In the multinational, phase 3 RELEVANCE trial, 1,030 patients with previously untreated follicular lymphoma were randomized to receive rituximab plus lenalidomide (R2; n=513) or rituximab-based immunochemotherapy (R-Chemo; n=517). In the final analysis, at 120 months of follow-up, median PFS was comparable between the treatment groups: 110.6 months with R2 versus 102.8 months with R-Chemo, according to Independent Review Committee assessment. The 10-year PFS rates were 46.4% and 46.6%, respectively. Median overall survival (OS) and time-to-next lymphoma treatment (TTNLT) were not reached in either arm; 10-year OS rates were 82.4% and 81.1%, respectively, and 10-year TTNLT rates were 62.2% and 66.3%, respectively. Overall, patients with POD24 had a poorer prognosis compared to those without POD24 (HR, 6.215; P<0.0001); however, no difference was observed between the study groups. The incidence of second primary malignancies (SPMs) was 2.11 cases per 100 patient-years (95% CI, 1.80-2.46). Only 9 transformations occurred after 24 months (3 with R2 versus 6 with R-chemo). In each study group, 87 patients died, mainly due to lymphoma progression and SPMs. This long-term follow-up of RELEVANCE confirmed that R2 provides a chemo-free alternative to immunochemotherapy in this patient population. Trial registration: NCT01476787 and NCT01650701; EudraCT: 2011-002792-42.

Innate immunity is increasingly recognized as a driver of neurodegeneration, though pathogenic mechanisms are incompletely understood. Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplastic disorder caused by activating somatic mutations in mitogen-activated protein kinase (MAPK) pathway genes, most commonly BRAFV600E, in myeloid precursors. A subset of LCH patients develop progressive neurodegeneration (LCH-ND). We generated a human induced pluripotent stem cell (iPSC) model from patients with somatic hematologic mosaicism for BRAFV600E. Brain macrophages/microglia from LCH iPSCs exhibit unique disease specific pathogenic features. Stepwise differentiation identified hematopoietic progenitors as hyperproliferative, whereas brain macrophages were apoptosis resistant. Through application of cerebral organoids and a humanized murine xenotransplantation model we identify marked heterogeneity of differentiation potential within clonal BRAFV600E lines in vivo. This model phenocopied human specific phenotypes including dense basal ganglia foci of abnormal macrophages, marked neurodegeneration with astrogliosis, and progressive ataxia. This approach will allow for preclinical testing of therapeutics for LCH-ND.

Malignant histiocytic neoplasms (MHNs) are rare tumors derived from the mononuclear phagocyte system (MPS), encompassing histiocytic sarcoma, Langerhans cell sarcoma, interdigitating dendritic cell sarcoma, and other high-grade MPS lineage tumors. Despite advances in understanding histiocytic neoplasms, MHNs remain diagnostically challenging and lack standardized treatment algorithms. Current classification systems differ in lineage framing and fail to address mixed or ambiguous phenotypes, contributing to diagnostic uncertainty and inconsistent care. To address these gaps, the Histiocyte Society convened an international working group of pathologists and oncologists, including World Health Organization (WHO) and International Consensus Classification (ICC) contributors, to harmonize nomenclature, define minimum diagnostic criteria, and develop pragmatic treatment recommendations. Using a modified Delphi process and case-based review, the group formulated over 40 consensus statements spanning classification, pathology, molecular testing, clinical evaluation, and therapeutic strategies. Key recommendations include adoption of a unified MHN designation, use of a minimum immunophenotypic panel, integration of broad molecular profiling, and documentation of prior hematopoietic malignancy. Treatment algorithms emphasize surgical resection for unifocal disease and targeted therapy or immune checkpoint inhibition for multifocal disease when actionable mutations or PD-L1 expression are present. These consensus recommendations aim to reduce diagnostic ambiguity, standardize reporting, and improve outcomes for both pediatric and adult patients. Future priorities include international registries to refine risk stratification and biomarker-driven trials exploring targeted therapy, immunotherapy, and combination approaches.

Complement activation has been reported in primary immune thrombocytopenia (ITP); however, its clinical relevance remains poorly understood. This study aimed to clarify the association between complement activation and various biomarkers and the clinical characteristics of patients with ITP. Forty patients with ITP were enrolled in this study. Platelet-bound C1q, C3d, and C4d were elevated in a substantial population of patients with ITP compared with healthy controls with highly variable titers, Hierarchical clustering analysis showed that patients with ITP could be classified into three groups according to their levels: all negative (Cluster 1), elevated C1q with negative to low C3d and C4d (Cluster 2), and high C3d and C4d (Cluster 3). Platelet-associated (PA) IgM was detected mostly in Cluster 3, and PA-IgG was detected in Clusters 2 and 3. The number of cases refractory to first-line therapy increased in Clusters 2 and 3. Complement deposition on the platelet surface correlated with an increased percentage of immature platelets. There was no significant association between complement activation and PA-GPIIb/IIIa or -GPIb/IX antibodies, C1s ratio in the plasma, and fatigue score. Our results suggest that PA-IgG and PA-IgM contribute differentially to the complement activation profile on the platelet surface, and are associated with increase in platelet turnover, characterizing a distinct subset of ITP patients with complement activation. Our findings also may provide a rationale for stratifying patients in future clinical trials of complement-targeted therapies.

Fixed-duration venetoclax combinations have become a standard first-line treatment in chronic lymphocytic leukemia (CLL). The phase 3 CLL13/GAIA trial assesses three time-limited combinations: venetoclax-rituximab (RV), venetoclax-obinutuzumab (GV), and venetoclax-obinutuzumab-ibrutinib (GIV) compared to chemoimmunotherapy (CIT). Fit patients with CLL without TP53 aberrations were randomized between six cycles of CIT (fludarabine-cyclophosphamide-rituximab [FCR], bendamustine-rituximab [BR]) or 12 cycles of RV, GV or GIV (GIV: ibrutinib continuation until cycle 36 if measurable residual disease [MRD] at months 12/15). In total, 926 patients were randomized (GIV: 231, GV: 229, RV: 237, CIT: 229 [FCR: 150, BR: 79]). With a median observation time of 63.8 months, 5-year progression-free survival (PFS) rates were 81.3% (GIV), 69.8% (GV), 57.4% (RV), and 50.7% (CIT). PFS was superior for GV and GIV compared to CIT and RV (p<0.001 in each case). In addition, GIV showed longer PFS than GV (p=0.0046). Venetoclax-based retreatment after venetoclax-based first-line regimens was efficacious with 2-year treatment-free survival >80% from second-line treatment. No differences in overall survival were observed between treatment arms (5-year rates, GIV 94.3%; GV 93.6%; RV 94.7%; CIT 90.7%). Incidence rates of severe infections were highest with CIT while cardiac events were most frequent with GIV. Patients treated with GV or RV reported rapid and significantly greater quality of life (QoL) improvements compared to patients treated with CIT. In the GIV arm, clinically relevant QoL improvements occurred later (month 15, after the end of treatment in most patients) than with GV/RV, likely due to a higher treatment-related symptom burden. The trial is registered at clinicltrial.gov with the identifier, NCT02950051.

The process of non-occlusive thrombus formation is well known, but the mechanism keeping the thrombus silent at the end stage remains unclear. The aim of this work was to evaluate the role of fibrin in limiting further growth of a thrombotic remnant. Intravital microscopy showed that attachment of platelets to a fibrin-rich thrombus stopped after partial thrombus disaggregation, indicating that the thrombus activation potential is lost, a stage we named the stillness phase. Histological analyses showed that 80% of internal cross-section area of thrombus remnant is bordered by fibrin while 20% of superficial thrombus area was covered only by few platelet layers, suggesting a role of fibrin in limiting platelet recruitment. This result was confirmed in a flow-based assay where fibrin-rich thrombi recruited circulating platelets inefficiently as compared to fibrin-poor thrombi. Moreover, we found that in vitro, lysis of fibrin with rtPA released active thrombin. This observation was confirmed in vivo as treating a thrombus with rtPA to promote fibrin breakdown during the stillness phase resulted in the release of thrombin, leading to an unexpected re-growth of the thrombus. This finding was further supported by the dynamics of thrombus formation in FgaEK mice, which displayed repeated cycles of thrombus growth and detachment after vessel injury, with an inability to reach the stillness phase, accompanied by the continuous release of active thrombin. Altogether, these findings identify a novel role of fibrin in maintaining an end-stage thrombotic remnant in an inactive state.

Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia caused by monoclonal IgM autoantibodies that bind to red blood cells and trigger hemolysis through activation of the classical complement pathway. Cold agglutinins are produced by a clonal population of lymphocytes recognized by the WHO as a low grade lymphoproliferative disorder. Traditional therapy relied on B-cell-targeted immunosuppression with rituximab which mainly yielded partial responses in about half of the patients. The combination of rituximab with fludarabine or bendamustine significantly increased and prolonged response rates, though with a substantial infectious risk. Sutimlimab, the first C1s complement inhibitor, has shown efficacy in rapidly and sustainably increasing hemoglobin levels, reducing hemolysis, and significantly improving quality of life. However, the drug does not act on the B-cell clone and does not decrease the cold agglutinins. Therefore, several unmet needs remain, including identifying patients who can discontinue sutimlimab while maintaining remission, developing combination strategies effective against cold-induced symptoms, and improving infection prevention and control of hemolytic flares. This perspective article briefly recapitulates the pathophysiology of CAD, outlines the evolution of its treatment landscape, and focuses on the role of sutimlimab-its clinical positioning, therapeutic benefits, and management considerations-offering insights into optimizing care for patients with this challenging condition.

Large scale sequencing efforts have defined up to 27 diagnostic entities in B-ALL, leaving few samples without subtype assignment. Extended genomic and transcriptomic profiling in routine diagnostics broadens the sample collection and holds the potential to identify novel B-ALL subtypes. By analyzing an aggregated set of 4,857 B-ALL patients from three cohorts, we identified a novel group of twenty cases (age 18-66 years, median: 34 years) characterized by a previously undescribed IGH::FENDRR rearrangement exclusive to this subtype (n=17/20), KRAS p.A146T/V/P mutations (n=17/20 vs. n=86/4,857; p<0.001) and distinct DNA-methylation/gene expression profiles, including overexpression of the lncRNA FENDRR and the transcription factor FOXF1 ('FOXF1/FENDRR') as well as JAK/STAT and RAS signaling signatures. A gene expression machine learning classifier identified FOXF1/FENDRR cases in two independent cohorts with high accuracy. Patients treated according to GMALL/GRAALL protocols showed very poor chemotherapy response with n=8/13 having induction failure or MRD ≥10-3 and n=8/12 remaining MRD positive after 1st consolidation / salvage. MRD-stratified intensification including blinatumomab (n=10) and/or allogenic stem cell transplantation (n=12) resulted in ongoing molecular remission in 13/16 cases. FOXF1/FENDRR patients represent a novel B-ALL subtype which might benefit from early immunotherapeutic treatment or targeted interventions.

Iron is an essential element for most cellular processes and recent evidence highlighted its role in regulating the function of hematopoietic stem cells (HSCs). Abnormal iron levels impact HSC quiescence and self-renewal, however, the mechanism by which iron overload (IO) influences HSC function is still unknown. Here, we show that intracellular IO impairs mitochondrial fitness and bioenergetics, inducing metabolic rewiring. In thalassemic mice, as a model of chronic IO, HSCs accumulate mitochondria with elevated reactive oxygen species (mtROS), low membrane potential and reduced oxidative phosphorylation (OXPHOS). Mitochondrial defects are confirmed in other two models of IO, sickle cell disease and iron-loaded wild-type mice, and in vivo iron reduction rescues HSC mitochondria. IO HSCs are highly proliferating and in presence of damaged mitochondria rely on glycolysis for energy production. Notably, restoration of mitochondrial function by targeting in vivo mtROS improved the quiescence and self-renewal of IO HSCs. Our results unravel the critical interplay between iron, ROS and mitochondrial activity in HSCs, revealing that IO shapes HSC metabolic programs.

FLT3-ITD mutation is associated with poor prognosis in acute myeloid leukemia (AML), yet its kinase-independent mechanisms remain unclear. To investigate kinase-independent immunosuppressive mechanisms in FLT3-ITD AML, we integrated single-cell RNA sequencing from two public datasets and multiparameter flow cytometry data from 104 primary patient samples, identifying profound CD8+ T cell exhaustion as a hallmark of the FLT3-ITD immune microenvironment. Mechanistically, FLT3-ITD acts as a mutation-specific scaffold that assembles a ternary complex with PKCι and STAT1, as demonstrated by co-immunoprecipitation and intracellular colocalization. This complex enables PKCι-mediated phosphorylation of STAT1 specifically at serine 727 (S727), driving CD276 transcription independent of the canonical tyrosine 701 (Y701) site. Chromatin immunoprecipitation, electrophoretic mobility shift, promoter-reporter assays, and phosphosite-mutant constructs confirmed that S727 phosphorylation is necessary and sufficient for CD276 transactivation. Multiplex immunohistochemistry of patient bone marrow validated co-elevation of pS727-STAT1 and CD276 in FLT3-ITD blasts, accompanied by CD8+ T cell depletion. Functionally, CD276 upregulation induced profound CD8+ T cell exhaustion, characterized by reduced cytotoxicity, impaired proliferation, diminished IFN-γ production and elevated inhibitory checkpoints expression. Targeting CD276 restored CD8+ T cell function by 1.2-1.7-fold (cytotoxicity), 1.4-1.7-fold (proliferation), 1.5-1.8-fold (IFN-γ secretion) and 25.4%-67.6% (checkpoints expression) in ex vivo co-culture. In patient-derived xenograft models, co-treatment with FLT3i (quizartinib) and CD276-targeting agents led to 72.9%-80.4% tumor burden reduction and enhanced CD8+ T cell function, outperforming quizartinib monotherapy. These findings define a scaffolded PKCι-pS727-STAT1 signaling axis that promotes immune evasion in FLT3-ITD AML, supporting combined FLT3 and CD276 targeting as a promising translational strategy in this aggressive leukemia subtype.