The phase 3 SYMPATICO study included an open-label cohort to evaluate the efficacy and safety of first-line ibrutinib plus venetoclax in patients with non-blastoid mantle cell lymphoma (MCL) ≥65 years (n=65), or ≥18 years with a TP53 mutation (TP53m) (n=11). Eligible patients received oral ibrutinib 560 mg once daily and venetoclax (5-week ramp-up to 400 mg once daily) for 2 years, then single-agent ibrutinib 560 mg until disease progression or unacceptable toxicity. In total, 78 patients were enrolled. With median time on study of 40.5 months (range, 0.6+ to 46.9), the complete response (CR) rate was 69% (95% CI, 58-79), and the overall response rate was 95% (95% CI, 87-99). The median duration of response was 37.1 months (95% CI, 30.3-not estimable [NE]). Median progression-free survival (mPFS) was 40.2 months (95% CI, 29.4-NE); median overall survival (OS) was not reached (3-year OS rate, 79% [95% CI, 68-86]). In patients ≥65 years, CR rates were 76% (no TP53m) and 44% (with TP53m), mPFS was 40.2 and 22.0 months, and 3-year OS was 85% and 66%, respectively. In adult patients <65 years (with TP53m), the CR rate was 73%, mPFS was 15.4 months, and 3-year OS was 73%. The most common treatment-emergent adverse events were diarrhea (49%), fatigue (37%), neutropenia (35%), and COVID-19 (32%). First-line ibrutinib plus venetoclax showed promising efficacy, with high CR rates and durable remissions, in patients with previously untreated non-blastoid MCL and may be an option for patients ≥65 years or patients of any age with TP53m. NCT03112174.

Bone marrow (BM) fibrosis in primary and post-polycythemia vera/essential thrombocythemia myelofibrosis (MF) has traditionally been considered a reactive process driven by cytokines, such as transforming growth factor (TGF)-β1, primarily produced by neoplastic megakaryocytes and platelets. These cytokines promote the differentiation of wild-type mesenchymal stromal cells into collagen- and fibronectin-producing myofibroblasts, thereby inducing BM fibrosis. However, hematopoietic-derived collagen-producing cells of monocyte lineage, termed fibrocytes, have also been implicated in this process. Here, we demonstrate that fibrocytes constitute a major collagen-producing cell population in the BM of patients with JAK2V617F-mutated MF, with additional contributions from myofibroblasts. Analysis of BM samples from patients with JAK2V617F-mutated myeloproliferative neoplasms (MPNs) revealed that fibrocytes accounted for nearly two-thirds of collagen-producing cells, whereas myofibroblasts represented a smaller subset. Using BM-derived fibrocytes from Jak2V617F transgenic mice (Jak2V617F mice), we performed a high-throughput drug screen and identified statins as inhibitors of fibrocyte proliferation in vitro. In vivo, pitavastatin treatment reduced fibrocyte numbers, ameliorated BM fibrosis, and improved anemia in Jak2V617F mice. Pitavastatin also decreased TGF-β1 production by neoplastic fibrocytes, resulting in reduced myofibroblast expansion. Peripheral blood-derived fibrocytes from patients with JAK2V617F-mutated MPNs were similarly sensitive to pitavastatin in vitro. Together, these findings suggest that fibrocytes substantially contribute to BM fibrosis in JAK2V617F-mutated MF and support further investigation of pitavastatin as a potential antifibrotic strategy in this molecular subset.

Iron deficiency is a highly prevalent nutrient deficiency and the most common cause of anemia. Although iron deficiency exacerbates cardiovascular disease, the direct impact of iron deficiency on the vasculature remains unstudied. We assessed iron levels across the vascular endothelium in mouse and human endothelial cells and found resistance artery endothelial cells have the lowest iron stores, suggesting they may be especially impacted by iron deficiency. Anemia has previously been shown to increase arterial NO signaling in patients, and we have previously shown endothelial a-globin scavenges nitric oxide (NO) in the resistance artery endothelium. We hypothesized iron regulates vascular function through regulation of endothelial a-globin. To test this, we used a mouse model of iron deficiency anemia (IDA). In female mice, IDA increased NO signaling, which was rescued to control levels by repletion of vascular iron with iron dextran. Despite being similarly anemic and having a similar reduction in a-globin protein, there were no changes in NO signaling across groups in male mice. We further measured whether a-globin was in its heme-bound (holo a-globin) or heme-free (apo a-globin) state and found males did not fully lose its functional, heme-bound a-globin. Using endothelial specific a-globin knockout mice, we show loss of endothelial a-globin is necessary for increased NO signaling in IDA and for the rescue of NO signaling by iron dextran in female mice. Altogether, the data presented here demonstrate iron is a determinant of endothelial identity and modulates endothelial NO signaling through the regulation of a-globin.

Hemophilia A (HA) phenotype is predicted by factor VIII (FVIII) activity. Most HA adeno-associated virus (AAV) trials incorporate the B-domain-deleted FVIII-SQ variant and one-stage assay (OSA) FVIII activity exceeds chromogenic substrate assay (CSA) values by 1.5-2-fold. This contrasts with recombinant FVIII-SQ (rFVIII-SQ), suggests altered biochemical properties, and highlights the need to determine which assay reflects hemostatic function. In gene therapy treated mice and SPK-8011 trial participants, AAV-derived FVIII-SQ (AAV-FVIII-SQ) activation and function within the intrinsic tenase enzyme complex was compared to rFVIII-SQ. In both species, AAV-FVIII-SQ demonstrated normal cofactor function and A2-domain stability. In mice, the assay discrepancy persisted without von Willebrand factor (vWF), indicating it is not driven by altered vWF interactions. Both species demonstrated enhanced thrombin-mediated activation of AAV-FVIII-SQ, detectable by OSA but not CSA. Negative binomial regression analysis of 23 SPK-8011 participants, representing 99 cumulative patient-years, trended toward better prediction of annualized bleeding rate with OSA than CSA. In vivo evaluation of AAV-FVIII-SQ in mice demonstrated that OSA activity better correlated with hemostatic function and corresponded to rFVIII-SQ function. These findings support that OSA FVIII activity reflects AAV-FVIII-SQ function within the intrinsic tenase complex, captures enhanced activation not detected by CSA, and best predicts clinical outcome.

The t(4;14) chromosomal translocation drives overexpression of the histone methyltransferase NSD2 and defines a high-risk segment of multiple myeloma (MM) patients. Herein, we report the discovery of NSD2-LDD, a cereblon-recruiting and PWWP1-mediated ligand directed degrader (LDD) that selectively and potently eliminates full length and PWWP1 domain containing NSD2 protein isoforms. NSD2-LDD treatment induces global loss of H3K36me2 leading to promoter-proximal spreading of H3K27me3 and re-wiring of cis-regulatory interactions that reverse t(4;14) transcriptional programs. These effects suppress MM disease-associated phenotypes including stromal adhesion, three-dimensional colony growth and paracrine signaling. By integrating patient single cell profiles with model 3D epigenomic and spatial transcriptomics, we delineate t(4;14) disease state together with the tumor-intrinsic reprogramming and resultant remodeling of the bone marrow microenvironment upon NSD2 degradation. In cell line derived xenografts and genetically engineered mouse models of t(4;14), NSD2-LDD extends median survival accompanied by tumoral H3K36me2 loss and niche re-modelling. Although the NSD2-LDD response is restricted to PWWP1-containining models, collectively this work validates NSD2 as a tractable dependency and supports clinical development of NSD2 degradation as a novel, targeted therapeutic strategy in high-risk MM.

The transition of hematopoietic stem cells (HSCs) from quiescence to lineage commitment requires precise post-transcriptional control, yet the contribution of mRNA isoform regulation remains poorly defined. Here, we identify a translationally controlled splicing program that contributes to HSC fate decisions. Using activity-based signatures of 305 splicing regulators, we uncover widespread post-transcriptional modulation of the spliceosome in stem and progenitor cells. The branch-point recognition factor Sf1 emerges as a key node, regulated by a conserved structured 5' UTR that cooperates with the RNA-binding protein Igf2bp2 to control its translation. Disrupting this cis-trans module reduces Sf1 protein synthesis and skews differentiation toward stem and erythroid programs. Mechanistically, Sf1-dependent alternative splicing remodels 5' UTRs of hematopoietic and DNA damage response genes, altering their translation and modulating DNA damage resolution. Together, these findings reveal an unrecognized translational layer controlling spliceosome activity and link RNA regulons, alternative splicing, and HSC fate determination.

Myelodysplastic neoplasms (MDS) feature hematopoietic deficits driven in part by transcript splicing abnormalities. Thus far, such disease-driving transcripts have been identified in association with specific splicing factor mutations. However, conserved aberrant splicing-derived transcripts that drive MDS independently of mutational status remain poorly studied despite representing global therapeutic targets. Here, we characterize an MDS-associated MBD1 isoform (MBD1-L) as a novel member of this class of transcripts. Rather than originating from a mutant splicing factor, the abnormal production of MBD1-L is driven by reduced WTAP expression in MDS. Overexpression of MBD1-L in healthy human HSPCs recapitulates archetypal MDS defects, including reduced terminal GLYA+ erythroid differentiation, suppressed cell cycling and impaired in vivo reconstitution capacity during increased hematopoietic demand in xenotransplantation assays. An integrated multiomics approach assessing DNA binding of MBD1 isoforms, and resulting changes in chromatin accessibility, histone mark deposition and transcriptional changes, revealed that these defects arise from an isoform-specific switching of MBD1's binding behavior. The MBD1-L isoform refocuses MBD1-L's heterochromatin-promoting activity from methylated to unmethylated CpGs and thus enacting broad downregulation of CpG-rich promoters as well as secondary epigenetic effects mediated by its downstream target BCOR. Remarkably, we also find that directly reversing abnormal MBD1 splicing across a broad range of primary human MDS samples using nanoparticle-encapsulated ASOs enhances in vitro erythroid differentiation, supporting the utility of RNA therapies for MDS treatment. Thus, our findings demonstrate MBD1-L to be a global, disease-driving splice variant across MDS, and illustrate the potential for RNA-based therapies in the broad treatment of MDS.

Watch & wait is the standard of care in asymptomatic early-stage chronic lymphocytic leukemia (CLL). The CLL12 trial investigated ibrutinib versus placebo in early-stage patients with intermediate to very high risk of progression, showing improved event-free survival (EFS) but no overall survival (OS) benefit10. Building on these findings, our analysis examined whether a significant benefit could be identified within distinct genetic subgroups. After a median follow-up of 69.3 months, there were 166 EFS and 32 OS events in 515 trial patients. In the placebo arm, del(17p), del(11q), +12, U-IGHV, and mutations in NOTCH1, ATM, NRAS/KRAS/BRAF, and NFKBIE correlated with shorter EFS. With ibrutinib, only del(17p) and TP53 and NFKBIE mutations significantly compromised EFS. Ibrutinib offered substantial EFS benefit in subgroups with U-IGHV, del(11q), +12, NOTCH1, ATM, and NFKBIE mutations. No EFS improvement was seen for asymptomatic early-stage patients with del(17p) or TP53 mutations. Ibrutinib provided no OS benefits in any genetic subgroup. Multivariable analysis revealed ibrutinib treatment as an independent favorable factor for EFS, while U-IGHV, del(17p), POT1, RAS/RAF, and NFKBIE mutations were adverse prognostic factors. The results confirm watch-and-wait as standard of care for early-stage CLL patients, especially in high-risk CLL characterized by del(17p) and/or mutated TP53. EudraCT Number: 2013-003211-22.

Pharmacological plasminogen reduction enhanced liver regeneration experimentally and clinically. siRNA-induced plasminogen deficiency promoted hepatocyte proliferation after partial hepatectomy in mice, contrasting genetic deficiency models. In the HeLiX trial, tranexamic acid reduced post-hepatectomy liver failure odds, suggesting a novel therapeutic strategy.

Thrombosis is a major contributor to global morbidity and mortality. Current standards of care target the extrinsic and/or common pathways of coagulation, effectively inhibiting thrombosis but also increasing bleeding risk, highlighting the unmet need for additional treatment options. Genetic deficiency in factor XI (FXI), a component of the intrinsic pathway, reduces thrombosis risk without spontaneous bleeding. We generated 2 FXI monoclonal antibodies (mAbs) with distinct profiles to provide new approaches to anticoagulation. Cenvacibart (REGN7508Cat) targets the catalytic domain to completely block FXI activity (induced by FXIIa or FXIa in the intrinsic pathway or thrombin in an intrinsic/common pathway amplification loop), thereby maximizing anticoagulation; amrecibart (REGN9933A2) targets the apple 2 domain of FXI/FXIa to specifically prevent FXI activity induced by FXIIa-delivering perhaps less anticoagulation but with potentially lower bleeding risk. We evaluated the anticoagulant effects of both mAbs in vitro in human/non-human primate plasma, in vivo in non-human primates, and healthy volunteers. Both mAbs inhibited intrinsic pathway-triggered coagulation, assessed by activated partial thromboplastin time (aPTT); cenvacibart exhibited a greater increase in aPTT versus amrecibart or other FXI-targeted inhibitors. Neither amrecibart nor cenvacibart affected the extrinsic pathway, assessed by prothrombin time (PT). In non-human primates, both mAbs prevented thrombosis without increasing bleeding. In first-in-human studies, both mAbs were generally well tolerated and dose-dependently inhibited intrinsic pathway-triggered coagulation, with durable aPTT prolongation without affecting PT. Amrecibart and cenvacibart may offer tailored therapies for patients with different bleeding risk profiles. The trials are registered at www.clinicaltrials.gov as #NCT05102136 and #NCT05603195.

NPM1-mutated acute myeloid leukemia (AML) is genetically well-defined, but clinical outcomes remain heterogeneous, suggesting that quantitative clonal features may refine current risk stratification. We analyzed 688 intensively treated NPM1-mutated AML integrating variant allele frequency (VAF), mutation order, and clonal architecture inferred by PyClone and ClonEvol. Co-mutations were present in 97% of patients (median = 3 per case), dominated by DNMT3A (49%), FLT3-ITD (46%), TET2 (22%), and IDH2 (20%). Prognostic modelling of NPM1 VAF identified an optimal cut-off of 31.44%, defining NPM1high and NPM1low groups. NPM1low correlated with splicing-related alterations and independently predicted inferior overall (HR = 1.46; p = 0.037) and relapse-free survival (HR = 1.40; p = 0.036). Gene-specific VAF analyses revealed divergent effects across partners, high DNMT3A, FLT3-OTHER, KRAS, and PTPN11 burdens were adverse, whereas high IDH2 VAF was protective. Combined models showed that patients with NPM1high and favorable co-mutation VAFs had the best outcomes, while dual unfavorable burdens conferred the poorest survival. Mutation ordering inferred from VAFs positioned NPM1 after epigenetic and splicing lesions but before signaling and transcription-factor mutations. Non-canonical orders, such as early FLT3-OTHER/TKD or WT1 prior to NPM1, significantly stratified outcomes. Clonal reconstruction revealed predominantly linear evolutionary trajectories (84.3%), with increased mutational burden and clonal diversity associating with inferior survival. Notably, intra-clonal co-localization of NPM1 with IDH1 or TET2 was associated with improved outcomes, whereas co-localization with WT1 predicted dismal prognosis. These results demonstrate that quantitative and structural dimensions of clonality refine the biological and prognostic landscape of NPM1-mutated AML beyond mutational status alone.

N7-methylguanosine (m7G), a prevalent modification in transfer RNAs (tRNAs), is primarily catalyzed by the methyltransferase METTL1. Although growing evidence supports a role for METTL1 in various tumors, its therapeutic potential and precise function in leukemia stem cell (LSC) homeostasis remain largely unexplored. Here, we identify METTL1 as a key regulator of LSC self-renewal and homing within bone marrow (BM) microenvironment through catalyzing m7G formation on a specific tRNA, tRNAPheGAA, thereby promoting leukemogenesis. Mechanistically, METTL1 loss significantly reduces m7G abundance and steady-state levels of tRNAPheGAA, leading to translation suppression and degradation of transcripts enriched with tRNAPheGAA-related codons, such as hematopoietic cell kinase (HCK). Decreased HCK expression disrupts CXCR4 signaling, impairing LSC self-renewal and BM homing. Therapeutically, we characterized a small-molecule METTL1 inhibitor (M1i; NSC137443), through high-throughput screening. Pharmacological inhibition of METTL1 demonstrated potent antitumor efficacy by reducing tRNA m7G levels and disrupting the tRNAPheGAA/HCK/CXCR4 cascade. Notably, targeting METTL1 significantly reduces LSC frequency, delays leukemogenesis, and prolongs survival in multiple acute myeloid leukemia models. Together, our findings establish a previously unrecognized role for METTL1 and its target tRNAPheGAA in LSC homeostasis and provide compelling proof-of-concept evidence that METTL1 is a druggable epitranscriptomic target for antileukemia therapy.

Drug resistance is a major challenge in cancer therapy, especially in hematologic malignancies in which kinase inhibitors have transformed treatment yet are frequently undermined by drug resistance. Although targeted protein degradation (TPD) offers a mechanistically distinct mode of action compared with inhibition-based therapeutic therapies, the potential value of TPD in drug-resistant blood cancer remains unclear. Here, we report the discovery of cereblon (CRBN)-recruiting molecular glue degraders (MGDs) targeting lymphocyte-specific tyrosine kinase (LCK), an oncogenic kinase in T-cell acute lymphoblastic leukemia (T-ALL). By high-throughput screening and medicinal chemistry optimization, we developed a series of MGDs that induced CRBN-dependent degradation of LCK as well as potent cytotoxicity in T-ALL in vitro. Structure-activity relationship analysis and ternary complex modeling revealed a noncanonical degron at the LCK-CRBN interface involving the G-loop, whose mutation disrupts this interaction. Unlike inhibitors and inhibitor-based proteolysis-targeting chimeras, these MGDs engage LCK in regions distal to the ATP-binding site, and thus their activities in T-ALL are not affected by gatekeeper LCK mutations that drive resistance to inhibitor-based therapeutics. Taken together, our data highlight the potential of LCK-targeting MGDs as a strategy to overcome kinase inhibitor resistance in T-ALL, offering a framework for targeting kinase dependencies in drug-refractory hematologic malignancies more broadly.

Multiple myeloma (MM), the second most prevalent hematologic malignancy, remains incurable, highlighting the need to identify molecular drivers of disease progression and new therapies. Using a CRISPR-Cas9 library screening approach in MM cells, we identified 22 essential transcription factors (TFs), including members of the interferon regulatory factor (IRF) family. Remarkably, in addition to the well-known IRF4, IRF2 emerged as a critical TF in MM. Cleavage under targets and release using nuclease (CUT&RUN) experiments demonstrated that IRF2 binds extensively to chromatin, both independently and in cooperation with IRF1 and IRF4. Although IRF2-unique regions were predominantly associated with active promoters, regions bound by IRF2/1/4 were biased toward introns. Functionally, IRF2 contributes to MM cell survival by suppressing necroptosis and promoting cell migration. Notably, IRF2-dependent transcriptional dysregulation was evident in precursor conditions such as monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM), suggesting a role in early disease evolution. In addition to its role as an early factor, IRF2 levels also seem to influence disease progression, as MMs with higher expression demonstrated worse progression-free survival (PFS) and overall survival (OS) in both univariate and multivariate analyses, even after adjusting for common MM genetic risk factors. In conclusion, IRF2 constitutes an underappreciated essential TF involved in the pathogenesis and clinical behavior of MM. Its inhibition leads to dysregulation of key signaling pathways in MM pathogenesis, highlighting its potential as a therapeutic target.