Whole-genome landscape of adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive neoplasm immunophenotypically resembling regulatory T cells, associated with human T-cell leukemia virus type-1. Here, we performed whole-genome sequencing (WGS) of 150 ATL cases to reveal the overarching landscape of genetic alterations in ATL. We discovered frequent (33%) loss-of-function alterations preferentially targeting the CIC long isoform, which were overlooked by previous exome-centric studies of various cancer types. Long but not short isoform-specific inactivation of Cic selectively increased CD4+CD25+Foxp3+ T cells in vivo. We also found recurrent (13%) 3'-truncations of REL, which induce transcriptional upregulation and generate gain-of-function proteins. More importantly, REL truncations are also common in diffuse large B-cell lymphoma, especially in germinal center B-cell-like subtype (12%). In the non-coding genome, we identified recurrent mutations in regulatory elements, particularly splice sites, of several driver genes. In addition, we characterized the different mutational processes operative in clustered hypermutation sites within and outside immunoglobulin/T-cell receptor genes and identified the mutational enrichment at the binding sites of host and viral transcription factors, suggesting their activities in ATL. By combining the analyses for coding and noncoding mutations, structural variations, and copy number alterations, we discovered 56 recurrently altered driver genes, including 11 novel ones. Finally, ATL cases were classified into 2 molecular groups with distinct clinical and genetic characteristics based on the driver alteration profile. Our findings not only help to improve diagnostic and therapeutic strategies in ATL, but also provide insights into T-cell biology and have implications for genome-wide cancer driver discovery.

Real-world clinical characteristics of post-essential thrombocythemia and post-polycythemia vera myelofibrosis.

There are few prospective studies on patients with post-essential thrombocythemia myelofibrosis (PET-MF) and post-polycythemia vera myelofibrosis (PPV-MF). Therefore, we conducted a nationwide longitudinal prospective survey to clarify the clinical characteristics of these diseases. A total of 197 PET-MF and 117 PPV-MF patients diagnosed between 2012 and 2021 were analyzed. The median age at diagnosis was 70.0 years for both diseases. The time from diagnosis of ET or PV to that of MF was 9.6 and 10.4 years, respectively, with no significant difference. Patients with PPV-MF had higher hemoglobin levels and white blood cell counts than those with PET-MF, whereas those with PET-MF had higher platelet counts than those with PPV-MF. Although splenomegaly was more frequent in patients with PPV-MF at diagnosis, there was no difference in the frequency of constitutional symptoms. Ruxolitinib was the most common treatment administered to 74.6% and 83.8% of patients with PET-MF and PPV-MF, respectively. Patients with PET-MF and PPV-MF had similar prognoses, with 3-year overall survival (OS) of 0.742 in PET-MF and 0.768 in PPV-MF patients. In both diseases, leukemic transformation was the leading cause of death, followed by infection. The 3-year OS for patients with PET/PPV-MF and primary MF diagnosed during the same period was 0.754 and 0.626, respectively, with no significant difference. This survey provides real-world clinical features and prognostic data on secondary myelofibrosis in the ruxolitinib era.

Impaired humoral immunity following COVID-19 vaccination in HTLV-1 carriers.

BACKGROUND: Whether human T-lymphotropic virus type 1 (HTLV-1) carriers can develop sufficient humoral immunity after coronavirus disease 2019 (COVID-19) vaccination is unknown. METHODS: To investigate humoral immunity after COVID-19 vaccination in HTLV-1 carriers, a multicenter, prospective observational cohort study was conducted at five institutions in southwestern Japan, an endemic area for HTLV-1. HTLV-1 carriers and HTLV-1-negative controls were enrolled for this study from January to December 2022. During this period, the third dose of the COVID-19 vaccine was actively administered. HTLV-1 carriers were enrolled during outpatient visits, while HTLV-1-negative controls included health care workers and patients treated by participating institutions for diabetes, hypertension, or dyslipidemia. The main outcome was the effect of HTLV-1 infection on the plasma anti-COVID-19 spike IgG (IgG-S) titers after the third dose, assessed by multivariate linear regression with other clinical factors. RESULTS: We analyzed 181 cases (90 HTLV-1 carriers, 91 HTLV-1-negative controls) after receiving the third dose. HTLV-1 carriers were older (median age 67.0 vs. 45.0 years, p < 0.001) and more frequently had diabetes, hypertension, or dyslipidemia than did HTLV-1-negative controls (60.0% vs. 27.5%, p < 0.001). After the third dose, the IgG-S titers decreased over time in both carriers and controls. Multivariate linear regression in the entire cohort showed that time since the third dose, age, and HTLV-1 infection negatively influenced IgG-S titers. After adjusting for confounders such as age, or presence of diabetes, hypertension, or dyslipidemia between carriers and controls using the overlap weighting propensity score method, and performing weighted regression analysis in the entire cohort, both time since the third dose and HTLV-1 infection negatively influenced IgG-S titers. CONCLUSIONS: The humoral immunity after the third vaccination dose is impaired in HTLV-1 carriers; thus, customized vaccination schedules may be necessary for them.

Integrated genetic and clinical prognostic factors for aggressive adult T-cell leukemia/lymphoma.

The prognosis of aggressive adult T-cell leukemia/lymphoma (ATL) is poor, and allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment. In order to identify favorable prognostic patients after intensive chemotherapy, and who therefore might not require upfront allo-HSCT, we aimed to improve risk stratification of aggressive ATL patients aged <70 years. The clinical risk factors and genetic mutations were incorporated into risk modeling for overall survival (OS). We generated the m7-ATLPI, a clinicogenetic risk model for OS, that included the ATL prognostic index (PI) (ATL-PI) risk category, and non-silent mutations in seven genes, namely TP53, IRF4, RHOA, PRKCB, CARD11, CCR7, and GATA3. In the training cohort of 99 patients, the m7-ATLPI identified a low-, intermediate-, and highrisk group with 2-year OS of 100%, 43%, and 19%, respectively (hazard ratio [HR] =5.46; P<0.0001). The m7-ATLPI achieved superior risk stratification compared to the current ATL-PI (C-index 0.92 vs. 0.85, respectively). In the validation cohort of 84 patients, the m7-ATLPI defined low-, intermediate-, and high-risk groups with a 2-year OS of 81%, 30%, and 0%, respectively (HR=2.33; P=0.0094), and the model again outperformed the ATL-PI (C-index 0.72 vs. 0.70, respectively). The simplified m7-ATLPI, which is easier to use in clinical practice, achieved superior risk stratification compared to the ATLPI, as did the original m7-ATLPI; the simplified version was calculated by summing the following: high-risk ATL-PI category (+10), low-risk ATL-PI category (-4), and non-silent mutations in TP53 (+4), IRF4 (+3), RHOA (+1), PRKCB (+1), CARD11 (+0.5), CCR7 (-2), and GATA3 (-3).

Calreticulin haploinsufficiency augments stem cell activity and is required for onset of myeloproliferative neoplasms in mice.

Mutations in JAK2, myeloproliferative leukemia virus (MPL), or calreticulin (CALR) occur in hematopoietic stem cells (HSCs) and are detected in more than 80% of patients with myeloproliferative neoplasms (MPNs). They are thought to play a driver role in MPN pathogenesis via autosomal activation of the JAK-STAT signaling cascade. Mutant CALR binds to MPL, activates downstream MPL signaling cascades, and induces essential thrombocythemia in mice. However, embryonic lethality of Calr-deficient mice precludes determination of a role for CALR in hematopoiesis. To clarify the role of CALR in normal hematopoiesis and MPN pathogenesis, we generated hematopoietic cell-specific Calr-deficient mice. CALR deficiency had little effect on the leukocyte count, hemoglobin levels, or platelet count in peripheral blood. However, Calr-deficient mice showed some hematopoietic properties of MPN, including decreased erythropoiesis and increased myeloid progenitor cells in the bone marrow and extramedullary hematopoiesis in the spleen. Transplantation experiments revealed that Calr haploinsufficiency promoted the self-renewal capacity of HSCs. We generated CALRdel52 mutant transgenic mice with Calr haploinsufficiency as a model that mimics human MPN patients and found that Calr haploinsufficiency restored the self-renewal capacity of HSCs damaged by CALR mutations. Only recipient mice transplanted with Lineage-Sca1+c-kit+ cells harboring both CALR mutation and Calr haploinsufficiency developed MPN in competitive conditions, showing that CALR haploinsufficiency was necessary for the onset of CALR-mutated MPNs.

Aberrant PD-L1 expression through 3'-UTR disruption in multiple cancers.

Successful treatment of many patients with advanced cancer using antibodies against programmed cell death 1 (PD-1; also known as PDCD1) and its ligand (PD-L1; also known as CD274) has highlighted the critical importance of PD-1/PD-L1-mediated immune escape in cancer development. However, the genetic basis for the immune escape has not been fully elucidated, with the exception of elevated PD-L1 expression by gene amplification and utilization of an ectopic promoter by translocation, as reported in Hodgkin and other B-cell lymphomas, as well as stomach adenocarcinoma. Here we show a unique genetic mechanism of immune escape caused by structural variations (SVs) commonly disrupting the 3' region of the PD-L1 gene. Widely affecting multiple common human cancer types, including adult T-cell leukaemia/lymphoma (27%), diffuse large B-cell lymphoma (8%), and stomach adenocarcinoma (2%), these SVs invariably lead to a marked elevation of aberrant PD-L1 transcripts that are stabilized by truncation of the 3'-untranslated region (UTR). Disruption of the Pd-l1 3'-UTR in mice enables immune evasion of EG7-OVA tumour cells with elevated Pd-l1 expression in vivo, which is effectively inhibited by Pd-1/Pd-l1 blockade, supporting the role of relevant SVs in clonal selection through immune evasion. Our findings not only unmask a novel regulatory mechanism of PD-L1 expression, but also suggest that PD-L1 3'-UTR disruption could serve as a genetic marker to identify cancers that actively evade anti-tumour immunity through PD-L1 overexpression.

Clinical significance of soluble CADM1 as a novel marker for adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/leukemia (ATLL) is an aggressive peripheral T-cell malignancy, caused by infection with the human T-cell leukemia virus type 1 (HTLV-1). We have recently shown that cell adhesion molecule 1 (CADM1), a member of the immunoglobulin superfamily, is specifically and consistently overexpressed in ATLL cells, and functions as a novel cell surface marker. In this study, we first show that a soluble form of CADM1 (sCADM1) is secreted from ATLL cells by mainly alternative splicing. After developing the Alpha linked immunosorbent assay (AlphaLISA) for sCADM1, we showed that plasma sCADM1 concentrations gradually increased during disease progression from indolent to aggressive ATLL. Although other known biomarkers of tumor burden such as soluble interleukin-2 receptor α (sIL-2Rα) also increased with sCADM1 during ATLL progression, multivariate statistical analysis of biomarkers revealed that only plasma sCADM1 was selected as a specific biomarker for aggressive ATLL, suggesting that plasma sCADM1 may be a potential risk factor for aggressive ATLL. In addition, plasma sCADM1 is a useful marker for monitoring response to chemotherapy as well as for predicting relapse of ATLL. Furthermore, the change in sCADM1 concentration between indolent and aggressive type ATLL was more prominent than the change in the percentage of CD4+CADM1+ ATLL cells. As plasma sCADM1 values fell within normal ranges in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients with higher levels of serum sIL-2Rα, a measurement of sCADM1 may become a useful tool to discriminate between ATLL and other inflammatory diseases, including HAM/TSP.

Higher average chemotherapy dose intensity improves prognosis in patients with aggressive adult T-cell leukemia/lymphoma.

OBJECTIVE AND METHOD: Adult T-cell leukemia/lymphoma (ATL) is an aggressive peripheral T-cell lymphoma with poor prognosis. We retrospectively reviewed the medical records of 312 patients with aggressive ATL and analyzed the effect of chemotherapy dose intensity on prognosis in clinical practice. RESULT: As first-line therapy, 62 patients underwent best supportive care (BSC) or single-agent chemotherapy, and 235 underwent intensive chemotherapy. The median survival time (MST) was 0.58 years in the 312 total patients, and 0.13 years and 0.75 years in the BSC/single-agent chemotherapy group and intensive chemotherapy group, respectively. The median average relative dose intensity (ARDI) of patients who received intensive chemotherapy was 60%. We divided patients into 3 groups according to ARDI. Those in the top tertile of ARDI (ARDI ≥ 75%, n = 82) had better overall survival compared with those in the intermediate tertile (45% ≤ ARDI < 75%, n = 79) (P < .0001), with MSTs of 4.69 and 0.75 years, respectively. The occurrence of organ dysfunction and infectious complications was comparable between the two ARDI groups. CONCLUSION: Higher ARDI improves prognosis in patients with aggressive ATL in clinical practice.

Prognostic relevance of integrated genetic profiling in adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is a heterogeneous group of peripheral T-cell malignancies characterized by human T-cell leukemia virus type-1 infection, whose genetic profile has recently been fully investigated. However, it is still poorly understood how these alterations affect clinical features and prognosis. We investigated the effects of genetic alterations commonly found in ATL on disease phenotypes and clinical outcomes, based on genotyping data obtained from 414 and 463 ATL patients using targeted-capture sequencing and single nucleotide polymorphism array karyotyping, respectively. Aggressive (acute/lymphoma) subtypes were associated with an increased burden of genetic and epigenetic alterations, higher frequencies of TP53 and IRF4 mutations, and many copy number alterations (CNAs), including PD-L1 amplifications and CDKN2A deletions, compared with indolent (chronic/smoldering) subtypes. By contrast, STAT3 mutations were more characteristic of indolent ATL. Higher numbers of somatic mutations and CNAs significantly correlated with worse survival. In a multivariate analysis incorporating both clinical factors and genetic alterations, the Japan Clinical Oncology Group prognostic index high-risk, older age, PRKCB mutations, and PD-L1 amplifications were independent poor prognostic factors in aggressive ATL. In indolent ATL, IRF4 mutations, PD-L1 amplifications, and CDKN2A deletions were significantly associated with shorter survival, although the chronic subtype with unfavorable clinical factors was only marginally significant. Thus, somatic alterations characterizing aggressive diseases predict worse prognosis in indolent ATL, among which PD-L1 amplifications are a strong genetic predictor in both aggressive and indolent ATL. ATL subtypes are further classified into molecularly distinct subsets with different prognosis. Genetic profiling might contribute to improved prognostication and management of ATL patients.

TP53 and PTEN mutations were shared in concurrent germ cell tumor and acute megakaryoblastic leukemia.

BACKGROUND: The occurrence of a mediastinal germ cell tumor (GCT) and hematological malignancy in the same patient is very rare. Due to its rarity, there have been only two reports of the concurrent cases undergoing detailed genetic analysis with whole-exome sequencing (WES), and the possible clonal relationship between the both tumors remained not fully elucidated. METHODS: We performed whole-exome sequencing analysis of mediastinal GCT and acute myeloid leukemia (AML) samples obtained from one young Japanese male adult patient with concurrent both tumors, and investigated the possible clonal relationship between them. RESULTS: Sixteen somatic mutations were detected in the mediastinal GCT sample and 18 somatic mutations in the AML sample. Mutations in nine genes, including TP53 and PTEN both known as tumor suppressor genes, were shared in both tumors. CONCLUSIONS: All in our case and in the previous two cases with concurrent mediastinal GCT and AML undergoing with whole-exome sequencing analysis, TP53 and PTEN mutations were commonly shared in both tumors. These data not only suggest that these tumors share a common founding clone, but also indicate that associated mediastinal GCT and AML harboring TP53 and PTEN mutations represent a unique biological entity.

Clinical characteristics of adult T-cell leukemia/lymphoma infiltration in the gastrointestinal tract.

BACKGROUND: Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell malignancy caused by human T-cell leukemia virus type 1. The clinical course of ATLL is very heterogeneous, and many organs, including the gastrointestinal (GI) tract, can be involved. However, there are few detailed reports on ATLL infiltration in the GI tract. We investigated the clinical characteristics of ATLL infiltration in the GI tract. METHODS: This retrospective observational single-center study included 40 consecutive ATLL patients who underwent GI endoscopy. The patients' demographic and clinical characteristics and endoscopic findings were analyzed retrospectively. Patients with ATLL who were diagnosed by histological examination were divided into two groups based on GI tract infiltration. RESULTS: Multivariate analysis revealed that the absence of skin lesions was significantly associated with GI infiltration (P < 0.05). Furthermore, the infiltration group tended to have similar macroscopic lesions in the upper and lower GI tracts, such as diffuse type, tumor-forming type, and giant-fold type. CONCLUSIONS: GI endoscopy may be considered for ATLL patients without skin lesions.

Monocyte-derived fibrocytes elimination had little contribution on liver fibrosis.

BACKGROUND: Monocyte-derived fibrocytes play an important role in the progression of fibrosis in the skin, lungs, heart and kidney. However, the contribution of fibrocytes to liver fibrosis is unclear. The aim of this study was to investigate whether fibrocytes contributed to fibrosis progression in the livers of carbon tetrachloride (CCl4)-treated mice. METHODS: C57BL/6J mice were divided into 4 groups: normal control group, CCl4-treated group, CCl4 + control liposome-treated group, and CCl4 + clodronate liposome-treated group. For the elimination of systemic monocyte and monocyte-derived fibrocyte, one group was treated with clodronate liposome, and another group with control liposome as a control. After 4 weeks of treatment, hepatic mononuclear cells were subjected to immunofluorescent (IF) staining and fluorescence-activated cell sorter (FACS) analysis to detect fibrocytes. Measurement of collagen-positive Sirius red stained area and collagen-I mRNA expression in the liver were performed to evaluate the degree of liver fibrosis quantitatively. RESULTS: In the liver of the CCl4-treated and CCl4 + control liposome-treated groups, the number of fibrocytes, the area positive for Sirius red staining and collagen-I mRNA expression significantly increased compared with those in the normal control group. In the liver of the CCl4 + clodronate liposome-treated group, few fibrocytes was observed as in the normal control group, but Sirius red staining positive area and collagen-I mRNA expression were increased and equivalent to the CCl4-treated and CCl4 + control liposome-treated groups. CONCLUSION: Monocyte-derived fibrocytes play a minimal role in CCl4-induced liver fibrosis. Cells other than fibrocytes such as hepatic stellate cells play a central role in liver fibrosis.

Outcome of allogeneic hematopoietic cell transplantation in patients with adult T-cell leukemia.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive peripheral T-cell neoplasm, and the outcome of patients with ATL after chemotherapy is poor. Allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is a curative treatment modality for ATL, and four factors, namely, age > 50 years, male recipient, lack of complete remission at transplantation, and transplantation of cord blood, were previously shown to be associated with poor survival. We retrospectively analyzed the outcome of 21 patients with ATL who had undergone allo-HSCT at our hospital during a 3-year period. Of 21 patients, all had at least one of the above risk factors, and 18 had two or more. With a median follow-up of 19.7 months for living patients, the 1- and 2-year overall survival (OS) rates after transplantation were 34% and 27%, respectively. All relapse/progression events occurred within 1 year after allo-HSCT, and the cumulative incidence of relapse/progression at 1 year after allo-HSCT was 46.9%. The 100-day and 1-year nonrelapse mortality (NRM) rates were 19% and 42%, respectively. No significant difference in OS was observed between myeloablative and reduced-intensity conditioning regimens. The 3-year OS (27%) of ATL patients who received allo-HSCT and who had at least one adverse factor was somewhat poorer than the 3-year OS of 33% identified in a nationwide study of allo-HSCT in ATL patients in Japan. The high relapse/progression and NRM rates are major problems to be solved to achieve better outcome.

Development of a complete human IgG monoclonal antibody to transferrin receptor 1 targeted for adult T-cell leukemia/lymphoma.

Iron is an essential nutrient for normal cell growth, and reprogramming of iron metabolism is essential to tumor cell survival and progression. HTLV-1-associated adult T-cell leukemia/lymphoma (ATLL) has no effective therapy and high levels of cell surface transferrin receptor 1 (TFR1) expression have been reported in ATLL by us and other groups. In this study, to develop a novel molecular-targeted therapy against TFR1 to modulate iron metabolism, we initially determined the expression pattern of several iron-related genes along with TFR1 and found that ATLL cells presented characteristic of an iron-deficiency state such as high expression of iron-regulatory protein 2 (IRP2) and low expression of its E3 ubiquitin-ligase, FBXL5. Therefore, we developed human IgG monoclonal antibodies to human TFR1 using a phage display method (ICOS method) to block the incorporation of the transferrin (TF)-iron complex into ATLL cells for inhibiting cell growth. One of the mAbs, JST-TFR09, presented its greater affinity to TFR1 on ATLL cells in flow cytometry (FCM) analysis than those of commercially available anti-TFR1 antibodies and identified high expression of TFR1 in most of the acute-type ATLL cells. Moreover, JST-TFR09 could interfere with binding between TFR1 and TF, which resulted in effective blockade of TFR1 internalization and induction of cell apoptosis by the treatment of ATLL cells with JST-TFR09. JST-TFR09 showed dual activities through direct cell cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC), and the treatment of JST-TFR09 significantly suppressed cell growth of ATLL cells with induction of apoptosis in in vitro and in vivo experiments. Thus, JST-TFR09 described here may become a promising therapeutic antibody for the treatment of ATLL.

Loss of TET2 has dual roles in murine myeloproliferative neoplasms: disease sustainer and disease accelerator.

Acquired mutations of JAK2 and TET2 are frequent in myeloproliferative neoplasms (MPNs). We examined the individual and cooperative effects of these mutations on MPN development. Recipients of JAK2V617F cells developed primary myelofibrosis-like features; the addition of loss of TET2 worsened this JAK2V617F-induced disease, causing prolonged leukocytosis, splenomegaly, extramedullary hematopoiesis, and modestly shorter survival. Double-mutant (JAK2V617F plus loss of TET2) myeloid cells were more likely to be in a proliferative state than JAK2V617F single-mutant myeloid cells. In a serial competitive transplantation assay, JAK2V617F cells resulted in decreased chimerism in the second recipients, which did not develop MPNs. In marked contrast, cooperation between JAK2V617F and loss of TET2 developed and maintained MPNs in the second recipients by compensating for impaired hematopoietic stem cell (HSC) functioning. In-vitro sequential colony formation assays also supported the observation that JAK2V617F did not maintain HSC functioning over the long-term, but concurrent loss of TET2 mutation restored it. Transcriptional profiling revealed that loss of TET2 affected the expression of many HSC signature genes. We conclude that loss of TET2 has two different roles in MPNs: disease accelerator and disease initiator and sustainer in combination with JAK2V617F.

Effects of mogamulizumab in adult T-cell leukemia/lymphoma in clinical practice.

OBJECTIVE: The efficacy of mogamulizumab in adult T-cell leukemia/lymphoma (ATLL) was reported in a previous phase 2 study. Compared with patients in clinical trials, however, most patients in real-life settings have demonstrated worse outcomes. METHOD: We retrospectively analyzed 96 patients with relapsed/refractory ATLL who received mogamulizumab treatment. RESULTS: Relapsed/refractory ATLL patients with a median age of 70 years received a median of five courses of mogamulizumab. Hematologic toxicity and skin rash were the most common adverse events, and both were manageable. Of 96 patients, 87 were evaluable for efficacy. The overall response rate was 36%, and the median progression-free survival (PFS) and overall survival (OS) from the start of mogamulizumab therapy were 1.8 and 4.0 months, respectively. Of the original 96 patients, only 25 fulfilled the inclusion criteria of the phase 2 study. Those who met the criteria demonstrated longer median PFS and OS durations of 2.7 and 8.5 months, respectively. The median OS from diagnosis in relapsed/refractory ATLL patients receiving mogamulizumab was 12 months, longer than the 5.8 months in a historical cohort without mogamulizumab. CONCLUSION: In clinical practice, mogamulizumab exhibited antitumor activity in patients with relapsed/refractory ATLL, with an acceptable toxicity profile. Mogamulizumab therapy improved the OS of ATLL patients.

[Approach to special issues associated with myeloproliferative neoplasms].

Myeloproliferative neoplasms are frequently complicated by thrombosis and bleeding. Therefore, not only their primary prevention, but also the management of special clinical issues is important. These issues include venous thromboembolic disorders such as splanchnic venous thromboembolism, as well as major bleeding, surgery, and pregnancy. As for the primary prevention of thrombosis, it has been proposed that low-risk essential thrombocythemia with newly reported risk factors (cardiovascular risks or JAK2V617F) might be included among the factors meriting prevention. As for management of the aforementioned special clinical issues, an expert consensus has been established, wherein the recommended treatment strategies are described. In Japan as well, clinical practice based on this consensus would be preferable.

[Genetic and epigenetic abnormalities in myeloproliferative neoplasms].

Mutations in JAK2, MPL and CALR are regarded as driver mutations, and are mutually exclusively detected in more than 90% of myeloproliferative neoplasms (MPNs). In addition, mutations in epigenetic regulator genes such as TET2 or DNMT3A are detected in MPNs. Although the roles of mutations in epigenetic regulator genes were clarified in normal hematopoiesis, their roles have remained unclear in malignant hematopoiesis of MPNs. We analyzed three lines of mutant mice: mice with JAK2V617F, a representative of driver gene mutations; mice with loss of TET2, a representative of epigenetic abnormalities; and mice with both. We thereby clarified two roles of loss of TET2 in malignant hematopoiesis of JAK2-mutated MPNs: one is "disease initiator and sustainer" via reinforcing the function of JAK2-mutated hematopoietic stem cells, and the other is "disease accelerator". New strategies in risk assessment or treatment are required, considering not only single but also multiple mutations.

[Functional analysis of TET2 using a knockdown mouse model].

In myeloid malignancies, mutations have occurred in epigenetic regulator genes, including Ten-Eleven-Translocation 2 (TET2). TET2 is an enzyme that catalyzes the conversion of 5-methylcytosine into 5-hydroxymethylcytosine (5-hmC) which is a key intermediate for oxidative DNA demethylation. We analyzed the in vivo phenotype of TET2 failure using Ayu17-449 (TET2(trap/trap)) mice created by the gene-trap method in which TET2 mRNA levels were decreased to about 20% of the level in wild-type (WT) mice. In TET2(trap/trap) mice the levels of 5-hmC in genomic DNA from bone marrow (BM) cells were decreased in comparison to WT mice. TET2(trap/trap) mice were born at an expected Mendelian frequency but died at a high rate by postnatal day 3, indicating TET2 to be essential for survival. In analysis of the hematopoietic system, transplantation of TET2(trap/trap), but not WT fetal liver cells, led to mild myeloid hyperplasia and splenomegaly in WT recipient mice, but no onsets of lethal hematological malignancies were observed during a follow-up period of 12 months. TET2 knockdown led to an increased serial replating capacity of BM cells in vitro and increased hematopoietic stem cell (HSC) self-renewal in vivo in competitive repopulation and serial transplantation assays. These data indicate that TET2 has a critical role in survival and HSC homeostasis.