Intensive chemotherapy is standard for AML but carries high risks of life-threatening complications, particularly in vulnerable patients. We aimed to compare the efficacy and safety of a low-dose chemotherapy (LDC) regimen for induction of AML. A randomized, multicenter, noninferiority trial was conducted in patients aged <18 years with AML. Patients received low-dose cytarabine, mitoxantrone or idarubicin, and G-CSF (LDC) or standard-dose induction chemotherapy (SDC) (cytarabine, daunomycin, and etoposide). All patients received post-remission consolidation with standard chemotherapy and/ or hematopoietic stem cell transplantation. The primary endpoint was to compare response rates between treatments. The secondary endpoints were to compare the outcomes, toxicity, and safety of the LDC and SDC regimens. The two treatment arms showed no significant differences in outcomes. Complete remission (CR/CRi) rates after induction were 95.1% and 95.3% in the LDC and SDC arms, respectively. Measurable residual disease < 0.1% after induction II was observed in 87.4% and 87.1% of patients in the LDC and SDC arms, respectively. Median time to neutrophil and platelet recovery was significantly shorter among patients receiving the LDC regimen. Patients in the LDC arm had a 4-year overall survival (OS) of 81.3% vs. 83.6% (P = .611) and a 4-year event-free survival (EFS) of 61.5% vs. 63.1% (P = .832). In conclusion, the LDC regimen was well tolerated and was associated with CR, EFS, and OS rates that were not inferior to those of patients treated with the SDC regimen. The trial was registered at Chinese Clinical Trial Registry (ChiCTR1800015883).

Transposable elements (TEs) are emerging regulators of hematopoiesis and leukemia, creating vulnerabilities exploitable for therapy. Recent evidence shows that TE reactivation induces innate immune signalling, DNA damage responses and dependence on Poly(ADP-ribose) polymerase (PARP)-mediated protection, enabling synthetic lethality with PARP inhibition even in homologous-recombination-proficient leukemias with epigenetic gene mutations. In this article, we highlight the biology underpinning this novel TE-PARP axis, its therapeutic implications and strategies to expand beyond HR-deficient cancers through rational combinations with immunotherapy and refined patient stratification.

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) is a bleeding disorder in which maternal antibodies target fetal and neonatal platelet alloantigens, most commonly human platelet alloantigen-1a (HPA-1a), resulting in fetal and neonatal thrombocytopenia severe enough to cause life-threatening organ bleeds, such as intracranial hemorrhage. Hemolytic disease of the fetus and newborn (HDFN) is an analogous disease caused by maternal exposure to fetal red blood cell (RBC) alloantigens, most commonly because of postpartum fetal maternal hemorrhage (FMH), that can be prevented by prophylactic administration of fetal RBC-specific antibodies. Unlike HDFN, the events that trigger FNAIT are unknown and can occur during first pregnancies, making FNAIT difficult to predict and prevent. Herein, we investigated the ability of in utero FMH to induce maternal alloimmunization to HPA-1a and cause FNAIT in a preclinical model. Transfusion of HPA-1a-positive platelets into wild-type (WT) mice in numbers representing moderate and severe FMH in humans induced production of equivalent levels of HPA-1a-specific antibodies in non-pregnant mice and mice pregnant with WT or HPA-1a-positive fetuses, causing FNAIT in the latter. Administration to pregnant females of the HPA-1a-specific monoclonal antibody RLYB212/mAb 26.4 prevented FMH-induced maternal alloimmunization to HPA-1a and FNAIT in genetically susceptible pups. In mice pregnant with HPA-1a-positive fetuses but not exposed to FMH, administration of RLYB212/mAb 26.4 did not cause FNAIT. Together, these findings identify in utero FMH as a potential trigger for maternal alloimmunization to fetal HPA-1a and provide proof of concept that prophylactic administration of HPA-1a-specific antibodies may safely and effectively prevent FMH-induced FNAIT in at-risk pregnancies.

The terms clonal monocytosis of undetermined significance (CMUS) and clonal cytopenia and monocytosis of undetermined significance (CCMUS) were introduced by the International Consensus Classification of Myeloid Neoplasms (ICC) to describe cases of clonal hematopoiesis (CH) and a concurrent monocytosis, that did not meet the diagnostic criteria of chronic myelomonocytic leukemia (CMML). To date, their practical relevance as clinicopathological entities at a population level has not been assessed. Here, we assess the prevalence, significance and natural history of CMUS and CCMUS amongst 431,531 UK Biobank participants through analysis of clinical, genomic and health outcome data. We find that CMUS with an absolute monocytosis and CCMUS are high-risk entities strongly associated with incident myeloid neoplasia (MN), cardiovascular and renal disease. Noting the overall higher monocyte counts in men and the low rate of progression of DNMT3A-CMUS, we show that amending the definition of CMUS/CCMUS to incorporate sex-specific monocyte thresholds and the exclusion of isolated DNMT3A mutations from the definition significantly strengthens the association with incident MN. Finally, given their association with poor outcomes, we develop MoSAIC, a machine learning classifier to infer the presence of SRSF2 mutations (associated with high MN risk) amongst individuals with monocytosis, based on complete blood count indices alone. We corroborate our findings in an independent cohort of 625,328 Danish primary care patients. Our findings underscore the clinical relevance of CMUS and CCMUS as distinct high-risk states within the spectrum of clonal hematopoiesis, and establish an evidence base to refine their diagnostic definition.

Immunotherapies, such as allogeneic hematopoietic cell transplantation and infusion of chimeric antigen receptor T (CAR-T) cells have significantly extended our therapeutic armamentarium against several hematological malignancies. Blocking negative regulators of immunity with immune checkpoint inhibitors has significantly improved the survival of patients with mainly solid tumors. Despite their beneficial effects, these therapies are also associated with severe, immune-mediated side effects. Here, we discuss biological similarities and differences of acute graft-versus-host disease (GVHD), cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), immune effector cell-associated hemophagocytic lymphohistiocytosis like syndrome (IEC-HS), immune effector cell-associated hematotoxicity (ICAHT), local immune effector cell-associated toxicity syndrome (LICATS), and immune-related adverse events after immune checkpoint inhibition (irAEs). Recent data have led to a better understanding of the role of myeloid cells and T-cells, including tissue-resident T-cells, in the pathophysiology of GVHD, CAR-T-cell associated immunotoxicities and irAEs. Further, we summarize approved, currently evaluated and potential future therapies for immune-mediated toxicities of cancer immunotherapies. This review will help to understand how therapeutic strategies target communalities of different side effects to overcome immune-mediated side effects of cancer immunotherapies.

Despite great progress in understanding the genomic basis of immature T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL) and acute leukemias of ambiguous lineage (ALAL), there are still cases that lack defining genetic markers, complicating risk stratification and limiting targeted therapeutic options. Recent studies have shown that enhancer hijacking drives oncogene activation in approximately half of T-ALL cases, with the BCL11B enhancer frequently involved. Here, we describe a subtype of leukemia with a distinct gene expression signature, and immunophenotype characterized by positivity for immature (CD38), myeloid (CD13), T-lymphoid (cytoplasmic (c)CD3, CD7), and B-lymphoid markers (CD19, CD79a, CD10). This subtype is defined by the t(14;16)(q32;q24) translocation, which places the FOXF1 gene and its antisense long noncoding RNA gene FENDRR under the regulatory control of the BCL11B enhancer, leading to their ectopic transcriptional activation. Common concomitant genetic lesions are loss-of-function alterations of GATA3, CDKN2A/CDKN2B deletion and activating JAK/STAT and NOTCH1 pathway mutations. Patients were predominantly children and adolescents/young adults (AYA) and experienced poor treatment outcome. High-throughput drug screening of 176 compounds demonstrated efficacy of combined BCL2-family proteins and JAK/STAT signaling inhibitors. Additionally, the clinical use of tyrosine kinase inhibitors in some of these cases showed therapeutic efficacy. Collectively, these findings identify BCL11B-enhancer mediated deregulation of FOXF1/FENDRR as a hallmark of a subtype of high-risk lineage ambiguous leukemia that is potentially amenable to targeted therapeutic intervention.

Hypofibrinogenemia reduces experimental venous thrombosis, but the impact on arterial thrombosis remains unknown. In a cohort of patients with congenital fibrinogen disorders, 19/264 (~7%) patients developed arterial thrombosis, including 4/41 (~10%) patients with hypofibrinogenemia. However, 0/8 patients with fibrinogen aC-region truncation mutations reported arterial thrombosis over 286 patient-years. To analyze the impact of hypofibrinogenemia and the fibrinogen aC-region on arterial thrombosis, two mouse models were employed: 1) wildtype mice treated with lipid nanoparticles encapsulating siRNA against fibrinogen (siFga) and 2) Fga270/270 hypofibrinogenemic mice expressing fibrinogen with a truncated aC-region. While siFga-treated hypofibrinogenemic mice developed occlusive carotid artery thrombi similarly to controls, Fga270/270 mice displayed suppressed carotid thrombosis following FeCl3 challenge, indicating loss of the aC-region but not hypofibrinogenemia alone reduces arterial thrombosis. To determine if protection from arterial thrombosis in Fga270/270 mice was linked to loss of aC-region-platelet glycoprotein VI receptor (GPVI) interaction, platelet GPVI was depleted by JAQ1 antibody administration. JAQ1-treated wildtype mice were protected from arterial thrombosis following 5% FeCl3 but not 10% FeCl3 challenge. Interestingly, JAQ administration suppressed arterial thrombosis in siFga-treated mice but did not enhance protection in Fga270/270 mice following 10% FeCl3 challenge. Our studies suggest the fibrinogen aC-region promotes arterial thrombosis in hypofibrinogenemic conditions.

B cell receptor (BCR) signaling is a key determinant of chronic lymphocytic leukemia (CLL) pathophysiology. CD49d, the alpha4 subunit of the very late antigen-4 (VLA-4) integrin, can be activated by BCR signals; however, its role in modulating BCR functionality remains unknown. We used knockout mouse models and primary human CLL stratified by CD49d expression to address this aspect. CD49d was required for bone marrow infiltration and shaped bone marrow infiltration patterns and patient outcomes in human CLL. In TCL1 transplantation models, loss of CD49d abrogated bone marrow homing and leukemic cell positioning within splenic niches. At the cellular level, CD49d-deficient murine TCL1 transgenic cells and human CD49d-low CLL cells failed to form efficient immune synapses with antigen-presenting membranes. Transcriptome analyses identified CD49d-dependent regulation of actin-associated pathways and distinct signatures of BCR responsiveness in human and mouse. Consistently, CD49d-low human CLL cells displayed aberrant actin remodeling following BCR stimulation, and a second aggressive murine CLL model reproduced the actin and engraftment defects. Kinome profiling linked impaired antigen-induced BCR responses in CD49d-deficient murine cells to altered kinase activity, and pharmacological actin perturbation phenocopied CD49d loss. In human CD49d-low CLL cells, a desynchronization of BCR-related downstream Syk and PLCɣ activation was found. Mechanistically, the CD49d-BCR interplay involved their co-localization, and CD49d converged with BCR signaling on a focal adhesion kinase-actin axis. In summary, our findings establish CD49d as a key regulator of BCR functionality in CLL, linking integrins to cytoskeletal dynamics and antigen responsiveness.

The molecular classification of T-cell acute lymphoblastic leukemia (T-ALL) remains incomplete, limiting risk stratification and the development of targeted therapies. Enhancer hijacking is a critical oncogenic mechanism that deregulates proto-oncogenes by repositioning cis-regulatory regions via structural variants. Here, we performed an integrated analysis of pediatric and adult T-ALL and mixed phenotype acute leukemias (MPALs), using whole-genome and whole-transcriptome sequencing. This analysis identified a group of 14 patients with predominantly T-lineage neoplasms driven by a t(14;16)(q32;q24) translocation, harboring universal GATA3 mutations and CDKN2A/B deletions. Mechanistically, this translocation repositions the ThymoD locus downstream of BCL11B, causing monoallelic, ectopic overexpression of FENDRR and mesenchymal transcription factor genes FOXF1 and FOXC2, activating epithelial-mesenchymal transition (EMT) transcription signatures. Immunophenotypic and single-cell RNA-seq analyses revealed marked lineage ambiguity with myeloid and B-cell differentiation potentials specific to this subtype. Furthermore, functional analyses in CD34-positive cord blood cells demonstrated that FOXF1 overexpression promotes myeloid differentiation while suppressing T-cell differentiation, serving as a key factor for lineage specification. Clinically, this subtype was detected in 0.15-4.0% of T-ALL/MPAL cases depending on the cohort, showing a median age of 15 years and enrichment in adolescents and young adults (AYA). Importantly, patients with t(14;16)(q32;q24) have an extremely poor prognosis, showing a trend toward worse outcomes than high-risk groups such as KMT2A-rearranged early T-cell progenitor (ETP)-like, SPI1-rearranged, and LMO2 γδ-like T-ALLs. The unique molecular landscape and poor prognosis of patients with the t(14;16)(q32;q24) translocation underscore the need for the development of novel subtype-specific therapeutic approaches.

Briquilimab is a monoclonal antibody inhibiting stem cell factor (SCF) binding to CD117 (c-Kit). Based on preclinical data demonstrating the antibody clears hematopoietic stem and progenitor cells (HSPC) and myeloid malignant cells, we conducted a phase 1 trial examining briquilimab plus non-myeloablative fludarabine (flu) and total body irradiation (TBI) as conditioning for older adults with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing matched donor allogeneic hematopoietic cell transplantation (HCT). Briquilimab was infused 10-14 days before transplant day (TD) 0; fludarabine 30mg/m2 and TBI 2-3 Gy were administered on TD -4 to -2 and TD0, respectively. Graft-versus-host disease prophylaxis consisted of tacrolimus, sirolimus, and mycophenolate mofetil. Thirty-two patients enrolled (n=13 AML in complete remission [CR], n=3 AML in relapse, n=16 MDS). Median age was 70 years and most had detectable measurable residual disease at screening. There were no briquilimab infusion reactions, dose limiting toxicities, or primary graft failure events; briquilimab clearance was predictable across patients. Among the AML in CR cohort, 1-year EFS was 69.2% (95% CI, 37.3, 87.2); 1-year OS was 75% (95% CI, 40.8, 91.2). Among the MDS cohort, 1-year EFS was 53.8% (26.8, 74.8); 1-year OS was 76.4% (42.7, 91.8). One of 3 AML patients in relapse experienced a transient response. Marrow samples obtained before and after briquilimab and prior to flu/TBI demonstrated AML/MDS HSPC depletion (mean 62.4±22.7%) with resultant 3-fold increase in serum SCF. In summary, we demonstrate the feasibility, safety, and proof of concept of CD117 targeting with briquilimab as HCT conditioning for AML/MDS. The trial is registered at clinicaltrials.gov; using identifier: NCT04429191.

Secondary myelofibrosis (SMF) represents a late stage of polycythemia vera and essential thrombocythemia, with overall survival (OS) currently defined by the MYelofibrosis SECondary to PV and ET (MYSEC) Prognostic Model (MYSEC-PM). To identify additional myeloid neoplasm-associated cancer gene variants (CGVs) associated with SMF outcome, we evaluated next-generation sequencing panel testing in 644 patients within the MYSEC cohort. Overall, 429 (66.6%) subjects reported at least one CGV, with ASXL1, TET2 and DNMT3A being the most frequently involved. Specific molecular profiles affected OS (p < .001): U2AF1, TP53 or SRSF2 variants (UTS, 9.3% of cases, median OS 4.1 years) and ASXL1 without UTS (25.3%, median OS 8.4 years). By integrating these genetic signatures within the MYSEC-PM through penalized Cox regressions, we identified the following independent predictors (p from < .0001 to .02) and weighted: hemoglobin <11 g/dl (1 point), circulating blasts ⩾3% (2), platelets <150 × 109/l (2), age (0.21 points/year), ASXL1 without UTS mutations (1) and any UTS mutations (3). Finally, we developed the MYSEC-molecular prognostic model (MYSEC-mPM) allocating 582 SMF patients into four categories with different OS (p < .001): low (median OS 18.0 years, 95%CI: 14.2-not reached; score <14), intermediate-1 (8.8. years, 95%CI: 7.7-9.7; score 14-16), intermediate-2 (4.6 years, 95%CI: 3.1-7.2; score 17-18), and high risk (1.9 years, 95%CI: 1.2-2.5; score ⩾19). Additionally, in 381 SMF with available cytogenetics, the MYSEC-mPM was implemented with complex/monosomal karyotype, generating the karyotype-enhanced MYSEC-kmPM. Our study shows that genomic and cytogenetic profiling improve survival prediction in SMF, outperforming the MYSEC-PM.

Protein disulfide isomerase (PDI) functions in thrombus formation in vivo and represents a viable target for antithrombotic therapy. PDI is a redox sensor that can either reduce or oxidize substrates depending on the redox environment. Yet whether PDI functions primarily as a reductase or an oxidase in the context of thrombus formation is unknown. We have used pharmacological approaches and PDI mutants to determine how the redox state of PDI affects thrombus formation. LOC14, which inhibits PDI reductase activity and induces PDI oxidation, promoted thrombus formation in arteries exposed to FeCl3 and enhanced injury-induced platelet accumulation and fibrin formation in cremaster arterioles. Substitution of a single sulfur atom with oxygen in LOC14 reversed these prothrombotic effects. Blocking antibodies targeting PDI also reversed the effect of LOC14. Evaluation of sulfenylation-mediated PDI oxidation using C53A, C56A, R120D and T101A PDI mutants showed that the sulfenylation mechanism of PDI resembles that of H2O2 reduction by peroxiredoxins. These studies identified PDI mutants that failed to undergo H2O2-mediated oxidation, but showed normal reductase activity. When tested in vivo, either wild-type PDI or the R120D mutant fully restored normal thrombus formation following morphilino-induced knockdown of PDI. In contrast, the R120D mutant PDI was unable to fully restore thrombus formation in the setting of oxidative stress induced in mice with genetic deletion of glutathione peroxidase 3 null (GPx3-/-). These studies show that PDI-catalyzed oxidization drives thrombus formation in vivo and demonstrate a mechanism of peroxide-mediated oxidation of PDI that contributes to the prothrombotic response of oxidative stress.