Antiphospholipid antibodies targeting β2-glycoprotein I (β2GPI) are a hallmark of antiphospholipid syndrome (APS), associated with an increased risk of thrombosis and pregnancy morbidity. Among these, antibodies targeting domain I (DI) are common in individuals at higher risk; however, their epitopes and prevalence among APS phenotypes remain unclear. Here, we use a large collection of 29 structurally and functionally validated β2GPI variants to provide new insights into the molecular mechanisms of autoantibody recognition in APS. Using the prototypic human-derived monoclonal anti-DI antibody MBB2, we identified positively charged residue R39 as the key driver of MBB2 binding, followed by residues R43, N56, and T57. Structural analyses revealed that although R39 is solvent exposed, R43 is not, because it is caged by residues N56 and T57. The narrow epitope footprint explains why MBB2 exhibits a modest affinity for soluble β2GPI. The cage structure accounts for the epitope being conformational rather than linear. Mutational analyses of immunoglobulin G anti-β2GPI antibodies from 52 patients with triple-positive APS, 37 with a history of thrombosis and 15 nonvascular obstetric patients, confirmed significant reactivity against DI and showed signatures of 2 conformational epitopes: one similar to MBB2 (epitope I), in which the presence of R39 is essential, and another that does not require R39 (epitope II). Although less frequent than epitope II in our cohort, epitope I reactivity was notably enriched in patients with vascular-obstetric APS. Varying epitope specificities for DI may therefore aid in identifying different APS phenotypes and predicting clinical outcomes.

MLL rearrangements (MLLrs) are the most common cause of congenital and infant leukemias. MLLrs arise prior to birth and can transform fetal/neonatal progenitors with the help of only a few additional cooperating mutations. Despite the low threshold for transformation, infant leukemias are rare, and congenital leukemias, which arise before birth, are even less common. These observations raise the question of whether mechanisms exist to suppress leukemic transformation during fetal life, thereby protecting the developing fetus from malignancy during a period of rapid hematopoietic progenitor expansion. To test this possibility, we used a mouse model of temporally controlled MLL::ENL expression to show that fetal MLL::ENL exposure establishes a heritable, leukemia-resistant state within hematopoietic progenitors that persists after birth. When we induced MLL::ENL expression prior to birth and transplanted hematopoietic stem and progenitor cells, very few recipient mice developed acute myeloid leukemia (AML) despite robust engraftment. When we induced MLL::ENL expression shortly after birth, all recipient mice developed a highly penetrant AML. Fetal MLL::ENL expression imposed a negative selective pressure on hematopoietic progenitors before birth followed by loss of self-renewal gene expression and enhanced myeloid differentiation after birth that precluded transformation. These changes did not occur when MLL::ENL expression initiated shortly after birth. The fetal barrier to transformation was enforced by the histone methyltransferase MLL3, and it could be overcome by cooperating mutations, such as NrasG12D. Heritable fetal protection against leukemic transformation may contribute to the low incidence of congenital and infant leukemias in humans.

Calprotectin, a calcium- and zinc-binding protein that comprises the subunits S100A8 and S100A9, has been extensively studied as a biomarker of gastrointestinal (GI) inflammation through fecal and serum analyses. However, its role in intestinal tissue remains poorly understood because of the limited availability of biopsy specimens. In this study, we analyzed S100A8 and S100A9 messenger RNA (mRNA) expression in 579 intestinal biopsy specimens from allogeneic stem cell transplantation recipients and observed a strong association with acute GI graft-versus-host disease (aGI-GVHD; P< .001). Neutrophil infiltration correlated with the severity of aGI-GVHD (P< .001), and calprotectin expression was strongly linked to Toll-like receptor 4 (TLR4; P< .001) and TLR2 (P< .001) expression. Both TLR4 and aGI-GVHD were associated with elevated calprotectin mRNA levels (P< .001). When patients received broad-spectrum antibiotics at disease onset, calprotectin expression was suppressed (S100A8, P = .001; S100A9, P = .01). GI site-specific differences in calprotectin expression were identified: during severe aGI-GVHD, levels increased up to 30-fold in the small intestine and up to fivefold in the large intestine with respect to mild or no aGI-GVHD, whereas under homeostasis, the large intestine exhibited higher baseline calprotectin (P = .001). The high clinical relevance of this finding is evident from the observation that calprotectin expression was prognostic for transplant-related mortality. Our study suggests that (1) calprotectin is a potential biopsy biomarker in aGI-GvHD and (2) calprotectin expression and neutrophil infiltration possibly indicate translocation of microbiota, which (3) may be modulated by antibiotics.

Immune thrombocytopenia (ITP) is characterized by the overproduction of antiplatelet autoantibodies. Although B-cell depletion therapies show promise in ITP, their high relapse rates suggest a potential de novo breakdown of tolerance during an early stage of B-cell development. Here, we investigated how central B-cell tolerance mechanisms affect autoantibody production in ITP. Paired single-cell RNA/B-cell receptor (BCR) sequencing and bulk BCR sequencing revealed reduced V-J genomic distances in immunoglobulin kappa-chain (IGK) genes within bone marrow and peripheral B cells from patients with ITP, along with decreased expression of recombination-activating gene in the immature B cells, suggesting insufficient receptor editing. Single-cell antibody cloning demonstrated increased autoreactive and polyreactive naïve B cells in ITP, indicating defective central B-cell tolerance. Through an in vivo study, we established a causal link between receptor editing defects and antiplatelet antibody production, validating the immature B-cell stage as the key phase of dysregulation. These findings suggest that insufficient receptor editing of immature B cells triggers central B-cell tolerance deficiency and autoantibody accumulation in ITP.

To identify genetic variants that influence myeloproliferative neoplasm (MPN) phenotypes, we undertook a 2-stage patient-only genome-wide association study. MPN subtypes (essential thrombocythemia [ET]; polycythemia vera [PV]) were compared with each other to healthy controls and stratified analyses was performed for chromosome 9p aberrations, JAK2 V617F mutation burden, and sex. The ET vs PV analysis identified known associations: (1) at HBS1L-MYB that increased ET risk (Pmeta = 7.93 × 10-6, odds ratio [OR] = 1.28) and reduced PV risk (Pmeta = 9.43 × 10-5, OR = 0.81) and (2) at GFI1B-GTF3C5 that predisposed to PV only (Pmeta = 1.43 × 10-9, OR = 1.38). Two further linked intronic variants, rs2425786 and rs2425788, at CDH22/CD40 were significant in females only (Pmeta = 2.67 × 10-8), with predisposition to PV (Pmeta = .0006, OR = 1.3) and reduction of ET risk (Pmeta = 7.82 × 10-5, OR = 0.75). A polygenic risk score consisting of 48 variants from 31 loci demonstrated moderate discriminative performance for ET and PV (area under the curve [AUC] = 0.718) and was improved by optimization for disease subtype (AUCET = 0.724 and AUCPV = 0.755). Overall, our results reveal that multiple germline variants influence MPN phenotype, with HBS1L-MYB and a novel sex-specific association with CDH22/CD40 being the strongest determinants.

The mechanisms that lead to extramedullary tropism of acute myeloid leukemia (eAML) remain obscure and no specific therapeutic approaches for this entity exist. Because the long-term survival of eAML is poor, a deeper understanding of the immune microenvironment and leukemia phenotypes underlying this entity is warranted. Here, we performed bulk and single-cell transcriptome profiling of 23 eAML biopsies from 10 patients with isolated extramedullary disease in skin and subcutaneous tissue. Unlike normal healthy skin, we found leukemia cutis to be heavily immune infiltrated; in extramedullary relapse after allogeneic stem cell transplantation, >90% of T/natural killer cells were donor derived. eAML-associated T cells expressed a clear signature of T-cell exhaustion, dissimilar to leukemia-associated immune populations in bone marrow relapse (n = 7) but related to acute and chronic skin inflammation. Furthermore, HLA class II was downregulated in 4 of 7 leukemia cutis specimens, consistent with an immune escape phenotype in eAML. Extramedullary and bone marrow-resident leukemia cells differed with regard to the expression of 8 homing receptor molecules (ICAM1 [encoding CD54], PECAM1 [CD31], ITGA4, ITGA6, ITGAL, ITGB4, ITGA5, and ITGAV). Serial samples obtained from 1 leukemia cutis throughout consecutive immune checkpoint blockade with ipilimumab followed by nivolumab showed a consistently high degree of overlap between local and circulating T-cell receptor sequences, suggesting that only a minority of eAML-associated T cells are leukemia specific. Our analysis reveals eAML to associate with complex changes in leukemia and T-cell gene expression profiles that suggest multiple potential avenues for therapeutic targeting.

Marginal zone lymphomas (MZLs) are a heterogeneous group of low-grade B-cell neoplasms classified into different entities by the current lymphoma classifications. They share some features, but differ significantly in clinical presentation, associated inflammatory conditions, anatomic sites of involvement, and molecular alterations. Etiopathogenesis is strongly linked to chronic antigenic stimulation and specific infections or autoimmune disorders for extranodal disease. Genetic hallmarks include constitutive NF-κB activation and common trisomies 3 and 18, alongside subtype-specific lesions such as translocations in extranodal MZL, recurrent KLF2/NOTCH2 mutations in both nodal and splenic MZL, and deletions involving chromosome 7q, predominantly observed in splenic MZL. Diagnosis can be challenging due to overlapping features with other lymphomas such as follicular and lymphoplasmacytic lymphomas; integrating morphology, immunophenotype, and molecular data is essential. Transformation to aggressive diffuse large B-cell lymphoma occurs in 3% to 15% of cases and is associated with the accumulation of genetic lesions, particularly in cell cycle, NF-κB, and epigenetic regulators, with subtype-specific drivers including TNFAIP3, TP53, and CDKN2A/B alterations. The tumor microenvironment plays a critical but understudied role, influenced by chronic antigen stimulation and involving complex interactions with immune cells that can promote immune suppression and influence therapeutic response. Understanding the heterogeneity of MZLs across their classification, genetic landscapes, and interaction with the microenvironment is crucial for accurate diagnosis, prognosis, and the development of effective targeted therapies.

Immunoglobulin M (IgM) monoclonal gammopathy of undetermined significance (IgM-MGUS) and asymptomatic Waldenström macroglobulinemia (WM; aWM) are precursor conditions of symptomatic WM with an annual 1.5% to 12% risk of progression. Although clinical prognostic models exist for risk stratification, it remains challenging to distinguish asymptomatic patients who will eventually progress from those who will not. Hence, the characterization of genomic features that shape disease progressors could potentially improve risk stratification. We performed whole-exome sequencing on 229 samples from 139 patients, including 9 patients with sequential samples. We observed an increasing mutation burden through the stages of disease evolution. Genes such as CD79B, ARID1A, and CREBBP were more often mutated in the aWM progressed (aWMpr) compared with the stable aWM (aWMst) group, whereas MYD88L265 variant allele frequency was significantly higher in patients with aWMpr than those with aWMst. In addition, patients with IgM-MGUS with MYD88WT genotype showed a distinct genomic profile compared with the MYD88MUT patients. Furthermore, the presence of more aneuploidies showed a significant association with a higher risk of progression to the symptomatic disease. Overall, our study shows that genomic profiling of patients' tumor at the time of aWM diagnosis might represent an improved strategy for identifying patients at high risk to progression who could benefit from earlier intervention.

Neutrophils interact with the external milieu in both tissue and blood microenvironments and are emerging as important regulators of blood coagulation. In this study, we explored whether complement induces neutrophil extracellular trap (NET) formation and related blood coagulation using human donor-derived neutrophils. Complement C1q induces NETosis in lipopolysaccharide (LPS) O127-primed neutrophils, whereas LPS alone does not induce NETosis. Bulk RNA sequencing revealed a unique LPS-driven altered neutrophil state, and complement sensitivity for NETosis was found to be transcriptionally dependent. Using an arrayed CRISPR knockout screen in the neutrophil-like differentiated HL60 cells, we identified that SCARF1 and complement receptor 3 are required for C1q-NETosis. Given NETs contain procoagulatory components such as DNA and histones, we investigated whether C1q-related NETs influenced blood coagulation. LPS+C1q-NETs were associated with reduced coagulation activity compared with LPS treatment alone. We further found that LPS upregulated tissue factor expression and coagulation-related activity in neutrophils. Furthermore, neutrophils secrete anticoagulant proteins, including protein C and tissue factor pathway inhibitors, during C1q-mediated NET formation that functionally regulate NET-related coagulation. C1q-NETs also activate the coagulation factors XII and XI, facilitating both intrinsic coagulation and kallikrein-dependent bradykinin production. This study elucidates how NETs regulate both procoagulatory and anticoagulatory components that may influence the pathophysiology of disease.

Aging is a critical risk factor for platelet hyperreactivity and thrombosis, yet the mechanisms involved remain poorly understood. This study investigates the role of ubiquitination in platelet function during aging. We identified heightened platelet reactivity in aged mice and human donors. Proteomic analysis of ubiquitin (Ub)-modified proteins and western blot revealed a reduction in overall ubiquitination in aged platelets, correlated with increased expression of deubiquitinating enzymes. Notably, ubiquitin specific peptidase 25 (USP25) was significantly upregulated in platelets from aged individuals. Functional assays indicated that USP25 deficiency impairs platelet function and delays arterial thrombus formation. Mechanistic investigations integrating Ub-modified proteomics and mass spectrometry demonstrated that USP25 enhances platelet hyperreactivity by stabilizing talin-1 through deubiquitination, maintaining its levels across various tissues, including the liver and spleen. Additionally, AZ1, a USP25/28 inhibitor, effectively suppressed platelet functions in both aged human and mouse models and decreased age-dependent platelet hyperreactivity and thrombus formation. Collectively, the findings delineate a remodeling of platelet ubiquitination during aging and establish USP25-mediated talin-1 stabilization as a key modulator of platelet hyperactivity in the older population.

Diffuse large B-cell lymphoma (DLBCL) poses a challenge in hematology given its varied symptoms, and the complex interplay between disease and treatment effects on health-related quality of life (HRQoL). The phase 3 POLARIX study demonstrated superior progression-free survival and a similar safety profile with polatuzumab vedotin plus rituximab, cyclophosphamide, doxorubicin, and prednisone (Pola-R-CHP) vs R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) in patients with previously untreated DLBCL. Here, we evaluate HRQoL through patient-reported outcome (PRO) instruments to fully characterize the patient experience in the POLARIX study. Changes from baseline in HRQoL, lymphoma symptoms, and gastrointestinal (GI) symptoms were assessed, as well as incidence and severity of common symptoms by PROs vs clinician-reported adverse events (AEs). Baseline characteristics of PRO-evaluable patients (N = 874) were consistent. Comparison between PROs and clinician-reported AEs revealed a notable discordance; patients generally reported a higher incidence of symptoms than clinicians, emphasizing the need for patient-centric tools to accurately capture the patient experience. Both treatments exhibited rapid and sustained improvements in HRQoL and lymphoma symptoms, with the most substantial improvements seen in global health status/QoL, lymphoma symptoms, fatigue, role, emotional, and social functioning. GI symptoms (diarrhea, constipation, nausea, and vomiting) were generally similar between treatment arms and returned to baseline levels after treatment completion. These HRQoL data underscore the complementarity of PROs, as an adjunct to clinician-reported AEs, in evaluating the efficacy and tolerability of new treatments, including Pola-R-CHP, which may represent a new benchmark for patient-reported HRQoL in previously untreated DLBCL. This trial was registered at www.clinicaltrials.gov as NCT03274492.