Allogeneic Stem Cell Transplantation in Myelofibrosis.

Myeloproliferative neoplasm (MPN) is a category in the World Health Organization classification of myeloid tumors. BCR-ABL1-negative MPN is a subcategory that includes primary myelofibrosis (MF), post-essential thrombocythemia MF, and post-polycythemia vera MF. These disorders are characterized by stem cell-derived clonal myeloproliferation. Clinically, these diseases present with anemia and splenomegaly and significant constitutional symptoms such as severe fatigue, symptoms associated with an enlarged spleen and liver, pruritus, fevers, night sweats, and bone pain. Multiple treatment options may provide symptom relief and improved survival; however, allogeneic stem cell transplantation (HCT) remains the only potentially curative option. The decision for a transplant is based on patient prognosis, age, comorbidities, and functional status. This review describes the recent data on various peritransplantation factors and their effect on outcomes of patients with MF and new therapeutic areas, such as the use and timing of Janus kinase inhibitors with HCT and gives overall conclusions from the available data in the published literature.

Long-term follow-up of essential thrombocythemia patients treated with anagrelide: subgroup analysis according to JAK2/CALR/MPL mutational status.

BACKGROUND: Anagrelide represents a treatment option for essential thrombocythemia, although its place in therapy remains controversial. AIM: To assess the impact of mutational status in response rates and development of adverse events during long-term use of anagrelide. METHODS: We retrospectively evaluated 67 patients with essential thrombocythemia treated with anagrelide during 68 (4-176) months. RESULTS: Mutational frequencies were 46.3%, 28.3%, and 1.5% for JAK2V617F, CALR and MPL mutations. Anagrelide yielded a high rate of hematologic responses, which were complete in 49.25% and partial in 46.25%, without differences among molecular subsets. The rate of thrombosis during treatment was one per 100 patient-years, without excess bleeding. Anemia was the major adverse event, 30.3% at 5-yr follow-up, being more frequent in CALR(+) (P < 0.05). Myelofibrotic transformation developed in 14.9% (12.9%, 21%, and 12.5% in JAK2V617F(+), CALR(+), and triple-negative patients, respectively, P = NS) and those treated >60 months were at higher risk, OR (95% CI) 9.32 (1.1-78.5), P < 0.01, indicating the need for bone marrow monitoring during prolonged treatment. CONCLUSION: Although CALR(+) patients were at higher risk of developing anemia, anagrelide proved effective among all molecular subsets, indicating that mutational status does not seem to represent a major determinant of choice of cytoreductive treatment among essential thrombocythemia therapies.

Mutant calreticulin-expressing cells induce monocyte hyperreactivity through a paracrine mechanism.

Mutations in the calreticulin gene (CALR) were recently identified in approximately 70-80% of patients with JAK2-V617F-negative essential thrombocytosis and primary myelofibrosis. All frameshift mutations generate a recurring novel C-terminus. Here we provide evidence that mutant calreticulin does not accumulate efficiently in cells and is abnormally enriched in the nucleus and extracellular space compared to wildtype calreticulin. The main determinant of these findings is the loss of the calcium-binding and KDEL domains. Expression of type I mutant CALR in Ba/F3 cells confers minimal IL-3-independent growth. Interestingly, expression of type I and type II mutant CALR in a nonhematopoietic cell line does not directly activate JAK/STAT signaling compared to wildtype CALR and JAK2-V617F expression. These results led us to investigate paracrine mechanisms of JAK/STAT activation. Here we show that conditioned media from cells expressing type I mutant CALR exaggerate cytokine production from normal monocytes with or without treatment with a toll-like receptor agonist. These effects are not dependent on the novel C-terminus. These studies offer novel insights into the mechanism of JAK/STAT activation in patients with JAK2-V617F-negative essential thrombocytosis and primary myelofibrosis.

Expansion of circulating CD56bright natural killer cells in patients with JAK2-positive chronic myeloproliferative neoplasms during treatment with interferon-α.

In recent years, major molecular remissions have been observed in patients with JAK2-positive chronic myeloproliferative neoplasms (MPNs) after therapy with IFN-α. IFN-α is known to have altering effects on immune cells involved in immune surveillance and might consequently enhance anti-tumor immune response against the JAK2-mutated clone. The objective of this study was to investigate circulating levels and phenotype of natural killer cells in 29 JAK2-positive MPN patients during IFN-α treatment. Furthermore, functional studies of NK cells upon target-cell recognition and cytokine stimulation were performed. The CD56(bright) and CD56(dim) NK cell subtypes display different properties in terms of cytokine production and cytotoxicity, respectively. Our results show a significant increase in the proportion of CD56(bright) NK cells and a decreasing CD56(dim) population during treatment with IFN-α compared to patients that are untreated, treated with hydroxyurea and healthy controls, P < 0.0001. Furthermore, an overall increase in cytokine-dependent (IL-12 and IL-15) IFN-γ expression by CD56(dim) NK cells during IFN-α treatment was observed. In contrast, our data indicate a compromised NK cell response to target-cell recognition during treatment with IFN-α in four patients. We also report low levels of circulating NK cells in untreated patients compared to healthy donors, patients treated with hydroxyurea and IFN-α, P = 0.02. Based on our findings, one might speculate whether treatment with IFN-α skews the human NK population toward a helper type that may assist in CD8(+) T cell priming in lymphoid tissues at the expense of their immediate cytotoxic functions in peripheral blood and tissues.

Proinflammatory Cytokine IL-6 and JAK-STAT Signaling Pathway in Myeloproliferative Neoplasms.

The recent JAK1/2 inhibitor trial in myeloproliferative neoplasms (MPNs) showed that reducing inflammation can be more beneficial than targeting gene mutants. We evaluated the proinflammatory IL-6 cytokine and JAK-STAT signaling pathway related genes in circulating CD34(+) cells of MPNs. Regarding laboratory data, leukocytosis has been observed in polycythemia vera (PV) and JAK2V617F mutation positive versus negative primary myelofibrosis (PMF) patients. Moreover, thrombocytosis was reduced by JAK2V617F allele burden in essential thrombocythemia (ET) and PMF. 261 significantly changed genes have been detected in PV, 82 in ET, and 94 genes in PMF. The following JAK-STAT signaling pathway related genes had augmented expression in CD34(+) cells of MPNs: CCND3 and IL23A regardless of JAK2V617F allele burden; CSF3R, IL6ST, and STAT1/2 in ET and PV with JAK2V617F mutation; and AKT2, IFNGR2, PIM1, PTPN11, and STAT3 only in PV. STAT5A gene expression was generally reduced in MPNs. IL-6 cytokine levels were increased in plasma, as well as IL-6 protein levels in bone marrow stroma of MPNs, dependent on JAK2V617F mutation presence in ET and PMF patients. Therefore, the JAK2V617F mutant allele burden participated in inflammation biomarkers induction and related signaling pathways activation in MPNs.

Increase in circulating CD4⁺CD25⁺Foxp3⁺ T cells in patients with Philadelphia-negative chronic myeloproliferative neoplasms during treatment with IFN-α.

Recent reports have described complete or major molecular remission in patients with polycythemia vera after long-term treatment with the immunomodulatory agent IFN-α2. Accordingly, there are reasons to believe that the immune system is a key player in eradicating the JAK2 mutated clone in these patients. Foxp3(+) regulatory T cells play a pivotal role in maintaining immune homeostasis and, importantly, preventing immune reactivity to self-antigens; however, their suppressive activity can compromise an effective antitumor immune response, and high frequencies of regulatory T cells in peripheral blood have been reported in both hematologic and solid cancers. We have analyzed the number, phenotype, and function of circulating CD4(+)CD25(+)Foxp3(+) T cells in patients with chronic myeloproliferative neoplasms. Surprisingly, we found a marked expansion of this subset of lymphocytes in patients treated with IFN-α2 (13.0%; 95% confidence interval [CI] 10.8% to 15.2%) compared with healthy donors (6.1%; 95% CI 4.9% to 7.2%), patients with untreated chronic myeloproliferative neoplasms (6.9%; 95% CI 5.8% to 7.4%), or patients treated with hydroxyurea (5.8%; 95% CI 4.3% to 7.4%; P < .0001).

Clearance of circulating activated platelets in polycythemia vera and essential thrombocythemia.

Essential thrombocythemia (ET) and polycythemia vera (PV) are characterized by persistent platelet activation. The mechanisms involved in their clearance are poorly characterized. In the present study, we report that leukocytes were actively involved in platelet disposal in 51 patients with ET and 30 with PV, but not in 70 age- and sex-matched controls. The fraction of circulating neutrophils and monocytes that had phagocytosed platelets, as assessed by flow cytometry, was significantly higher in patients with PV or ET, independently of hydroxyurea treatment, than in controls. Platelet phagocytosis by circulating leukocytes was confirmed by confocal and electron microscopy. The lack of effect of hydroxyurea, which disrupts the P-selectin/P-selectin glycoprotein ligand 1 (PSGL-1) interaction, suggests a P-selectin-independent mechanism. This hypothesis was confirmed in an ad hoc animal model based on the in vivo injection of activated platelets from P-selectin(+/+) and P-selectin(-/-) mice. P-selectin expression was associated with an earlier and effective clearance of platelets by neutrophils. A second delayed, P-selectin-independent phase actively involved monocytes. Our results suggest that phagocytic clearance of platelets by leukocytes occurs in PV and ET, possibly involving P-selectin-dependent and -independent pathways, thus representing a novel mechanism to remove activated platelets from the circulation.

Allogeneic hematopoietic cell transplantation for advanced polycythemia vera and essential thrombocythemia.

Allogeneic hematopoietic cell transplantation (HCT) is curative for selected patients with advanced essential thrombocythemia (ET) or polycythemia vera (PV). From 1990 to 2007, 75 patients with ET (median age 49 years) and 42 patients with PV (median age 53 years) underwent transplantations at the Fred Hutchinson Cancer Research Center (FHCRC; n = 43) or at other Center for International Blood and Marrow Transplant Research (CIBMTR) centers (n = 74). Thirty-eight percent of the patients had splenomegaly and 28% had a prior splenectomy. Most patients (69% for ET and 67% for PV) received a myeloablative (MA) conditioning regimen. Cumulative incidence of neutrophil engraftment at 28 days was 88% for ET patients and 90% for PV patients. Acute graft-versus-host disease (aGVHD) grades II to IV occurred in 57% and 50% of ET and PV patients, respectively. The 1-year treatment-related mortality (TRM) was 27% for ET and 22% for PV. The 5-year cumulative incidence of relapse was 13% for ET and 30% for PV. Five-year survival/progression-free survival (PFS) was 55%/47% and 71%/48% for ET and PV, respectively. Patients without splenomegaly had faster neutrophil and platelet engraftment, but there were no differences in TRM, survival, or PFS. Presence of myelofibrosis (MF) did not affect engraftment or TRM. Over 45% of the patients who undergo transplantations for ET and PV experience long-term PFS.

Evaluation of interleukin-23 plasma levels in patients with polycythemia vera and essential thrombocythemia.

Essential thrombocythemia (ET), polycythemia vera (PV) and myelofibrosis share the same acquired genetic lesion, JAK2V617F. It is believed that cytokines participate in the activation of JAK2V617F. In this study, we analyzed the plasma levels of interleukin (IL)-23, IL-10 and IL-22 in patients with PV and ET. In the same subjects we also performed analysis of the JAK2(V617F) mutation, and evaluated a possible relationship between interleukin levels and thrombotic complications or with the symptom pruritus. Plasma levels of IL-23 were significantly increased in all patients with MPN in comparison to controls. Moreover, there was a significant difference between the levels of IL-23 in patients affected by PV and those measured in controls (8.57±3.69pg/mL vs. 6.55±4.125pg/mL; p<0.03). No difference was found between IL-23 levels in ET patients and controls. No statistically significant differences were found between the levels of IL-23, Il-22 or IL-10 in PV or ET subjects with or without thrombosis, in patients with or without pruritus, or according the JAK2V617F burden. In PV patients the JAK2 burden and Hb levels correlated with occurrence of pruritus. Our study seems to point out a possible involvement of IL-23 in the pathogenesis of PV.

Whole-blood transcriptional profiling of interferon-inducible genes identifies highly upregulated IFI27 in primary myelofibrosis.

Gene expression profiling studies have unraveled deregulation of several genes that might be of pathogenetic importance for the development and phenotype of the Philadelphia-negative chronic myeloproliferative neoplasms. In the context of interferon-alpha2 as a promising therapeutic agent, we focused upon the transcriptional profiling of interferon-associated genes in patients with essential thrombocythemia (ET) (n = 19), polycythemia vera (PV) (n = 41), and primary myelofibrosis (PMF) (n = 9). Using whole-blood transcriptional profiling and accordingly obtaining an integrated signature of genes expressed in several immune cells (granulocytes, monocytes, B cells, T cells, platelets), we have identified a number of interferon-associated genes to be significantly deregulated but with a highly significant deregulation of interferon-inducible gene 27 (IFI27) (ET, PV, and PMF, fold change 8, 16, and 30, respectively). The striking deregulation of IFI genes may reflect a hyperstimulated but insufficient immune system being most enhanced in patients with advanced myelofibrosis, in whom the IFI27 gene displayed an exceedingly high expression. The interferon signature may reflect primary myelofibrosis as the burn-out phase of chronic inflammation which ultimately elicits clonal evolution and expansion owing to an exaggerated but incompetent antitumor immune response. Finally, IFI27 may be a novel biomarker of disease activity and tumor burden in patients with CMPNs.

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.

Lower response to BNT162b2 vaccine in patients with myelofibrosis compared to polycythemia vera and essential thrombocythemia.

In a population of 42 Philadelphia negative myeloproliferative neoplasm patients, all on systemic active treatment, the likelihood of responding to anti-SARS-CoV-2 BNT162b2 vaccine at 2 weeks after the second dose was significantly lower in the ten patients with myelofibrosis compared to the 32 with essential thrombocythemia (n = 17) and polycythemia vera (n = 15) grouped together, both in terms of neutralizing anti-SARS-CoV-2 IgG titers and seroprotection rates (32.47 AU/mL vs 217.97 AU/mL, p = 0.003 and 60% vs 93.8%, p = 0.021, respectively). Ruxolitinib, which was the ongoing treatment in five patients with myelofibrosis and three with polycythemia vera, may be implicated in reducing vaccine immunogenicity (p = 0.076), though large prospective study is needed to address this issue.

Platelet Toll-Like Receptors Mediate Thromboinflammatory Responses in Patients With Essential Thrombocythemia.

Essential thrombocythemia (ET) is comprised among chronic myeloproliferative neoplasms (MPN) and is caused by driver mutations in JAK2, CALR, and MPL, which lead to megakaryocyte proliferation and prominent thrombocytosis. Thrombosis remains the main cause of morbidity in ET and is driven by the interplay between blood cells, the endothelium, the clotting cascade, and host-derived inflammatory mediators. Platelet activation plays a key role in the thrombotic predisposition, although the underlying mechanisms remain poorly defined. In addition to their role in hemostasis, platelets participate in innate immunity and inflammation owing to the expression of toll-like receptors (TLR), which recognize inflammatory signals, triggering platelet functional responses. Considering the impact of inflammation on ET procoagulant state, we assessed the contribution of TLR2 and TLR4 to platelet hemostatic and inflammatory properties in ET patients, by using Pam3CSK4 and lipopolysaccharide (LPS) as specific TLR2 and TLR4 ligands, respectively. TLR2 ligation induced increased surface translocation of α-granule-derived P-selectin and CD40L, which mediate platelet interaction with leukocytes and endothelial cells, respectively, and higher levels of dense granule-derived CD63 in patients, whereas PAC-1 binding was not increased and LPS had no effect on these platelet responses. Platelet-neutrophil aggregate formation was elevated in ET at baseline and after stimulation of both TLR2 and TLR4. In addition, ET patients displayed higher TLR2- and TLR4-triggered platelet secretion of the chemokine RANTES (CCL5), whereas von Willebrand factor release was not enhanced, revealing a differential releasate pattern for α-granule-stored inflammatory molecules. TLR-mediated hyperresponsiveness contrasted with impaired or preserved responses to classic platelet hemostatic agonists, such as TRAP-6 and thrombin. TLR2 and TLR4 expression on the platelet surface was normal, whereas phosphorylation of downstream effector ERK1/2 was higher in patients at baseline and after incubation with Pam3CSK4, which may partly explain the enhanced TLR2 response. In conclusion, exacerbated response to TLR stimulation may promote platelet activation in ET, boosting platelet/leukocyte/endothelial interactions and secretion of inflammatory mediators, overall reinforcing the thromboinflammatory state. These findings highlight the role of platelets as inflammatory sentinels in MPN prothrombotic scenario and provide additional evidence for the close intertwining between thrombosis and inflammation in this setting.

Cytokine Profiling in Myeloproliferative Neoplasms: Overview on Phenotype Correlation, Outcome Prediction, and Role of Genetic Variants.

Among hematologic malignancies, the classic Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are considered a model of inflammation-related cancer development. In this context, the use of immune-modulating agents has recently expanded the MPN therapeutic scenario. Cytokines are key mediators of an auto-amplifying, detrimental cross-talk between the MPN clone and the tumor microenvironment represented by immune, stromal, and endothelial cells. This review focuses on recent advances in cytokine-profiling of MPN patients, analyzing different expression patterns among the three main Philadelphia-negative (Ph-negative) MPNs, as well as correlations with disease molecular profile, phenotype, progression, and outcome. The role of the megakaryocytic clone as the main source of cytokines, particularly in myelofibrosis, is also reviewed. Finally, we report emerging intriguing evidence on the contribution of host genetic variants to the chronic pro-inflammatory state that typifies MPNs.

Novel and combination therapies for polycythemia vera and essential thrombocythemia: the dawn of a new era.

INTRODUCTION: Essential thrombocythemia (ET) and polycythemia vera (PV) belong to the BCR-ABL1-negative myeloproliferative neoplasms and are characterized by the clonal proliferation of hematopoietic stem and progenitor cells. The contribution of aberrant immune regulation within the bone marrow microenvironment to ET and PV pathogenesis as well as the underlying molecular landscape is becoming increasingly understood. AREAS COVERED: Authors searched PubMed and conference abstracts in August 2020 for preclinical and clinical studies to provide an overview of the immune pathobiology in ET and PV and the rationale for several novel agents. A discussion of recent clinical trials on interferon and ruxolitinib in ET and PV patients is provided followed by an outline of the future challenges in the field particularly for novel therapeutics and an increasingly individualized, molecularly driven approach to treatment selection. Several novel agents are currently being actively evaluated and are reviewed herein as well. EXPERT OPINION: While hydroxyurea remains the first-line treatment for cytoreduction in most high-risk ET and PV patients, the disease-modifying potential of IFN is promising and could make it a preferred option for selected patients. Advances in molecular testing will enable a more individualized approach to prognostication and treatment selection.

The calreticulin (CALR) exon 9 mutations are promising targets for cancer immune therapy.

The calreticulin (CALR) exon 9 mutations are found in ∼30% of patients with essential thrombocythemia and primary myelofibrosis. Recently, we reported spontaneous immune responses against the CALR mutations. Here, we describe that CALR-mutant (CALRmut)-specific T cells are able to specifically recognize CALRmut cells. First, we established a T-cell culture specific for a CALRmut epitope. These specific T cells were able to recognize several epitopes in the CALRmut C terminus. Next, we established a CALRmut-specific CD4+ T-cell clone by limiting dilution. These CD4+ T cells recognized autologous CALRmut monocytes and hematopoietic stem cells, and T-cell recognition of target cells was dependent on the presence of CALR. Furthermore, we showed that the CALRmut response was human leukocyte antigen (HLA)-DR restricted. Finally, we demonstrated that the CALRmut-specific CD4+ T cells, despite their phenotype, were cytotoxic to autologous CALRmut cells, and that the cytotoxicity was mediated by degranulation of the T cells. In conclusion, the CALR exon 9 mutations are targets for specific T cells and thus are promising targets for cancer immune therapy such as peptide vaccination in patients harboring CALR exon 9 mutations.

Increased B cell activation is present in JAK2V617F-mutated, CALR-mutated and triple-negative essential thrombocythemia.

Essential thrombocythemia (ET) is a BCL-ABL1-negative myeloproliferative neoplasm. We have reported that increased activated B cells can facilitate platelet production mediated by cytokines regardless JAK2 mutational status in ET. Recently, calreticulin (CALR) mutations were discovered in ~30% JAK2/MPL-unmutated ET and primary myelofibrosis. Here we sought to screen for CALR mutations and to evaluate B cell immune profiles in a cohort of adult Taiwanese ET patients. B cell populations, granulocytes/monocytes membrane-bound B cell-activating factor (mBAFF) levels, B cells toll-like receptor 4 (TLR4) expression and intracellular levels of interleukin (IL)-1ß/IL-6 and the expression of CD69, CD80, and CD86 were quantified by flow cytometry. Serum BAFF concentration was measured by ELISA. 48 healthy adults were used for comparison. 19 (35.2%) of 54 ET patients harbored 8 types of CALR exon 9 mutations including 4 (7.4%) patients with concomitant JAK2V617F mutations. Compared to JAK2V617F mutation, CALR mutations correlated with younger age at diagnosis (p=0.04), higher platelet count (p=0.004), lower hemoglobin level (p=0.013) and lower leukocyte count (p=0.013). Multivariate analysis adjusted for age, sex, follow-up period and hematological parameters confirmed that increased activated B cells were universally present in JAK2-mutated, CALR-mutated and triple-negative ET patients when compared to healthy adults. JAK2- and CALR-mutated ET have significantly higher fraction of B cells with TLR4 expression when compared to triple-negative ET (p=0.019 and 0.02, respectively). CALR-mutated ET had significantly higher number of CD69-positive activated B cells when compared to triple-negative ET (p=0.035). In conclusion, increased B cell activation is present in ET patients across different mutational subgroups.