Activated mesenchymal stem/stromal cells promote myeloid cell differentiation via CCL2/CCR2 signaling.

Myeloid cells, which originate from hematopoietic stem/progenitor cells (HSPCs), play a crucial role in mitigating infections. This study aimed to explore the impact of mesenchymal stem/stromal cells (MSCs) on the differentiation of HSPCs and progenitors through the C-C motif chemokine CCL2/CCR2 signaling pathway. Murine MSCs, identified as PDGFRα+Sca-1+ cells (PαS cells), were found to secrete CCL2, particularly in response to lipopolysaccharide stimulation. MSC-secreted CCL2 promoted the differentiation of granulocyte/macrophage progenitors into the myeloid lineage. MSC-derived CCL2 plays an important role in the early phase of myeloid cell differentiation in vivo. Single-cell RNA sequencing analysis confirmed that CCL2-mediated cell fate determination was also observed in human bone marrow cells. These findings provide valuable insights for investigating the in vivo effects of MSC transplantation.

Impact of non-driver gene mutations on thrombo-haemorrhagic events in ET patients.

Risk-adapted therapy is recommended to prevent major clinical complications, such as thrombo-haemorrhagic events, in patients with essential thrombocythaemia (ET). In this study, we analysed the association between non-driver gene mutations and thrombo-haemorrhagic events in 579 patients with ET. ASXL1 and TP53 mutations were frequently identified in patients with ET complicated by thrombosis (22.7% and 23.1%, respectively), and the DNMT3A mutation was frequently identified in patients who experienced haemorrhage (15.2%). Multivariate analyses of thrombosis-free survival (TFS) revealed that ASXL1 and TP53 mutations are associated with thrombosis (hazard ratio [HR] = 3.140 and 3.752 respectively). Patients harbouring the ASXL1 or TP53 mutation had significantly worse TFS rates than those without mutation (p = 0.002 and p < 0.001 respectively). Furthermore, JAK2V617F-mutated patients with accompanying ASXL1 mutations showed significantly shorter TFS compared with those without ASXL1 mutations (p = 0.003). Multivariate analyses of haemorrhage-free survival (HFS) revealed that the DNMT3A mutation (HR = 2.784) is associated with haemorrhage. DNMT3A-mutated patients showed significantly shorter HFS than those without the mutation (p = 0.026). Non-driver gene mutations should be considered in treatment strategies and may provide important information for personalised treatment approaches.

Diagnosis- and Prognosis-Related Gene Alterations in BCR::ABL1-Negative Myeloproliferative Neoplasms.

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are a group of hematopoietic malignancies in which somatic mutations are acquired in hematopoietic stem/progenitor cells, resulting in an abnormal increase in blood cells in peripheral blood and fibrosis in bone marrow. Mutations in JAK2, MPL, and CALR are frequently found in BCR::ABL1-negative MPNs, and detecting typical mutations in these three genes has become essential for the diagnosis of BCR::ABL1-negative MPNs. Furthermore, comprehensive gene mutation and expression analyses performed using massively parallel sequencing have identified gene mutations associated with the prognosis of BCR::ABL1-negative MPNs such as ASXL1, EZH2, IDH1/2, SRSF2, and U2AF1. Furthermore, single-cell analyses have partially elucidated the effect of the order of mutation acquisition on the phenotype of BCR::ABL1-negative MPNs and the mechanism of the pathogenesis of BCR::ABL1-negative MPNs. Recently, specific CREB3L1 overexpression has been identified in megakaryocytes and platelets in BCR::ABL1-negative MPNs, which may be promising for the development of diagnostic applications. In this review, we describe the genetic mutations found in BCR::ABL1-negative MPNs, including the results of analyses conducted by our group.

MPL gene mutation is a possible risk factor for thrombosis in patients with essential thrombocythemia in Japan.

OBJECTIVES: Since MPL mutation is a rare driver gene mutation found in a small number of essential thrombocythemia (ET) patients, the clinical characteristics of patients with MPL mutations and their association with thrombotic events have not yet been elucidated in Japan. METHODS: We enrolled 579 Japanese ET patients based on the diagnostic criteria of the WHO classification 2017 and compared clinical characteristics of MPL-mutated patients (n = 22; 3.8%) to JAK2V617F-mutated (n = 299; 51.6%), CALR-mutated (n = 144; 24.9%), and triple-negative (TN) (n = 114; 19.7%) patients. RESULTS: Thrombosis during follow up was observed in 4 out of 22 (18.2%) in the MPL-mutated group, which was the highest among all driver gene mutation groups (JAK2V617F-mutated, 8.7%; CALR-mutated, 3.5%; TN,1.8%). The MPL- and JAK2V617F-mutated groups had worse thrombosis-free survival (TFS) than the CALR-mutated (p = 0.043) and TN groups (p = 0.006). Univariable analysis revealed that a history of thrombosis was a possible risk factor for thrombosis among MPL-mutated patients (hazard ratio: 9.572, p = 0.032). CONCLUSIONS: MPL-mutated ET patients should require more intensive management to prevent recurrence of thrombosis.

Clinical characteristics of Japanese patients with myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis.

Myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) is a rare disease, which presents with features of myelodysplastic syndromes with ring sideroblasts and essential thrombocythemia, as well as anemia and marked thrombocytosis. SF3B1 and JAK2 mutations are often found in patients, and are associated with their specific clinical features. This study was a retrospective analysis of 34 Japanese patients with MDS/MPN-RS-T. Median age at diagnosis was 77 (range, 51-88) years, and patients had anemia (median hemoglobin: 9.0 g/dL) and thrombocytosis (median platelet count: 642 × 109/L). Median overall survival was 70 (95% confidence interval: 68-not applicable) months during the median follow-up period of 26 (range: 0-91) months. A JAK2V617F mutation was detected in 46.2% (n = 12) of analyzed patients (n = 26), while an SF3B1 mutation was detected in 87.5% (n = 7) of analyzed patients (n = 8). Like those with myelodysplastic syndromes or myeloproliferative neoplasms, patients often received erythropoiesis-stimulating agents and aspirin to improve anemia and prevent thrombosis. This study, which was the largest to describe the real-world characteristics of Japanese patients with MDS/MPN-RS-T, showed that the patients had similar characteristics to those in western countries.

Clinical features of acquired erythrocytosis: Low levels of serum erythropoietin in a subset of non-neoplastic erythrocytosis patients.

BACKGROUND: Acquired erythrocytosis can be classified into polycythemia vera (PV) and non-neoplastic erythrocytosis (NNE). The vast majority of PV patients harbor JAK2 mutations, but differentiating JAK2 mutation-negative PV from NNE is challenging due to a lack of definitive molecular markers. METHODS: We studied the clinical features of 121 patients with erythrocytosis of which 47 (38.8%) were JAK2 mutation-positive and also fulfilled the diagnostic criteria for PV, and 67 (55.4%) JAK2 mutation-negative erythrocytosis patients who were diagnosed as NNE. Diagnosis was strictly based on driver mutation analysis and central pathology review. RESULTS: No JAK2 mutation-negative PV patients were found in our cohort. The NNE group showed significantly younger (p < 0.01) age with higher frequency of smoking (p < 0.001), alcohol consumption (p < 0.001), and diabetes mellitus (p < 0.05), whereas the PV group (n = 47) showed significantly higher white blood cell count, platelet count, and lactate dehydrogenase (p < 0.001). Although serum erythropoietin (EPO) levels were significantly higher in NNE compared to PV (p < 0.001), approximately 40% of the NNE patients had EPO levels below the lower range of normal, fulfilling a minor diagnostic criterion of PV and raising the possibility of PV misdiagnosis. CONCLUSION: Low EPO levels in JAK2 mutation-negative erythrocytosis may not be a reliable diagnostic criterion for distinguishing PV from NNE.

Non-driver gene mutation analysis in a large cohort of polycythemia vera and essential thrombocythemia.

OBJECTIVES: A proportion of patients with polycythemia vera (PV) and essential thrombocythemia (ET) harbor non-driver mutations associated with poor prognosis. In this study, we analyzed the frequency of non-driver mutations in a large Japanese PV and ET cohort. Furthermore, we studied the relationship of these mutations and prognosis in Japanese patients. METHODS: We enrolled 843 Japanese patients with PV or ET. Non-driver mutations were analyzed by target resequencing using next-generation sequencing. The association of the mutations with the prognosis was estimated using multivariable logistic regression analysis and log-rank test. RESULTS: Non-driver mutations were detected in 31.1% and 24.5% patients with PV and ET, respectively. Among them, ASXL1 mutations were identified as a risk factor for leukemic/myelofibrotic transformation in PV and ET patients (hazard ratio: 4.68, p = .006). The higher-risk groups of the mutation-enhanced international prognostic system (MIPSS)-PV and MIPSS-ET incorporating non-driver mutations exhibited significantly shorter overall survival compared with the low-risk group (p < .001). CONCLUSIONS: These results implicate the importance of studying non-driver mutations for predicting the prognosis and survival of Japanese PV and ET patients.

Establishment of isogenic induced pluripotent stem cells with or without pathogenic mutation for understanding the pathogenesis of myeloproliferative neoplasms.

Identification and functional characterization of disease-associated genetic traits are crucial for understanding the pathogenesis of hematologic malignancies. Various in vitro and in vivo models, including cell lines, primary cells, and animal models, have been established to examine these genetic alterations. However, their nonphysiologic conditions, diverse genetic backgrounds, and species-specific differences often limit data interpretation. To evaluate somatic mutations in myeloproliferative neoplasms (MPNs), we used CRISPR/Cas9 combined with the piggyBac transposon system to establish isogenic induced pluripotent stem (iPS) cell lines with or without JAK2V617F mutation, a driver mutation of MPNs. We induced hematopoietic stem/progenitor cells (HSPCs) from these iPS cells and observed phenotypic differences during hematopoiesis using fluorescence-activated cell sorting analysis. HSPCs with pathogenic mutations exhibited cell-autonomous erythropoiesis and megakaryopoiesis, which are hallmarks in the bone marrow of patients with MPNs. Furthermore, we used these HSPCs as a model to validate therapeutic compounds and showed that interferon alpha selectively inhibited erythropoiesis and megakaryopoiesis in mutant HSPCs. These results demonstrate that genome editing is feasible for establishing isogenic iPS cells, studying genetic elements to understand the pathogenesis of MPNs, and evaluating therapeutic compounds against MPNs.

Reevaluation of cardiovascular risk factors for thrombotic events in 580 Japanese patients with essential thrombocythemia.

Risk-adapted therapy is recommended to prevent thrombosis in essential thrombocythemia (ET) patients. An advanced age, a history of thrombosis, and the presence of the JAK2V617F mutation are well-defined risk factors for thrombosis in ET; however, the impact of cardiovascular risk (CVR) factors on thrombosis in ET remains elusive. Therefore, we herein investigated the impact of CVR factors on thrombosis in 580 ET patients who met the 2017 World Health Organization Classification diagnostic criteria. A univariate analysis identified hypertriglyceridemia and multiple CVR factors as strong risk factors for thrombosis (hazard ratio [HR] 3.530, 95% confidence interval [CI] 1.630-7.643, P = 0.001 and HR 3.368, 95% CI 1.284-8.833, P = 0.014, respectively) and hyper-LDL cholesterolemia as a potential risk factor (HR 2.191, 95% CI 0.966-4.971, P = 0.061). A multivariate analysis revealed that hypertriglyceridemia was an independent risk factor for thrombosis (HR 3.364, 95% CI 1.541-7.346, P = 0.002). Furthermore, poor thrombosis-free survival was observed in patients with a serum triglyceride level ≥ 1.2 mmol/L (HR = 2.592, P = 0.026 vs. < 1.2 mmol/L) or two or more CVR factors (P = 0.011 vs. no CVR factors and P = 0.005 vs. one CVR factor). These results revealed the impact of CVR factors on thrombosis in ET. Since CVR factors are manageable, lifestyle interventions, such as the control of serum triglyceride levels, may effectively prevent thrombosis in ET patients.

Causes of Thrombocytosis: A Single-center Retrospective Study of 1,202 Patients.

Objective Thrombocytosis can occur as a primary event accompanying hematological diseases or as a secondary event. Since the publication of the World Health Organization classification in 2008, thrombocytosis is now generally defined as a platelet count above 450×109/L. Furthermore, the discovery of driver-gene mutations in myeloproliferative neoplasms (MPNs) has simplified the diagnostic approach for thrombocytosis. To identify the causes of thrombocytosis using this new definition, we conducted a retrospective study. Methods We identified outpatients and inpatients aged 20 years or older with platelet counts >450×109/L in a half-year period at a single institute and analyzed the causes of thrombocytosis and associated clinical characteristics. Results Among 1,202 patients with thrombocytosis, 150 (12.5%) had primary and 999 (83.1%) had secondary thrombocytosis. Of these patients with primary thrombocytosis, 129 (86%) had at least 1 molecular marker indicative of MPNs. The major causes of secondary thrombocytosis were tissue injury (32.2%), infection (17.1%), chronic inflammatory disorders (11.7%) and iron deficiency anemia (11.1%). The median platelet count and the incidence of thrombosis were significantly higher in patients with primary thrombocytosis than in those with secondary thrombocytosis. Conclusion Thrombocytosis mainly occurs as a secondary event; however, it is important to determine the cause of and prevent thrombosis, particularly in cases of primary thrombocytosis.

von Willebrand factor activity levels are influenced by driver mutation status in polycythemia vera and essential thrombocythemia patients with well-controlled platelet counts.

von Willebrand factor ristocetin cofactor (vWF activity) and platelet count (PLT) are negatively correlated in patients with polycythemia vera (PV) and essential thrombocythemia (ET). However, vWF activity does not always normalize upon controlling PLT in those patients. To address this issue, we investigated the correlation between vWF activity and PLT in PV and ET patients. The negative correlation between vWF activity and PLT was stronger in calreticulin mutation-positive (CALR+) ET than in Janus kinase 2 mutation-positive (JAK2+) PV or ET groups. When PLT were maintained at a certain level (<600 × 109 /L), low vWF activity (<50%) was more frequently observed in JAK2+ PV patients than in JAK2+ ET (p = .013) or CALR+ ET (p = .013) groups, and in PV and ET patients with ≥50% JAK2+ allele burden than in those with allele burden <50% (p = .015). High vWF activity (>150%) was more frequent in the JAK2+ ET group than in the CALR+ ET group (p = .005), and often associated with vasomotor symptoms (p = .002). This study suggests that some patients with JAK2+ PV or ET have vWF activity outside the standard range even with well-controlled PLT, and that the measurement of vWF activity is useful for assessing the risk of thrombosis and hemorrhage.

Clinical and biological relevance of CREB3L1 in Philadelphia chromosome-negative myeloproliferative neoplasms.

Cyclic AMP-response element-binding protein 3-like 1 (CREB3L1) is a gene involved in the unfolded protein response (UPR). Recently, we demonstrated that CREB3L1 is specifically overexpressed in the platelets of patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). In this study, we aimed to show the clinical and biological relevance of CREB3L1 in these hematological diseases. Overexpression of CREB3L1 was specific to platelets in MPNs and associated with a higher risk of thrombosis and fibrotic transformation in essential thrombocythemia (ET) and polycythemia vera (PV) cases, respectively. Furthermore, we found that UPR genes were downregulated in platelets of patients with ET and PV, which were more pronounced in patients harboring the JAK2 V617F mutation. However, CREB3L1 overexpression does not alter UPR gene expression or cell proliferation in UT-7/TPO/CALRm cells exogenously expressing mutated calreticulin and HEL cells harboring endogenous JAK2 V617F. Furthermore, CREB3L1 overexpression did not modulate sensitivity to endoplasmic reticulum stress in these cell lines. Taken together, our data show 1) a potential role of CREB3L1 expression in platelets as a new marker of high-risk MPNs and 2) an association between CREB3L1 overexpression and UPR gene downregulation in these patients' platelets, with CREB3L1 not altering UPR in our in vitro models and possibly further in vivo mechanisms being involved.

Eliminating chronic myeloid leukemia stem cells by IRAK1/4 inhibitors.

Leukemia stem cells (LSCs) in chronic myeloid leukemia (CML) are quiescent, insensitive to BCR-ABL1 tyrosine kinase inhibitors (TKIs) and responsible for CML relapse. Therefore, eradicating quiescent CML LSCs is a major goal in CML therapy. Here, using a G0 marker (G0M), we narrow down CML LSCs as G0M- and CD27- double positive cells among the conventional CML LSCs. Whole transcriptome analysis reveals NF-κB activation via inflammatory signals in imatinib-insensitive quiescent CML LSCs. Blocking NF-κB signals by inhibitors of interleukin-1 receptor-associated kinase 1/4 (IRAK1/4 inhibitors) together with imatinib eliminates mouse and human CML LSCs. Intriguingly, IRAK1/4 inhibitors attenuate PD-L1 expression on CML LSCs, and blocking PD-L1 together with imatinib also effectively eliminates CML LSCs in the presence of T cell immunity. Thus, IRAK1/4 inhibitors can eliminate CML LSCs through inhibiting NF-κB activity and reducing PD-L1 expression. Collectively, the combination of TKIs and IRAK1/4 inhibitors is an attractive strategy to achieve a radical cure of CML.

Validation and reliability of current guidelines for the treatment of essential thrombocythemia under real-world clinical settings in Japan.

OBJECTIVE: Current guidelines for essential thrombocythemia (ET) patients recommend different treatment approaches based on thrombosis risk stratification models. However, these recommendations may not be applicable to some patients under real clinical settings. Therefore, we carried out a retrospective real-world validation study. METHODS: Thrombosis-free survival (TFS) was compared between treatment naïve ET patients receiving different treatment approaches. ET patients were stratified by three representative risk models, the conventional, the International Prognostic Score for thrombosis in ET (IPSET-thrombosis), and revised IPSET-thrombosis. Treatment decisions were largely made by individual physicians, taking into account patient preferences and backgrounds. RESULTS: A total of 179 ET patients were included, and thrombotic events were observed in 26 patients. TFS was significantly longer in high-risk patients of all risk models receiving a combination of cytoreductive therapy (CRT) and antiplatelet therapy (APT) compared to CRT alone. Similar results were seen in intermediate-risk patients stratified by IPSET-thrombosis. In contrast, in very low- and low-risk patients of all risk models, TFS was not affected by addition of CRT, indicating that observation or APT alone is an appropriate treatment approach for these patients. CONCLUSION: We demonstrate that current guidelines provide optimal treatment approaches for Japanese ET patients under real-world clinical settings.

In silico-labeled ghost cytometry.

Characterization and isolation of a large population of cells are indispensable procedures in biological sciences. Flow cytometry is one of the standards that offers a method to characterize and isolate cells at high throughput. When performing flow cytometry, cells are molecularly stained with fluorescent labels to adopt biomolecular specificity which is essential for characterizing cells. However, molecular staining is costly and its chemical toxicity can cause side effects to the cells which becomes a critical issue when the cells are used downstream as medical products or for further analysis. Here, we introduce a high-throughput stain-free flow cytometry called in silico-labeled ghost cytometry which characterizes and sorts cells using machine-predicted labels. Instead of detecting molecular stains, we use machine learning to derive the molecular labels from compressive data obtained with diffractive and scattering imaging methods. By directly using the compressive 'imaging' data, our system can accurately assign the designated label to each cell in real time and perform sorting based on this judgment. With this method, we were able to distinguish different cell states, cell types derived from human induced pluripotent stem (iPS) cells, and subtypes of peripheral white blood cells using only stain-free modalities. Our method will find applications in cell manufacturing for regenerative medicine as well as in cell-based medical diagnostic assays in which fluorescence labeling of the cells is undesirable.

Cell-autonomous megakaryopoiesis associated with polyclonal hematopoiesis in triple-negative essential thrombocythemia.

A subset of essential thrombocythemia (ET) cases are negative for disease-defining mutations on JAK2, MPL, and CALR and defined as triple negative (TN). The lack of recurrent mutations in TN-ET patients makes its pathogenesis ambiguous. Here, we screened 483 patients with suspected ET in a single institution, centrally reviewed bone marrow specimens, and identified 23 TN-ET patients. Analysis of clinical records revealed that TN-ET patients were mostly young female, without a history of thrombosis or progression to secondary myelofibrosis and leukemia. Sequencing analysis and human androgen receptor assays revealed that the majority of TN-ET patients exhibited polyclonal hematopoiesis, suggesting a possibility of reactive thrombocytosis in TN-ET. However, the serum levels of thrombopoietin (TPO) and interleukin-6 in TN-ET patients were not significantly different from those in ET patients with canonical mutations and healthy individuals. Rather, CD34-positive cells from TN-ET patients showed a capacity to form megakaryocytic colonies, even in the absence of TPO. No signs of thrombocytosis were observed before TN-ET development, denying the possibility of hereditary thrombocytosis in TN-ET. Overall, these findings indicate that TN-ET is a distinctive disease entity associated with polyclonal hematopoiesis and is paradoxically caused by hematopoietic stem cells harboring a capacity for cell-autonomous megakaryopoiesis.

[Clinical impact of gene mutations on myeloproliferative neoplasms in Japan].

Myeloproliferative neoplasms (MPN) are caused by somatic mutations in hematopoietic stem/progenitor cells and result in excessive increase in the blood cell mass in the peripheral blood and/or fibrosis in the bone marrow. JAK2, CALR, and MPL mutations are well-known driver mutations of MPN and are widely applied as diagnostic markers of MPN. Moreover, several studies using massive parallel sequencing technologies have shown that mutations in ASXL1, EZH2, SRSF2, and IDH1/2 affect the prognosis of overt primary myelofibrosis and have further clarified that the mutation order may influence the MPN phenotype. More recently, our group identified that CREB3L1 mRNA was overexpressed in a platelet- and megakaryocyte-specific manner in driver mutation positive MPN and that the quantitation of this gene expression can be used as a diagnostic marker for MPN. In this educational lecture, we discuss the clinical impacts of the mutations frequently identified in MPN patients.

Cytoplasmic DNA accumulation preferentially triggers cell death of myeloid leukemia cells by interacting with intracellular DNA sensing pathway.

Accumulating evidence indicates the presence of cytoplasmic DNAs in various types of malignant cells, and its involvement in anti-cancer drug- or radiotherapy-mediated DNA damage response and replication stress. However, the pathophysiological roles of cytoplasmic DNAs in leukemias remain largely unknown. We observed that during hematopoietic stem cell transplantation (HSCT) in mouse myeloid leukemia models, double-stranded (ds)DNAs were constitutively secreted in the form of extracellular vesicles (EVs) from myeloid leukemia cells and were transferred to the donor cells to dampen their hematopoietic capabilities. Subsequent analysis of cytoplasmic DNA dynamics in leukemia cells revealed that autophagy regulated cytoplasmic dsDNA accumulation and subsequent redistribution into EVs. Moreover, accumulated cytoplasmic dsDNAs activated STING pathway, thereby reducing leukemia cell viability through reactive oxygen species (ROS) generation. Pharmaceutical inhibition of autophagosome formation induced cytoplasmic DNA accumulation, eventually triggering cytoplasmic DNA sensing pathways to exert cytotoxicity, preferentially in leukemia cells. Thus, manipulation of cytoplasmic dsDNA dynamics can be a novel and potent therapeutic strategy for myeloid leukemias.

Crucial role of hematopoietic JAK2 V617F in the development of aortic aneurysms.

JAK2V617F is the most frequent driver mutation in myeloproliferative neoplasms (MPNs) and is associated with vascular complications. However, the impact of hematopoietic JAK2V617F on the aortic aneurysms (AAs) remains unknown. Our cross-sectional study indicated that 9 (23%) out of 39 MPN patients with JAK2V617F exhibited the presence of AAs. Next, to clarify whether the hematopoietic JAK2V617F contributes to the AAs, we applied a bone marrow transplantation (BMT) with the donor cells from Jak2V617F transgenic (JAK2V617F) mice or control wild-type (WT) mice into lethally irradiated apolipoprotein E-deficient mice. Five weeks after BMT, the JAK2V617F-BMT mice and WT-BMT mice were subjected to continuous angiotensin II infusion to induce AA formation. Four weeks after angiotensin II infusion, the abdominal aorta diameter in JAK2V617F-BMT mice was significantly enlarged compared to that in the WT-BMT mice. Additionally, the abdominal AA-free survival rate was significantly lower in the JAK2V617F-BMT mice. Hematopoietic JAK2V617F accelerated aortic elastic lamina degradation as well as activation of matrix metalloproteinase (MMP)-2 and MMP-9 in the abdominal aorta. The numbers of infiltrated macrophages were significantly upregulated in the abdominal aorta of the JAK2V617F-BMT mice accompanied by STAT3 phosphorylation. The accumulation of BM-derived hematopoietic cells carrying JAK2V617F in the abdominal aorta was confirmed by use of reporter GFP-transgene. BM-derived macrophages carrying JAK2V617F showed increases in mRNA expression levels of Mmp2, Mmp9, and Mmp13. Ruxolitinib decreased the abdominal aorta diameter and the incidence of abdominal AA in the JAK2V617F-BMT mice. Our findings provide a novel feature of vascular complications of AAs in MPNs with JAK2V617F.