Myelodysplastic syndromes (MDS), which are hematopoietic stem cell malignancies, are often accompanied by signs of chronic inflammation, that can in turn drive the pathogenetic process. The precise mechanisms dysregulating inflammatory and innate immune signaling in MDS hematopoietic stem and progenitor cells (HSPCs) remain under investigation. We report that mice lacking Tet2 developed a hyper-inflammatory state, which can be further fueled by LPS-induced inflammation. This chronic inflammation temporarily promotes the self-renewal and myeloid differentiation of Tet2-deficient HSPCs; however, it ultimately accelerates HSC exhaustion and triggers MDS development in chimeric mouse models. Driving this phenotype was the activation of the NLRC4 inflammasome pathway. Notably, Nlrc4 depletion in Tet2-deficient mice impaired MDS development and improved the survival of these mice. These findings uncover a novel mechanistic basis for the MDS-associated inflammation and provide new targeting opportunities in its management.

Abstract Myelodysplastic syndromes (MDS) are clinically and biologically diverse disorders, emphasizing the need for personalized treatment approaches. The International Working Group for Prognostication of MDS (IWG_PM) recently introduced a molecular classification, referred to as the MDS taxonomy, that categorizes patients into 16 subgroups based on 21 gene mutations, 6 cytogenetic abnormalities, and loss of heterozygosity (LOH) at TP53 and TET2 loci. This study sought to validate and enhance the clinical relevance of the MDS taxonomy by analyzing a large retrospective cohort (n = 5136) and transcriptomic data from a prospective cohort (n = 477). The taxonomy successfully identified subgroups with distinct clinical characteristics and disease progression patterns. However, incorporating gene interactions from taxonomy subgroups did not improve the prognostic performance of the Molecular International Prognostic Scoring System (IPSS‐M). We further assessed whether the taxonomy could guide management in patients receiving disease‐modifying therapies. Except for the “TP53‐complex” subgroup, taxonomy classifications were not predictive of hypomethylating agent response or transplant outcomes. Nonetheless, they correlated with overall survival, suggesting that while both IPSS‐M and the taxonomy capture disease biology, other non‐genetic factors may influence treatment response. RNA sequencing confirmed the biological distinctiveness of the taxonomy groups. Transcriptomic profiling of CD34+ bone marrow cells revealed unique, homogeneous gene expression patterns, particularly within the AML‐like, biTET2, SF3B1, and TP53‐complex subgroups. Further integration of multi‐omics data may refine MDS classification, improving clinical decision‐making and guiding the development of targeted therapies.

While many sequence-specific transcription factors (TFs) have been identified as key regulators of hematopoietic stem cell (HSC) lineage determination, the function of general TFs in HSC behavior is poorly understood. To evaluate the function of the TFIID subunit TAF1 in normal hematopoiesis, we generated Taf1 conditional knockout (cKO) mice and identified an essential role of TAF1 in fetal hematopoiesis. Surprisingly, TAF1 deletion in adult mice was not lethal to hematopoiesis; rather, we observed a marked expansion of the hematopoietic stem and progenitor cell (HSPC) compartment, with increased self-renewal and impaired differentiation capacity of these cells. TAF1-null HSPCs failed to produce mature blood cells in chimeric mice; these cells also failed to upregulate key differentiation genes when induced to differentiate in vitro. TAF1 loss not only disrupted TFIID chromatin recruitment but also reduced RNA polymerase II (RNAPII) promoter-proximal pausing. Thus, HSPCs utilize distinct transcriptional regulatory mechanisms to undergo differentiation versus maintaining self-renewal.

Notable treatment advances have been made in recent years for patients with myelodysplastic syndromes/neoplasms (MDS), and several new drugs are under development. For example, the emerging availability of oral MDS therapies holds the promise of improving patients' health-related quality of life (HRQoL). Within this rapidly evolving landscape, the inclusion of HRQoL and other patient-reported outcomes (PROs) is critical to inform the benefit/risk assessment of new therapies or to assess whether patients live longer and better, for what will likely remain a largely incurable disease. We provide practical considerations to support investigators in generating high-quality PRO data in future MDS trials. We first describe several challenges that are to be thoughtfully considered when designing an MDS-focused clinical trial with a PRO endpoint. We then discuss aspects related to the design of the study, including PRO assessment strategies. We also discuss statistical approaches illustrating the potential value of time-to-event analyses and their implications within the estimand framework. Finally, based on a literature review of MDS randomized controlled trials with a PRO endpoint, we note the PRO items that deserve special attention when reporting future MDS trial results. We hope these practical considerations will facilitate the generation of rigorous PRO data that can robustly inform MDS patient care and support treatment decision-making for this patient population.

ASXL1 mutation frequently occurs in all forms of myeloid malignancies and is associated with aggressive disease and poor prognosis. ASXL1 recruits Polycomb repressive complex 2 (PRC2) to specific gene loci to repress transcription through trimethylation of histone H3 on lysine 27 (H3K27me3). ASXL1 alterations reduce H3K27me3 levels, which results in leukemogenic gene expression and the development of myeloid malignancies. Standard therapies for myeloid malignancies have limited efficacy when mutated ASXL1 is present. We discovered upregulation of lysine demethylase 6B (KDM6B), a demethylase for H3K27me3, in ASXL1-mutant leukemic cells, which further reduces H3K27me3 levels and facilitates myeloid transformation. Here, we demonstrated that heterozygous deletion of Kdm6b restored H3K27me3 levels and normalized dysregulated gene expression in Asxl1Y588XTg hematopoietic stem/progenitor cells (HSPCs). Furthermore, heterozygous deletion of Kdm6b decreased the HSPC pool, restored their self-renewal capacity, prevented biased myeloid differentiation, and abrogated progression to myeloid malignancies in Asxl1Y588XTg mice. Importantly, administration of GSK-J4, a KDM6B inhibitor, not only restored H3K27me3 levels but also reduced the disease burden in NSG mice xenografted with human ASXL1-mutant leukemic cells in vivo. This preclinical finding provides compelling evidence that targeting KDM6B may be a therapeutic strategy for myeloid malignancies with ASXL1 mutations.

An important epigenetic component of tyrosine kinase signaling is the phosphorylation of histones, and epigenetic readers, writers, and erasers. Phosphorylation of protein arginine methyltransferases (PRMTs), have been shown to enhance and impair their enzymatic activity. In this study, we show that the hyperactivation of Janus kinase 2 (JAK2) by the V617F mutation phosphorylates tyrosine residues (Y149 and Y334) in coactivator-associated arginine methyltransferase 1 (CARM1), an important target in hematologic malignancies, increasing its methyltransferase activity and altering its target specificity. While non-phosphorylatable CARM1 methylates some established substrates (e.g. BAF155 and PABP1), only phospho-CARM1 methylates the RUNX1 transcription factor, on R223 and R319. Furthermore, cells expressing non-phosphorylatable CARM1 have impaired cell-cycle progression and increased apoptosis, compared to cells expressing phosphorylatable, wild-type CARM1, with reduced expression of genes associated with G2/M cell cycle progression and anti-apoptosis. The presence of the JAK2-V617F mutant kinase renders acute myeloid leukemia (AML) cells less sensitive to CARM1 inhibition, and we show that the dual targeting of JAK2 and CARM1 is more effective than monotherapy in AML cells expressing phospho-CARM1. Thus, the phosphorylation of CARM1 by hyperactivated JAK2 regulates its methyltransferase activity, helps select its substrates, and is required for the maximal proliferation of malignant myeloid cells. Coactivator-associated arginine methyltransferase 1 (CARM1) is an important target in hematologic malignancies. In this work, the authors show that the hyperactivation of Janus kinase 2 (JAK2) by the V617F mutation phosphorylates CARM1 which regulates its methyltransferase activity and alters its target specificity.

SETD2 is the only enzyme responsible for transcription-coupled histone H3 lysine 36 trimethylation (H3K36me3). Mutations in SETD2 cause human diseases including cancer and developmental defects. In mice, Setd2 is essential for embryonic vascular remodeling. Given that many epigenetic modifiers have recently been found to possess noncatalytic functions, it is unknown whether the major function(s) of Setd2 is dependent on its catalytic activity or not. Here, we established a site-specific knockin mouse model harboring a cancer patient-derived catalytically dead Setd2 (Setd2-CD). We found that the essentiality of Setd2 in mouse development is dependent on its methyltransferase activity, as the Setd2(CD/CD) and Setd2(-/-) mice showed similar embryonic lethal phenotypes and largely comparable gene expression patterns. However, compared with Setd2(-/-), the Setd2(CD/CD) mice showed less severe defects in allantois development, and single-cell RNA-seq analysis revealed differentially regulated allantois-specific 5 ' Hoxa cluster genes in these two models. Collectively, this study clarifies the importance of Setd2 catalytic activity in mouse development and provides a new model for comparative study of previously unrecognized Setd2 functions.

Myelodysplastic neoplasms/syndromes (MDS) are a heterogeneous group of biologically distinct entities characterized by variable degrees of ineffective hematopoiesis. Recently, 2 classification systems (the 5th edition of the World Health Organization Classification of Haematolymphoid tTumours and the International Consensus Classification) further subcharacterized MDS into morphologically and genetically defined groups. Accurate diagnosis and subclassification of MDS require a multistep systemic approach. The International Consortium for MDS (icMDS) summarizes a contemporary, practical, and multimodal approach to MDS diagnosis and classification.

The development of dendritic cells (DCs), including antigen-presenting conventional DCs (cDCs) and cytokine-producing plasmacytoid DCs (pDCs), is controlled by the growth factor Flt3 ligand (Flt3L) and its receptor Flt3. We genetically dissected Flt3L-driven DC differentiation using CRISPR-Cas9–based screening. Genome-wide screening identified multiple regulators of DC differentiation including subunits of TSC and GATOR1 complexes, which restricted progenitor growth but enabled DC differentiation by inhibiting mTOR signaling. An orthogonal screen identified the transcriptional repressor Trim33 (TIF-1γ) as a regulator of DC differentiation. Conditional targeting in vivo revealed an essential role of Trim33 in the development of all DCs, but not of monocytes or granulocytes. In particular, deletion of Trim33 caused rapid loss of DC progenitors, pDCs, and the cross-presenting cDC1 subset. Trim33-deficient Flt3 + progenitors up-regulated pro-inflammatory and macrophage-specific genes but failed to induce the DC differentiation program. Collectively, these data elucidate mechanisms that control Flt3L-driven differentiation of the entire DC lineage and identify Trim33 as its essential regulator.

SF3B1 mutations frequently occur in cancer yet lack targeted therapies. Clinical trials of XPO1 inhibitors, selinexor and eltanexor, in high-risk myelodysplastic neoplasms (MDS) revealed responders were enriched with SF3B1 mutations. Given that XPO1 (Exportin-1) is a nuclear exporter responsible for the export of proteins and multiple RNA species, this led to the hypothesis that SF3B1-mutant cells are sensitive to XPO1 inhibition, potentially due to altered splicing. Subsequent RNA sequencing after XPO1 inhibition in SF3B1 wildtype and mutant cells showed increased nuclear retention of RNA transcripts and increased alternative splicing in the SF3B1 mutant cells particularly of genes that impact apoptotic pathways. To identify novel drug combinations that synergize with XPO1 inhibition, a forward genetic screen was performed with eltanexor treatment implicating anti-apoptotic targets BCL2 and BCLXL, which were validated by functional testing in vitro and in vivo. These targets were tested in vivo using Sf3b1K700E conditional knock-in mice, which showed that the combination of eltanexor and venetoclax (BCL2 inhibitor) had a preferential sensitivity for SF3B1 mutant cells without excessive toxicity. In this study, we unveil the mechanisms underlying sensitization to XPO1 inhibition in SF3B1-mutant MDS and preclinically rationalize the combination of eltanexor and venetoclax for high-risk MDS.

<p>Caspase activities in T3M-1 Cl-10 cells infected with recombinant retroviruses for the indicated proteins.</p>

Expression level of ELF4 in stably transduced T3M-1 Cl-10 cells

The guidelines for classification, prognostication, and response assessment of myelodysplastic syndromes/neoplasms (MDS) have all recently been updated. In this report on behalf of the International Consortium for MDS (icMDS) we summarize these developments. We first critically examine the updated World Health Organization (WHO) classification and the International Consensus Classification (ICC) of MDS. We then compare traditional and molecularly based risk MDS risk assessment tools. Lastly, we discuss limitations of criteria in measuring therapeutic benefit and highlight how the International Working Group (IWG) 2018 and 2023 response criteria addressed these deficiencies and are endorsed by the icMDS. We also address the importance of patient centered care by discussing the value of quality-of-life assessment. We hope that the reader of this review will have a better understanding of how to classify MDS, predict clinical outcomes and evaluate therapeutic outcomes.

Maximilian Stahl, Omar Abdel-Wahab, Andrew H. Wei, Michael R. Savona, Mina L. Xu, Zhuoer Xie, Justin Taylor, Daniel Starczynowski, Guillermo F. Sanz, David A. Sallman, Valeria Santini, Gail J. Roboz, Mrinal M. Patnaik, Eric Padron, Olatoyosi Odenike, Aziz Nazha, Stephen D. Nimer, Ravindra Majeti, Richard F. Little, Steven Gore, Alan F. List, Vijay Kutchroo, Rami S. Komrokji, Tae Kon Kim, Nina Kim, Christopher S. Hourigan, Robert P. Hasserjian, Stephanie Halene, Elizabeth A. Griffiths, Peter L. Greenberg, Maria Figueroa, Pierre Fenaux, Fabio Efficace, Amy E. DeZern, Matteo G. Della Porta, Naval G. Daver, Jane E. Churpek, Hetty E. Carraway, Andrew M. Brunner, Uma Borate, John M. Bennett, Rafael Bejar, Jacqueline Boultwood, Sanam Loghavi, Jan Philipp Bewersdorf, Uwe Platzbecker, David P. Steensma, Mikkael A. Sekeres, Rena J. Buckstein, and Amer M. Zeidan

Bromodomain‐containing protein 4 (BRD4) is overexpressed and functionally implicated in various myeloid malignancies. However, the role of BRD4 in normal hematopoiesis remains largely unknown. Here, utilizing an inducible Brd4 knockout mouse model, we find that deletion of Brd4 ( Brd4 Δ/Δ ) in the hematopoietic system impairs hematopoietic stem cell (HSC) self‐renewal and differentiation, which associates with cell cycle arrest and senescence. ATAC‐seq analysis shows increased chromatin accessibility in Brd4 Δ/Δ hematopoietic stem/progenitor cells (HSC/HPCs). Genome‐wide mapping with cleavage under target and release using nuclease (CUT&RUN) assays demonstrate that increased global enrichment of H3K122ac and H3K4me3 in Brd4 Δ/Δ HSC/HPCs is associated with the upregulation of senescence‐specific genes. Interestingly, Brd4 deletion increases clipped H3 (cH3) which correlates with the upregulation of senescence‐specific genes and results in a higher frequency of senescent HSC/HPCs. Re‐expression of BRD4 reduces cH3 levels and rescues the senescence rate in Brd4 Δ/Δ HSC/HPCs. This study unveils an important role of BRD4 in HSC/HPC function by preventing H3 clipping and suppressing senescence gene expression.

<p>Enriched GO terms for genes adjacent to ELF4 binding regions</p>

<p>Expression of ELF1, ELF2, ELF3, ELF4, and ELF5 in T3M-1 Cl-10, HT1080, HEC59 and MCF10A cell lines</p>

Supplementary Figures 1-5, Table 1 from DNA Damage Signaling in Hematopoietic Cells: A Role for Mre11 Complex Repair of Topoisomerase Lesions

Expression level of ELF4 in trasient transfection assays