Single-Cell Analyses Reveal Megakaryocyte-Biased Hematopoiesis in Myelofibrosis and Identify Mutant Clone-Specific Targets.

Myelofibrosis is a severe myeloproliferative neoplasm characterized by increased numbers of abnormal bone marrow megakaryocytes that induce fibrosis, destroying the hematopoietic microenvironment. To determine the cellular and molecular basis for aberrant megakaryopoiesis in myelofibrosis, we performed single-cell transcriptome profiling of 135,929 CD34+ lineage- hematopoietic stem and progenitor cells (HSPCs), single-cell proteomics, genomics, and functional assays. We identified a bias toward megakaryocyte differentiation apparent from early multipotent stem cells in myelofibrosis and associated aberrant molecular signatures. A sub-fraction of myelofibrosis megakaryocyte progenitors (MkPs) are transcriptionally similar to healthy-donor MkPs, but the majority are disease specific, with distinct populations expressing fibrosis- and proliferation-associated genes. Mutant-clone HSPCs have increased expression of megakaryocyte-associated genes compared to wild-type HSPCs, and we provide early validation of G6B as a potential immunotherapy target. Our study paves the way for selective targeting of the myelofibrosis clone and illustrates the power of single-cell multi-omics to discover tumor-specific therapeutic targets and mediators of tissue fibrosis.

Unravelling Intratumoral Heterogeneity through High-Sensitivity Single-Cell Mutational Analysis and Parallel RNA Sequencing.

Single-cell RNA sequencing (scRNA-seq) has emerged as a powerful tool for resolving transcriptional heterogeneity. However, its application to studying cancerous tissues is currently hampered by the lack of coverage across key mutation hotspots in the vast majority of cells; this lack of coverage prevents the correlation of genetic and transcriptional readouts from the same single cell. To overcome this, we developed TARGET-seq, a method for the high-sensitivity detection of multiple mutations within single cells from both genomic and coding DNA, in parallel with unbiased whole-transcriptome analysis. Applying TARGET-seq to 4,559 single cells, we demonstrate how this technique uniquely resolves transcriptional and genetic tumor heterogeneity in myeloproliferative neoplasms (MPN) stem and progenitor cells, providing insights into deregulated pathways of mutant and non-mutant cells. TARGET-seq is a powerful tool for resolving the molecular signatures of genetically distinct subclones of cancer cells.

Interferon and myeloproliferative neoplasms: Evolving therapeutic approaches.

Interferons (IFNs) are a diverse group of cytokines whose potent antitumor effects have piqued the interest of scientists for decades. Some of the most sustained clinical accomplishments have been in the field of myeloproliferative neoplasms (MPNs). Here, we discuss how both historical and novel breakthroughs in our understanding of IFN function may lead to more effective therapies for MPNs. The particular relevance and importance of modulating the novel IFN-regulated ULK1 pathway to optimize IFN responses is highlighted.

Inferring the initiation and development of myeloproliferative neoplasms.

The developmental history of blood cancer begins with mutation acquisition and the resulting malignant clone expansion. The two most prevalent driver mutations found in myeloproliferative neoplasms-JAK2V617F and CALRm-occur in hematopoietic stem cells, which are highly complex to observe in vivo. To circumvent this difficulty, we propose a method relying on mathematical modeling and statistical inference to determine disease initiation and dynamics. Our findings suggest that CALRm mutations tend to occur later in life than JAK2V617F. Our results confirm the higher proliferative advantage of the CALRm malignant clone compared to JAK2V617F. Furthermore, we illustrate how mathematical modeling and Bayesian inference can be used for setting up early screening strategies.

JAK2V617F-dependent down regulation of SHP-1 expression participates in the selection of myeloproliferative neoplasm cells in the presence of TGF-ß.

Myeloproliferative neoplasms (MPNs) are characterized by an increased production of blood cells due to the acquisition of mutations such as JAK2V617F. TGF-ß, whose secretion is increased in MPN patients, is known to negatively regulate haematopoietic stem cell (HSC) proliferation. Using an isogenic JAK2V617F or JAK2 wild-type UT-7 cell line we observed that JAK2V617F cells resist to TGF-ß antiproliferative activity. Although TGF-ß receptors and SMAD2/3 expressions are similar in both cell types, TGF-ß-induced phosphorylation of SMAD2/3 is reduced in UT-7 JAK2V617F cells compared with JAK2 WT cells. We confirmed that JAK2V617F mutated cells are resistant to the antiproliferative effect of TGF-ß in a competitive assay as we observed a positive selection of JAK2V617F cells when exposed to TGF-ß. Using cell lines, CD34-positive cells from MPN patients and bone marrow cells from JAK2V617F knock-in mice we identified a down regulation of the SHP-1 phosphatase, which is required for the regulation of HSC quiescence by TGF-ß. The transduction of SHP-1 cDNA (but not a phosphatase inactive cDNA) restores the antiproliferative effect of TGF-ß in JAK2V617F mutated cells. Finally, SC-1, a known agonist of SHP-1, antagonized the selection of JAK2V617F mutated cells in the presence of TGF-ß. In conclusion, we show a JAK2-dependent down regulation of SHP-1 in MPN patients' cells which is related to their resistance to the antiproliferative effect of TGF-ß. This may participate in the clonal selection of cancer cells in MPNs.

Increased mRNA expression for serotonin receptor 1B (HTR1B) is associated with thrombosis in BCR::ABL1-negative myeloproliferative neoplasms.

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are clonal haematopoietic stem cell disorders characterized by specific driver mutations and an increased risk of both macrothrombosis and microthrombosis. Serotonin receptor type 1B (HTR1B) was found to be expressed by various solid tumours, and also primary bone marrow mononuclear cells from myelodysplastic neoplasm and acute myeloid leukaemia patients, representing a potential therapeutic target. In this study we assessed for the first time the expression levels of HTR1B mRNA in the peripheral blood mononuclear cells (PBMC) of 85 newly diagnosed MPN patients, consisting of 28 polycythemia vera, 25 essential thrombocythemia and 32 primary myelofibrosis cases. Levels of HTR1B expression between MPN subtypes and control group were not significantly different. However, at clinical data examination, it was observed that MPN patients with a recent history of major thrombosis and/or signs of impaired microcirculation exhibited significantly higher HTR1B expression levels compared to non-thrombotic MPNs and control group. Moreover, thrombotic MPN patients had significantly higher HTR1B expression than patients with recent thrombosis and absence of MPN diagnostic criteria. These findings suggest that increased levels of HTR1B expression in PBMC might be associated with thrombosis in MPN patients, but larger studies are needed for confirmation, including testing of the receptor protein expression level.

Cardiovascular Risk in Philadelphia-Negative Myeloproliferative Neoplasms: Mechanisms and Implications-A Narrative Review.

Myeloproliferative neoplasms (MPNs), encompassing disorders like polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are characterized by clonal hematopoiesis without the Philadelphia chromosome. The JAK2 V617F mutation is prevalent in PV, ET, and PMF, while mutations in MPL and CALR also play significant roles. These conditions predispose patients to thrombotic events, with PMF exhibiting the lowest survival among MPNs. Chronic inflammation, driven by cytokine release from aberrant leukocytes and platelets, amplifies cardiovascular risk through various mechanisms, including atherosclerosis and vascular remodeling. Additionally, MPN-related complications like pulmonary hypertension and cardiac fibrosis contribute to cardiovascular morbidity and mortality. This review consolidates recent research on MPNs' cardiovascular implications, emphasizing thrombotic risk, chronic inflammation, and vascular stiffness. Understanding these associations is crucial for developing targeted therapies and improving outcomes in MPN patients.

New advances in the role of JAK2 V617F mutation in myeloproliferative neoplasms.

The JAK2 V617F mutation is the most common driver gene in myeloproliferative neoplasm (MPN), which means that the JAK/STAT signaling pathway is persistently activated independent of cytokines, and plays an important part in the onset and development of MPN. The JAK inhibitors, although widely used in the clinical practice, are unable to eradicate MPN. Therefore, the unavoidable long-term treatment poses a serious burden for patients with MPN. It is established that the JAK2 V617F mutation, in addition its role in the JAK/STAT pathway, can promote cell proliferation, differentiation, anti-apoptosis, DNA damage accumulation, and other key biologic processes through multiple pathways. Other than that, the JAK2 V617F mutation affects the cardiovascular system through multiple mechanisms. Although JAK inhibitors cannot eradicate MPN cells, the combined use of JAK inhibitors and other drugs may have surprising effects. This requires an in-depth understanding of the mechanism of action of the JAK2 V617F mutation. In this review, the authors explored the role of the JAK2 V617F mutation in MPN from multiple aspects, including the mechanisms of non-JAK/STAT pathways, the regulation of cellular methylation, the induction of cellular DNA damage accumulation, and effects on the cardiovascular system, with the objective of providing valuable insights into multidrug combination therapy for MPN.

Myeloproliferative neoplasms in the adolescent and young adult population: A comprehensive review of the literature.

Myeloproliferative neoplasms (MPN) are characterized by a clonal proliferation of myeloid lineage cells within the bone marrow. The classical BCR-ABL negative MPNs are comprised of polycythaemia vera, essential thrombocythaemia and primary myelofibrosis. Historically, the majority of MPNs are diagnosed in adults older than 60 years of age; however, in recent years, there has been recognition of MPNs in the adolescent and young adult (AYA) population. AYAs with MPN, typically defined as between the ages of 15 and 39 years old, may comprise up to 20% of patients diagnosed with MPN. They demonstrate unique patterns of driver mutations and thrombotic events and remain at risk for progression to more aggressive disease states. Given the likely long length of time they will live with their disease, there is a significant unmet need in identifying well-tolerated and effective treatment options for these patients, particularly with the advent of disease modification. In this review, we provide a comprehensive overview of the clinical features, disease course and management of AYA patients with MPN and, in doing so, highlight key characteristics that distinguish them from their older counterparts.

Should oligomonocytic CMML be classified as an independent disease entity?

The 2022 WHO Classification revised the diagnostic criteria of CMML and included the variant, formerly known as oligomonocytic CMML (O-CMML), into the CMML disease. CMML is currently subtyped into MD-CMML and MP-CMML. In a recent study, Castaño-Díez et al. showed that the newly included O-CMML has unique clinical features and is an independent favourable risk factor, and proposed to view O-CMML as an independent subtype of CMML, parallel to MD-CMML and MP-CMML. Commentary on: Castaño-Díez et al. Characteristics and long-term outcome in a large series of chronic myelomonocytic leukaemia patients including 104 formerly referred to as oligomonocytic. Br J Haematol 2024;204:892-897.

Essential thrombocythaemia: A contemporary approach with new drugs on the horizon.

Essential thrombocythaemia (ET) is a myeloproliferative neoplasm characterized by an increased risk of vascular complications and a tendency to progress to myelofibrosis and acute leukaemia. ET patients have traditionally been stratified into two thrombosis risk categories based on age older than 60 years and a history of thrombosis. More recently, the revised IPSET-thrombosis scoring system, which accounts for the increased risk linked to the JAK2 mutation, has been incorporated into most expert recommendations. However, there is increasing evidence that the term ET encompasses different genomic entities, each with a distinct clinical course and prognosis. Moreover, the effectiveness and toxicity of cytoreductive and anti-platelet treatments differ depending on the molecular genotype. While anti-platelets and conventional cytoreductive agents, mainly hydroxycarbamide (hydroxyurea), anagrelide and pegylated interferon, remain the cornerstone of treatment, recent research has shed light on the effectiveness of novel therapies that may help improve outcomes. This comprehensive review focuses on the evolving landscape of treatment strategies in ET, with an emphasis on the role of molecular profiling in guiding therapeutic decisions. Besides evidence-based management according to revised IPSET-thrombosis stratification, we also provide specific observations for those patients with CALR-, MPL-mutated and triple-negative ET, as well as cases with high-risk mutations.

Autoimmune myelofibrosis: A Mayo Clinic series of 22 patients.

We describe the clinical phenotype, management strategies and outcomes of 22 patients with autoimmune myelofibrosis (AIMF); median age: 45 years; 77% females; 83% with autoimmune disease, pancytopenia in 32% and transfusion-requiring anaemia in 59%. All informative cases were negative for JAK2 (n = 18) and CALR/MPL mutations (n = 12). Fourteen of nineteen (74%) evaluable patients achieved complete response (CR) based on the resolution of cytopenias. First-line treatments included steroids +/- immunosuppressive agents, cyclosporin and mycophenolate with CR in 7 of 13 (54%), 1 of 2 (50%) and 1 of 2 (50%) respectively. Rituximab salvage therapy yielded CR in 4 of 5 (80%) cases. The current study provides information on steroid-sparing treatments for AIMF.

Clinical utility of investigations in triple-negative thrombocytosis: A real-world, multicentre evaluation of UK practice.

Diagnosis of essential thrombocythaemia (ET) is challenging in patients lacking JAK2/CALR/MPL mutations. In a retrospective evaluation of 320 patients with 'triple-negative thrombocytosis', we assessed utility of bone marrow histology (90.9% of patients) and myeloid gene panel (MGP, 55.6%). Supportive histology ('myeloproliferative neoplasm-definite/probable', 36.8%) was associated with higher platelet counts and varied between centres. 14.6% MGP revealed significant variants: 3.4% JAK2/CALR/MPL and 11.2% other myeloid genes. Final clinical diagnosis was strongly predicted by histology, not MGP. 23.7% received cytoreduction (17.6% under 60 years). Real-world 'triple-negative' ET diagnosis currently depends heavily on histology; we advocate caution in MGP-negative cases and that specific guidelines are needed.

Decreased spermatogonial numbers in boys with severe haematological diseases.

This study examines spermatogonial numbers in testicular samples from 43 prepubertal patients undergoing haematopoietic stem cell transplantation (HSCT). High-dose chemotherapy and/or radiation during HSCT can impact spermatogenesis requiring fertility preservation. Results show that 49% of patients have decreased and 19% severely depleted spermatogonial pool prior to HSCT. Patients with Fanconi anaemia exhibit significantly reduced spermatogonial numbers. Patients with immunodeficiency or aplastic anaemia generally present within the normal range, while results in patients with myelodysplastic syndrome or myeloproliferative neoplasm vary. The study emphasizes the importance of assessing spermatogonial numbers in patients with severe haematological diseases for informed fertility preservation decisions.

Sailing in deceptive calm: Navigating the undercurrents of essential thrombocythaemia.

The discovery of driver mutations in myeloproliferative neoplasms has significantly contributed to the management of patients with essential thrombocythaemia (ET). High-quality evidence has started to pave the way for targeted therapy. The review by Ferrer-Marín et al. further advances this discussion, highlighting how molecular profiling, including non-driver gene mutations, is set to revolutionize personalized treatment approaches for ET patients. Commentary on: Ferrer-Marín et al. Essential thrombocythemia: a contemporary approach with new drugs on the horizon. Br J Haematol 2024;204:1605-1616.

The CALR mutations enhance the expression of the immunosuppressive proteins GARP and LAP on peripheral blood lymphocytes through increased binding of activated platelets.

Recently, an antibody which inhibits the glycoprotein A repetitions predominant (GARP)-mediated release of active transforming growth factor beta (TGFß) from the TGFß propeptide latency-associated peptide (LAP) showed preclinical activity in a murine model of the chronic myeloproliferative neoplasms (MPN). Consequently, we investigated the expression of the immunosuppressive molecules LAP and GARP on peripheral blood lymphocytes from 56 MPN patients and 11 healthy donors (HD). We found that lymphocytes from patients with MPN express higher levels of LAP and GARP with no strong differences found between the different MPN diagnoses. The impact of clinical parameters on the expression of LAP and GARP by lymphocytes showed that patients with calreticulin (CALR)mut MPN have increased expression compared with HD and patients with the Januskinase2 (JAK2) mutation. The fraction of lymphocytes bound to activated platelets (aPLT) strongly correlate to LAP and GARP expression suggesting that it is not the lymphocytes themselves but aPLT, which confer the increased expression of GARP and LAP on MPN patient lymphocytes. Notably, no differences in neither platelet counts nor anti-thrombotic therapy was identified between patients with JAK2- and CALRmut patients. Analysis of platelet gene expression failed to identify differences in expression of relevant genes between JAK2- and CALRmut patients.

Ratio of stemness to interferon signalling as a biomarker and therapeutic target of myeloproliferative neoplasm progression to acute myeloid leukaemia.

Progression to aggressive secondary acute myeloid leukaemia (sAML) poses a significant challenge in the management of myeloproliferative neoplasms (MPNs). Since the physiopathology of MPN is closely linked to the activation of interferon (IFN) signalling and that AML initiation and aggressiveness is driven by leukaemia stem cells (LSCs), we investigated these pathways in MPN to sAML progression. We found that high IFN signalling correlated with low LSC signalling in MPN and AML samples, while MPN progression and AML transformation were characterized by decreased IFN signalling and increased LSC signature. A high LSC to IFN expression ratio in MPN patients was associated with adverse clinical prognosis and higher colony forming potential. Moreover, treatment with hypomethylating agents (HMAs) activates the IFN signalling pathway in MPN cells by inducing a viral mimicry response. This response is characterized by double-stranded RNA (dsRNA) formation and MDA5/RIG-I activation. The HMA-induced IFN response leads to a reduction in LSC signature, resulting in decreased stemness. These findings reveal the frequent evasion of viral mimicry during MPN-to-sAML progression, establish the LSC-to-IFN expression ratio as a progression biomarker, and suggests that HMAs treatment can lead to haematological response in murine models by re-activating dsRNA-associated IFN signalling.

British Society for Haematology guidelines to improve the care of asplenic patients: Much work done, some remaining and a call for national registries.

Asplenic patients are at high risk of serious infectious or thrombotic complications, especially when they are not adequately informed of the risk and not closely followed. Ladhani et al. on behalf of the British Society for Haematology propose updated guidelines for managing these patients. Healthcare professionals need to improve infection prevention in patients with hypofunctional or absent spleen through better identification and immunisation using established national registries. Commentary on: Ladhani et al. Prevention and treatment of infection in patients with absent or hypofunctional spleen: A British Society for Haematology guideline. Br J Haematol 2024;204:1672-1686.

Antineoplastic effects of pharmacological inhibitors of aurora kinases in CSF3RT618I-driven cells.

Myeloproliferative neoplasms (MPN) are consolidated as a relevant group of diseases derived from the malfunction of the hematopoiesis process and have as a particular attribute the increased proliferation of myeloid lineage. Among these, chronic neutrophilic leukemia (CNL) is distinguished, caused by the T618I mutation of the CSF3R gene, a trait that generates ligand-independent receptor activation and downstream JAK2/STAT signaling. Previous studies reported that mutations in BCR::ABL1 and JAK2V617F increased the expression of the aurora kinase A (AURKA) and B (AURKB) in Ba/F3 cells and their pharmacological inhibition displays antineoplastic effects in human BCR::ABL1 and JAK2V617F positive cells. Delimiting the current scenario, aspects related to the AURKA and AURKB as a potential target in CSF3RT618I-driven models is little known. In the present study, the cellular and molecular effects of pharmacological inhibitors of aurora kinases, such as aurora A inhibitor I, AZD1152-HQPA, and reversine, were evaluated in Ba/F3 expressing the CSF3RT618I mutation. AZD1152-HQPA and reversine demonstrated antineoplastic potential, causing a decrease in cell viability, clonogenicity, and proliferative capacity. At molecular levels, all inhibitors reduced histone H3 phosphorylation, aurora A inhibitor I and reversine reduced STAT5 phosphorylation, and AZD1152-HQPA and reversine induced PARP1 cleavage and γH2AX expression. Reversine more efficiently modulated genes associated with cell cycle and apoptosis compared to other drugs. In summary, our findings shed new insights into the use of AURKB inhibitors in the context of CNL.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissue: Myeloid Neoplasms.

In this manuscript, we review myeloid neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5), focusing on changes from the revised fourth edition (WHO-HEM4R). Disease types and subtypes have expanded compared with WHO-HEM4R, mainly because of the expansion in genomic knowledge of these diseases. The revised classification is based on a multidisciplinary approach including input from a large body of pathologists, clinicians, and geneticists. The revised classification follows a hierarchical structure allowing usage of family (class)-level definitions where the defining diagnostic criteria are partially met or a complete investigational workup has not been possible. Overall, the WHO-HEM5 revisions to the classification of myeloid neoplasms include major updates and revisions with increased emphasis on genetic and molecular drivers of disease. The most notable changes have been applied to the sections of acute myeloid leukemia and myelodysplastic neoplasms (previously referred to as myelodysplastic syndrome) with incorporation of novel, disease-defining genetic changes. In this review we focus on highlighting the updates in the classification of myeloid neoplasms, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of myeloid neoplasms in routine practice.