Secreted mutant calreticulins as rogue cytokines in myeloproliferative neoplasms.

Mutant calreticulin (CALR) proteins resulting from a -1/+2 frameshifting mutation of the CALR exon 9 carry a novel C-terminal amino acid sequence and drive the development of myeloproliferative neoplasms (MPNs). Mutant CALRs were shown to interact with and activate the thrombopoietin receptor (TpoR/MPL) in the same cell. We report that mutant CALR proteins are secreted and can be found in patient plasma at levels up to 160 ng/mL, with a mean of 25.64 ng/mL. Plasma mutant CALR is found in complex with soluble transferrin receptor 1 (sTFR1) that acts as a carrier protein and increases mutant CALR half-life. Recombinant mutant CALR proteins bound and activated the TpoR in cell lines and primary megakaryocytic progenitors from patients with mutated CALR in which they drive thrombopoietin-independent colony formation. Importantly, the CALR-sTFR1 complex remains functional for TpoR activation. By bioluminescence resonance energy transfer assay, we show that mutant CALR proteins produced in 1 cell can specifically interact in trans with the TpoR on a target cell. In comparison with cells that only carry TpoR, cells that carry both TpoR and mutant CALR are hypersensitive to exogenous mutant CALR proteins and respond to levels of mutant CALR proteins similar to those in patient plasma. This is consistent with CALR-mutated cells that expose TpoR carrying immature N-linked sugars at the cell surface. Thus, secreted mutant CALR proteins will act more specifically on the MPN clone. In conclusion, a chaperone, CALR, can turn into a rogue cytokine through somatic mutation of its encoding gene.

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.

Predictive significance of high neutrophil ratio for thrombosis in myeloproliferative neoplasms: JSH-MPN-R18 subanalysis.

Thrombosis in myeloproliferative neoplasms (MPNs) is an important clinical problem, and risk-stratified management is essential. To identify the clinical characteristics of thrombosis in patients with MPNs, a nationwide multi-institutional retrospective analysis (JSH-MPN-R18) was conducted. The aim of the present study was to perform a sub-analysis of JSH-MPN-R18 findings to clarify the predictive parameters for thrombosis among complete blood count (CBC) results. Among the patients enrolled in JSH-MPN-R18, those with essential thrombocythemia (ET; n = 1152) and polycythemia vera (PV; n = 456) were investigated. We analyzed and compared CBC parameters between patients with and those without any thrombotic events using Welch's T-test. Statistical analyses were performed using the R statistical software. Thrombotic events were observed in 74 patients with ET. In multivariate analysis, only the neutrophil ratio was slightly but significantly higher for ET patients with thrombosis than for those without (p < 0.05). Of note, the absolute neutrophil count (aNeu) was considered a useful predictive tool for thrombosis among patients classified as low-risk according to the revised International Prognostic Score of Thrombosis for Essential Thrombocythemia. Among PV patients, those with thrombosis showed significantly higher hematocrit and aNeu than did those without thrombosis. As a thrombosis-associated factor, the neutrophil ratio was slightly but significantly elevated in patients with ET. This myeloid skew might reflect a higher value of JAK2 V617F allelic frequency in patients with ET with thrombosis; this was not clarified in JSH-MPN-R18. Further accumulation of evidence, including genetic information for JAK2 and other passenger mutations, is warranted.

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.

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.

[Novel therapeutics in myeloproliferative neoplasms: beyond JAK inhibitors].

The discovery of driver genes such as JAK2 in myeloproliferative neoplasms (MPN) led to a better understanding of MPN pathogenesis as a constitutive activation of the JAK/STAT signal. Following these findings, several types of JAK inhibitors have been developed. Ruxolitinib, a JAK1/2 inhibitor licensed for polycythemia vera and myelofibrosis, demonstrated efficacy in regulating hematocrit levels, lowering spleen volume, and relieving MPN-related symptoms. However, some patients with myelofibrosis are refractory to JAK inhibitors, and some are intolerant due to cytopenia. Furthermore, JAK inhibitors did not slow the progression of acute leukemia, indicating the need for new therapeutic methods for myelofibrosis. Novel medicines, including BCL inhibitor, MDM2 inhibitor, LSD1 inhibitor, PI3K inhibitor, BET inhibitor and telomerase inhibitor, are presently being evaluated in clinical studies for myelofibrosis with the potential to enhance clinical outcomes.

[Interferon therapy for polycythemia vera].

The effectiveness of interferon (IFN) in patients with myeloproliferative neoplasms (MPNs) including polycythemia vera (PV) has been reported for more than three decades. However, because of its toxicity and tolerability, the use of IFN has been restricted. With the recent development of pegylated-IFN, the use of IFN has been highlighted again for effectively treating MPNs. Guidelines in Western countries recommend IFN as the first choice for cytoreduction alongside hydroxyurea, particularly for young and pregnant patients. Furthermore, a novel IFN, ropeginterferon alfa-2b, allows biweekly injection and exhibits durable high hematological and molecular responses leading to the approvement of its use in Western countries. Although IFN is not yet been approved for use against PV in Japan's National Health Insurance System as of February 2023, a phase 2 study has shown efficacy, safety, and tolerability of ropeginterferon alfa-2b in Japanese patients with PV, providing hope for future development.

A pilot study examining the efficacy of hochuekkito for improving quality of life in patients with myeloproliferative neoplasms.

BACKGROUND: The prognosis of Philadelphia chromosome-negative myeloproliferative neoplasms is relatively favorable, but the quality of life can be severely affected by myeloproliferative neoplasm-related symptoms such as fatigue, pruritus, night sweats, bone pain, fever and weight loss. In this study, we administered hochuekkito, a traditional herbal medicine, to patients with myeloproliferative neoplasms and investigated whether there was a reduction in myeloproliferative neoplasm-related symptoms. METHODS: We conducted a randomized parallel-group pilot study. Patients were assigned to a hochuekkito administration or non-hochuekkito administration group. Myeloproliferative neoplasm-related symptoms based on Myeloproliferative Neoplasm Symptom Assessment Form total symptom score and European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 were examined before hochuekkito administration and 4 and 8 weeks after administration. RESULTS: Among the 42 patients included in the analysis, 21 were assigned to the hochuekkito group and 21 were assigned to the control group. After administering hochuekkito, the median values of Myeloproliferative Neoplasms Symptom Assessment Form total symptom score at 4 and 8 weeks in the hochuekkito group demonstrated a decreasing trend; however, the difference between the two groups was not significant. CONCLUSIONS: In this study, we were unable to demonstrate significant differences between the hochuekkito and control groups in terms of the efficacy of hochuekkito in treating myeloproliferative neoplasm-related symptoms. However, there were cases that presented prominent improvement in symptoms in the hochuekkito group. The only reported adverse event was grade 1 impaired hepatic function. Therefore, hochuekkito might be a therapeutic option for patients with severely affected quality of life due to myeloproliferative neoplasm-related symptoms.

[Real world data on myeloproliferative neoplasms in Japan].

Since the discovery of the JAK2V617F, MPL gene, and Calreticulin gene mutations, remarkable changes have occurred in the identification of the pathology of Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). The diagnostic criteria of polycythemia vera, essential thrombocythemia, and primary myelofibrosis in the world health organization classification systems have also been amended to include these driver gene mutations. Additionally, treatment algorithms for each disease have been reviewed. Following these changes, real world data form several countries based on national surveys have been reported. In Japan, the Japanese Society of Hematology has conducted a prospective study, named the JSH-MPN-15 study, to investigate the overall survival and risk factors of patients with MPNs. Furthermore, the retrospective JSH-MPN-R18 study was conducted and the results have been coming out. In this lecture, the results of these studies will be discussed.

[Systemic chemotherapy combined with thrombopoietin receptor agonist for the treatment of diffuse large B-cell lymphoma complicated with aplastic anemia].

Immunosuppressive therapies, including antithymocyte globulin and cyclosporine (CsA), are used for the treatment of aplastic anemia, but they reportedly cause lymphoproliferative diseases. Here, we report two cases of aplastic anemia in which diffuse large B-cell lymphoma developed during treatment with CsA. In both the cases, CsA was discontinued and combination therapy with R-CHOP (rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine sulfate, and prednisolone) plus the thrombopoietin receptor agonist eltrombopag was initiated. Furthermore, supportive care, including blood transfusion and granulocyte colony-stimulating factor, was provided. After six or eight courses of R-CHOP therapy, a complete metabolic response was achieved without serious adverse events. These cases illustrate the safety of combining R-CHOP with eltrombopag therapy in patients at a high risk of severe pancytopenia.

CREB3L1 overexpression as a potential diagnostic marker of Philadelphia chromosome-negative myeloproliferative neoplasms.

Discrimination of Philadelphia-negative myeloproliferative neoplasms (Ph-MPNs) from reactive hypercytosis and myelofibrosis requires a constellation of testing including driver mutation analysis and bone marrow biopsies. We searched for a biomarker that can more easily distinguish Ph-MPNs from reactive hypercytosis and myelofibrosis by using RNA-seq analysis utilizing platelet-rich plasma (PRP)-derived RNAs from patients with essential thrombocythemia (ET) and reactive thrombocytosis, and CREB3L1 was found to have an extremely high impact in discriminating the two disorders. To validate and further explore the result, expression levels of CREB3L1 in PRP were quantified by reverse-transcription quantitative PCR and compared among patients with ET, other Ph-MPNs, chronic myeloid leukemia (CML), and reactive hypercytosis and myelofibrosis. A CREB3L1 expression cutoff value determined based on PRP of 18 healthy volunteers accurately discriminated 150 driver mutation-positive Ph-MPNs from other entities (71 reactive hypercytosis and myelofibrosis, 6 CML, and 18 healthy volunteers) and showed both sensitivity and specificity of 1.0000. Importantly, CREB3L1 expression levels were significantly higher in ET compared with reactive thrombocytosis (P < .0001), and polycythemia vera compared with reactive erythrocytosis (P < .0001). Pathology-affirmed triple-negative ET (TN-ET) patients were divided into a high- and low-CREB3L1-expression group, and some patients in the low-expression group achieved a spontaneous remission during the clinical course. In conclusion, CREB3L1 analysis has the potential to single-handedly discriminate driver mutation-positive Ph-MPNs from reactive hypercytosis and myelofibrosis, and also may identify a subgroup within TN-ET showing distinct clinical features including spontaneous remission.

Mechanism underlying the development of myeloproliferative neoplasms through mutant calreticulin.

Deregulation of cytokine signaling is frequently associated with various pathological conditions, including malignancies. In patients with myeloproliferative neoplasms (MPNs), recurrent somatic mutations in the calreticulin (CALR) gene, which encodes a molecular chaperone that resides in the endoplasmic reticulum, have been reported. Studies have defined mutant CALR as an oncogene promoting the development of MPN, and deciphered a novel molecular mechanism by which mutant CALR constitutively activates thrombopoietin receptor MPL and its downstream molecules to induce cellular transformation. The mechanism of interaction and activation of MPL by mutant CALR is unique, not only due to the latter forming a homomultimeric complex through a novel mutant-specific sequence generated by frameshift mutation, but also for its ability to interact with immature asparagine-linked glycan for eventual engagement with immature MPL in the endoplasmic reticulum. The complex formed between mutant CALR and MPL is then transported to the cell surface, where it induces constitutive activation of downstream kinase JAK2 bound to MPL. Refined structural and cell biological studies can provide an in-depth understanding of this unusual mechanism of receptor activation by a mutant molecular chaperone. Mutant CALR is also involved in modulation of the immune response, transcription, and intracellular homeostasis, which could contribute to the development of MPN. In the present article, we comprehensively review the current understanding of the underlying molecular mechanisms for mutant molecular chaperone-induced cellular transformation.

[Recent advances in polycythemia vera treatment].

Since the discovery of the gain-of-function mutation JAK2 V617F, significant progress has been made in clarifying the pathology and developing novel agents for myeloproliferative neoplasms, including polycythemia vera (PV). The treatment strategy for PV is to first classify patients into either high- or low-risk groups for thrombosis. All patients with PV should be treated with low-dose aspirin and phlebotomy. In addition, for high-risk PV patients, cytoreductive therapy is recommended. Although hydroxyurea (HU) is the most popular agent for PV treatment, the advantages of ruxolitinib, a JAK inhibitor, for patients who are intolerant or resistant to HU were recently reported. Furthermore, the ability of interferon-α to selectively eliminate the malignant clone and induce complete molecular response was previously demonstrated. In this article, important clinical trials associated with the treatment strategy for PV and recent advances in PV treatments are described.

Clinical and molecular features of patients with prefibrotic primary myelofibrosis previously diagnosed as having essential thrombocythemia in Japan.

OBJECTIVE: Prefibrotic/early primary myelofibrosis (pre-PMF) and essential thrombocythemia (ET) exhibited different features of bone marrow; however, this is not always easy to judge objectively, making pathologists' distinction often suboptimal. In the WHO 2008 criteria, pre-PMF was not defined as a subgroup of PMF; therefore, affected patients were at a higher risk of misdiagnosis with ET. In this study, we examined the prevalence of pre-PMF patients among those previously diagnosed with ET in Japan. METHOD: We reviewed bone marrow specimens and clinical and molecular parameters of patients who were previously diagnosed with ET by the WHO 2008 criteria. RESULTS: Among 107 ET patients, 13 patients were redefined as having pre-PMF. Pre-PMF patients exhibited a higher frequency of MPL mutation and increased platelet counts compared to true ET patients. Molecular analysis revealed the frequencies of high-risk molecular mutations, such as ASXL1, EZH2, and SRSF2, were significantly increased in pre-PMF patients than those in true ET patients. CONCLUSION: These results demonstrated the value of reexamining clinical records for patients diagnosed with ET by the WHO 2008 criteria and emphasized that adequate examinations of patients' bone marrow are crucial for an accurate diagnosis of pre-PMF and ET.

[Efficacy and safety of ruxolitinib in patients with myelofibrosis: a single-center retrospective analysis].

We retrospectively analyzed 30 patients with myelofibrosis who had been treated with ruxolitinib at our hospital. Although dose reduction was required for 13 patients due to anemia or thrombocythemia, it was later possible to increase the dose of ruxolitinib in 10 patients (77%). A total of five patients became transfusion dependent. Among them, one patient who continued ruxolitinib therapy exhibited subsequent symptom improvement and reduction in splenomegaly while also becoming transfusion independent. Four patients whose platelet counts were <50×109/l were also treated with ruxolitinib, one of whom was able to continue ruxolitinib therapy for 25 months with some response. For one patient, ruxolitinib therapy was withdrawn due to non-response. However, upon reintroduction of ruxolitinib after 5 months without treatment, spleen size and LD levels decreased, which lasted for around 5 months. This retrospective study supports the current understanding on ruxolitinib therapy for Japanese patients with cytopenia.

Skewed megakaryopoiesis in human induced pluripotent stem cell-derived haematopoietic progenitor cells harbouring calreticulin mutations.

Somatic mutations in the calreticulin (CALR) gene have been found in most patients with JAK2- and MPL-unmutated Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). It has recently been shown that mutant CALR constitutively activates the thrombopoietin receptor MPL and, thus, plays a causal role in the development of MPNs. However, the roles of mutant CALR in human haematopoietic cell differentiation remain predominantly elusive. To examine the impact of the 5-base insertion mutant CALR gene (Ins5) on haematopoietic cell differentiation, we generated induced pluripotent stem cells from an essential thrombocythaemia (ET) patient harbouring a CALR-Ins5 mutation and from a healthy individual (WT). Megakaryopoiesis was more prominent in Ins5-haematopoietic progenitor cells (Ins5-HPCs) than in WT-HPCs, implying that the system recapitulates megakaryocytosis observed in the bone marrow of CALR-mutant ET patients. Ins5-HPCs exhibited elevated expression levels of GATA1 and GATA2, suggesting a premature commitment to megakaryocytic differentiation in progenitor cells. We also demonstrated that 3-hydroxy anagrelide markedly perturbed megakaryopoiesis, but not erythropoiesis. Collectively, we established an in vitro model system that recapitulates megakaryopoiesis caused by mutant CALR. This system can be used to validate therapeutic compounds for MPN patients harbouring CALR mutations and in detailed studies on mutant CALR in human haematological cell differentiation.

Activation of the thrombopoietin receptor by mutant calreticulin in CALR-mutant myeloproliferative neoplasms.

Recurrent somatic mutations of calreticulin (CALR) have been identified in patients harboring myeloproliferative neoplasms; however, their role in tumorigenesis remains elusive. Here, we found that the expression of mutant but not wild-type CALR induces the thrombopoietin (TPO)-independent growth of UT-7/TPO cells. We demonstrated that c-MPL, the TPO receptor, is required for this cytokine-independent growth of UT-7/TPO cells. Mutant CALR preferentially associates with c-MPL that is bound to Janus kinase 2 (JAK2) over the wild-type protein. Furthermore, we demonstrated that the mutant-specific carboxyl terminus portion of CALR interferes with the P-domain of CALR to allow the N-domain to interact with c-MPL, providing an explanation for the gain-of-function property of mutant CALR. We showed that mutant CALR induces the phosphorylation of JAK2 and its downstream signaling molecules in UT-7/TPO cells and that this induction was blocked by JAK2 inhibitor treatment. Finally, we demonstrated that c-MPL is required for TPO-independent megakaryopoiesis in induced pluripotent stem cell-derived hematopoietic stem cells harboring the CALR mutation. These findings imply that mutant CALR activates the JAK2 downstream pathway via its association with c-MPL. Considering these results, we propose that mutant CALR promotes myeloproliferative neoplasm development by activating c-MPL and its downstream pathway.

The 2014 BCSH criteria and the 2016 WHO criteria for essential thrombocythemia: A comparison in a large-scale cohort.

OBJECTIVE: There are currently 2 representative diagnostic criteria for essential thrombocythemia (ET), the 2014 British Committee for Standards in Hematology Guidelines (BCSH) criteria and the 2016 World Health Organization (WHO) criteria. We compare and discuss the advantages and disadvantages of the 2 criteria. METHOD: We applied the 2 criteria to 403 patients with thrombocytosis and suspected myeloproliferative neoplasms (MPN) and compared patient populations. RESULTS: The BCSH criteria diagnosed ET in 279 patients (BCSH-ET) whereas the WHO criteria diagnosed ET in 203 patients (WHO-ET). There were 83 patients diagnosable only by the BCSH criteria (BCSH-only-ET), of which under the WHO classification, 69 patients fell under the category of MPN, unclassifiable (MPN-u), 12 patients were PMF, prefibrotic/early stage (pre-PMF), and 2 patients were polycythemia vera. Patient characteristics such as age, hemoglobin, hematocrit, platelet counts, lactate dehydrogenase levels, JAK2V617F allele burdens, prevalence of myelofibrosis and splenomegaly, and frequencies of thrombotic events and treatment did not differ between WHO-ET and BCSH-only-ET, but BCSH-only-ET patients showed higher WBC counts and higher JAK2V617F mutation frequencies. CONCLUSION: The BCSH criteria diagnosed ET in a broader range of patients encompassing a significant number of patients who would otherwise be diagnosed as pre-PMF or MPN-u.

[Transfusion independence achieved with pomalidomide therapy in a patient with primary myelofibrosis].

Primary myelofibrosis (PMF) is commonly associated with anemia. IMiD® immunomodulatory drugs including thalidomide and lenalidomide have been shown to be effective in improving anemia associated with PMF. However, because of adverse events, their use has been restricted. Herein we report the case of a 67-year-old male patient with transfusion-dependent PMF treated with the immunomodulatory drug pomalidomide in a clinical trial. Significant improvements in anemia and thrombocytopenia were observed with pomalidomide, and the patient recovered from transfusion dependence for 8 months. Although phase 3 trial failed to show the superiority of pomalidomide over placebo, pomalidomide may have some benefit in selected patients with transfusion-dependent PMF.