Clinical significance of circulating microparticles in Ph- myeloproliferative neoplasms

Red Blood Cell Contribution to Thrombosis in Polycythemia Vera and Essential Thrombocythemia

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPN) characterized by clonal erythrocytosis and thrombocytosis, respectively. The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. Despite a debated notion that red blood cells (RBCs) play a passive and minor role in thrombosis, there has been increasing evidence over the past decades that RBCs may play a biological and clinical role in PV and ET pathophysiology. This review summarizes the main mechanisms that suggest the involvement of PV and ET RBCs in thrombosis, including quantitative and qualitative RBC abnormalities reported in these pathologies. Among these abnormalities, we discuss increased RBC counts and hematocrit, that modulate blood rheology by increasing viscosity, as well as qualitative changes, such as deformability, aggregation, expression of adhesion proteins and phosphatidylserine and release of extracellular microvesicles. While the direct relationship between a high red cell count and thrombosis is well-known, the intrinsic defects of RBCs from PV and ET patients are new contributors that need to be investigated in depth in order to elucidate their role and pave the way for new therapeutical strategies.

Splanchnic Vein Thrombosis in Myelofibrosis-An Underappreciated Hallmark of Disease Phenotype

Splanchnic vein thrombosis (SVT) encompasses thrombosis in the vessels of the splanchnic basin and has a relatively rare occurrence with a reported frequency in the general population of 1-2%. An episode of seemingly unprovoked SVT almost always triggers a diagnostic work-up for a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN), since atypical site thrombosis is a hallmark of MPN-associated thrombophilia. Primary myelofibrosis (PMF) is a rare MPN with an estimated incidence between 0.1 and 1/100,000 per year. Although prothrombotic tendency in PMF is not envisioned as a subject of specific therapeutic management, unlike other MPNs, such as polycythemia vera (PV) and essential thrombocythemia (ET), thrombotic risk and SVT prevalence in PMF may be comparably high. Additionally, unlike PV and ET, SVT development in PMF may depend more on procoagulant mechanisms involving endothelium than on blood cell activation. Emerging results from registry data also suggest that PMF patients with SVT may exhibit lower risk and better prognosis, thus highlighting the need for better thrombotic risk stratification and identifying a subset of patients with potential benefit from antithrombotic prophylaxis. This review highlights specific epidemiological, pathogenetic, and clinical features pertinent to SVT in myelofibrosis.

Mechanisms of platelet activation in cancer-associated thrombosis: a focus on myeloproliferative neoplasms

Platelets are anucleate blood cells that play key roles in thrombosis and hemostasis. Platelets are also effector cells in malignancy and are known to home into the microenvironment of cancers. As such, these cells provide central links between the hemostatic system, inflammation and cancer progression. Activation of platelets by cancers has been postulated to contribute to metastasis and progression of local tumor invasion. Similarly, cancer-activated platelets can increase the risk of development of both arterial and venous thrombosis; a major contributor to cancer-associated morbidity. Platelet granules secretion within the tumor environment or the plasma provide a rich source of potential biomarkers for prediction of thrombotic risk or tumor progression. In the case of myeloproliferative neoplasms (MPNs), which are characterized by clonal expansion of myeloid precursors and abnormal function and number of erythrocytes, leukocytes and platelets, patients suffer from thrombotic and hemorrhagic complications. The mechanisms driving this are likely multifactorial but remain poorly understood. Several mouse models developed to recapitulate MPN phenotype with one of the driving mutations, in JAK2 (JAK2V617F) or in calreticulin (CALR) or myeloproliferative leukemia virus oncogene receptor (MPL), have been studied for their thrombotic phenotype. Variability and discrepancies were identified within different disease models of MPN, emphasizing the complexity of increased risk of clotting and bleeding in these pathologies. Here, we review recent literature on the role of platelets in cancer-associated arterial and venous thrombosis and use MPN as case study to illustrate recent advances in experimental models of thrombosis in a malignant phenotype. We address major mechanisms of tumor-platelet communication leading to thrombosis and focus on the role of altered platelets in promoting thrombosis in MPN experimental models and patients with MPN. Recent identification of platelet-derived biomarkers of MPN-associated thrombosis is also reviewed, with potential therapeutic implications.

JAK-STAT inhibition reduces endothelial prothrombotic activation and leukocyte-endothelial proadhesive interactions

BACKGROUND

Vascular activation is characterized by increased proinflammatory, pro thrombotic, and proadhesive signaling. Several chronic and acute conditions, including Bcr-abl-negative myeloproliferative neoplasms (MPNs), graft-vs-host disease, and COVID-19 have been noted to have increased activation of the janus kinase (JAK)-signal transducer and downstream activator of transcription (STAT) pathways. Two notable inhibitors of the JAK-STAT pathway are ruxolitinib (JAK1/2 inhibitor) and fedratinib (JAK2 inhibitor), which are currently used to treat MPN patients. However, in some conditions, it has been noted that JAK inhibitors can increase the risk of thromboembolic complications.

OBJECTIVES

We sought to define the anti-inflammatory and antithrombotic effects of JAK-STAT inhibitors in vascular endothelial cells.

METHODS

We assessed endothelial activation in the presence or absence of ruxolitinib or fedratinib by using immunoblots, immunofluorescence, qRT-PCR, and function coagulation assays. Finally, we used endothelialized microfluidics perfused with blood from normal and JAK2V617F+ individuals to evaluate whether ruxolitinib and fedratinib changed cell adhesion.

RESULTS

We found that both ruxolitinib and fedratinib reduced endothelial cell phospho-STAT1 and STAT3 signaling and attenuated nuclear phospho-NK-κB and phospho-c-Jun localization. JAK-STAT inhibition also limited secretion of proadhesive and procoagulant P-selectin and von Willebrand factor and proinflammatory IL-6. Likewise, we found that JAK-STAT inhibition reduced endothelial tissue factor and urokinase plasminogen activator expression and activity.

CONCLUSIONS

By using endothelialized microfluidics perfused with whole blood samples, we demonstrated that endothelial treatment with JAK-STAT inhibitors prevented rolling of both healthy control and JAK2V617F MPN leukocytes. Together, these findings demonstrate that JAK-STAT inhibitors reduce the upregulation of critical prothrombotic pathways and prevent increased leukocyte-endothelial adhesion.

JAK2V617F mutation and circulating extracellular vesicles in essential thrombocythemia

The clinical course of essential thrombocythemia (ET) is complicated with thrombosis which significantly impacts patients' mortality. Studies have identified JAK2V617F mutation as an independent risk factor for thrombosis. Circulating extracellular vesicles (EVs) were evaluated in several studies regarding myeloproliferative neoplasms and thrombosis as potential biomarkers. The present study investigates the relationship between JAK2V617F mutation and EVs levels in 119 ET patients. Our analyses revealed that JAK2V617F-positive patients are at a significantly increased risk of thrombosis within five years before the ET diagnosis (hazard ratio [95% CI]: 11.9 [1.7-83.7], P = 0.013), and that JAK2V617F mutation is an independent risk factor for thrombosis at ET diagnosis or during the follow-up (hazard ratio [95% CI]: 3.56 [1.47-8.62], P = 0.005). ET patients have higher levels of platelet-EVs, erythrocyte-EVs and procoagulant activity of EVs than the healthy population. Absolute and relative counts of platelet-EVs are increased in the presence of JAK2V617F mutation (P = 0.018, P = 0.024, respectively). In conclusion, our results support the role of JAK2V617F mutation in the pathogenesis of thrombosis in essential thrombocythemia through enhancing platelet activation.

Liquid biopsies and minimal residual disease in myeloid malignancies

Minimal residual disease (MRD) assessment through blood component sampling by liquid biopsies (LBs) is increasingly being investigated in myeloid malignancies. Blood components then undergo molecular analysis by flow cytometry or sequencing techniques and can be used as a powerful tool for prognostic and predictive purposes in myeloid malignancies. There is evidence and more is evolving about the quantification and identification of cell-based and gene-based biomarkers in myeloid malignancies to monitor treatment response. MRD based acute myeloid leukemia protocol and clinical trials are currently incorporating LB testing and preliminary results are encouraging for potential widespread use in clinic in the near future. MRD monitoring using LBs are not standard in myelodysplastic syndrome (MDS) but this is an area of active investigation. In the future, LBs can replace more invasive techniques such as bone marrow biopsies. However, the routine clinical application of these markers continues to be an issue due to lack of standardization and limited number of studies investigating their specificities. Integrating artificial intelligence (AI) could help simplify the complex interpretation of molecular testing and reduce errors related to operator dependency. Though the field is rapidly evolving, the applicability of MRD testing using LB is mostly limited to research setting at this time due to the need for validation, regulatory approval, payer coverage, and cost issues. This review focuses on the types of biomarkers, most recent research exploring MRD and LB in myeloid malignancies, ongoing clinical trials, and the future of LB in the setting of AI.

Extracellular Vesicles in Myeloid Neoplasms

Myeloid neoplasms arise from malignant primitive cells, which exhibit growth advantage within the bone marrow microenvironment (BMM). The interaction between these malignant cells and BMM cells is critical for the progression of these diseases. Extracellular vesicles (EVs) are lipid bound vesicles secreted into the extracellular space and involved in intercellular communication. Recent studies have described RNA and protein alterations in EVs isolated from myeloid neoplasm patients compared to healthy controls. The altered expression of various micro-RNAs is the best-described feature of EVs of these patients. Some of these micro-RNAs induce growth-related pathways such as AKT/mTOR and promote the acquisition of stem cell-like features by malignant cells. Another well-described characteristic of EVs in myeloid neoplasms is their ability to suppress healthy hematopoiesis either via direct effect on healthy CD34+ cells or via alteration of the differentiation of BMM cells. These results support a role of EVs in the pathogenesis of myeloid neoplasms. mainly through mediating the interaction between malignant and BMM cells, and warrant further study to better understand their biology. In this review, we describe the reported alterations of EV composition in myeloid neoplasms and the recent discoveries supporting their involvement in the development and progression of these diseases.

The pathobiology of platelet and megakaryocyte extracellular vesicles: A (c)lot has changed

Platelet-derived extracellular vesicles (PEVs) were originally studied for their potential as regulators of coagulation, a function redundant with that of their parent cells. However, as the understanding of the diverse roles of platelets in hemostasis and disease has developed, so has the understanding of PEVs. In addition, the more recent revelation of constitutively released megakaryocyte-derived extracellular vesicles (MKEVs) in circulation provides an interesting counterpoint and avenue for investigation. In this review, we highlight the historical link of PEVs to thrombosis and hemostasis and provide critical updates. We also expand our discussion to encompass the roles that distinguish PEVs and MKEVs from their parent cells. Furthermore, the role of extracellular vesicles in disease pathology, both as biomarkers and as exacerbators, has been of great interest in recent years. We highlight some of the key roles that PEVs and MKEVs play in autoimmune blood cell disorders, liver pathology, and cardiovascular disease. We then look at the future of PEVs and MKEVs as candidates for novel therapeutics.

Platelet Extracellular Vesicles Are Taken up by Canine T Lymphocytes but Do Not Play a Role in Their Proliferation, Differentiation and Cytokine Production In Vitro

Eukaryotic and prokaryotic cells in physiological and pathological conditions form membrane-bound extracellular vesicles, known as EVs. The ability of these submicron structures to transfer their cargoes (miRNA, DNA, protein, cytokines, receptors, etc.) into recipient cells is described. Recent data revealed that platelet-derived extracellular vesicles (PEVs) crosstalk promotes cancer growth and metastasis formation. Moreover, they exert immunosuppressive activities on phagocytes. This EV subpopulation is the most abundant amongst all types in circulation. According to the authors' best knowledge, there is no information regarding the impact of PEVs on canine lymphocytes. The aim of this study was to evaluate the influence of PEVs on lymphocyte proliferation, phenotype and cytokine production in vitro. In the study, it was demonstrated (i) that PEVs interact differently with lymphocyte subsets and are preferentially associated with T-lymphocytes PBMC, while (ii) they are rarely detected in association with B-lymphocytes, and there is evidence that (iii) PEV uptake is observed after 7 h of co-culturing with lymphocytes. In addition, obtained data support the notion that PEVs do not influence in vitro lymphocyte proliferation, differentiation and cytokine production in a canine model.

Thrombosis and hemorrhage in myeloproliferative neoplasms: The platelet perspective

Classical myeloproliferative neoplasm (MPN), also known as BCR-ABL-negative MPN, is a clonal disease characterized by abnormal expansion of hematopoietic stem cells. It has been demonstrated that MPN patients are more susceptible to thrombotic events compared to the general population. Therefore, researchers have been exploring the treatment for MPN thrombosis. However, antithrombotic therapies have brought another concern for the clinical management of MPN because they may cause bleeding events. When thrombosis and bleeding, two seemingly contradictory complications, occur in MPN patients at the same time, they will lead to more serious consequences. Therefore, it is a major challenge to achieving the best antithrombotic effect and minimizing bleeding events simultaneously. To date, there has yet been a perfect strategy to meet this challenge and therefore a new treatment method needs to be established. In this article, we describe the mechanism of thrombosis and bleeding events in MPN from the perspective of platelets for the first time. Based on the double-sided role of platelets in MPN, optimal antithrombotic treatment strategies that can simultaneously control thrombosis and bleeding at the same time may be formulated by adjusting the administration time and dosage of antiplatelet drugs. We argue that more attention should be paid to the critical role of platelets in MPN thrombosis and MPN bleeding in the future, so as to better manage adverse vascular events in MPN.

An Abnormal Host/Microbiomes Signature of Plasma-Derived Extracellular Vesicles Is Associated to Polycythemia Vera

Polycythemia Vera (PV) is a myeloproliferative neoplasm with increased risk of thrombosis and progression to myelofibrosis. Chronic inflammation is commonly observed in myeloproliferative neoplasms including PV. The inflammatory network includes the extracellular vesicles (EVs), which play a role in cell-cell communication. Recent evidence points to circulating microbial components/microbes as potential players in hemopoiesis regulation. To address the role of EVs in PV, here we investigated phenotype and microbial DNA cargo of circulating EVs through multidimensional analysis. Peripheral blood and feces were collected from PV patients (n=38) and healthy donors (n=30). Circulating megakaryocyte (MK)- and platelet (PLT)-derived EVs were analyzed by flow cytometry. After microbial DNA extraction from feces and isolated EVs, the 16S rDNA V3-V4 region was sequenced. We found that the proportion of circulating MK-derived EVs was significantly decreased in PV patients as compared with the healthy donors. By contrast, the proportion of the PLT-derived EVs was increased. Interestingly, PV was also associated with a microbial DNA signature of the isolated EVs with higher diversity and distinct microbial composition than the healthy counterparts. Of note, increased proportion of isolated lipopolysaccharide-associated EVs has been demonstrated in PV patients. Conversely, the gut microbiome profile failed to identify a distinct layout between PV patients and healthy donors. In conclusion, PV is associated with circulating EVs harbouring abnormal phenotype and dysbiosis signature with a potential role in the (inflammatory) pathogenesis of the disease.

The Power of Extracellular Vesicles in Myeloproliferative Neoplasms: "Crafting" a Microenvironment That Matters

Myeloproliferative Neoplasms (MPN) are acquired clonal disorders of the hematopoietic stem cells and include Essential Thrombocythemia, Polycythemia Vera and Myelofibrosis. MPN are characterized by mutations in three driver genes (JAK2, CALR and MPL) and by a state of chronic inflammation. Notably, MPN patients experience increased risk of thrombosis, disease progression, second neoplasia and evolution to acute leukemia. Extracellular vesicles (EVs) are a heterogeneous population of microparticles with a role in cell-cell communication. The EV-mediated cross-talk occurs via the trafficking of bioactive molecules such as nucleic acids, proteins, metabolites and lipids. Growing interest is focused on EVs and their potential impact on the regulation of blood cancers. Overall, EVs have been suggested to orchestrate the complex interplay between tumor cells and the microenvironment with a pivotal role in "education" and "crafting" of the microenvironment by regulating angiogenesis, coagulation, immune escape and drug resistance of tumors. This review is focused on the role of EVs in MPN. Specifically, we will provide an overview of recent findings on the involvement of EVs in MPN pathogenesis and discuss opportunities for their potential application as diagnostic and prognostic biomarkers.

Liquid Biopsy and Potential Liquid Biopsy-Based Biomarkers in Philadelphia-Negative Classical Myeloproliferative Neoplasms: A Systematic Review

Myeloproliferative neoplasms (MPNs) are rare, clonal disorders of the hematopoietic stem cell in which an uncontrolled proliferation of terminally differentiated myeloid cells is noted. Polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) are included in the category of Philadelphia-negative, so-called classical MPNs. The potential applications of liquid biopsy and liquid biopsy-based biomarkers have not been explored in MPNs until now. Thus, a systematic search was computed in PubMed/MEDLINE, Web of Science and The Cochrane Library and, in total, 198 potentially relevant papers were detected. Following the removal of duplicates (n = 85), 113 records were screened. After the exclusion of irrelevant manuscripts based on the screening of their titles and abstracts (n = 81), we examined the full texts of 33 manuscripts. Finally, after we applied the exclusion and inclusion criteria, 27 original articles were included in this review. Overall, the data analyzed in this review point out that liquid biopsy and liquid biopsy-based biomarkers (cell-free DNA, extracellular vesicles, microparticles, circulating endothelial cells) could be used in MPNs for diagnostic and prognostic purposes. Future research is needed to clarify whether this technique can be employed to differentiate between MPN subtypes and secondary causes of erythrocytosis, thrombocytosis and myelofibrosis, as well as to predict the development of thrombosis.

Platelets and extracellular vesicles and their cross talk with cancer

Platelets play significant and varied roles in cancer progression, as detailed throughout this review series, via direct interactions with cancer cells and by long-range indirect interactions mediated by platelet releasates. Microvesicles (MVs; also referred to as microparticles) released from activated platelets have emerged as major contributors to the platelet-cancer nexus. Interactions of platelet-derived MVs (PMVs) with cancer cells can promote disease progression through multiple mechanisms, but PMVs also harbor antitumor functions. This complex relationship derives from PMVs' binding to both cancer cells and nontransformed cells in the tumor microenvironment and transferring platelet-derived contents to the target cell, each of which can have stimulatory or modulatory effects. MVs are extracellular vesicles of heterogeneous size, ranging from 100 nm to 1 µm in diameter, shed by living cells during the outward budding of the plasma membrane, entrapping local cytosolic contents in an apparently stochastic manner. Hence, PMVs are encapsulated by a lipid bilayer harboring surface proteins and lipids mirroring the platelet exterior, with internal components including platelet-derived mature messenger RNAs, pre-mRNAs, microRNAs, and other noncoding RNAs, proteins, second messengers, and mitochondria. Each of these elements engages in established and putative PMV functions in cancer. In addition, PMVs contribute to cancer comorbidities because of their roles in coagulation and thrombosis and via interactions with inflammatory cells. However, separating the effects of PMVs from those of platelets in cancer contexts continues to be a major hurdle. This review summarizes our emerging understanding of the complex roles of PMVs in the development and progression of cancer and cancer comorbidities.

The pathobiology of thrombosis, microvascular disease, and hemorrhage in the myeloproliferative neoplasms

Thrombotic, vascular, and bleeding complications are the most common causes of morbidity and mortality in the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). In these disorders, circulating red cells, leukocytes, and platelets, as well as some vascular endothelial cells, each have abnormalities that are cell-intrinsic to the MPN driver mutations they harbor (eg, JAK2 V617F). When these cells are activated in the MPNs, their interactions with each other create a highly proadhesive and prothrombotic milieu in the circulation that predisposes patients with MPN to venous, arterial, and microvascular thrombosis and occlusive disease. Bleeding problems in the MPNs are caused by the MPN blood cell-initiated development of acquired von Willebrand disease. The inflammatory state created by MPN stem cells in their microenvironment extends systemically to amplify the clinical thrombotic tendency and, at the same time, preferentially promote further MPN stem cell clonal expansion, thereby generating a vicious cycle that favors a prothrombotic state in these diseases.

Novel Pathophysiological Mechanisms of Thrombosis in Myeloproliferative Neoplasms

PURPOSE OF REVIEW

Thrombosis remains a leading cause of morbidity and mortality in BCR/ABL negative myeloproliferative neoplasms (MPN). Circulating blood cells are both increased in quantity and qualitatively abnormal in MPN, resulting in an increased thrombotic risk. Herein, we review recently elucidated mechanisms of MPN thrombosis and discuss implications of drugs currently under investigation for MPN.

RECENT FINDINGS

Recent studies highlight that in JAK2^V617F granulocytes and platelets, thrombo-inflammatory genes are upregulated. Furthermore, in JAK2^V617F granulocytes, protein expression of integrin CD11b, tissue factor, and leukocyte alkaline phosphatase are all increased. Overall, myeloid cells, namely neutrophils, may contribute in several ways, such as through increased adhesion via β1 integrin binding to VCAM1, increased infiltration, and enhanced inducibility to extrude neutrophil extracellular traps. Non-myeloid inflammatory cells may also contribute via secretion of cytokines. With regard to red blood cells, number, rigidity, adhesion, and generation of microvesicles may lead to increased vascular resistance as well as increased cell-cell interactions that promote rolling and adhesion. Platelets may also contribute in a similar fashion. Lastly, the vasculature is also increasingly appreciated, as several studies have demonstrated increased endothelial expression of pro-coagulant and pro-adhesive proteins, such as von Willebrand factor or P-selectin in JAK2^V617F endothelial cells. With the advent of molecular diagnostics, MPN therapeutics are advancing beyond cytoreduction. Our increased understanding of pro-inflammatory and thrombotic pathophysiology in MPN provides a rational basis for evaluation of in-development MPN therapeutics to reduce thrombosis.

Pathogenesis of cardiovascular events in BCR-ABL1-negative myeloproliferative neoplasms

Thrombosis, both in arterial and venous territories, is the major complication of myeloproliferative neoplasms and is responsible for a high rate of morbidity and mortality. The currently accepted risk factors are an age over 60 years and a history of thrombosis. However, many complex mechanisms contribute to this increased prothrombotic risk, with involvement of all blood cell types, plasmatic factors, and endothelial cells. Besides, some cardiovascular events may originate from arterial vasospasm that could contribute to thrombotic complications. In this review, we discuss recent results obtained in mouse models in the light of data obtained from clinical studies. We emphasize on actors of thrombosis that are currently not targeted with current therapeutics but could be promising targets, i.e, neutrophil extracellular traps and vascular reactivity.

Clinical relevance of extracellular vesicles in hematological neoplasms: from liquid biopsy to cell biopsy

In the era of precision medicine, liquid biopsy is becoming increasingly important in oncology. It consists in the isolation and analysis of tumor-derived biomarkers, including extracellular vesicles (EVs), in body fluids. EVs are lipid bilayer-enclosed particles, heterogeneous in size and molecular composition, released from both normal and neoplastic cells. In tumor context, EVs are valuable carriers of cancer information; in fact, their amount, phenotype and molecular cargo, including proteins, lipids, metabolites and nucleic acids, mirror nature and origin of parental cells rendering EVs appealing candidates as novel biomarkers. Translation of these new potential diagnostic tools into clinical practice could deeply revolutionize the cancer field mainly for solid tumors but for hematological neoplasms, too.

Erythrocyte-derived microvesicles induce arterial spasms in JAK2V617F myeloproliferative neoplasm

Arterial cardiovascular events are the leading cause of death in patients with JAK2V617F myeloproliferative neoplasms (MPNs). However, their mechanisms are poorly understood. The high prevalence of myocardial infarction without significant coronary stenosis or atherosclerosis in patients with MPNs suggests that vascular function is altered. The consequences of JAK2V617F mutation on vascular reactivity are unknown. We observe here increased responses to vasoconstrictors in arteries from Jak2V617F mice resulting from a disturbed endothelial NO pathway and increased endothelial oxidative stress. This response was reproduced in WT mice by circulating microvesicles isolated from patients carrying JAK2V617F and by erythrocyte-derived microvesicles from transgenic mice. Microvesicles of other cellular origins had no effect. This effect was observed ex vivo on isolated aortas, but also in vivo on femoral arteries. Proteomic analysis of microvesicles derived from JAK2V617F erythrocytes identified increased expression of myeloperoxidase as the likely mechanism accounting for their effect. Myeloperoxidase inhibition in microvesicles derived from JAK2V617F erythrocytes suppressed their effect on oxidative stress. Antioxidants such as simvastatin and N-acetyl cysteine improved arterial dysfunction in Jak2V617F mice. In conclusion, JAK2V617F MPNs are characterized by exacerbated vasoconstrictor responses resulting from increased endothelial oxidative stress caused by circulating erythrocyte-derived microvesicles. Simvastatin appears to be a promising therapeutic strategy in this setting.

Prevalence of definite antiphospholipid syndrome in carriers of the JAK2V617F mutation

INTRODUCTION

Patients with Philadelphia-negative myeloproliferative neoplasms (MPNs), particularly those carrying the JAK2^V617F mutation, are at increased risk of thrombosis. While an association of MPNs with autoimmune disorders has been established, the prevalence of inherited or acquired thrombophilias in JAK2^V617F-positive patients remains obscure. We therefore investigated the coincidence of the JAK2^V617F mutation with additional thrombogenic risk factors.

METHODS

In a retrospective study, we analyzed all patients referred for thrombophilia work-up between 01/2011 and 08/2019, in whom additional JAK2^V617F mutation analysis was performed because of thromboembolic events that were recurrent, atypically located and/or associated with abnormal blood counts.

RESULTS

Of 472 tested patients, 49 (10.4%) were JAK2^V617F-positive. While the frequency of inherited thrombophilias (factor V Leiden and prothrombin G20210A mutation, deficiency of antithrombin, protein C, protein S) was not different between the two groups, the prevalence of definite antiphospholipid syndrome (APS), mostly associated with a moderate- or high-risk antibody profile, was significantly higher in patients with (22.4%) than in those without (8.4%) JAK2^V617F mutation (p < 0.01). All evaluable JAK2^V617F-positive patients with APS were subsequently diagnosed with MPN. In patients with JAK2^V617F mutation, presence of concomitant APS was associated with a significantly younger age (49 ± 14 vs. 60 ± 15 years) at the time of thrombophilia work-up (p < 0.05).

CONCLUSION

We found a significant association between JAK2^V617F-positive MPN and definite APS. The presence of concomitant APS in patients carrying the JAK2^V617F mutation may lead to earlier manifestation of thromboembolic events and may warrant more aggressive antithrombotic treatment strategies to prevent recurrence.

Platelet Microparticle Controversial Role in Cancer

Platelet-derived microparticles (PMPs) are a group of micrometer-scale extracellular vesicles released by platelets upon activation that are responsible for the majority of microvesicles found in plasma. PMPs’ physiological properties and functions have long been investigated by researchers. In this regard, a noticeable area of studies has been devoted to evaluating the potential roles and effects of PMPs on cancer progression. Clinical and experimental evidence conflictingly implicates supportive and suppressive functions for PMPs regarding cancer. Many of these functions could be deemed as a cornerstone for future considerations of PMPs usage in cancer targeted therapy. This review discusses what is currently known about PMPs and provides insights for new and possible research directions for further grasping the intricate interplay between PMPs and cancer.

Platelets Extracellular Vesicles as Regulators of Cancer Progression-An Updated Perspective

Extracellular vesicles (EVs) are a diverse group of membrane-bound structures secreted in physiological and pathological conditions by prokaryotic and eukaryotic cells. Their role in cell-to-cell communications has been discussed for more than two decades. More attention is paid to assess the impact of EVs in cancer. Numerous papers showed EVs as tumorigenesis regulators, by transferring their cargo molecules (miRNA, DNA, protein, cytokines, receptors, etc.) among cancer cells and cells in the tumor microenvironment. During platelet activation or apoptosis, platelet extracellular vesicles (PEVs) are formed. PEVs present a highly heterogeneous EVs population and are the most abundant EVs group in the circulatory system. The reason for the PEVs heterogeneity are their maternal activators, which is reflected on PEVs size and cargo. As PLTs role in cancer development is well-known, and PEVs are the most numerous EVs in blood, their feasible impact on cancer growth is strongly discussed. PEVs crosstalk could promote proliferation, change tumor microenvironment, favor metastasis formation. In many cases these functions were linked to the transfer into recipient cells specific cargo molecules from PEVs. The article reviews the PEVs biogenesis, cargo molecules, and their impact on the cancer progression.

The role of circulating monocytes and JAK inhibition in the infectious-driven inflammatory response of myelofibrosis

Myelofibrosis (MF) is characterized by chronic inflammation and hyper-activation of the JAK-STAT pathway. Infections are one of the main causes of morbidity/mortality. Therapy with Ruxolitinib (RUX), a JAK1/2 inhibitor, may further increase the infectious risk. Monocytes are critical players in inflammation/immunity through cytokine production and release of bioactive extracellular vesicles. However, the functional behavior of MF monocytes, particularly during RUX therapy, is still unclear. In this study, we found that monocytes from JAK2V617F-mutated MF patients show an altered expression of chemokine (CCR2, CXCR3, CCR5) and cytokine (TNF-α-R, IL10-R, IL1β-R, IL6-R) receptors. Furthermore, their ability to produce and secrete free and extracellular vesicles-linked cytokines (IL1β, TNF-α, IL6, IL10) under lipopolysaccharides (LPS) stimulation is severely impaired. Interestingly, monocytes from RUX-treated patients show normal level of chemokine, IL10, IL1β, and IL6 receptors together with a restored ability to produce intracellular and to secrete extracellular vesicles-linked cytokines after LPS stimulation. Conversely, RUX therapy does not normalize TNF-R1/2 receptors expression and the LPS-driven secretion of free pro/anti-inflammatory cytokines. Accordingly, upon LPS stimulation, in vitro RUX treatment of monocytes from MF patients increases their secretion of extracellular vesicles-linked cytokines but inhibits the secretion of free pro/anti-inflammatory cytokines. In conclusion, we demonstrated that in MF the infection-driven response of circulating monocytes is defective. Importantly, RUX promotes their infection-driven cytokine production suggesting that infections following RUX therapy may not be due to monocyte failure. These findings contribute to better interpreting the immune vulnerability of MF and to envisaging strategies to improve the infection-driven immune response.

Polycythemia Vera-Associated Complications: Pathogenesis, Clinical Manifestations, And Effects On Outcomes

Polycythemia vera is a Philadelphia-negative chronic myeloproliferative neoplasm, characterized by erythrocytosis, which is unique, compared to essential thrombocytosis and primary myelofibrosis. Though longevity can usually be expected, vascular morbidity is associated with this condition, as well as a propensity to evolve into myelofibrosis (post-PV MF) and acute myeloid leukemia. In addition, patients can have a pronounced symptom burden. Herein, contributors to the symptomatic burden, as well as the thrombotic and transformative tendencies are reviewed. From a symptom perspective, some are explained by cytokine release, others by microvascular complications, whereas certain symptoms can herald disease evolution. Thrombosis has multifactorial contributors, including but not limited to gender, and inflammatory stress; investigators have recently hypothesized that microparticles and Neutrophil Extracellular Trap Formations may add to thrombotic burden. Finally, we examine the progression to post-PV MF as well as leukemic transformation, highlighting well-established risk factors including age and leukocytosis, certain treatments, and the presence of “non-driver” mutations.

Thrombin Generation and Cancer: Contributors and Consequences

The high occurrence of cancer-associated thrombosis is associated with elevated thrombin generation. Tumour cells increase the potential for thrombin generation both directly, through the expression and release of procoagulant factors, and indirectly, through signals that activate other cell types (including platelets, leukocytes and erythrocytes). Furthermore, cancer treatments can worsen these effects. Coagulation factors, including tissue factor, and inhibitors of coagulation are altered and extracellular vesicles (EVs), which can promote and support thrombin generation, are released by tumour and other cells. Some phosphatidylserine-expressing platelet subsets and platelet-derived EVs provide the surface required for the assembly of coagulation factors essential for thrombin generation in vivo. This review will explore the causes of increased thrombin production in cancer, and the availability and utility of tests and biomarkers. Increased thrombin production not only increases blood coagulation, but also promotes tumour growth and metastasis and as a consequence, thrombin and its contributors present opportunities for treatment of cancer-associated thrombosis and cancer itself.

Thrombosis in the Philadelphia Chromosome-Negative Myeloproliferative Neoplasms

The myeloproliferative neoplasms (MPNs) are clonal stem cell-derived diseases. This chapter focuses on the subcategory of Philadelphia (Ph) chromosome-negative classical MPNs, polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF). These MPNs are associated with both microvascular and macrovascular thrombosis, which may occur in the venous and arterial circulation. Erythrocytosis, leukocytosis, and increased JAK2V617F allele burden are known to be risk factors. In this chapter, we review the thrombotic and hemostatic manifestations of the Philadelphia (Ph) chromosome-negative classical MPNs, including the clinical manifestations, the pathophysiology, as well as management.

Platelet Microparticles and miRNA Transfer in Cancer Progression: Many Targets, Modes of Action, and Effects Across Cancer Stages

Platelet-derived microparticles (PMPs) have long been known to increase in circulation in the presence of cancer, and have been considered to be cancer promoting by multiple mechanisms including shrouding of circulating tumor cells allowing immune evasion, inducing a procoagulant state associated with increased risk for venous thromboembolic events in cancer patients, and supporting metastatic dissemination by establishment of niches for anchorage of circulating tumor cells. These modes of PMP-enhanced progression of late stage cancer are generally based on the adhesive and procoagulant surfaces of PMPs. However, it is now clear that PMPs can also act as intercellular signaling vesicles, by fusion with target cells and transfer of a broad array of platelet-derived molecular contents including growth factors, angiogenic modulators, second messengers, lipids, and nucleic acids. It is also now well established that PMPs are major repositories of microRNAs (miRNAs). In recent years, new roles of PMPs in cancer have begun emerging, primarily reflecting their ability to transfer miRNA contents and modulate gene expression in target cells, allowing PMPs to affect cancer development at many stages. PMPs have been shown to interact with and transfer miRNAs to various blood vascular cells including endothelium, macrophages and neutrophils. As each of these contributes to cancer progression, PMP-mediated miRNA transfer can affect immune response, NETosis, tumor angiogenesis, and likely other cancer-associated processes. Recently, PMP miRNA transfer was found to suppress primary tumor growth, via PMP infiltration in solid tumors, anchorage to tumor cells and direct miRNA transfer, resulting in tumor cell gene suppression and inhibition of tumor growth. This mini-review will summarize current knowledge of PMP-miRNA interactions with cancer-associated cells and effects in cancer progression, and will indicate new research directions for understanding platelet-cancer interactions.