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A 73-year-old woman with Sjögren's syndrome and autoimmune neutropenia (AIN) associated with large granular lymphocytosis of the polyclonal T cell type, demonstrated autoimmune thrombocytopenia (AIT) at diagnosis of sigmoid colon cancer. Ten months later, both AIN and AIT had exacerbated to agranulocytosis and severe thrombocytopenia below 10×10(9)/L, respectively. There were no dysplastic features of bone marrow hematopoietic cells. Furthermore, an in vitro assay of hematopoietic progenitors showed normal granuloid and erythroid colony formation. Although we serially treated her with prednisolone (oral), filgrastim, intravenous high-dose immunoglobulin infusion, cyclophosphamide (oral), danazol, cyclosporine A (oral), and rituximab, number of neutrophils and platelets elevated only temporarily. During the course of agranulocytosis and severe thrombocytopenia, the patient also developed autoimmune hemolytic anemia (AIHA). She died of pneumonia 5 months after the onset of agranulocytosis. This case is very unique and novel in terms of autoimmune phenomena simultaneously directed to granulocytes, platelets, and red blood cells under the background of Sjögren's syndrome.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN), currently considered to originate from immature plasmacytoid dendritic cells (DC), is a rare and aggressive CD4+CD56+ neoplasm that frequently involves the skin and bone marrow. We present a case of an 80-year-old man with a CD4+CD56+ BPDCN that affected the orbital cavity and bone marrow. Although BPDCN has not been reported to express any lineage-specific markers, the neoplastic cells strongly expressed the CD13 antigen. Therefore, in addition to pathological examination, we attempted to induce in vitro morphological and surface marker changes with IL-3 and CD40 ligand. After treatment with these cytokines, the tumor cells enlarged markedly, acquired many fine dendrites, similar to mature DC, and showed enhanced expression of antigens specific to DC or antigen-presenting cells, such as CD40, CD80, CD83 and CD86. To the best of our knowledge, this is the first report of BPDCN expressing a myeloid antigen, CD13, although CD33 expression has been described in some cases. The present patient received 2 courses of combination chemotherapy consisting of cytarabine and etoposide, which resulted in complete remission. Given that the cellular origin of plasmacytoid DC is still controversial, myeloid antigen expression involving CD13 may not exclude a diagnosis of BPDCN.

Background: Although several prognostic indicators of de novo acute myeloid leukemia (AML) patients have been identified, the clinical significance of minimal residual disease (MRD) needs to be evaluated further in Japanese adult patients.Methods: Using three color flow cytometry, we identified leukemia-associated phenotypes (LAP) in bone marrow specimens at diagnosis and assessed the relationship between clinical outcomes and the presence of marrow MRD in 33 patients who achieved a morphologic complete remission (CR) and were followed after CR.Results: Of 33 consecutive patients, we detected MRD in 20 patients after achieving CR (Group A) and did not in 13 patients (Group B), with 2-year overall survival (OS) rates of 49.0% and 84.6%, respectively (P =.0317), and relapse-free survival (RFS) rates of 13.7% and 91.7%, respectively (P=.0010). By multivariate analysis, MRD-positivity at post-induction was found to be associated with a shorter duration of RFS (P=.0042). Notably, we achieved MRD negativity in only 2 patients (10%) of Group A in spite of subsequent intensive consolidation therapies and found that the fluctuation of the MRD level during consolidation therapies was not a significant prognostic factor. Four patients in Group A underwent allogeneic hematopoietic stem-cell transplantation (HSCT) when in the CR state and did not experience relapse at a median follow-up period of 20.5 months after HSCT.Conclusions: MRD is critical for predicting de novo AML outcomes. Most MRD-positive patients cannot achieve MRD negativity with conventional chemotherapy. Thus, HSCT may be the primary therapeutic option for these patients.

A 19-year-old girl with T-lymphoblastic lymphoma (T-LBL) was referred to our hospital because of refractory disease. After complete remission was achieved by the JALSG ALL-97 protocol, she received a bone marrow transplantation (BMT) from an unrelated, HLA-matched donor with myeloablative conditioning. Four months after BMT, T-LBL relapsed and donor lymphocyte infusion was ineffective. After partial remission was achieved with l-asparaginase therapy, she received 2 antigen-mismatched cord blood transplantation with non-myeloablative conditioning; however, sustained engraftment of cord blood stem cells has failed. This was associated with the reappearance of the blood cells from the first donor and the disappearance of leukemic cells from both the peripheral blood and bone marrow. Computed tomography showed no enlarged lymph nodes. The patient and the cord blood donor shared two minor histocompatibility antigens (mHAgs), while these mHAgs were not detected in the blood cells of the first donor. TCR analysis disclosed expanded oligoclonal Vbeta2T cells in the peripheral blood at relapse, and these cells secreted IFN-gamma in response to stimulation by the patient's leukemic cells. Moreover, these cells exhibited cytotoxicity against both leukemic cells and cord blood mononuclear cells. These results strongly suggest that Vbeta2T cells, derived from the first donor, may have been cytotoxic lymphocytes against both leukemic cells and cord blood stem cells.

The prognosis of angioimmunoblastic T cell lymphoma (AITL) is poor because of chemotherapy-resistance and the short duration of remission. In recent years, cyclosporin A (CyA) has been employed as a alternative treatment for AITL in some patients with the rationale that CyA inhibits the activity and proliferation of neoplastic T cells. We herein report 4 chemotherapy-resistant AITL patients who were treated with oral CyA. The dosage of CyA was individually determined in each patient in order to achieve a blood CyA concentration of around 200 ng/ml at the trough level. A patient in whom AITL had relapsed 3 months after high dose chemotherapy with autologous hematopoietic stem cell transplantation (HSCT) achieved a sustained complete remission (CR) with CyA and underwent allogeneic HSCT. In 2 patients who had failed to respond to conventional chemotherapies, the circulating lymphoma cells rapidly disappeared after the initiation of CyA, and one of these patients demonstrated a durable CR. The other patient showed a good response to CyA, but the agent was discontinued because of infection. The remaining one patient with advanced AITL did not respond to CyA and died of disease progression. To our knowledge, the efficacy of CyA for chemotherapy-resistant AITL, even in a leukemic state, has not previously been reported.

Bacillus cereus is a growing concern as a cause of life-threatening infections in patients with hematologic malignancies. However, the risk factors for patients with unfavorable outcomes have not been fully elucidated. At our institution, we observed the growth of B. cereus in blood culture in 68 patients with (23) or without (45) hematologic malignancies treated from September 2002 to November 2009. We defined a case as having sepsis when more than two blood culture sets were positive for B. cereus or only a single set was positive in the absence of other microorganisms in patients who had definite infectious lesions. We determined 12 of 23 patients with hematologic malignancies as having sepsis, as well as 10 of 45 patients without hematologic malignancies (p = 0.012). Of the 12 patients with hematologic malignancies, four patients with acute leukemia died of B. cereus sepsis within a few days. In our cohort, risk factor analysis demonstrated that a neutrophil count of 0/mm(3), central venous (CV) catheter insertion, and the presence of central nervous system (CNS) symptoms were significantly associated with a fatal prognosis (p = 0.010, 0.010, and 0.010, respectively). Analysis of data from our cohort in conjunction with those from 46 previously reported patients with B. cereus sepsis identified similar risk factors, that is, acute leukemia, extremely low neutrophil count, and CNS symptoms (p = 0.044, 0.004, and 0.002, respectively). These results indicate that appropriate prophylaxis and early therapeutic intervention against possible B. cereus sepsis are crucially important in the treatment of hematologic malignancies.

A 21-year-old man who was diagnosed with Diamond-Blackfan anemia at 2 years of age came to our hospital with the hope of undergoing bone marrow transplantation (BMT). He had been red cell transfusion-dependent for about 8 years; at presentation he had transfusion-induced hemochromatosis, a subsequent low left ventricular ejection fraction (LVEF) of 43%, and diabetes mellitus requiring insulin therapy. He received unrelated BMT with reduced intensity conditioning and sufficient GVHD prophylaxis. Regardless of the cardiac dysfunction, he had an uneventful course during pre- and post-grafting periods, and is currently doing well with an improved LVEF (55%), although he is still insulin dependent.

A 50-year-old woman was emergently admitted because of rapidly progressive unconsciousness, renal failure, hepatic dysfunction, hemolytic anemia, thrombocytopenia, and high-grade fever in July, 2008. Based on clinical and laboratory findings, we made a tentative diagnosis of thrombotic thrombocytopenic purpura (TTP) and immediately initiated the plasma exchange (PE). Despite the PE, she developed panperitonitis due to multiple intestinal perforation and massive splenic infarction within a week after the admission. Thrombosis of arterioles at perforated portion in the resected small and large intestines was histologically confirmed. Therefore, we made a definite diagnosis of catastrophic antiphospholipid syndrome (CAPS) based on the presence of antiphosphatidylserine-prothrombin complex antibodies (aPS/PT) throughout the course and lupus anticoagulant that was revealed positive on one occasion, and multiple thrombotic lesions. The underlying disease of CAPS appeared to be lupus erythematosus because of her clinical history and laboratory findings such as persistent leukopenia. Although it has been reported that CAPS causes systemic thrombosis at microvessels mostly within a week from the onset and the mortality rate in this disorder is as high as 50%, we successfully treated her in combination with high-dose corticosteroid, anticoagulation, concentrated human IgG, surgical procedures, and hemodialysis in addition to PE. Early diagnosis of CAPS and immediate start of PE may have contributed to the successful treatment.

A 64-year-old woman suffering from progressive amyloid A (AA) amyloidosis of the gastrointestinal (GI) tract, associated with active rheumatoid arthritis, was transferred to our hospital due to hypovolemic shock. Although intensive care, including treatment with prednisolone and methotrexate, improved the hypovolemic shock, paralytic ileus became dominant instead of the marked diarrhea, suggesting the terminal stage of AA amyloidosis of the GI tract. Thus, we administered tocilizumab, a humanized anti-interleukin 6 receptor antibody (8 mg/kg, repeated every 4 weeks). Two weeks after the first injection of tocilizumab, serum AA rapidly returned to their normal ranges in accordance with the amelioration of paralytic ileus and systemic joint pain. Surprisingly, after three courses of tocilizumab treatment, colon biopsy revealed no amyloid deposition. Tocilizumab is a promising agent to treat secondary AA amyloidosis by strongly suppressing serum AA levels.

We report here two patients with chronic disseminated intravascular coagulation (chronic DIC) secondary to aortic aneurysm, who were successfully treated with continuous subcutaneous infusion of heparin. The patients were 69- and 89-year-old males, who were admitted to our hospital because of thrombocytopenia and marked bleeding tendency. The underlying conditions were aortic dissection and aortic aneurysm, respectively. Coagulation test demonstrated that these patients had DIC, and a diagnosis of chronic DIC secondary to aortic aneurysm was made. Anti-coagulation treatment with oral camostat mesylate and daily subcutaneous infusion of heparin calcium was started. However, the treatment was insufficient to control chronic DIC, and these patients developed recurrent severe subcutaneous hemorrhages. Therefore, we attempted continuous subcutaneous infusion of heparin using a mobile infusion pump. This delivery of heparin markedly improved the coagulopathy, and the hemorrhagic episode disappeared with good compliance in the use of infusion equipment in these patients. Continuous subcutaneous infusion of heparin using a mobile infusion pump is effective and useful for long term treatment of chronic DIC by the outpatient department.

A 30-year-old woman developed severe liver dysfunction 1 year after bone marrow transplantation (BMT) from an HLA-identical sibling donor for B lymphoblastic leukemia (B-ALL) during the tapering of cyclosporin A. The histologic picture resembled autoimmune hepatitis (AIH), although neither autoantibody nor hypergammaglobulinemia was detected. She entered hepatic coma, and underwent living donor liver transplantation from the same donor on day 421 after BMT. She is well 18 months after the procedure, showing normal liver function and hematopoiesis. AIH-like hepatic graft-versus-host disease (GVHD) has not been documented. This patient is the second case of living donor liver transplantation for hepatic GVHD from the same donor.

A 62-year-old man was diagnosed with human immunodeficiency virus (HIV) infection while suffering from recurrent herpes zoster infection. Laboratory examination revealed CD4(+) lymphocyte count 16 cells/mul and HIV loading 150,000 copies/ml at presentation. In addition, he had multiple lymph node swelling. Histologic diagnosis of a biopsied lymph node was diffuse, large, B cell-type malignant lymphoma. The karyotype of the lymphoma cells was t(8;14)(q24;q32), which was confirmed by G-banding and fluorescent in situ hybridization. Positron emission tomography (PET)-combined CT scanning revealed systemic extranodal tumors involving the gastrointestinal tract, pancreas, and bone marrow. The clinical stage of the lymphoma was IVB and the international prognosis index was categorized as high. Complete remission (CR) of the lymphoma was obtained after 2 courses of CHOP (cyclophosphamide, adriamycin, vincristine, prednisolone) chemotherapy and 4 subsequent courses of rituximab-combined CHOP (R-CHOP). Highly active antiretroviral therapy (HAART) was started at the initiation of CHOP. Because of the poor prognosis of AIDS-related lymphoma, he received autologous peripheral blood stem cell transplantation with the MEAM protocol (ranimustine, etoposide, cytarabine, melphalan) as a conditioning procedure without a severe infectious episode. He remains in CR 24 months after the transplantation.

A 32-year-old male with chronic hepatitis B was admitted to a hospital with cellulitis in the right leg in September 2006. Pancytopenia, hepatosplenomegaly, and systemic superficial lymph node swelling were noted, and he was referred to our hospital. He developed fever and liver dysfunction in June 2007 and underwent a splenectomy. His pancytopenia subsequently improved. A pathologic diagnosis of hepatosplenic alphabeta T cell lymphoma was made by examining spleen tissue and biopsy specimens of the liver and mesenteric lymph node. He had stage IVB disease because neoplastic T cells were noted in the bone marrow. The response of the lymphoma to conventional chemotherapy including the CHOP (cyclophosphamide, adriamycin, vincristine, prednisolone) and DeVIC (dexamethasone, etoposide, ifoshamide, carboplatin) regimens was poor and transient. A partial remission was obtained with an ESHAP (etoposide, cisplatin, cytarabine, methylprednisolone) regimen. Therefore, we planned a bone marrow transplantation (BMT) from an HLA-haploidentical sibling donor. He was moved to the Department of Hematology, Hyogo Medical College, to receive this BMT as part of a clinical trial. During the conditioning procedure for the transplantation, however, he died of septicemia. Since hepatosplenic alphabeta T cell lymphoma is very rare with only 23 reported cases to date, herein we report this case and discuss the therapeutic strategy.

Pulmonary alveolar proteinosis (PAP) is a rare disorder characterized by the abnormal accumulation of alveolar surfactant protein in alveolar spaces. We report herein a rare case of myelodysplastic syndrome (MDS-RAEB) complicated by severe PAP, and successful allogeneic bone marrow transplantation (BMT) for both disorders. An unrelated BMT was planned for a 48-year-old male with advanced MDS-RAEB. Just before the initiation of the conditioning regimen for unrelated BMT in March 2007, he developed dyspnea. A diagnosis of PAP was made based on findings of chest X-ray, CT scanning, and the fluid obtained by bronchoalveolar lavage. To improve his dyspnea and improve BMT safety, whole lung lavage (WLL) was performed twice, with the partial improvement of PAP. Unrelated allogeneic BMT was performed in September 2007. We had to perform a third WLL because of the worsening of PAP on day 26 after BMT. Despite many infectious complications after BMT, GVHD was relatively mild. PAP had almost disappeared 6 months after BMT. He was well with favorable hematopoiesis 20 months after the BMT without any specific treatment. There has been no report of an MDS patient with PAP in whom 3 WLL procedures were performed before and after allogeneic BMT.

A 73-year-old man was hospitalized with fever, erythema, generalized superficial lymphadenopathy and marked neutropenia in July 2007. Hematologic examination demonstrated a white blood cell count of 1,400/microl with 0% neutrophils, and 18% abnormal lymphocytes. A bone marrow aspirate showed marked myeloid hypoplasia. A diagnosis of drug-induced agranulocytosis was made. Although neutrophil counts immediately returned to normal levels in response to filgrastim, fever, skin rash and systemic lymphadenopathy were all persistent. He also developed autoimmune hemolytic anemia and a second episode of agranulocytosis. The causative agent of the both episodes of agranulocytosis appeared to be acetaminophen. The histologic picture of a biopsied lymph node showed diffuse infiltration of polymorphous lymphoid cells with clear cytoplasm and proliferation of arborizing capillary vessels. Based on the histologic findings, PCR, and immunohistologic analyses, he was diagnosed with angioimmunoblastic T cell lymphoma (AILT) in leukemic state. The response of the lymphoma to conventional chemotherapy (CHOP and ESHAP) was poor. We next performed an immunomodulatory therapy using cyclosporine A to suppress cytokine production by neoplastic T cells. The treatment resulted in a partial remission of AILT including disappearance of circulating lymphoma cells. To our knowledge, this is the first published report of AILT complicated by drug-induced agranulocytosis.

Two types of CCAAT-enhancer-binding protein α (C/EBPα) mutants are found in acute myeloid leukemia (AML) patients: N-terminal frame-shift mutants (C/EBPα-N m ) generating p30 as a dominant form and C-terminal basic leucine zipper domain mutants (C/EBPα-C m ). We have previously shown that C/EBPα-K304_R323dup belonging to C/EBPα-C m , but not C/EBPα-T60fsX159 belonging to C/EBPα-N m , alone induced AML in mouse bone marrow transplantation (BMT) models. Here we show that various C/EBPα-C m mutations have a similar, but not identical, potential in myeloid leukemogenesis. Notably, like C/EBPα-K304_R323dup, any type of C/EBPα-C m tested (C/EBPα-S299_K304dup, K313dup, or N321D) by itself induced AML, albeit with different latencies after BMT; C/EBPα-N321D induced AML with the shortest latency. By analyzing the gene expression profiles of C/EBPα-N321D- and mock-transduced c-kit + Sca-1 + Lin − cells, we identified Csf1r as a gene downregulated by C/EBPα-N321D. In addition, leukemic cells expressing C/EBPα-C m exhibited low levels of colony stimulating factor 1 receptor in mice. On the other hand, transduction with C/EBPα-N m did not influence Csf1r expression in c-kit + Sca-1 + Lin − cells, implying a unique role for C/EBPα-C m in downregulating Csf1r . Importantly, Csf1r overexpression collaborated with C/EBPα-N321D to induce fulminant AML with leukocytosis in mouse BMT models to a greater extent than did C/EBPα-N321D alone. Collectively, these results suggest that C/EBPα-C m -mediated downregulation of Csf1r has a negative, rather than a positive, impact on the progression of AML involving C/EBPα-C m , which might possibly be accelerated by additional genetic and/or epigenetic alterations inducing Csf1r upregulation.

Mutations in a variety of genes have been identified in MDS patients. Among them, mutations of additional sex combs-like 1 (ASXL1), found in 15-20% of MDS patients, have been identified as an independent poor prognostic factor. We previously demonstrated that C-terminal–truncating ASXL1 mutations (ASXL1-MT) inhibited myeloid differentiation and induced an MDS-like disease in mice after 1~2 years by inhibiting polycomb repressive complex 2–mediated methylation of histone H3K27 (Inoue et al. J Clin Invest. 2013). Given that ASXL1 mutations have been shown to be related to high-risk MDS or leukemic transformation, it is not clear how ASXL1-mutated MDS clones can transform into advanced MDS or AML. First, we examined genetic alterations in 368 WHO-defined MDS patients; ASXL1 mutations were detected in 64 of them (17.39%). Intriguingly, the patients with ASXL1 mutations had a significantly higher incidence of the concurrent SET binding protein 1 (SETBP1) mutation than those with the wild-type ASXL1 (6 out of 64, 9.38% vs. 2 out of 304, 0.66%, P=0.0005). Moreover, among ASXL1-mutated MDS patients, those harboring SETBP1 mutations had a higher incidence of leukemic transformation than those without (P=0.042), and MDS patients with both mutations had a significantly shorter overall survival compared to those without SETBP1 mutations (median, 10.5 vs. 22.5 months, P=0.046). In addition, we demonstrated that most SETBP1 mutations, such as D868N, occur in the PEST domain of the SKI homology region, preventing ubiquitination and subsequent proteasomal degradation. These results prompted us to investigate whether SETBP1 mutations play a critical role in the leukemic transformation of ASXL1-mutated MDS cells. In in vitro experiments, the expression of SETBP1-D868N enhanced myeloid colony formation of ASXL1-MT-transduced LSK cells, augmenting ASXL1-MT-induced differentiation blocking of 32Dcl3 cells. Of note, SETBP1-D868N collaborated with ASXL1-MT to induce AML after a short latency (median survival, 73 days) in a murine BMT model, while all mice expressing either ASXL1-MT or SETBP1-D868N survived for 6 months after transplantation (P To clarify the molecular mechanism leading to leukemic transformation, we first investigated the Pp2a-Akt pathway because SETBP1 protein has been shown to interact with SET oncoprotein, resulting in Pp2a phosphorylation and subsequent inhibition. Consistent with previous reports using overexpression systems of SETBP1 wild type protein (SETBP1-WT), BM cells of leukemic mice displayed phosphorylated Pp2a and Akt compared to those of the control mice. Administration of FTY720, a Pp2a activator, efficiently repressed the growth rate in vitro and slightly improved the survival of serially transplanted mice. Next, using RNA-seq and GSEA, we demonstrated that SETBP1-D868N enriched hematopoietic stem cell-related genes and posterior Hoxa genes. Chromatin immnoprecipitation assay showed that both SETBP1-WT and SETBP1-D868N interacted with the promoter regions of Hoxa9 and Hoxa10, raising the possibility that a gain-of-function mutant of SETBP1 enhances transcription of these genes, directly or indirectly. Moreover, GSEA indicated global repression of the TGF-β signaling pathway and reciprocal upregulation of the Myc pathway in leukemic mice. In conclusion, our data provide evidence for the role of SETBP1 mutations in leukemic transformation and suggest the resulting deregulated pathways as potential therapeutic targets to prevent disease progression in MDS. Disclosures Harada: Kyowa Hakko Kirin Co., Ltd.: Research Funding.

Successful allogeneic bone marrow transplantation for chronic myelomonocytic leukemia complicated by refractory aortitis

Recurrent mutations of ASXL1 (Additional sex combs-like1) are found in various hematological malignancies including myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia, and acute myeloid leukemia (AML) with myelodysplasia-related changes. Additionally, ASXL1 mutations are linked with adverse survival in a variety of myeloid malignancies. A previous study demonstrated that loss of ASXL1 in mice promotes myeloid transformation by impairing polycomb repressive complex 2 (PRC2)-mediated gene repression at a number of critical loci and leads to myeloid transformation. However, most ASXL1 mutations are heterozygous and located in the 5’ region of the last exon, indicating a dominant-negative or gain-of-function feature of a truncated ASXL1 protein. Therefore, we investigated if the C-terminal truncated form of ASXL1 (ASXL1-MT) contributes to the development of myeloid malignancies. To this end, we examined the effects of ASXL1-MT using in vitro and in vivo experiments. In in vitro experiment, expression of ASXL1-MT inhibited G-CSF-induced myeloid differentiation of 32Dcl3 cells. In a mouse bone marrow transplantation (BMT) model, ASXL1-MT induced multilineage dysplasia, differentiation block, slowly progressive pancytopenia, BM hyperplasia and splenomegaly. The transduced mice died of severe anemia after a long latency (median survival, 400.5 days), and some of the mice progressed to overt leukemia. Thus, the current model displays all of the features of human MDS. In addition, ASXL1-MT collaborated with N-RAS-G12V, which confers a proliferative advantage, in inducing progression of N-RAS-G12V-induced myeloproliferative neoplasm (MPN) to AML, suggesting that ASXL1-MT contributes to leukemic transformation by inhibiting differentiation of MPN cells. To clarify the molecular mechanism for differentiation block and MDS development induced by ASXL1-MT, we performed expression profiles of 32Dcl3 cells transduced with ASXL1-MT and BM cells of the MDS mice. Of note, gene set enrichment analysis (GSEA) of BM cells of the MDS mice indicated that ASXL1-MT induced an expression profile which inversely correlated with known PRC target genes. In fact, ASXL1-MT remarkably derepressed expression of posterior Hoxa genes, including Hoxa5, Hoxa9 and Hoxa10, which are epigenetically silenced by PRC2 in mature cells. In consistent with this, H3K27me3 was globally reduced in ASXL1-MT transduced cells. We also found ASXL1-MT as well as wild type ASXL1 (ASXL1-WT) can bind to EZH2 and, importantly, co-expression of ASXL1-MT with ASXL1-WT efficiently inhibited the binding between ASXL1-WT and EZH2, suggesting a dominant-negative role of ASXL1-MT against the PRC2 function. Using a chromatin immunoprecipitation (ChIP) assay, we confirmed that H3K27me3 and Ezh2-bindig profoundly decreased around the promoter regions of Hoxa5, Hoxa9, and Hoxa10 in the MDS mice, correlating with the upregulation of their mRNA expression. On the other hand, we found that ASXL1-MT reduced the expression of Clec5a, a type 2 transmembrane receptor and that this reduction was associated with differentiation block of the 32Dcl3 cells. Moreover, utilizing an shRNA or a mutant form of Clec5a, we identified that Clec5a plays essential roles in myeloid differentiation of 32Dcl3 cells. Lastly, we searched for microRNAs deregulated by ASXL1-MT since a large subset of microRNAs are found to be transcriptionally regulated by PRC2. Among upregulated microRNAs related to myeloid malignancies, we found that miR-125a targeted 3’UTR of Clec5a gene, repressed Clec5a expression and inhibited granulocytic differentiation in vitro. Intriguingly, H3K27me3 and Ezh2-bindig greatly decreased around the miR-125a gene in the BM cells of the MDS mice, similar to the results of ChIP assays around Hoxa genes. The present results indicate that ASXL1-MT which results in a truncated protein product may (1) inhibit PRC2-function by impairing the interaction of EZH2 with the ASXL1-WT and (2) promote myeloid transformation through impaired PRC2-mediated repression of posterior HOXAs and miR-125a, and subsequent suppression of CLEC5A. HOXA9 and CLEC5A expression were shown to be high and low, respectively, in MDS patients with ASXL1-MT. Our data provide evidence for a novel axis in MDS pathogenesis and implicate both mutant forms of ASXL1 and miR-125a as therapeutic targets in MDS. Disclosures: No relevant conflicts of interest to declare.

Abstract 2820 RUNX1/AML1 mutations have been frequently detected in patients with myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML). RUNX1 mutations are rarely detected in lower-risk MDS, whereas approximately 20% patients with higher-risk MDS (H-MDS) have the mutations. The mutations were distributed throughout the RUNX1 protein, and replacement of D171 amino acid in runt homology domain was the most frequent target of mutations in the RUNX1 gene. The D171N mutant showed a loss of normal RUNX1 trans-activation potential and dominant-negative suppression. In mouse transplantation systems D171N-transduced mice exhibited AML with multilineage dysplasia in collaboration with Evi1 overexpression. However, EVI1 overexpression was very rare in patients. Instead, most of H-MDS patients with RUNX1 mutations displayed a high expression of BMI1. RUNX1 D171N mutant showed an increased self-renewal capacity, differentiation block, dysplasia in all 3 lineages, slightly increased immature cells and no proliferation ability using enforced expression in human CD34+ cells, and the D171N-transduced cells showed low expression level of BMI1. Both D171N and BMI1 transduced cells displayed long-term proliferation ability. When BMI1 transduced later into D171N cells, the cells expanded with a retained CD34+ cell fraction, suggesting that BMI1 have a potential to boost the D171N cells to H-MDS. To confirm the collaboration of BMI1 overexpression with D171N mutant in vivo, we performed mouse BMT using BM cells transduced with both D171N and BMI1. Ly-5.1 murine BM mononuclear cells infected with retrovirus harboring D171N/BMI1 or control vectors were transplanted into sublethally irradiated syngeneic Ly-5.2 mice. Mice that received transplants of BMI1-transduced cells remained healthy over the observation period (n=12/12), as well as those that were transplanted with empty vectors-transduced cells (n=4/4). Most of the mice that received transplants of D171N -transduced cells developed MDS/AML mainly 6–8 months after transplantation (n=6/11, P BMI1 is well-known to be essential for self-renewal of HSCs, in part via repression of genes involved in senescence, and self-renewal of HSCs is enhanced by BMI1 expression. To address the mechanisms by which BMI1 would contribute to MDS/AML development, we analyzed gene expressions involved in BMI1 downstream signaling pathways. It is suggested that BMI1 overexpression may act as one of the partner abnormalities collaborating with master gene mutations for MDS-genesis. RUNX1 D171N mutant showed no proliferation ability using enforced expression in human CD34+ cells, and D171N-transduced mice exhibited MDS/AML in collaboration with Evi1 overexpression. In addition, co-transduction of D171N and BMI1 into BM cells resulted in faster induction of MDS/AML in BMT mice. Taken together, the RUNX1 mutant may require collaborating genes such as EVI1 and BMI1 to develop MDS/AML. We confirmed that BMI1 have a potential to boost the D171N cells to MDS/AML in vivo. Disclosures: No relevant conflicts of interest to declare.