how this state is established remains unclear. In mice, dormancy has been proposed to arise postnatally in the bone marrow, whereas fetal liver HSCs are generally considered uniformly proliferative. Here, we investigated whether HSC dormancy is instead established during embryogenesis. Using inducible histone H2B fused with green fluorescent protein (H2B-GFP) for long-term label retention, transcriptomics, and competitive transplantation assays, we identified a rare low-dividing HSC population specified during embryonic development that persists into adulthood. Analysis of single-cell data from human fetal liver reveals a transcriptionally analogous HSC population expressing a dormant signature. Mechanistically, we find that Notch signaling drives HSC activation in the fetal liver, whereas cells that evade Notch input adopt a dormant state. Genetic and pharmacological perturbations reveal a defined developmental window in which transient reduction of Notch exposure promotes quiescence and enhances long-term repopulating capacity, whereas sustained Notch inhibition impairs HSC function. Equivalent Notch modulation in adult HSCs fails to induce dormancy. These findings demonstrated that HSC dormancy is established during embryonic development and uncover a temporally restricted role for Notch signaling in programming lifelong stem cell behavior.</div></div><div>Dormant hematopoietic stem cells (HSCs) are deeply quiescent, metabolically restrained cells that sustain lifelong hematopoiesis, yet when and how this state is established remains unclear. In mice, dormancy has been proposed to arise postnatally in the bone marrow, whereas fetal liver HSCs are generally considered uniformly proliferative. Here, we investigated whether HSC dormancy is instead established during embryogenesis. Using inducible histone H2B fused with green fluorescent protein (H2B-GFP) for long-term label retention, transcriptomics, and competitive transplantation assays, we identified a rare low-dividing HSC population specified during embryonic development that persists into adulthood. Analysis of single-cell data from human fetal liver reveals a transcriptionally analogous HSC population expressing a dormant signature. Mechanistically, we find that Notch signaling drives HSC activation in the fetal liver, whereas cells that evade Notch input adopt a dormant state. Genetic and pharmacological perturbations reveal a defined developmental window in which transient reduction of Notch exposure promotes quiescence and enhances long-term repopulating capacity, whereas sustained Notch inhibition impairs HSC function. Equivalent Notch modulation in adult HSCs fails to induce dormancy. These findings demonstrated that HSC dormancy is established during embryonic development and uncover a temporally restricted role for Notch signaling ","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105878"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2037 – LEUKEMIC STEM CELL SUBTYPES DETERMINE VENETOCLAX RESISTANCE AND THERAPEUTIC VULNERABILITIES IN AML","authors":"Alexander Waclawiczek, Aino-Maija Leppä, Simon Renders, Ines Bergerweiss, Karolin Stumpf, Carsten Müller-Tidow, Andreas Trumpp","doi":"10.1016/j.exphem.2026.105565","DOIUrl":"10.1016/j.exphem.2026.105565","url":null,"abstract":"<div><div>Acute myeloid leukemia (AML) is hierarchically organized, with a small subpopulation of leukemic stem cells (LSCs) driving the disease by continuously generating more differentiated progeny. The central role of LSCs makes them the primary therapeutic target of venetoclax (VEN)-based therapy. However, heterogeneous BCL-2 family expression within LSCs drives resistance, suggesting an underexplored LSC complexity.</div><div>We investigated LSC heterogeneity by analyzing the functionality (xenograft) and transcriptome of GPR56<sup>+</sup> HSPCs and CD64<sup>+</sup> monocytic blasts from >150 AML patients. GPR56<sup>+</sup> HSPCs represented the LSC-containing subpopulation in the vast majority of patients, and VEN resistance was associated with accelerated engraftment kinetics and serial repopulation capacity. We identified four functionally distinct LSC subclasses defined by hematopoietic lineage stage: HSC-LSCs overexpressed immature markers with reduced cell cycle activity; LMPP- and MEP-LSCs were primed toward early myeloid differentiation, with MEP-LSCs uniquely retaining erythroid and megakaryocytic potential. A rare fourth subclass, monocytic/dendritic (MoDe)-LSCs, gave rise exclusively to monocytic blasts in xenografts and operated entirely outside the primitive HSPC hierarchy, as further confirmed by cell type-resolved mutation profiling.</div><div>Importantly, LSC subtype determined BCL-2 family expression ratios, predicting treatment response independently of genetic background. Diagnosis-relapse paired analysis revealed therapy-driven LSC plasticity toward a BCL-xL-high MEP state at relapse in a substantial proportion of patients. VEN treatment in xenografts recapitulated this MEP-lineage plasticity, which was reversible upon treatment discontinuation. Together, these findings uncover the functional heterogeneity of LSCs and subtype-specific vulnerabilities, offering biomarker-guided therapeutic opportunities.</div></div><div>Acute myeloid leukemia (AML) is hierarchically organized, with a small subpopulation of leukemic stem cells (LSCs) driving the disease by continuously generating more differentiated progeny. The central role of LSCs makes them the primary therapeutic target of venetoclax (VEN)-based therapy. However, heterogeneous BCL-2 family expression within LSCs drives resistance, suggesting an underexplored LSC complexity.</div><div>We investigated LSC heterogeneity by analyzing the functionality (xenograft) and transcriptome of GPR56<sup>+</sup> HSPCs and CD64<sup>+</sup> monocytic blasts from >150 AML patients. GPR56<sup>+</sup> HSPCs represented the LSC-containing subpopulation in the vast majority of patients, and VEN resistance was associated with accelerated engraftment kinetics and serial repopulation capacity. We identified four functionally distinct LSC subclasses defined by hematopoietic lineage stage: HSC-LSCs overexpressed immature markers with reduced cell cycle activity; LMPP- and MEP-LSCs were prim","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105565"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3257 – RELIABILITY OF MEAN PLATELET VOLUME AS AN INFLAMMATORY MARKER WHEN ACUTECHOLECYSTITIS COEXITS WITH IRON DEFICIENCY ANEMIA.","authors":"Suma Kaza, Vasu Alluri, Mahathi Thotakura","doi":"10.1016/j.exphem.2026.105579","DOIUrl":"10.1016/j.exphem.2026.105579","url":null,"abstract":"<div><h3>Background</h3><div>Patients with iron deficiency anemia (IDA) have been reported to have an increased incidence of gallstones. Mean platelet volume (MPV) reflects both size and platelet activation in inflammatory disease. A review of the literature shows that MPV in acute cholecystitis can range from 6.5 to 8.8 femtoliters (fL).</div></div><div>Patients with iron deficiency anemia (IDA) have been reported to have an increased incidence of gallstones. Mean platelet volume (MPV) reflects both size and platelet activation in inflammatory disease. A review of the literature shows that MPV in acute cholecystitis can range from 6.5 to 8.8 femtoliters (fL).</div><div><h3>Objectives</h3><div>1. To evaluate MPV alterations in subjects with acute cholecystitis alone, acute cholecystitis coexisting with IDA, and those with IDA. 2. Biochemical analysis of gallstones in the cholecystectomy specimen.</div><div>Methods: A 1-year cross-sectional study of 52 patients who underwent cholecystectomy; imaging suggested cholelithiasis; histopathologic examination of the gallbladder was performed. Hemogram, including complete blood picture, hemoglobin level, cell counts, and MPV; serum cholesterol level; and serum iron level were measured on a fasting venous blood sample taken the day before surgery. All tests were done using fully automated hematology and biochemistry analyzers. Biochemical analysis of 1 stone from each cholecystectomy specimen was done using manual semiquantitative titrimetric and colorimetric methods.</div></div><div>1. To evaluate MPV alterations in subjects with acute cholecystitis alone, acute cholecystitis coexisting with IDA, and those with IDA. 2. Biochemical analysis of gallstones in the cholecystectomy specimen.</div><div>Methods: A 1-year cross-sectional study of 52 patients who underwent cholecystectomy; imaging suggested cholelithiasis; histopathologic examination of the gallbladder was performed. Hemogram, including complete blood picture, hemoglobin level, cell counts, and MPV; serum cholesterol level; and serum iron level were measured on a fasting venous blood sample taken the day before surgery. All tests were done using fully automated hematology and biochemistry analyzers. Biochemical analysis of 1 stone from each cholecystectomy specimen was done using manual semiquantitative titrimetric and colorimetric methods.</div><div><h3>Results</h3><div>In total, 62% of the gallstones were of the cholesterol type. Serum iron level was reduced in 38.46%. Serum cholesterol level was raised in 86.54%. MPV was lower in individuals with acute cholecystitis in the background of IDA: 6.5 + 0.4 fL compared with that in those with acute cholecystitis alone: 6.6 + 0.2 fL, whereas the group with IDA had the lowest value, 6.4 + 0.6 fL.</div><div>Conclusion: MPV may not be a reliable inflammatory marker in subjects with acute cholecystitis who have coexisting IDA. IDA is implicated not only in cholesterol stone formation but also influences MP","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105579"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3261 – HIGH RESOLUTION IDENTIFICATION OF LEUKEMIC CELL STATES USING A MULTIMODAL MANUAL CURATION FRAMEWORK","authors":"Moritz Berg, Nesrine Aroua, Patrick Stelmach, Shuiping Lin, Maria Puschhof, Andreas Trumpp","doi":"10.1016/j.exphem.2026.105583","DOIUrl":"10.1016/j.exphem.2026.105583","url":null,"abstract":"<div><div>Acute myeloid leukemia (AML) is a heterogeneous disease of the hematopoietic system characterized by the accumulation of dysfunctional stem and progenitor cells in the bone marrow. Relapse is driven by minimal residual disease, largely composed of leukemic stem cells (LSCs) that regenerate the leukemic hierarchy and confer chemotherapy resistance. Recently, tandem duplications (TD) of the upstream binding transcription factor (<em>UBTF</em>) gene have emerged as a common genomic alteration in pediatric AML and have also been identified in adults. The mechanisms driving UBTF-TD AML remain poorly understood and are further complicated by cellular heterogeneity, which shapes therapy resistance. High resolution characterization of UBTF-TD AML cell states is therefore required. We benchmarked Seurat and single-cell ANnotation using Variational Inference (scANVI)-based reference mapping in healthy hematopoiesis and AML as a performance baseline. Reference mapping reliably identified differentiated lineages but showed limited accuracy for progenitor populations, especially in AML. To address this, we designed a multimodal manual framework that integrates data-driven clustering, gene set enrichment, and profiling of surface markers. When applied to a cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) cohort of six patients with AML UBTF-TD (31,256 cells) spanning diagnosis and relapse, this framework enabled the resolution of leukemic progenitor cell states beyond the resolution achievable by reference mapping alone. Notably, an antigen-presenting hematopoietic stem cell population and a transcriptionally distinct pediatric AML-like subpopulation were characterized. Compositional analysis uncovered that AML UBTF-TD cellular composition is more primitive at relapse than at diagnosis, which is consistent with the known role of LSCs in disease recurrence. Compared with reference mapping based annotation, the manual curation recapitulated compositional patterns and cell states while providing additional biological resolution.</div></div><div>Acute myeloid leukemia (AML) is a heterogeneous disease of the hematopoietic system characterized by the accumulation of dysfunctional stem and progenitor cells in the bone marrow. Relapse is driven by minimal residual disease, largely composed of leukemic stem cells (LSCs) that regenerate the leukemic hierarchy and confer chemotherapy resistance. Recently, tandem duplications (TD) of the upstream binding transcription factor (<em>UBTF</em>) gene have emerged as a common genomic alteration in pediatric AML and have also been identified in adults. The mechanisms driving UBTF-TD AML remain poorly understood and are further complicated by cellular heterogeneity, which shapes therapy resistance. High resolution characterization of UBTF-TD AML cell states is therefore required. We benchmarked Seurat and single-cell ANnotation using Variational Inference (scANVI)-based reference mapping in heal","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105583"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3275 – DIFFERENTIAL IMPACT OF AGING ON SKELETAL BONE MARROW NICHES: VULNERABILITY OF CALVARIA AND RESILIENCE OF VERTEBRAE","authors":"Sanyam Jain, Anjali Kusumbe","doi":"10.1016/j.exphem.2026.105879","DOIUrl":"10.1016/j.exphem.2026.105879","url":null,"abstract":"<div><div>A healthy bone marrow niche is essential for sustaining hematopoiesis and ensuring successful transplantation outcomes. Aging progressively compromises the bone marrow microenvironment, leading to impairment of hematopoietic stem cell function. Although a recent study suggests that skull marrow is resistant to aging, our findings indicate that the skull (calvarial) marrow is a fragile and degenerating environment. Aging calvarial niches exhibit a consistent loss of mesenchymal stem/progenitor cells and osteoprogenitors, suppression of osteogenic, angiogenic, and lymphatic programs, adipocyte accumulation, fibroblast expansion, vascular aging, DNA replication stress, impaired telomere maintenance, mitochondrial dysfunction, cellular senescence, and heightened inflammation, as demonstrated by both transcriptomic and proteomic analyses. Importantly, decreased expression of endothelial-derived hematopoietic stem cell maintenance factors, rarefaction of sinusoidal endothelium, and chimeric antigen receptor (CAR)-stromal cells reflect substantial degradation of the hematopoietic niche in old calvaria. Although the proportion of CD45⁺ cells increases with age across multiple skeletal sites, including the calvaria, this expansion correlates with enlargement of the bone marrow cavity due to cortical bone thinning and trabecular bone loss, rather than reflecting preserved/enhanced hematopoietic niche function. Comparative proteomic analyses across skeletal sites further reveal that vertebral marrow niches exhibit remarkable resilience to aging. Relative to calvarial and femoral niches, vertebral niches show reduced signatures of inflammaging, mitochondrial dysfunction, and DNA damage. Collectively, the concordant transcriptomic and proteomic evidence challenges the notion of skull-specific resistance to aging and instead identifies vertebral bone marrow as the most resilient niche during skeletal aging.</div></div><div>A healthy bone marrow niche is essential for sustaining hematopoiesis and ensuring successful transplantation outcomes. Aging progressively compromises the bone marrow microenvironment, leading to impairment of hematopoietic stem cell function. Although a recent study suggests that skull marrow is resistant to aging, our findings indicate that the skull (calvarial) marrow is a fragile and degenerating environment. Aging calvarial niches exhibit a consistent loss of mesenchymal stem/progenitor cells and osteoprogenitors, suppression of osteogenic, angiogenic, and lymphatic programs, adipocyte accumulation, fibroblast expansion, vascular aging, DNA replication stress, impaired telomere maintenance, mitochondrial dysfunction, cellular senescence, and heightened inflammation, as demonstrated by both transcriptomic and proteomic analyses. Importantly, decreased expression of endothelial-derived hematopoietic stem cell maintenance factors, rarefaction of sinusoidal endothelium, and chimeric antigen receptor (CAR)-stromal cells reflect su","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105879"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2043 – LEUKEMIA STEM CELL EXPANSION CULTURES REVEAL CLONAL DRIVERS OF LEUKEMOGENESIS AND THERAPY RESPONSE","authors":"Andrea Polazzi, Indranil Singh, Alex Maya Pombo, Marta López-Osias, Celine Bauer, Maria Guarini, Pedro Sánchez Sánchez, Luna Goulet, Carmen Gallardo, Daniel Daniel Fernández-Perez, Robert Bowman, Alejo Rodriguez-Fraticelli","doi":"10.1016/j.exphem.2026.105571","DOIUrl":"10.1016/j.exphem.2026.105571","url":null,"abstract":"<div><div>Leukemia stem cells (LSCs) are the architects of disease initiation and chemoresistance in acute myeloid leukemia (AML), yet their inherent rarity and the lack of scalable expansion models have hindered the study of their clonal dynamics. We overcome these barriers by developing Polymer-based Leukemic STem cell Cultures (PLSTCs), a defined system that propagates AML stem cells at unprecedented scale. PLSTCs achieve a >1,000-fold enrichment in functional LSCs compared with conventional media, validated by human-matched gene signatures and robust in vivo leukemia-initiating activity. By combining this platform with genomic LARRY barcoding, we reveal that AML LSCs exist as a spectrum of self-renewing “clonotypes” with stable, heritable transcriptional programs. Longitudinal tracking in vivo demonstrates that specific primitive LSC states hold superior engraftment potential and drive leukemic fitness. Crucially, under the selective pressure of induction chemotherapy (AraC/Doxo), we identified LSC clones that are intrinsically primed for resistance through a latent megakaryocytic-erythroid (MegE)-like program. Upon treatment, these cells undergo a striking fate-switch, abandoning myeloid trajectories to expand as MegE-like leukemic cells in the spleen. To decode the regulatory logic of this state, we performed a targeted CROPseq screen, identifying the chondroitin sulfate (CS) synthesis enzyme Csgalnact1 as a critical vulnerability for LSC maintenance. Pharmacological inhibition of the CS pathway via ABC chondroitinase abolished self-renewal and crippled the ability of LSCs to recover from chemotherapy. Our study establishes PLSTCs as a scalable platform for the comprehensive interrogation of primary LSCs heterogeneity and uncovers a targetable, nongenetic mechanism of plasticity that drives therapeutic escape in AML.</div></div><div>Leukemia stem cells (LSCs) are the architects of disease initiation and chemoresistance in acute myeloid leukemia (AML), yet their inherent rarity and the lack of scalable expansion models have hindered the study of their clonal dynamics. We overcome these barriers by developing Polymer-based Leukemic STem cell Cultures (PLSTCs), a defined system that propagates AML stem cells at unprecedented scale. PLSTCs achieve a >1,000-fold enrichment in functional LSCs compared with conventional media, validated by human-matched gene signatures and robust in vivo leukemia-initiating activity. By combining this platform with genomic LARRY barcoding, we reveal that AML LSCs exist as a spectrum of self-renewing “clonotypes” with stable, heritable transcriptional programs. Longitudinal tracking in vivo demonstrates that specific primitive LSC states hold superior engraftment potential and drive leukemic fitness. Crucially, under the selective pressure of induction chemotherapy (AraC/Doxo), we identified LSC clones that are intrinsically primed for resistance through a latent megakaryocytic-erythroid (MegE)-like program. ","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105571"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"1022 – INHERITED BONE MARROW FAILURE AND GERMLINE PREDISPOSITION TO MYELOID NEOPLASIA: SOMATIC GENETIC REVERSION AND CLONAL ADAPTATION IN HEMATOPOIETIC STEM CELLS","authors":"Jörg Cammenga","doi":"10.1016/j.exphem.2026.105517","DOIUrl":"10.1016/j.exphem.2026.105517","url":null,"abstract":"<div><div>Inherited bone marrow failure syndromes (IBMFS) and germline predisposition syndromes to myeloid neoplasms represent a group of hereditary disorders characterized by impaired hematopoiesis and an increased risk of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). These conditions are more common than previously appreciated, accounting for a significant proportion of childhood MDS and a subset of adult MDS/AML cases. IBMFS and germline predisposition syndromes result in decreased fitness of hematopoietic stem cells (HSCs), creating selective pressure for the acquisition of compensatory genetic alterations that may be either adaptive or maladaptive. Adaptive compensation restores HSC fitness toward normal levels, whereas maladaptive compensation promotes transformation to a myeloid neoplasm.</div><div>A remarkable feature of several IBMFS and germline predisposition syndromes is somatic genetic reversion, also termed “natural gene therapy.” This process occurs when a hematopoietic stem/progenitor cell acquires a secondary genetic event that mitigates or eliminates the effect of the inherited pathogenic variant. The reverted clone may gain a selective advantage and expand within the hematopoietic compartment, leading to improved blood counts and delayed disease progression.</div><div>The mechanisms of somatic genetic reversion are highly dependent on the mode of inheritance and the underlying biology of the respective IBMFS or predisposition syndrome. Somatic genetic reversion can be classified as either primary, affecting the same gene that causes the disease, or secondary, affecting a different gene whose alteration also results in increased cellular fitness.</div><div>This presentation provided an overview of the different IBMFS and germline predisposition syndromes associated with myeloid neoplasms, with a particular focus on the mechanisms of somatic genetic reversion and the insights they provide into HSC biology.</div><div>This presentation was made possible through a joint initiative of the International Society for Experimental Hematology (ISEH) and the European Hematology Association aimed at fostering collaborations between basic scientists and clinician-scientists in this area of hematology.</div></div><div>Inherited bone marrow failure syndromes (IBMFS) and germline predisposition syndromes to myeloid neoplasms represent a group of hereditary disorders characterized by impaired hematopoiesis and an increased risk of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). These conditions are more common than previously appreciated, accounting for a significant proportion of childhood MDS and a subset of adult MDS/AML cases. IBMFS and germline predisposition syndromes result in decreased fitness of hematopoietic stem cells (HSCs), creating selective pressure for the acquisition of compensatory genetic alterations that may be either adaptive or maladaptive. Adaptive compensation restores HSC fitness towar","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105517"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"2029 – INTRAVITAL IMAGING OF CALCIUM NETWORK TOPOLOGY REVEALED THE IMMUNE-MODULATORY LOCI IN THE BONE MARROW","authors":"Cih-Li Hong, Montgomery Whalen, Kevin Lee, Shinya Yari, Adam Tyrlik, Arutyun Bagramyan, Laura Calvi, Maria Maryanovich, Shu-Chi Yeh, Charles Lin","doi":"10.1016/j.exphem.2026.105557","DOIUrl":"10.1016/j.exphem.2026.105557","url":null,"abstract":"<div><div>Intercellular communications through calcium signaling orchestrates coordinated cell functions across diverse tissues. Bone marrow stromal cells (BMSCs) form an extended 3D network in the marrow and secrete cytokines essential for regulating blood and immune cell formation. Yet, the degree of coordination and heterogeneity among the BMSCs in the interconnected network remain poorly understood. Here, we developed an intravital calcium imaging platform using LepR-cre; Salsa6f mice, in which tdTomato and a calcium flux indicator (GCaMP6f) are expressed in BMSC lineages. We identified a subset of BMSCs that communicate via intercellular calcium waves (ICWs). The ICWs are provoked by acute inflammatory challenges (lipopolysaccharide [LPS], 1.4 mg/kg), and follow circadian rhythms. Further analyses from the single-cell RNA sequencing data suggest that the BMSC subset express high level of leukocyte chemoattractant Ccl2. Validations using intravital tracking confirmed that ICW initiation led to aggregation of CCR2+ leukocytes within 2 hours after LPS administration, forming “hot spots” within the systemic inflammatory landscape. As gap junctions have been reported to regulate timed cytokine secretion, we next generated triple transgenic LepR-cre; Cx43 floxed; Salsa6f mice. Cx43 deficiency reduced ICWs and led to a more diffused CCR2 cell distribution in contrast to the designated hot spots found in the WT mice. Functionally, Cx43 deficiency blunted the responses of IL-1β and IL-10 in the bone marrow after LPS challenge, whereas CXCL12 was not affected. Together, our intravital imaging toolbox uncovered the presence of immune modulatory loci in the bone marrow, where BMSCs coordinate through ICWs to work in spatially and temporally controlled manner.</div></div><div>Intercellular communications through calcium signaling orchestrates coordinated cell functions across diverse tissues. Bone marrow stromal cells (BMSCs) form an extended 3D network in the marrow and secrete cytokines essential for regulating blood and immune cell formation. Yet, the degree of coordination and heterogeneity among the BMSCs in the interconnected network remain poorly understood. Here, we developed an intravital calcium imaging platform using LepR-cre; Salsa6f mice, in which tdTomato and a calcium flux indicator (GCaMP6f) are expressed in BMSC lineages. We identified a subset of BMSCs that communicate via intercellular calcium waves (ICWs). The ICWs are provoked by acute inflammatory challenges (lipopolysaccharide [LPS], 1.4 mg/kg), and follow circadian rhythms. Further analyses from the single-cell RNA sequencing data suggest that the BMSC subset express high level of leukocyte chemoattractant Ccl2. Validations using intravital tracking confirmed that ICW initiation led to aggregation of CCR2+ leukocytes within 2 hours after LPS administration, forming “hot spots” within the systemic inflammatory landscape. As gap junctions have been reported to regulate timed cytokin","PeriodicalId":12202,"journal":{"name":"Experimental hematology","volume":"162 ","pages":"Article 105557"},"PeriodicalIF":2.7,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}