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Inflammation is associated with the pathogenesis of Myelodysplastic syndromes (MDS). Emerging evidence suggests that MDS hematopoietic stem and progenitor cells (HSPCs) exhibit an altered response to systemic low-grade inflammation, which contributes to their competitive advantage over wild-type HSPCs and ensuing hematopoietic defects. Deletion of the long arm of chromosome 5 (del(5q)) is the most common chromosomal abnormality in patients with MDS. Although this subtype of MDS contains several haploinsufficient genes that directly impact innate immune signaling, the effects of an inflammatory milieu on del(5q) MDS HSPCs remains poorly defined. Utilizing a model of del(5q)-like MDS, wherein two 5q genes, miR-146a and TIFAB, are deleted, we found that chronic low-grade inflammation impaired the function of del(5q)-like MDS HSPCs and contributed to a more severe disease. The del(5q)-like MDS HSPCs exposed to chronic inflammation became less quiescent, but without changes in cell viability. In response to inflammation, mouse and human del(5q) MDS HSPCs activated a partial p53 response. The impaired function and reduced cellular quiescence of del(5q) MDS HSPCs exposed to inflammation could be restored by deletion of p53. Since TP53 mutations are highly enriched in del(5q) AML patients following an initial MDS diagnosis, increased p53 activation in del(5q) MDS HSPCs due to inflammation may create a selective pressure for genetic inactivation of p53. These findings uncover the contribution of systemic inflammation on dyshematopoiesis in del(5q) MDS and provide a potential explanation for acquired p53 mutations in myeloid malignancies with del(5q).

Dysregulation of innate immune signaling pathways is implicated in various hematologic malignancies. However, these pathways have not been systematically examined in acute myeloid leukemia (AML). We report that AML hematopoietic stem and progenitor cells (HSPCs) exhibit a high frequency of dysregulated innate immune-related and inflammatory pathways, referred to as oncogenic immune signaling states. Through gene expression analyses and functional studies in human AML cell lines and patient-derived samples, we found that the ubiquitin-conjugating enzyme UBE2N is required for leukemic cell function in vitro and in vivo by maintaining oncogenic immune signaling states. It is known that the enzyme function of UBE2N can be inhibited by interfering with thioester formation between ubiquitin and the active site. We performed in silico structure-based and cellular-based screens and identified two related small-molecule inhibitors UC-764864/65 that targeted UBE2N at its active site. Using these small-molecule inhibitors as chemical probes, we further revealed the therapeutic efficacy of interfering with UBE2N function. This resulted in the blocking of ubiquitination of innate immune- and inflammatory-related substrates in human AML cell lines. Inhibition of UBE2N function disrupted oncogenic immune signaling by promoting cell death of leukemic HSPCs while sparing normal HSPCs in vitro. Moreover, baseline oncogenic immune signaling states in leukemic cells derived from discrete subsets of patients with AML exhibited a selective dependency on UBE2N function in vitro and in vivo. Our study reveals that interfering with UBE2N abrogates leukemic HSPC function and underscores the dependency of AML cells on UBE2N-dependent oncogenic immune signaling states.

Despite evidence of chronic inflammation in myelodysplastic syndrome (MDS) and cell-intrinsic dysregulation of Toll-like receptor (TLR) signaling in MDS hematopoietic stem and progenitor cells (HSPCs), the mechanisms responsible for the competitive advantage of MDS HSPCs in an inflammatory milieu over normal HSPCs remain poorly defined. Here, we found that chronic inflammation was a determinant for the competitive advantage of MDS HSPCs and for disease progression. The cell-intrinsic response of MDS HSPCs, which involves signaling through the noncanonical NF-κB pathway, protected these cells from chronic inflammation as compared to normal HSPCs. In response to inflammation, MDS HSPCs switched from canonical to noncanonical NF-κB signaling, a process that was dependent on TLR-TRAF6-mediated activation of A20. The competitive advantage of TLR-TRAF6-primed HSPCs could be restored by deletion of A20 or inhibition of the noncanonical NF-κB pathway. These findings uncover the mechanistic basis for the clonal dominance of MDS HSPCs and indicate that interfering with noncanonical NF-κB signaling could prevent MDS progression.

When an aqueous salt solution freezes, a freeze-concentrated solution (FCS) separates from the ice. The properties of the FCS may differ from those of a supercooled bulk solution of the same ionic strength at the same temperature. The fluorescence and lifetime characteristics of 6-cyano-2-naphthol (6CN) were studied in frozen NaCl solutions in order to provide insight into the solution properties of the FCS. While the photoacidity of 6CN in an FCS is similar to that in solution, several anomalous behaviors are observed. Fluorescence spectra indicate that the solubility of 6CN is significantly enhanced in the FCS (50 mM or higher) compared to that in the bulk NaCl solution where the solubility limit is 250 μM. The high solubility induces the aggregation of 6CN in the FCS, which is not detected in bulk solutions. This trend becomes marked as the initial NaCl concentration decreases and the FCS is confined in a small space. The fluorescence lifetimes of 6CN in the FCS support the spectroscopy results. In addition to the species identified by fluorescence spectroscopy, excimers are assigned from lifetime measurements in the FCS. The excimer formation is also a result of the enhanced solubility of 6CN in the FCS.

Myeloid/lymphoid neoplasms with PDGFRB rearrangement are a distinct type of myeloid neoplasms that occur in association with rearrangement of PDGFRB at 5q32. The hematological features most often show prominent eosinophilia. We herein report a patient with myeloid/lymphoid neoplasms with PDGFRB rearrangement with t (5;10) (q33;q22) who showed atypical chronic myeloid leukemia-like clinical features without eosinophilia and achieved an optimal response to imatinib. A sequence analysis showed a CCDC6-PDGFRB fusion gene with a new break point in the PDGFRB gene. This is the sixth case of myeloid/lymphoid neoplasm with PDGFRB rearrangement harboring a CCDC6-PDGFRB fusion gene, and it has a new breakpoint in the PDGFRB fusion gene.

The efficacy of pharmacokinetically (PK) guided, once-daily administration of busulfan (BU) was evaluated in elderly patients with acute myeloid leukemia/myelodysplastic syndrome (AML/MDS). Twenty-one patients (median age 61) received 30 mg/m

Clonal hematopoiesis (CH) is an aging-associated condition characterized by the clonal outgrowth of pre-leukemic cells that acquire specific mutations. Although individuals with CH are healthy, they are at an increased risk of developing myeloid malignancies, suggesting that additional alterations are needed for the transition from a pre-leukemia stage to frank leukemia. To identify signaling states that cooperate with pre-leukemic cells, we used an in vivo RNAi screening approach. One of the most prominent genes identified was the ubiquitin ligase TRAF6. Loss of TRAF6 in pre-leukemic cells results in overt myeloid leukemia and is associated with MYC-dependent stem cell signatures. TRAF6 is repressed in a subset of patients with myeloid malignancies, suggesting that subversion of TRAF6 signaling can lead to acute leukemia. Mechanistically, TRAF6 ubiquitinates MYC, an event that does not affect its protein stability but rather represses its functional activity by antagonizing an acetylation modification.

The novel small molecule PTC596 inhibits microtubule polymerization and its clinical development has been initiated for some solid cancers. We herein investigated the preclinical efficacy of PTC596 alone and in combination with proteasome inhibitors in the treatment of multiple myeloma (MM). PTC596 inhibited the proliferation of MM cell lines as well as primary MM samples in vitro, and this was confirmed with MM cell lines in vivo. PTC596 synergized with bortezomib or carfilzomib to inhibit the growth of MM cells in vitro. The combination treatment of PTC596 with bortezomib exerted synergistic effects in a xenograft model of human MM cell lines in immunodeficient mice and exhibited acceptable tolerability. Mechanistically, treatment with PTC596 induced cell cycle arrest at G2/M phase followed by apoptotic cell death, associated with the inhibition of microtubule polymerization. RNA sequence analysis also revealed that PTC596 and the combination with bortezomib affected the cell cycle and apoptosis in MM cells. Importantly, endoplasmic reticulum stress induced by bortezomib was enhanced by PTC596, providing an underlying mechanism of action of the combination therapy. Our results indicate that PTC596 alone and in combination with proteasome inhibition are potential novel therapeutic options to improve outcomes in patients with MM.

Mediastinal gray zone lymphoma (MGZL) is a provisional entity with intermediate features between classical Hodgkin lymphoma (cHL) and diffuse large B-cell lymphoma. Outcomes for patients with MGZL are reportedly poorer than those for patients with cHL or primary mediastinal large B-cell lymphoma. Additionally, no standard management guidelines for patients with MGZL are available, primarily due to its recent identification, rarity, and challenges in diagnosis. Although recent several studies have suggested dose-adjusted EPOCH-R (etoposide, doxorubicin, vincristine, cyclophosphamide, prednisolone, and rituximab) may improve outcomes in patients with MGZL, numerous patients still suffer from relapsed/refractory MGZL, and the optimal management for such patients remains uncertain. Here, we report the first case of successful treatment of refractory MGZL by tandem high-dose chemotherapy supported by autologous stem cell transplantations (auto-SCTs) and consolidative radiotherapy (RT). To date, the patient remains in CR 33 months after the completion of RT, with no significant complications. This case suggests that tandem auto-SCTs may be a promising therapeutic option for relapsed/refractory MGZL.

Introduction POEMS syndrome is a rare systemic disorder characterized by various symptoms, including polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy (M-protein), and skin changes, which is based on the presence of monoclonal plasma cells (PC). We previously reported the analysis of the clonal immunoglobulin λ light-chain variable region (IGLV) gene rearrangements in POEMS syndrome using next-generation sequencing (NGS), and the clone identification rate was 36.7% (Kawajiri-Manako C, Am J Hematol. 2018;93(9):1161). EuroFlow-based next-generation flow (EuroFlow-NGF) has also been standardized for detecting minimal residual disease in multiple myeloma (MM). However, multiparameter flow cytometry (MFC) utility in detecting clonal PC of POEMS syndrome remains unknown. Therefore, to clarify the feasibility of detecting the clonality with MFC, we analyzed PC of bone marrow samples in patients with POEMS syndrome by MFC and validated gating strategies of PC in POEMS syndrome. Methods Patients with newly diagnosed or relapsed POEMS syndrome (n=25) at Chiba University Hospital from April 2019 to July 2021 were included in this study. Primary bone marrow aspirations were performed after obtaining informed consent following the Declaration of Helsinki. The collected bone marrow samples were analyzed by the SRL-Flow protocols (single-tube 8-color: CD138/CD27/CD38/CD56/CD45/CD19/CyIgκ/CyIgλ), which is highly correlated with EuroFlow-NGF (Takamatsu H, Int J Hematol. 2019;109(4): 377). Furthermore, 21 cases for which data files were available from SRL Inc. were reanalyzed by gating PC with lower expression of CD45 regarding the previous study (Dao LN, Blood. 2011;117(24):6438). This study was approved by the ethics committee of Chiba University Graduate School of Medicine. Results Among 25 patients, the median age was 59 (25-77) years, and 13 (52.0%) were men. The types of M-proteins identified by immunofixation electrophoresis (IFE) were IgA-λ in 12 (48.0%), IgG-λ in 9 (36.0%), IgA-κ in 1 (4.0%), IgG-κ in 1 (4.0%), and negative in 2 patients (8.0%), respectively. The median serum VEGF level was 3,240 (747-9,060) pg/ml. SRL-Flow identified the clonal PC in 9 of 25 (36.0%, λ in 7 and κ in 2): 7 of 23 IFE-positive cases (30.4%) and 2 of 2 IFE-negative cases (100%). The median clone size was 0.03 (0.01-3.78)%, smaller than MM. Interestingly, the clone size was not correlated with the level of serum VEGF (r = -0.17). Aberrant expression of clonal PC in POEMS syndrome was similar to MM: CD19-56+ in 5 (55.6%), CD19-56- in 2 (22.2%), CD19dim56- in 1 (11.1%), and CD19-56dim in 1 (11.1%) patient, respectively. No clone was detected in PC with CD19+56-. The clone identification rate by single-tube 8-color SRL-Flow protocols was lower than expected. Therefore, we reanalyzed the data by gating PC with lower expression of CD45 and CD38. In the reanalysis, we gated broadly for CD38 dim-to-bright and CD138 dim-to-bright cells and narrowly for CD38 dim and CD45 negative-to-dim cells. As a result, we identified the clonal PC in 15 of 21 cases (71.4%, λ in 13 and κ in 2): 13 of 19 IFE-positive cases (68.4%) and 2 of 2 IFE-negative cases (100%)). Of the 15 cases in which monoclonal PC were identified by reanalysis, 8 were negative by SRL-Flow. Of these, 6 were identified by selective gating of CD45- and CD38 dim, and 2 were identified by selective gating of CD45- and CD38+. The median clone size was 0.008 (0.001-3.27)%, smaller than that of MM, and the clone size was not correlated with the level of serum VEGF (r = -0.15). The aberrant expression of the clonal PC in POEMS remained similar to MM for CD19 and CD56 expression: CD19-56+ in 3 (20.0%), CD19-56- in 7 (46.7%), CD19-56dim in 4 (26.7%), and CD19dim 56- in 1 (6.7%) patient, respectively. No clone was detected in PC with CD19+56-. Conclusions EuroFlow-based SRL-Flow protocols detected the clonal PC in about one-third of POEMS patients. Aberrant immunophenotype of clonal PC in POEMS syndrome was similar to MM for CD19 and CD56 expression; however, CD45 and CD38 expression of POEMS PC tended to be downregulated. Selective gating of PC with CD38dim and CD45 negative-to-dim detected clonal PC in 71.4% of cases. This novel gating strategy is more accessible and might improve the identification rate of clonal PC in POEMS syndrome. Disclosures Tsukamoto: Daiichi Sankyo: Honoraria. Yokote: Kowa Company, Ltd.: Honoraria, Other: Scholarship; MSD K.K.: Honoraria, Other: Scholarship, Courses endowed by company; Astellas Pharma Inc.: Honoraria, Other: Scholarship; Mitsubishi Tanabe Pharma Corporation: Honoraria, Other: Scholarship; Amgen K.K.: Honoraria; Taisho Pharmaceutical Co., Ltd.: Honoraria, Other: Scholarship, Research Funding; Nippon Boehringer Ingelheim Co., Ltd.: Honoraria, Other: Scholarship; Janssen Pharmaceutical K.K.: Honoraria; Kao Corporation: Other: Schlarship; Novo Nordisk Pharma Ltd.: Honoraria, Other: Scholarship; Teijin Pharma Limited: Other: Scholarship; Pfizer Japan Inc.: Honoraria, Other: Scholarship; Kyowa Kirin Co., Ltd.: Honoraria; Eli Lilly Japan K.K.: Honoraria, Other: Scholarship; Takeda Pharmaceutical Company Limited: Honoraria, Other: Scholarship; Sanofi K.K.: Honoraria; Ono Pharmaceutical Co., Ltd: Honoraria, Other: Scholarship; AstraZeneca K.K.: Honoraria; Daiichi Sankyo Company, Limited: Honoraria, Other: Scholarship; Novartis Pharma K.K.: Honoraria; Sumitomo Dainippon Pharma Co., Ltd.: Honoraria, Other: Scholarship; Shionogi Co., Ltd.: Other: Scholarship; Bayer Yakuhin, Ltd.: Other: Scholarship. Nakaseko: Novartis Pharma KK.: Honoraria. Takamatsu: Adaptive Biotechnologies, Eisai: Honoraria; SRL: Consultancy; Bristol-Myers Squibb: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding. Sakaida: Bristol Myers Squibb: Research Funding; Chugai: Research Funding; Ono: Research Funding; Kyowa Kirin: Research Funding.

Introduction: Recent studies based on next-generation sequencing revealed the genetic landscape of diffuse large B cell lymphoma (DLBCL). A new genetic classification system was proposed, including four groups; the BCL2 and SGK1 groups that were both associated with germinal center B-cell like (GCB) DLBCL, an MYD88 group that was associated with non-GCB DLBCL, and a NOTCH2 group that was not associated with a specific cell-of-origin (COO). Unfortunately, this classification method is somewhat complex and thus not fully accepted in clinical practice. Furthermore, part of all cases remained unclassified; as such, it is clear that the diversity of the genetic landscape of DLBCL is not yet fully understood. In this study, we performed a retrospective analysis of genetic abnormalities and their correlations with clinical characteristics in a Japanese cohort of patients diagnosed with DLBCL. Materials and Methods: We collected clinical data from 224 of a total of 234 patients who were diagnosed with DLBCL between 2013 and 2018 at Chiba University Hospital. We also collected formalin-fixed paraffin-embedded (FFPE) specimens obtained from 204 patients via standard diagnostic procedures. The COO for each sample was assessed using the Hans algorithm with immunohistochemical staining; rearrangements of BCL2, BCL6, and MYC were evaluated by fluorescence in situ hybridization. Targeted DNA sequencing was performed using a 144-gene custom panel. Results: Of the 224 DLBCL patients evaluated in our study, the median age at diagnosis was 69 years (range, 18 - 92 years). The median follow-up time was 34 months; three-year progression-free survival (PFS) was 63.2%, and three-year overall survival was 78.0%. COO was determined in 218 cases; 93 of these cases (41.5%) were classified as GCB type and 125 cases (55.8%) as non-GCB type. We successfully performed targeted DNA sequencing in 167 of the 204 FFPE samples. Compared to previous reports, our cohort included relatively higher frequencies of mutations in PIM1 (44.3%), KMT2D (40.7%), MYD88L265P (37.7%), and CD79B (24.5%); by contrast, we detected comparatively lower mutation frequencies in B2M (6.6%), ETV6 (5.4%), CDKN2A (4.7%), and TNFAIP3 (4.1%). Multivariate adjustment of genes extracted by univariate analysis and factors identified by International Prognostic Index score revealed that genetic mutations of MYD88L265P (Hazard ratio [HR] = 2.045), IL16 (HR = 4.848), and BCOR (HR = 6.295) were significant prognostic factors. Mutations in IL16 and BCOR are novel factors that will be used to predict poor prognosis. In the 167 sequenced cases, 110 were classified into the aforementioned four subtypes based on mutations detected in 23 genes together with rearrangements of BCL2 and BCL6; specifically, 47 cases were classified as members of the MYD88 group, 28 in the BCL2 group, 19 in the NOTCH2 group, and 16 in the SGK1 group. We identified a trend toward differential PFSs among the four groups (p = 0.18); three-year PFS was 51.2% among patients with MYD88 group, 59.6% in the BCL2 group, 63.2% in the NOTCH2 group, and 75.0% for the SGK1 group. When compared outcomes of patients in the BCL6 group, patients in the MYD88 group had significantly inferior PFS (p = 0.043) among the non-GCB DLBCL patients; those in the BCL2 group revealed a trend toward inferior PFS compared with those in the SGK1 group (p = 0.34) among the GCB DLBCL patients. We next focused on 28 cases of CD5-positive DLBCL; this is a distinct DLBCL subtype with poor prognosis that is identified more frequently among Asians. We observed significantly higher frequencies of frameshift or nonsense mutations in CD58 and missense mutations in MYD88L265P. Furthermore, evaluation of gene expression data for CD5-positive DLBCL reported in a published database (Miyazaki K et al. Int J Hematol. 2015) revealed diminished expression of CD58 (p = 0.01) and augmented expression of MYD88L265P (p < 0.001). These results suggest that there may be a specific correlation between genetic mutations and gene expression. Intriguingly, these specific genes are key regulators of the immune response, suggesting that inflammation contribute to the unfavorable outcome of CD5-positive DLBCL. Conclusion: Our study provides support for the genetic classification of DLBCL using targeted DNA sequencing to evaluate outcomes in our Japanese cohort. We also identified mutations in novel candidate genes that may be used to predict clinical outcomes. Disclosures Nakaseko: Novartis Pharma KK: Speakers Bureau; Pfizer Japan Inc.: Speakers Bureau. Kaneda:SRL Inc.: Research Funding; SCRUM Inc.: Research Funding; Tsubakimoto Chain Co.: Research Funding; Takeda Foundation: Research Funding; Princess Takamatsu Cancer Research Fund.: Research Funding; Wedge Co Ltd: Research Funding.

LR11 (also called SorLA or SORL1) is a type I membrane protein, originally identified as a biomarker for atherosclerosis and Alzheimer's disease. We recently found that LR11 was specifically expressed in Diffuse Large B-cell lymphoma (DLBCL) cells, and high serum sLR11 concentrations in retrospective cohort indicated inferior survival. In this study, we prospectively validated the clinical impact of serum sLR11 in 97 patients with newly-diagnosed, untreated DLBCL.Serum sLR11 concentrations were increased in DLBCL patients compared to normal controls (mean±SD: 21.2±27.6 vs. 8.8±1.8ng/ml, P0.0001), and significantly reduced at remission (mean±SD: 17.4±16.4 vs. 10.9±4.5ng/ml, P=0.02). Increased serum sLR11 concentrations were affected by tumor burden and bone marrow invasion. The 2-y OS and PFS were significantly lower in patients with high sLR11 concentrations (≤18.1ng/ml vs.18.1ng/ml; 2-y OS: 89.0% vs. 56.4%, P0.0001; 2-y PFS: 85.8% vs. 56.9%, P0.0001).Serum sLR11 is a tumor-derived biomarker for predicting the survival of newly diagnosed patients with DLBCL.

Myeloid/lymphoid neoplasms with PDGFRB rearrangement are a distinct type of myeloid neoplasms that occur in association with rearrangement of PDGFRB at 5q32. The hematological features most often show prominent eosinophilia. We herein report a patient with myeloid/lymphoid neoplasms with PDGFRB rearrangement with t (5;10) (q33;q22) who showed atypical chronic myeloid leukemia-like clinical features without eosinophilia and achieved an optimal response to imatinib. A sequence analysis showed a CCDC6-PDGFRB fusion gene with a new break point in the PDGFRB gene. This is the sixth case of myeloid/lymphoid neoplasm with PDGFRB rearrangement harboring a CCDC6-PDGFRB fusion gene, and it has a new breakpoint in the PDGFRB fusion gene.

Expression of the tumor suppressor gene NR4A3 is silenced in the blasts of acute myeloid leukemia (AML), irrespective of the karyotype. Although the transcriptional reactivation of NR4A3 is considered to have a broad-spectrum anti-leukemic effect, the therapeutic modalities targeting this gene have been hindered by our minimal understanding of the transcriptional mechanisms regulating its expression, particularly in human AML. Here we show the role of intragenic DNA hypermethylation in reducing the expression of NR4A3 in AML. Bisulfite sequencing analysis revealed that CpG sites at the intragenic region encompassing exon 3 of NR4A3, but not the promoter region, are hypermethylated in AML cell lines and primary AML cells. A DNA methyltransferase inhibitor restored the expression of NR4A3 following a reduction in DNA methylation levels at intragenic CpG sites. The in silico data revealed an enrichment of H3K4me1 and H2A.Z at exon 3 of NR4A3 in human non-malignant cells but that was excluded specifically in leukemia cells with CpG hypermethylation. This suggests that exon 3 represents a functional regulatory element involved in the transcriptional regulation of NR4A3. Our findings improve the current understanding of the mechanism underlying NR4A3 silencing and facilitate the development of NR4A3-targeted therapy.

We describe two cases of polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes (POEMS) syndrome patients with deteriorated extravascular volume overload without increased levels of vascular endothelial growth factor after the administration of cyclophosphamide + granulocyte colony-stimulating factor for stem cell mobilization. We then measured the serum levels of 27 cytokines from these cases using a multiplex suspension array system. The analysis revealed the changes of cytokine profiles before cyclophosphamide + granulocyte colony-stimulating factor and after the development of capillary leak symptoms in both cases. This may improve our current level of understanding of the pathogenesis of POEMS syndrome not driven by vascular endothelial growth factor.

Adoptive immunotherapies have been developed for antiviral agent-refractory cytomegalovirus (CMV) disease after stem cell transplantation (SCT). However, the application of such strategies is limited, particularly in terms of need for donor cooperation regarding blood sampling and inaccessibility in the setting of cord blood transplantation. Herein, we describe the first successful treatment of antiviral agent-refractory CMV enteritis after allogeneic SCT by the infusion of ex vivo-expanded donor-derived CD4(+) lymphocytes obtained from the recipient's peripheral blood.

TO THE EDITOR: Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome is a rare plasma cell disorder additionally characterized by extravascular volume overload, sclerotic bone lesions, and plasmacytomas. Although high-dose melphalan followed by

Recent genome sequencing revealed inactivating mutations in EZH2, which encodes an enzymatic component of polycomb-repressive complex 2 (PRC2), in patients with myelodysplastic syndrome (MDS), myeloproliferative neoplasms (MPNs), and MDS/MPN overlap disorders. We herein demonstrated that the hematopoietic-specific deletion of Ezh2 in mice induced heterogeneous hematopoietic malignancies. Myelodysplasia was detected in mice following the deletion of Ezh2, and resulted in the development of MDS and MDS/MPN. Thrombocytosis was induced by Ezh2 loss and sustained in some mice with myelodysplasia. Although less frequent, Ezh2 loss also induced T-cell acute lymphoblastic leukemia and the clonal expansion of B-1a B cells. Gene expression profiling showed that PRC2 target genes were derepressed upon the deletion of Ezh2 in hematopoietic stem and progenitor cells, but were largely repressed during the development of MDS and MDS/MPN. Chromatin immunoprecipitation-sequence analysis of trimethylation of histone H3 at lysine 27 (H3K27me3) revealed a compensatory function of Ezh1, another enzymatic component of PRC2, in this process. The deletion of Ezh1 alone did not cause dysplasia or any hematologic malignancies in mice, but abolished the repopulating capacity of hematopoietic stem cells when combined with Ezh2 loss. These results clearly demonstrated an essential role of Ezh1 in the pathogenesis of hematopoietic malignancies induced by Ezh2 insufficiency, and highlighted the differential functions of Ezh1 and Ezh2 in hematopoiesis.

Severe acute lung injury is a rare but life-threatening complication associated with bortezomib. We report a patient with multiple myeloma who developed a severe diffuse alveolar hemorrhage (DAH) immediately after the first bortezomib administration. The patient was suspected to have pulmonary involvement of myeloma, which caused DAH after rapidly eradicating myeloma cells in the lungs with bortezomib. Rechallenge with bortezomib was performed without recurrent DAH. In patients with multiple myeloma who manifest abnormal pulmonary shadow, we should be aware of early-onset severe DAH after bortezomib administration, which might be due to pulmonary involvement of myeloma cells.

Thrombopoietin-receptor agonists have been recently introduced for a second-line treatment of immune thrombocytopenia (ITP). Splenectomy has tended to be avoided because of its complications, but the response rate of splenectomy is 60–80% and it has still been considered for steroid-refractory ITP. We performed partial splenic embolization (PSE) as an alternative to splenectomy. Between 1988 and 2013, 91 patients with steroid-resistant ITP underwent PSE at our hospital, and we retrospectively analyzed the efficacy and long-term outcomes of PSE. The complete response rate (CR, platelets > 100 × 109/L) was 51% (n = 46), and the overall response rate (CR plus response (R), > 30 × 109/L) was 84% (n = 76). One year after PSE, 70% of patients remained CR and R. The group with peak platelet count after PSE ≥ 300 × 109/L (n = 29) exhibited a significantly higher platelet count than the group with platelet count

Infections of the central nervous system (CNS) with varicella zoster virus (VZV) is a rare occurrence after allogeneic hematopoietic stem cell transplantation. We herein report a case of VZV meningitis, radiculitis and myelitis that developed 8 months after cord blood transplantation, shortly after the cessation of cyclosporine and low-dose acyclovir. Although treatment with acyclovir did not achieve a satisfactory response, the patient was successfully treated with foscarnet. Our report indicates that VZV infection should be considered in allo-hematopoietic stem cell transplantation (HSCT) patients with CNS symptoms and that foscarnet may be effective for the treatment of acyclovir-resistant VZV infections of the CNS. The development of optimal prophylactic strategies and vaccination schedules may eradicate post-transplant VZV disease.

TET2 mutations have been frequently observed in myeloid malignancies including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), myeloproliferative neoplasm (MPN) and MDS/MPN [1–4]. TET...

Individuals with clonal hematopoiesis of indeterminant potential (CHIP) are healthy, however they are at an increased risk of developing hematopoietic malignancies. The most frequent mutations in CHIP target DNMT3A and TET2, also are observed in acute myeloid leukemia (AML), myeloproliferative neoplasms (MPN), and myelodysplastic syndromes (MDS). These findings indicate that additional alterations are needed for the transition from a pre-leukemic stage to frank leukemia, although the identity of such molecular events remains uncharacterized. To identify cellular states that cooperate with Tet2 loss, we used in vivo RNAi screening and identified the ubiquitin ligase TRAF6 required for malignant transformation of pre-leukemic TET2-deficient hematopoietic stem/progenitor cell (HSPC). Importantly, TRAF6 expression is significantly reduced in 25-50% of AML and MPN patients as compared to healthy controls. Furthermore, TET2 mutations are more strongly correlated with lower expression of TRAF6 as compared to patients with higher TRAF6 expression in certain subsets of AML. To evaluate the consequences of TRAF6 deletion on TET2-deficienct pre-leukemic cells, we generated mice in which TRAF6 and TET2 are conditionally deleted in hematopoietic cells (VavCre;Traf6fl/fl;Tet2fl/fl[DKO]). Traf6KO mice developed a lethal phenotype with signs of MPN, including lymphopenia, neutrophilia, and increased hemoglobin levels; however, this disease was not transplantable. In striking contrast, deletion of TRAF6 in the context of TET2-deficient HSPC resulted in a rapid, penetrant, aggressive, and transplantable MPN/AML. To firmly establish that TRAF6 exhibits tumor suppressor functions, we determined whether physiological levels of TRAF6 overexpression could prevent malignant transformation. Overexpression of TRAF6 in FLT3-ITD mice inhibited malignant myeloid cell expansion in FLT3-ITD mice, and rescued the survival of the animals. To uncover the molecular basis of TRAF6's tumor suppressor function, we performed gene expression profiling and proteomic characterization of TRAF6 ubiquitination substrates in leukemic cells. RNA-sequencing of HSPC revealed that deletion of TRAF6 resulted in a significant overexpression of MYC regulated genes in pre-leukemic HSPC. In support of these findings, the proteomic screen along with extensive in vitro validation experiments identified MYC as a substrate of TRAF6. Unlike the majority of reported ubiquitin-dependent post-translational modifications of MYC, we found that ubiquitination of MYC on Lysine (K) 148 by TRAF6 does not affect its protein stability but rather antagonizes acetylation of MYC on the same lysine and thus suppresses MYC oncogenic activity. We extended these observations to investigate whether inflammatory signaling via Toll-like receptors (TLRs) can antagonize MYC function and suppress leukemic cells. Stimulation of TLRs on leukemic cells resulted in TRAF6-dependent ubiquitination of MYC at K148, which coincided with repositioning of MYC off of its target gene promoters and enhancers, and ultimately in the suppression of leukemic cell viability. Our results demonstrate that TRAF6 functions as a tumor suppressor via its ubiquitination activity that antagonizes K148 acetylation leading to a decrease of MYC transcriptional activity without affecting its protein abundance. Our findings identify TRAF6 as a novel, context-dependent tumor suppressor in myeloid neoplasms, and suggest that innate immune signaling via TLR/TRAF6 could explain why some of the clonal hematopoiesis patients develop AML and others do not. Disclosures Lowe: Blueprint Medicines: Consultancy, Equity Ownership; PMV Pharmaceuticals: Consultancy, Equity Ownership; Petra Pharmaceuticals: Consultancy, Equity Ownership; Constellation Pharma: Consultancy, Equity Ownership; Mirimus: Consultancy, Equity Ownership; ORIC pharmaceuticals: Consultancy, Equity Ownership; Faeth Therapeutics: Consultancy, Equity Ownership. Starczynowski:Kurome Therapeutics: Consultancy.

Although Hodgkin lymphoma (HL) is readily cured with conventional chemoradiotherapy, patients still develop refractory or relapsed HL even after allogeneic stem cell transplantation (allo-SCT) [1]....

Deletion of Ezh2 results in transcriptional repression of developmental regulator genes, derepression of oncogenic polycomb targets, and induction of MDS/MPN-like disease in mice that is exacerbated by concurrent deletion of Tet2., Polycomb group (PcG) proteins are essential regulators of hematopoietic stem cells. Recent extensive mutation analyses of the myeloid malignancies have revealed that inactivating somatic mutations in PcG genes such as EZH2 and ASXL1 occur frequently in patients with myelodysplastic disorders including myelodysplastic syndromes (MDSs) and MDS/myeloproliferative neoplasm (MPN) overlap disorders (MDS/MPN). In our patient cohort, EZH2 mutations were also found and often coincided with tet methylcytosine dioxygenase 2 (TET2) mutations. Consistent with these findings, deletion of Ezh2 alone was enough to induce MDS/MPN-like diseases in mice. Furthermore, concurrent depletion of Ezh2 and Tet2 established more advanced myelodysplasia and markedly accelerated the development of myelodysplastic disorders including both MDS and MDS/MPN. Comprehensive genome-wide analyses in hematopoietic progenitor cells revealed that upon deletion of Ezh2, key developmental regulator genes were kept transcriptionally repressed, suggesting compensation by Ezh1, whereas a cohort of oncogenic direct and indirect polycomb targets became derepressed. Our findings provide the first evidence of the tumor suppressor function of EZH2 in myeloid malignancies and highlight the cooperative effect of concurrent gene mutations in the pathogenesis of myelodysplastic disorders.

Although autologous stem cell transplantation can achieve excellent responses in patients with POEMS syndrome, the optimal regimen for peripheral blood stem cell (PBSC) collection is still controversial. We retrospectively investigated the safety and efficacy of 41 PBSC collecting procedures in 37 patients with POEMS syndrome. PBSC mobilization was performed using cyclophosphamide + granulocyte colony–stimulating factor (G-CSF) (CG, n = 14) or G-CSF alone (G, n = 27). Twelve (85.7%) patients in the CG group and all (100%) patients in the G group received induction chemotherapy before PBSC collection. The proportions of good mobilizers (≥2.0 × 106 CD34+ cells/kg) were comparable between the 2 groups (CG versus G: 78.6% versus 70.4%, P = .71). Two (14.3%) patients in the CG group developed severe capillary leak symptoms during the PBSC mobilization period, whereas no patient in the G group experienced severe adverse events. Appropriate induction therapies followed by the G-CSF monotherapy compose an optimal strategy for PBSC collection.

A 34-year-old man who had been referred to our hospital was diagnosed with acute promyelocytic leukemia (APL). All-trans retinoic acid (ATRA), oral administration, was initiated. On day 25, he developed fever and respiratory distress with bilateral pulmonary infiltrates, suggesting differentiation syndrome (DS) caused by ATRA. These symptoms showed amelioration after discontinuing ATRA and initiating methylprednisolone. ATRA was re-started on day 29 at half the original dose because of residual APL blasts. The patient subsequently developed fever, severe stomatitis, and oropharyngeal ulcers, which persisted even after discontinuing ATRA. On day 48, he suddenly developed severe abdominal pain with free air, observable on an abdominal X-ray, and underwent emergency ileocecal resection. Pathological examination of the resected ileocecal intestines revealed multiple ulcers and perforations. No leukemic cell infiltration was observed. In this case, only ATRA was administered for APL treatment. These findings suggest that ileocecal ulcerations and perforations, as well as oropharyngeal ulcers, might have been caused by DS or ATRA. Furthermore, DNA typing of the HLA-B locus revealed that the patient had HLA-B51 associated with Behçet's disease. Therefore, hypercytokinemia with DS might have induced Behçet's disease-like symptoms, including stomatitis and ileocecal perforation, complications that are particularly observed in patients with HLA-B51.

Somatic inactivating mutations in epigenetic regulators are frequently found in combination in myelodysplastic syndrome (MDS). However, the mechanisms by which combinatory mutations in epigenetic regulators promote the development of MDS remain unknown. Here we performed epigenomic profiling of hematopoietic progenitors in MDS mice hypomorphic for Tet2 following the loss of the polycomb-group gene Ezh2 (Tet2KD/KDEzh2Δ/Δ). Aberrant DNA methylation propagated in a sequential manner from a Tet2-insufficient state to advanced MDS with deletion of Ezh2. Hyper-differentially methylated regions (hyper-DMRs) in Tet2KD/KDEzh2Δ/Δ MDS hematopoietic stem/progenitor cells were largely distinct from those in each single mutant and correlated with transcriptional repression. Although Tet2 hypomorph was responsible for enhancer hypermethylation, the loss of Ezh2 induced hyper-DMRs that were enriched for CpG islands of polycomb targets. Notably, Ezh2 targets largely lost the H3K27me3 mark while acquiring a significantly higher level of DNA methylation than Ezh1 targets that retained the mark. These findings indicate that Ezh2 targets are the major targets of the epigenetic switch in MDS with Ezh2 insufficiency. Our results provide a detailed trail for the epigenetic drift in a well-defined MDS model and demonstrate that the combined dysfunction of epigenetic regulators cooperatively remodels the epigenome in the pathogenesis of MDS.

Immunosuppressive therapy (IST) with a combination of antithymocyte globulin (ATG) and cyclosporine (CsA) is an effective therapeutic modality for patients with aplastic anemia (AA) who are not eligible for allogeneic stem cell transplantation (Allo-SCT) from a human leukocyte antigen-identical sibling donor. However, there have been reports of some patients developing lymphoproliferative disorder (LPD) after IST for AA. We herein report a case of a 26-year-old man with severe AA (SAA) complicated by LPD after a single course of IST, who was successfully treated with Allo-SCT from an unrelated donor. Two months after starting IST for SAA, he developed LPD in the stomach. CsA was reduced, however, his neutrophil counts decreased, and CsA could not be discontinued. The patient was treated with rituximab monotherapy, and LPD resulted in complete remission. However, he failed IST for SAA and underwent Allo-SCT with reduced-intensity conditioning to recover his hematopoiesis. The patient has achieved complete hematopoietic recovery without the recurrence of LPD for five years after transplantation. This is the first report of successful Allo-SCT for SAA after the treatment of LPD caused by the use of rabbit ATG. This case provides useful information for the management of SAA with the development of LPD after IST.

Recent genome studies have identified recurrent somatic mutations in various myeloid malignancies, including acute myeloid leukemia, myelodysplastic syndrome and myeloproliferative neoplasm. These mutations frequently occur in epigenetic regulator genes, and functions of the proteins encoded by these genes in hematopoietic cells have been extensively analyzed, as reported recently. It is noteworthy that several epigenetic regulator genes, such as DNMT3A, TET2 and ASXL1, have also been identified in pre-leukemic stem cells. As targeting pre-leukemic stem cells would be a promising therapeutic approach, further investigations of epigenetic abnormalities in hematopoietic cells are anticipated to lead to the development of novel epigenetic therapies. In this review, we discuss recent genetic and functional data regarding epigenetic regulator genes and the future landscape of this new research field.

Posterior reversible encephalopathy syndrome (PRES) has been reported in childhood leukemia patients increasingly frequently. However, the development of PRES in adult leukemia patients during chemotherapy is very rare. We present a case of PRES in an adult patient with acute lymphoblastic leukemia (ALL) after remission induction chemotherapy. A 28-year-old woman with ALL was administered remission induction chemotherapy consisting of cyclophosphamide, daunorubicin, vincristine, prednisone, and L-asparaginase. After initiation of chemotherapy, the patient developed paralytic ileus and hypertension, and on day 30, she suddenly developed generalized convulsions, loss of visual acuity, and muscle weakness in the legs. Magnetic resonance imaging findings and her signs and symptoms were typical of PRES. The symptoms gradually improved following treatment with an anticonvulsant and an antihypertensive agent, and the patient underwent allogeneic bone marrow transplantation. She has completely recovered from PRES and has been asymptomatic without leukemia relapse. During remission induction chemotherapy for ALL, PRES may be caused by multiple drugs, such as L-asparaginase, vincristine, and corticosteroids, with different mechanisms of action. PRES should be recognized as an important complication, which will occur more frequently with the increased intensity of chemotherapy for adult ALL patients.

Fetal liver hematopoietic stem cells (HSCs) seed bone marrow (BM) and undergo reprograming into adult-type HSCs that are largely quiescent and restricted in their self-renewal activity. Here we report that in the absence of the polycomb-group gene Ezh2, a cohort of fetal-specific genes, including let-7 target genes, were activated in BM hematopoietic stem/progenitor cells (HSPCs), leading to acquisition of fetal phenotypes by BM HSPCs, such as enhanced self-renewal activity and production of fetal-type lymphocytes. The Lin28b/let-7 pathway determines developmentally timed changes in HSPC programs. Of note, many of the fetal-specific let-7 target genes, including Lin28, appear to be transcriptionally repressed by Ezh2-mediated H3K27me3 in BM HSPCs, and Ezh2 loss results in their ectopic expression, particularly in hematologic malignancies that develop in the absence of Ezh2. These findings suggest that Ezh2 cooperates with let-7 microRNAs in silencing the fetal gene signature in BM HSPCs and restricts their transformation.

Acute myeloid leukemia (AML) with mixed lineage leukemia-eleven-nineteen lysine-rich leukemia (MLL-ELL) is a rare subtype of MLL-rearranged AML. The outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for patients with this disease remains unknown. In the present study, we retrospectively investigated the efficacy of allo-HSCT in eight adult MLL-ELL-positive AML patients. Although all eight patients achieved first complete remission (CR1), three (37.5 %) patients experienced relapse after induction therapy. Five (62.5 %) patients underwent allo-HSCT during CR1, whereas two (25.0 %) underwent allo-HSCT during disease relapse, and one (12.5 %) during CR2. All three patients who received allo-HSCT beyond CR1 died due to AML progression after allo-HSCT. Of the five patients who received allo-HSCT during CR1, three (60.0 %) remained alive at study conclusion. The overall survival rate at five years was 50.0 %. Intriguingly, clonally expanded non-leukemic cells expressing MLL-ELL during consolidation therapy were found to be eradicated after allo-HSCT during the monitoring of minimal residual disease in one patient; this indicates that allo-HSCT is efficacious for eliminating pre-leukemic cells resistant to chemotherapy. In conclusion, allo-HSCT soon after CR1 represents a promising therapeutic option for adult AML patients with MLL-ELL, although the outcome of allo-HSCT for patients beyond CR1 was dismal.

Successful treatment with rituximab and donor lymphocyte infusions for fulminant EBV-associated lymphoproliferative disorder that developed 14 years after unrelated BMT

Loss-of-function mutations of EZH2, a catalytic component of polycomb repressive complex 2 (PRC2), are observed in ~\n10% of patients with myelodysplastic syndrome (MDS), but are rare in acute myeloid leukaemia (AML). Recent studies have shown that EZH2 mutations are often associated with RUNX1 mutations in MDS patients, although its pathological function remains to be addressed. Here we establish an MDS mouse model by transducing a RUNX1S291fs mutant into hematopoietic stem cells and subsequently deleting Ezh2. Ezh2 loss significantly promotes RUNX1S291fs-induced MDS. Despite their compromised proliferative capacity of RUNX1S291fs/Ezh2-null MDS cells, MDS bone marrow impairs normal hematopoietic cells via selectively activating inflammatory cytokine responses, thereby allowing propagation of MDS clones. In contrast, loss of Ezh2 prevents the transformation of AML via PRC1-mediated repression of Hoxa9. These findings provide a comprehensive picture of how Ezh2 loss collaborates with RUNX1 mutants in the pathogenesis of MDS in both cell autonomous and non-autonomous manners.

The expression of NR4A3, which is a member of the gene encoding NR4A orphan nuclear receptor subfamily, has been reported to be commonly silenced in blasts of patients with acute myeloid leukemia (AML), irrespective of karyotype. In line with this finding, Nr4a1-/-/Nr4a3-/- mice rapidly develop AML within one month following birth (Mullican et al., 2007). In addition, Nr4a1+/-/Nr4a3-/- and Nr4a1-/-/Nr4a3+/- mice show myelodysplastic/myeloproliferative neoplasms (Ramirez-Herrick et al., 2011), suggesting that NR4A3 functions as a tumor suppressor gene in myeloid malignancies. The extremely short latency of AML development in Nr4a1-/-/Nr4a3+/- mice indicates that silencing these tumor suppressors is sufficient to induce AML and that NR4A3 has a crucial role in the pathogenesis of AML. Thus, unveiling the molecular mechanism that regulates NR4A3 expression in AML would facilitate the development of novel therapies, including transcriptional reactivation of the gene. However, the therapeutic modalities targeting NR4A3 have been hindered by our minimal understanding of the mechanism underlying reduced NR4A3 expression, particularly in human AML cells. Abnormal epigenetic regulation is a common mechanism in the pathogenesis of several types of cancers. For instance, the expression of several tumor suppressor genes, such as p16 and MLH1, is repressed due to DNA hypermethylation at their promoter regions. Given that loss-of-function mutations in NR4A3 have not been reported in AML to date, we hypothesized that DNA hypermethylation contributes to a reduction in NR4A3 expression in AML. To test our hypothesis, we analyzed DNA methylation status of NR4A3 in human AML cells. We first compared the level of NR4A3 expression in eight human AML cell lines and two human primary AML samples, with that in CD34+ mononuclear bone marrow (BM) cells from healthy human controls. As expected, the expression of NR4A3 was markedly reduced in all of the AML cell lines and primary AML cells compared with that in the cells of the healthy controls. To evaluate the function of NR4A3 in human AML cells, we ectopically overexpressed NR4A3 in a human AML cell line (NB4 cells). The growth of NR4A3 -overexpressing NB4 cells was remarkably compromised compared with that of the controls, suggesting a tumor suppressive function of NR4A3 in both human AML and murine cells. To investigate the DNA methylation status of NR4A3, we performed bisulfite sequencing assays using eight human AML cell lines (HL60, NB4, Kasumi, TF1, U937, K562, MOLM13, and THP1) as well as CD34+ BM cells from healthy controls. Unexpectedly, a hypermethylated CpG site in the promoter region was not detected in any of the cell lines. However, the drastically or mildly methylated region including twenty eight CpGs was identified approximately 3 kb downstream of the transcription start site in six AML cell lines (97.5%, 78.3%, 77.1%, 89.9%, 95.2%, and 86.9% in HL60, NB4, Kasumi, TF1, U937, and K562, respectively) and two mixed lineage leukemia-related cell lines (31.0% and 53.6% in MOLM13 and THP1, respectively), whereas this site was hypomethylated in the controls (n = 2; mean, 12.7%; range, 7.1%-18.2%). To evaluate the contribution of this hypermethylated region to reduced NR4A3 expression, the six AML cell lines with heavily hypermethylated CpGs at NR4A3 and two human primary AML cell samples were treated with a DNA methyltransferase inhibitor (decitabine; DAC) for three or five days. DAC exposure inhibited cell growth and restored the expression of NR4A3 in all AML cell lines and primary cells in a dose- and time-dependent manner. Next, we examined the status of DNA methylation at the CpG site following DAC treatment with bisulfite sequencing assays. The frequencies of methylated CpG in HL60, NB4, and K562 cells was reduced from 97.5% to 53.6%, 78.3% to 68.5%, and 86.9% to 67.5% after DAC treatment, respectively. In contrast, the methylation status in Kasumi, TF1, and U937 cells did not significantly changed after DAC treatment. Our findings in the present study suggest that DNA hypermethylation may partially account for the transcriptional inactivation of NR4A3 in AML. However, the mechanism of reduced NR4A3 expression is complex and variable depending on the genetic background. We are currently working on a more detailed analysis of DNA methylation using human primary cells, by extending the regions for investigation, such as enhancer regions. Disclosures Nakaseko: Novartis: Honoraria, Research Funding, Speakers Bureau; Otsuka: Honoraria, Research Funding; BMS: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau.

Somatic loss-of-function mutations of epigenetic regulators are frequently found in MDS patients. Although DNA hypomethylating agents have been shown to improve the clinical outcomes in patients with MDS, it remains unknown how altered DNA methylation promotes the development of MDS. We have recently shown that concurrent loss of Tet2 and Ezh2 promotes the development of MDS in mice compared with the individual loss by utilizing hypomorphic Tet2 mice and Ezh2 conditional knockout mice. In this study, we transplanted Cre-ERT (WT), Tet2KD/KD, Cre-ERT;Ezh2fl/fl, and Tet2KD/KD;Cre-ERT;Ezh2fl/fl fetal liver cells into lethally irradiated recipient mice, and deleted Ezh2 at 4 weeks post-transplantation. To understand how DNA hypermethylation contributed to the development of MDS, we performed Reduced Representation Bisulfite Sequence (RRBS) in Lin- Sca1+ Kit+ (LSK) stem/progenitor cells isolated from WT, Tet2KD/KD, Ezh2Δ/Δ, and Tet2KD/KD Ezh2Δ/Δ mice. Both Tet2 loss and Ezh2 loss caused hypermethylation in CpG islands (CGIs) and promoter regions. However, the impact of Tet2 loss was much evident in the enhancer elements and ~20 % of them underwent hypermethylation upon Tet2 loss. Combined loss of Tet2 and Ezh2 caused hypermethylation in the transcriptional regulatory regions including both the promoter regions and enhancer elements. Importantly, the majority of hyper-differentially methylated regions (hyper-DMRs) in Tet2KD/KD Ezh2Δ/Δ -MDS LSK cells showed a distribution that was distinct from those of single mutant LSK cells and only the hyper-DMRs in the enhancer elements in Tet2KD/KD Ezh2Δ/Δ -MDS LSK cells correlated with a significant reduction in gene expression levels. Hyper-DMRs in MDS LSK cells were significantly enriched in genes involved in transcriptional regulation and cell differentiation by GO analysis. These findings suggest that combined loss of Tet2 and Ezh2 cooperatively remodeled DNA methylation to an extent not observed in either mutant allele alone and contributed to the pathogenesis of MDS. Notably, we found that 375 out of 780 hyper-DMRs in Tet2KD/KD Ezh2Δ/Δ MDS HSPCs were overlapped with DMRs in CD34+ HSPCs in patients with MDS (Maegawa S, et al. Genome Research 2014). We next focused on the 131 genes with hyper-DMRs that showed reduced expression levels in Tet2KD/KD Ezh2Δ/Δ -MDS LSK cells. Those included Gata2, Gata3, Evi1, and Nr4a2. Given that Nr4a2/Nurr1, a nuclear receptor transcription factor, restricts the proliferation of hematopoietic stem cells (HSCs), we transduced WT and Tet2KD/KD Ezh2Δ/Δ HSCs with an Nr4a2 retrovirus in vitro. We found that exogenous Nr4a2 severelyimpairs proliferative capacity of Tet2KD/KD Ezh2Δ/Δ HSCs but moderately that of WT HSCs, implying that MDS HSCs are more susceptible to activation of Nr4a2 compared to WT HSCs. Next, we sought to determine whether DMRs in CGIs were associated with altered histone modifications upon the deletion of Ezh2, we performed chromatin immunoprecipitation (ChIP) sequencing by using H3K27me3 and H3K4me3 antibodies. We defined canonical polycomb repressive complexes 2 (PRC2) targets by >2-fold enrichment of H3K27me3 and bivalent genes by enrichment of both H3K27me3 and H3K4me3 in WT LSK cells. We found that approximately half of the hyper-DMRs in CGIs were enriched in canonical PRC2 targets and bivalent genes in LSK cells of all mutant genotypes. Notably, these hyper-DMRs in PRC2 targets, including bivalent genes, were significantly associated with reduced expression levels only in Tet2KD/KD Ezh2Δ/Δ -MDS LSK cells but not in either single mutant alone. We also observed that these PRC2 targets with hyper-DMRs still retained reduced but higher levels of H3K27me3 compared to the others despite the absence of Ezh2, implying that both DNA hypermethylation and residual H3K27me3 by Ezh1 cooperate to repress the transcription of these genes critical for hematopoiesis. Finally, we examined the impact of decitabine, a demethylating agent in vivo. Although the treatment of decitabine did not improve the survival of Tet2KD/KD Ezh2Δ/Δ -MDS mice, it partly resolved hyper-DMRs at critical genes including Gata2, Gata3, and Nr4a2, followed by a significant elevation in platelets counts in vivo. Taken together, our study unveils the cooperative biological function of aberrant DNA methylation and histone modifications in the pathogenesis of MDS. Disclosures Nakaseko: BMS: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau; Otsuka: Honoraria, Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau.

Low-dose trimethoprim–sulfamethoxazole for Pneumocystis jiroveci pneumonia prophylaxis after allogeneic hematopoietic SCT

Introduction: Chronic myeloid leukemia (CML) is characterized by the myeloproliferative clonal hyperplasia caused by the protein product of the BCR-ABL fusion gene. However, the mechanism underlying the release of increased numbers of myeloid cells from bone marrow (BM) to circulation which causes the accompanied remarkably high count of peripheral white blood cells (WBC) has not been fully elucidated. We have recently reported that G-CSF treatment induced the shedding of an LDL receptor family member LR11 (also called SorLA or SORL1) from myeloid cells, and the released soluble receptor accelerate the trans-endothelial migration of myeloid cells in cooperation with an endothelial activator, tumor necrosis factor-a (TNF-a) (Shimizu et al Ann Hematol 2014). Another group showed that the levels of TNF- a and G-CSF production by CML stem/progenitor cells were increased in the BM of CML. Thus, we hypothesized that the expanded mobilization of peripheral cells in CML is caused by the abnormally induced shedding activity which releases the two soluble key molecules for the migration of clonally expanded cells from BM to peripheral blood. Based on these backgrounds, we examined soluble LR11 levels in the BM of CML patients. Materials and methods: We analyzed 11 patients (comprising three CML, six acute myeloid leukemia (AML) and two immune thrombocytopenia (ITP)), who underwent bone marrow aspiration at the time of diagnosis in Chiba University Hospital between 2011 and 2012. We measured the levels of sLR11 in supernatants of BM by an ELISA method. We also examined the levels of TNF-a and MMP9 in some patients. Then we compared with clinical data including WBC and total nuclear cell count (TNC) of BM. Results: sLR11 levels of supernatant of BM in CML patients were significantly higher than AML patients (134.5+-215.7 ng/ml vs 15.0+-46.1 ng/ml, p=0.0389, Mann-Whitney test, Figure 1). The levels of two ITP patients were 14.8, 14.2 ng/ml respectively. There was no significant correlation between TNC and the levels of sLR11 (p=0.4386) in all patients. However, the WBC counts in CML patients (53,400+-60,253/ml) were slightly higher than AML patients (2970+-34,624/ml) (p=0.1967, Mann-Whitney test, Figure 2). We next evaluated myeloid TNF-a and MMP9 levels in patients with CML or other hematological malignancy). A CML patient revealed remarkably higher levels of TNF- a (16.8 pg/ml), and also MMP9 (22,000 pg/ml), compared with other hematological diseases. Conclusions: soluble LR11 levels were largely increased in the BM of patients with CML. Considering that the myeloid TNF-a level was increased in a case among them, the increased soluble LR11 in BM may induce myeloid cell release from BM into peripheral blood through the cooperative activation of trans-endothelial migration in cooperation with TNF-a. Figure 1. The levels of sLR11 in BM in patients with CML and AML. (p=0.0389) Figure 1. The levels of sLR11 in BM in patients with CML and AML. (p=0.0389) Figure 2. The WBC count in the patients, CML and AML. (p=0.1967) Figure 2. The WBC count in the patients, CML and AML. (p=0.1967) Disclosures No relevant conflicts of interest to declare.