In thrombosis and hemostasis, the formation of a platelet-fibrin thrombus or clot is a highly controlled process that varies, depending on the pathological context. Major signaling pathways in platelets are well established. However, studies with genetically modified mice have identified the contribution of hundreds of additional platelet-expressed proteins in arterial thrombus formation and bleeding. Using phenotype information of 540 mouse genes, involved in arterial thrombosis and hemostasis, we review current insights into established and novel platelet signaling mechanisms. We discuss pathways involved in platelet adhesion, shape change, integrin activation, intracellular vesicle trafficking and protein processing, granule secretion, aggregate formation and procoagulant activity. Specific attention is paid to the signaling routes used by ITAM-linked, ITIM-linked and G protein-coupled receptors, as well as downstream events feeding into GTPase regulation and protein kinase activation. We further summarize known alterations in platelet responses under conditions of venous, inflammatory and infection-dependent thrombosis, taking into account interactions of platelets with the endothelium, leukocytes and red blood cells. Understanding the genes and proteins involved in platelet signaling in the context of hemostasis, thrombosis and inflammation may lead to improved therapies to prevent and treat thrombotic disorders.

Adenosine-to-inosine (A-to-I) RNA editing is a prevalent RNA modification essential for cell survival. The process is catalyzed by the adenosine deaminase acting on RNA (ADAR) enzyme family that converts adenosines in double-stranded RNAs (dsRNAs) into inosines, which are read as guanosines during translation. Deep sequencing has helped to reveal that A-to-I editing occurs across various types of RNAs, affecting their functions. RNA editing detection is now so sophisticated that we can achieve a high level of accuracy and sensitivity to identify low-abundance edited events. Consequently, A-to-I editing has been implicated in various biological processes, including immune and stress responses, cancer progression, and stem cell fate determination. In particular, a crucial role for this process has been recently reported in hematopoietic cell development and hematologic malignancy progression. Results from genetic mouse models have demonstrated the impact of ADARs' catalytic activity on hematopoietic cells, complemented by insights from human cell studies. Meanwhile, clinical studies have implicated ADAR enzymes and RNA editing events in hematologic malignancies and highlighted their potential as prognostic indicators. In this review, we outline the regulatory mechanisms of RNA editing in both normal hematopoiesis and hematologic malignancies. We then speculate on how targeting ADAR expression and site-specific RNA substrates might serve as a therapeutic avenue for affected patients.

Most patients with diffuse large B-cell lymphoma (DLBCL) treated with immunotherapies such as bispecific antibodies (BsAbs) or chimeric antigen receptor (CAR) T cells fail to achieve durable treatment responses, underscoring the need for a deeper understanding of mechanisms that regulate the immune environment and response to treatment. Here, an integrative multiomics approach was applied to multiple large independent data sets to characterize DLBCL immune environments and to define their association with tumor cell-intrinsic genomic alterations and outcomes to CD19-directed CAR T-cell and CD20 × CD3 BsAb therapies. This approach effectively segregated DLBCLs into 4 immune quadrants (IQs) defined by cell-of-origin and immune-related gene set expression scores. These quadrants consisted of activated B cell-like (ABC) hot, ABC cold, germinal center B cell-like (GCB) hot, and GCB cold DLBCLs. Recurrent genomic alterations were enriched in each IQ, suggesting that lymphoma cell-intrinsic alterations contribute significantly to orchestrating unique DLBCL immune environments. For instance, SOCS1 loss-of-function mutations were significantly enriched among GCB hot DLBCLs, identifying a putative subset of inflamed DLBCLs that may be inherently susceptible to immunotherapy. In patients with relapsed/refractory DLBCL, DLBCL-IQ assignment correlated significantly with clinical benefit with a CD20 × CD3 BsAb (N = 74), but not with CD19-directed CAR T cells (Stanford, N = 51; Memorial Sloan Kettering Cancer Center, N = 69). Thus, DLBCL-IQ provides a new framework to conceptualize the DLBCL immune landscape and suggests the endogenous immune environment has a more significant impact on outcomes to BsAb than CAR T-cell treatment.

Antibodies to β2-glycoprotein I (β2GPI) cause thrombosis in antiphospholipid syndrome; however, the role of β2GPI in coagulation in vivo is not understood. To address this issue, we developed β2GPI-deficient mice (Apoh-/-) by deleting exons 2 and 3 of Apoh using CRISPR/Cas9 and compared the development of thrombosis in wild-type (WT) and Apoh-/- mice using rose bengal- and FeCl3-induced carotid thrombosis, laser-induced cremaster arteriolar injury, and inferior vena cava (IVC) stasis models. We also compared tail bleeding times and activation of platelets from WT and Apoh-/- mice in the absence and presence of β2GPI. Apoh-/- mice demonstrated prolonged time to occlusion of the carotid after exposure to rose bengal or FeCl3 and reduced platelet and fibrin accumulation in cremasteric arterioles after laser injury. Significantly smaller thrombi formed in the IVC of Apoh-/- mice 48 hours after IVC occlusion. The activated partial thromboplastin time and prothrombin time, as well as activated partial thromboplastin time reagent and tissue factor-induced thrombin generation times, of Apoh-/- and WT plasma revealed no differences. However, we observed significant prolongation of tail bleeding in Apoh-/- mice and reduced P-selectin expression and fibrinogen binding to activated α2bβ3 on platelets from these mice after stimulation with thrombin; these changes were reversed by β2GPI. A protease activated receptor 3 (PAR3) antibody blocked thrombin-induced activation of WT platelets and the ability of β2GPI to restore thrombin-induced activation of Apoh-/- platelets. These studies demonstrate that β2GPI may promote platelet activation by enhancing the ability of PAR3 to present thrombin to PAR4.

Babesiosis in sickle cell disease (SCD) is marked by severe anemia but the underlying red blood cell (RBC) rheologic parameters remain largely undefined. Here, we describe altered RBC deformability from both primary (host RBC sickle hemoglobin mediated) and secondary changes (Babesia parasite infection mediated) to the RBC membrane using wild-type AA, sickle trait AS, and sickle SS RBCs. Our ektacytometry analysis demonstrates that the changes in the host RBC biomechanical properties, before and after Babesia infection, reside on a spectrum of severity, with wild-type infected AA cells, despite showing a significant reduction of deformability under both shear and osmolarity gradients, exhibiting only a mild phenotype, compared with infected AS RBCs that show median changes in deformability and infected SS RBCs that exhibit the most dramatic impact of infection on cellular rheology, including an increase in point of sickling values. Furthermore, using ImageStream cytometric technology to quantify changes in cellular shape and area along with a tunable resistive pulse sensor to measure release of extracellular vesicles from these host RBCs, before and after infection, we offer a potential mechanistic basis for this extreme SS RBC rheologic profile, which include enhanced sickling rates and altered osmotic fragility, loss of RBC surface area, and hypervesiculation in infected SS host RBCs. These results underline the importance of understanding the impact of intraerythrocytic parasitic infections of SCD RBCs, especially on their cellular membranes and studying the mechanisms that lead to hyperhemolysis and extreme anemia in patients with SCD.

Follicular lymphoma is the most common subtype of indolent lymphoma. Despite multiple trials over the past decade showing improved progression-free survival with new first-line therapeutic strategies -such as anti-CD20 maintenance therapy and new glycoengineered anti-CD20 antibodies- no standardized approach has been widely adopted in routine clinical practice. Several factors may explain this, including the increased incidence of infectious adverse events associated with these therapies, particularly during the COVID-19 pandemic, and the lack of overall survival benefit despite long-term follow-up. A general consensus has emerged acknowledging the high prognostic variability of follicular lymphoma, which complicates the adoption of a one-size-fits-all first-line treatment strategy. A plethora of prognostic scores (FLIPI, FLIPI2, PRIMA-PI, m7-FLIPI, FLEX, 23-gene score, etc) has been proposed but none can reliably identify the ~20% of patients that will die within 10 years of first-line immunochemotherpay and for whom a critical medical need remains despite recent therapeutic improvements. Consequently, current prognostic models mainly serve as tools to cross-compare and stratify clinical trials. In this review, we highlight current and future strategies aimed at reshaping frontline treatment paradigms to improve outcomes, including tailored approaches based on risk- or response-adapted designs, development of new predictive -rather than prognostic- tools, approaches to reduce adverse events to enhance health-related quality of life, and the potential use of T-cell-engaging therapies to improve survival in the highest risk patients.

Blood clots are complex structures composed of blood cells and proteins held together by the structural framework provided by an insoluble fibrin network. Factor (F)XIII is a protransglutaminase essential for stabilizing the fibrin network. Activated FXIII(a) introduces novel covalent crosslinks within and between fibrin and other plasma and cellular proteins, and thereby promotes fibrin biochemical and mechanical integrity. These irreversible modifications are also major determinants of clot composition and functional properties. As such, FXIII has central roles in hemostasis and wound healing, thrombosis, and many proinflammatory diseases associated with coagulation activation. FXIII's biochemical properties are as interesting as its biology is unusual, giving rise to unique and still undefined mechanisms. Here we review features underlying FXIII biology, biochemical function, biophysical impact, and (patho)physiologic implications in hemostasis, thrombosis, and disease.

T-cell prolymphocytic leukemia (T-PLL) is an aggressive lymphoid malignancy with limited treatment options. To discover new treatment targets for T-PLL, we performed high-throughput drug sensitivity screening on 30 primary patient samples ex vivo. After screening >2800 unique compounds, we found T-PLL to be more resistant to most drug classes, including chemotherapeutics, than other blood cancers. Furthermore, we discovered previously unreported vulnerabilities of T-PLL. T-PLL cells exhibited a particular sensitivity to drugs targeting autophagy (thapsigargin and bafilomycin A1), nuclear export (selinexor), and inhibitor of apoptosis proteins (IAPs; birinapant), sensitivities that were also shared by other T-cell malignancies. Through bulk and single-cell RNA sequencing, we found these compounds to activate the Toll-like receptor (bafilomycin A1), p53 (selinexor), and tumor necrosis factor α (TNF-α)/NF-κB signaling pathways (birinapant) in T-PLL cells. Focusing on birinapant for its potential in drug repurposing, we uncovered that IAP inhibitor-induced cell death was primarily necroptotic and dependent on TNF-α. Through spectral flow cytometry, we confirmed the absence of cleaved caspase-3 in IAP inhibitor-treated T-PLL cells and show that IAP inhibition reduces the proliferation of T-PLL cells stimulated ex vivo, while showing only a limited effect on nonmalignant T-cells. In summary, our study maps the drug sensitivity of T-PLL across a broad range of targets and identifies new therapeutic approaches for T-PLL by targeting IAPs, exportin 1, and autophagy, highlighting potential candidates for drug repurposing and novel treatment strategies.

Recent advances in acute myeloid leukemia (AML) come from studies investigating older adults aged <60 years, those aged ≥75 years, or less fit adults. Uncertainty exists for the management of otherwise healthy adults with AML in their 60s and 70s, which also represents a significant proportion of AML cases. We discuss current considerations in older, fit adults with AML, including determination of fitness, factors beyond fitness that should be assessed, and challenges and innovations to improve patient outcomes.

Leukopoiesis is lethally arrested in mice lacking the master transcriptional regulator PU.1. Depending on the animal model, subtotal PU.1 loss either induces acute myeloid leukemia or arrests early B-cell and dendritic-cell development. Although humans with absolute PU.1 deficiency have not been reported, a small cadre of congenital agammaglobulinemia patients with sporadic, inborn PU.1 haploinsufficiency was recently described. To better estimate the penetrance, clinical complications, immunophenotypic features, and malignancy risks of PU.1-mutated agammaglobulinemia (PU.MA), a collection of 134 novel or rare PU.1 variants from publicly available databases, institutional cohorts, previously published reports, and unsolved agammaglobulinemia cases were functionally analyzed. In total, 25 loss-of-function (LOF) variants were identified in 33 heterozygous carriers from 21 kindreds across 13 nations. Of individuals harboring LOF PU.1 variants, 22 were agammaglobulinemic, 5 displayed antibody deficiencies, and 6 were unaffected, indicating an estimated disease penetrance of 81.8% with variable expressivity. In a cluster of patients, disease onset was delayed, sometimes into adulthood. All LOF variants conveyed effects via haploinsufficiency, either by destabilizing PU.1, impeding nuclear localization, or directly interfering with transcription. PU.MA patient immunophenotypes consistently demonstrated B-cell, conventional dendritic-cell, and plasmacytoid dendritic-cell deficiencies. Associated infectious and noninfectious symptoms hewed closely to X-linked agammaglobulinemia and not monogenic dendritic-cell deficiencies. No carriers of LOF PU.1 variants experienced hematologic malignancies. Collectively, in vitro and clinical data indicate heterozygous LOF PU.1 variants undermine humoral immunity but do not convey strong leukemic risks.

Desmopressin (1-desamino-8-d-arginine vasopressin [DDAVP]) can be used to prevent or stop bleeding. However, large interindividual variability is observed in DDAVP response and determinants are largely unknown. In this systematic review and meta-analysis, we aimed to identify the response to DDAVP and the factors that determine DDAVP response in patients. We included studies with patients with any bleeding disorder receiving DDAVP. First and second screening round and risk of bias assessment were performed by independent reviewers. The main outcome was proportion of patients with complete (factor level >50 U/dL) or partial (30-50 U/dL) response to DDAVP. Determinants of response including disease type, age, sex, von Willebrand factor (VWF) and factor VIII (FVIII) mutations, and baseline factor levels were investigated. In total, 591 articles were found and 103 were included. Of these, 71 articles (1772 patients) were suitable for the study's definition of response. Meta-analysis showed a pooled response proportion of 0.71 (0.64; 0.78) and a significant difference in response between disease subtypes. For hemophilia A, baseline FVIII activity (FVIII:C) was a borderline significant determinant of response. In patients with von Willebrand disease (VWD) type 1, VWF antigen (VWF:Ag), VWF activity, and FVIII:C were significant determinants. A large variation in response was observed for specific mutations in VWF and FVIII. Response to DDAVP varied between disease subtypes and was largely determined by the baseline levels of FVIII:C for hemophilia A and VWF:Ag for VWD. Our findings highlight the significant differences in response and emphasize the need for a standardized response definition and further research into response mechanisms.

Previous studies have reported that chronic lymphocytic leukemia (CLL) shows a de novo chromatin activation pattern compared with normal B cells. Here, we explored whether the level of chromatin activation is related to the clinical behavior of CLL. We identified that, in some regulatory regions, increased de novo chromatin activation is linked to clinical progression, whereas, in other regions, it is associated with an indolent course. We next developed 2 prognostic scores for progressive and indolent disease, respectively, calculated a single score representing the balance between them, and further generated surrogate scores based on gene and protein expression of the target genes. The balance score outperformed the clinical impact of the 2 individual scores, because it seemed to capture the prognostic information provided by each of them. Biologically, CLLs with higher balance score showed increased activation of tumor necrosis factor alpha (TNF-α)/NF-κB and mTOR signaling pathways. Regulatory programs related to progression were predominantly activated in the lymph node microenvironment, whereas those linked to indolent disease appeared to be microenvironment independent. Finally, we thoroughly validated the balance score as a powerful and independent quantitative prognostic factor for time to first treatment across independent CLL cohorts and data modalities, such as chromatin, transcriptome, or proteome data. Our findings support the concept that de novo acquisition of chromatin changes in CLL cells plays a dual biological role, and the balance between proprogression and proindolence is a strong independent determinant of CLL prognosis.

Immunomodulatory drug (IMiD) resistance is a key clinical challenge in myeloma treatment. Previous data suggest almost one-third of myeloma patients acquire genetic alteration of the key IMiD effector cereblon (CRBN) by the time they are pomalidomide refractory. Some events, including stop codons/frameshift mutations and copy loss, have clearly explicable effects on CRBN protein function. Missense mutations have also been reported throughout the length of CRBN but their functional impact has not been systematically studied. This study modeled selected missense mutations and examined their effect on CRBN function also analyzing whether any mutations deleterious to IMiD action could be overcome using the novel cereblon E3 ligase modulators (CELMoDs). Three patterns of response to missense mutations were apparent: mutations that led to complete loss of CRBN function for all agents, those that had no effect on CRBN function, and those with agent-dependent effect on CRBN function. The latter group of 4 mutations were profiled in more detail with confirmatory experiments demonstrating an ability of the more potent CELMoDs to lead to neosubstrate degradation and cell death even though IMiDs were not active. Dynamic modeling based on a newly generated crystal structure of the DDB1/CRBN/lenalidomide complex, with greater resolution than those published to date, helped to understand the impact of these mutations. These results have important implications for the interpretation of CRBN sequencing results from patients for future therapy decisions, particularly differentiating those who may, despite relapsing on IMiDs with CRBN mutations, have the potential to still benefit from the use of CELMoD agents.