A significant number of reports have described hematopoietic improvement after iron chelation therapy in iron-overloaded (IO) patients. These observations indicate negative impacts of excess iron on hematopoiesis. To investigate how excess iron affects hematopoiesis, we generated IO mice and examined hematopoietic parameters in these mice. IO mice did not show significant defects in the hematopoietic data of peripheral blood. Myeloid progenitor cells in the bone marrow were increased in IO mice, but the number and function of the erythroid progenitors and hematopoietic stem cells were not significantly affected. However, bone marrow transplantation from normal donors to IO recipients showed delayed hematopoietic reconstitution. Quantitative RT-PCR analyses of the bone marrow stromal cells demonstrated remarkably reduced expressions of several important cytokines, e.g. CXCL12, VCAM-1, Kit-ligand and IGF-1, in the IO mice. In addition, erythropoietin and thrombopoietin levels were significantly suppressed, and oxidative stress was significantly increased in the IO bone marrow and liver. Our findings thus indicate that excess iron can damage bone marrow stromal cells and other vital organs that support hematopoiesis, presumably via increased oxidative stress.

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Many chemical mediators regulate neutrophil recruitment to inflammatory sites. Although the actions of each of these chemical mediators have been demonstrated with neutrophils in vitro, how they act cooperatively or counteract each other in vivo remains largely unknown. To understand the behaviors of neutrophils in vivo, the activities of intracellular signaling molecules must be visualized in living tissues. For this purpose, we can use genetically-encoded biosensors based on the principle of Förster resonance energy transfer (FRET). In this review, we first provide an overview of FRET biosensors and then describe how we can utilize these biosensors to visualize the activity changes of signaling molecules in neutrophils during extravasation. In relation to this topic, we will also describe the development of transgenic mice expressing the FRET biosensors and in vivo two-photon excitation microscopy.

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During the last decade, multiphoton fluorescent microscopy has launched a new era in the field of biology. By using this advanced imaging technique we have established a system for visualizing the in situ behaviors of a diversity of living cells within intact tissues and organs. Among them we succeeded in visualizing the various dynamic phenomena within bones, a mysterious organ wherein various hematopoietic and immune cells are produced and functioning. However, these cell types are poorly understood with conventional methodologies such as histological analyses of decalcified bone sections. We have thus far focused on the behavior of osteoclasts, a type of specialized macrophage contributing to physiological turnover of bone tissues as well as pathological bone destruction, and have revealed novel mechanisms controlling the migration and function of osteoclasts in situ. Functional coupling between bone-destroying osteoclasts and bone-replenishing osteoblasts could also be visualized demonstrating a genuine mode of ‘cross-talk’ among these cell types. Furthermore, we have recently imaged in situ behaviors of different hematopoietic cells in bone marrow. Herein we present our latest data on cellular dynamics in the bone cavity, and discuss the applications of this novel methodology for future studies in the field of hematology.

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Mechanistic/mammalian target protein of rapamycin (mTOR) is an evolutionarily conserved kinase that plays a critical role in sensing and responding to growth factors, cytokines and nutrients, including amino acids and glucose. Although mTOR was originally discovered as a target protein of rapamycin, the inhibitory effects of rapamycin on mTORC1 substrates are complex. Recent studies using genetic approaches have clearly demonstrated the physiological roles of mTOR complexes in regulating the maintenance of hematopoietic and leukemia stem cells. Advances in understanding of how mTOR signaling is involved in mechanisms of normal hematopoiesis and leukemogenesis may lead to novel therapeutic approaches that can successfully eradicate leukemia.

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Identification of cellular constituents of the hematopoietic stem cell (HSC) niche has recently been the subject of intensive investigation. To investigate the spatial localization of the HSC niches in bone marrow, we have established a whole-mount immunofluorescence imaging technique in which the 3D spatial relationships between stromal structures and HSCs in the BM can be precisely determined. The imaging assessment combined with computational simulations has uncovered a significant association between HSCs and arterioles, ensheathed exclusively by rare Nestin^bright NG2⁺ pericytes (Nes^peri cells), distinct from sinusoid-associated Nestin^dim Leptin receptor (LepR)⁺ (Nes^retic) cells which reportedly represent peri-vascular niche cells. Depletion of NG2⁺ cells using NG2-creERTM / inducible diphtheria toxin receptor (iDTR) mice changed HSC localization away from arterioles, induced HSC cycling and reduced long-term repopulation of HSCs in BM, suggesting that periarteriolar NG2⁺ cells form quiescent niches for HSCs. These results form the basis of studies that will allow us to genetically dissect the functions of distinct vascular niches. This vascular niche model, in which arterioles and sinusoids differentially regulate HSC quiescence and proliferation, respectively, have implications for the behavior of healthy HSC and may be useful in the future for evaluating the niches for cancer (leukemic) stem cells.

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

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Unmet needs of current hemophilia A treatment include the requirement for frequent intravenous infusions, inhibitor development, and containment of high medical costs. In order to overcome these issues, we produced FVIII which mimics a bispecific antibody against FIXa/FX. ACE910 demonstrated hemostatic effects on both ongoing and spontaneous joint bleeding in the primate acquired hemophilia A model. Recently, a phase 1 study for PK, PD, and the safety of ACE910 was initiated. The t1/2 was approximately 30 days. There were no severe ACE910 related adverse events. Furthermore, bleeding was remarkably decreased by weekly subcutaneous administration in patients with severe hemophilia A, regardless of whether an inhibitor was used. ACE910 has the remarkable advantages of prophylactic efficacy which can be achieved by convenient subcutaneous administrations at a markedly reduced frequency.

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Venous thromboembolism is a multifactorial disease resulting from complex interactions among genetic and environmental factors. To date, numerous genetic defects have been found in families with hereditary thrombophilia, but there may still be many undiscovered causative gene mutations. We investigated a possible causative gene defect in a large Japanese family with inherited thrombophilia, and found a novel missense mutation in the prothrombin gene (p.Arg596Leu) resulting in a variant prothrombin (prothrombin Yukuhashi). The mutant prothrombin had moderately lower activity than wild type prothrombin in clotting assays, but formation of the thrombin-antithrombin (TAT) complex was substantially impaired resulting in prolonged thrombin activity. A thrombin generation assay revealed that the peak activity of the mutant prothrombin was fairly low, but its inactivation was extremely slow in reconstituted plasma. The Leu596 substitution caused a gain-of-function mutation in the prothrombin gene, resulting in resistance to antithrombin and susceptibility to thrombosis. We also showed the effects of the prothrombin Yukuhashi mutation on the thrombomodulin-protein C anticoagulation system, recent development of a laboratory test detecting antithrombin resistance in plasma, and another antithrombin resistant mutation found in other thrombophilia families.

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Extranodal NK/T-cell lymphoma, nasal type (ENKL), accounts for less than 3% of malignant lymphomas in Japan. Based on the results of prospective clinical trials, ENKL treatment has dramatically improved during the last decade in Japan. The Lymphoma Study Group of the Japan Clinical Oncology Group (JCOG) conducted a phase I/II study (JCOG0211) of concurrent chemoradiotherapy for newly-diagnosed, localized ENKL. The trial showed an excellent 5-year overall survival rate (70%) and acceptable toxicity of RT-2/3DeVIC. The NK-cell Tumor Study Group in Japan, together with Asian collaborators, conducted clinical trials (SMILE-PI & PII) of SMILE chemotherapy for patients with newly-diagnosed stage IV, or relapsed/refractory ENKL. The overall response rate for 2 cycles of SMILE in 38 evaluated patients was 79%. The 2013 Japanese Society of Hematology guidelines recommend RT-2/3DeVIC for the treatment of newly-diagnosed ENKL of stage IE and contiguous stage IIE with cervical node involvement. For other ENKL, SMILE or other L-asparaginase-containing chemotherapies are recommended. A large retrospective study evaluating the efficacy and toxicity of these new treatments in clinical practice is currently underway in Japan. Close cooperation between radiation oncologists and international collaboration will be the key factors in developing better first-line treatments for ENKL.

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Aggressive natural killer cell leukemia (ANKL) is a malignant disorder of mature NK cells that is relatively common in East Asia. It is associated with Epstein-Barr virus in more than 80% of patients. The median survival is not more than three months after diagnosis. In a recent survey of 34 cases with ANKL, the median patient age was 40 years and the age distribution followed a bimodal pattern. Morphologically, the ANKL cells varied from large granular lymphocytes to atypical cells with pleomorphic-like appearances. Clinical characteristics include fever, liver dysfunction, hemophagocytic syndrome, and a rapidly progressive course. In one third of patients, tumor cells in peripheral blood or the bone marrow are below 20% at initial presentation, which might lead to diagnostic delay. L-asparaginase-based chemotherapy plus allogeneic hematopoietic stem cell transplantation (HSCT) is a potential therapeutic option with curative intent.  As for extranodal NK/T cell lymphoma, nasal type, HSCT could be anticipated to provide survival benefit or a chance of cure for patients in clinical stage II to IV with complete remission at transplantation. However, the optimal stem cell source, timing of transplantation, and preconditioning regimen require further elucidation.

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TET (Ten Eleven Translocation) family proteins are dioxygenases that convert methylcytosine to hydroxymethylcytosine, and play an important role in the DNA demethylation process. Most notably, TET2 mutations have frequently been identified in myeloid malignancies, such as myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), chronic myelomonocytic leukemia, and acute myeloid leukemias, as well as angioimmunoblastic T-cell lymphoma and a proportion of peripheral T-cell lymphomas. To date, various types of Tet2 knockout/knockdown mice have been generated. Tet2 mutations induce enhanced self-renewal ability and competitive repopulation capacity in hematopoietic stem cells, and various MPN/MDS-like diseases and T-cell lymphoma consequently develop in model mice. These findings appear to have a strong correlation with the recently identified TET2 mutations in a significant proportion of healthy elderly people, and suggest that TET2 mutations lead to a pre-cancer state in hematopoietic stem/progenitor cells. In conclusion, TET2 might play a major role as a gate keeper for hematopoietic stem/progenitor cells preventing them from developing into various hematologic malignancies by acquiring additional disease-specific gene mutations.

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

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Human T-lymphotropic virus type-I (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma and HTLV-1 associated myelopathy/tropical spastic paraparesis. Currently, mother-to-child transmission via breastfeeding and sexual intercourse are considered to be the two major routes for HTLV-1 infection. We surveyed four clinics in Japan (two HTLV-1 carrier clinics in non-endemic areas and one in an endemic area, and one hematology clinic in a highly endemic area) and reviewed the management of carriers. In HTLV-1 carrier clinics, more than half of visitors had learned of their infections based on an examination conducted either for blood donation or pregnancy. Although half of visitors had known of their infection more than 2 years prior to their visit, they became to visit the clinics probably due to recent awareness of HTLV-1 in public and of carrier clinics. They requested a detailed explanation, and check-ups for infection and its related diseases. In contrast, most visitors in highly endemic areas had apparently received good explanations from their primary care physicians. It is noteworthy that neither parent of more than half of the carriers who visited the two clinics in the non-endemic area had been born outside of Kyushu, a highly endemic area, indicating that carriers will disperse from known endemic areas. Configuring an appropriate and efficient system to support carriers is necessary, especially in non-endemic areas.

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We retrospectively investigated treatment outcomes with soluble recombinant thrombomodulin (rTM) for disseminated intravascular coagulation (DIC) associated with hematological malignancies (acute leukemia and malignant lymphoma) at our hospital. After rTM administration, DIC scores improved in 29 of 39 cases with hematological malignancies (74.36%). Although one case with recurrent and refractory APL died due to cerebral bleeding during rTM administration, no bleeding-associated adverse events were observed in the other 38 cases. DIC improvement was augmented in cases with acute leukemia when rTM was introduced in the pre-DIC state. CRP decreased in 26 of 36 cases with hematological malignancies (72.22%) after rTM introduction, and CRP decreased particularly significantly in cases with malignant lymphoma, suggesting rTM to exert anti-inflammatory activity. Taken together, these observations indicate that rTM, which rarely causes bleeding-associated adverse events, is an excellent agent in terms of both efficacy and safety for treating DIC associated with hematological malignancies, and the potential anti-inflammatory activity of this agent was also suggested.

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A 78-year-old male, who had CKD and chronic heart failure, was referred to our hospital for evaluation of leukocytosis. His bone marrow contained 12% blast cells and chromosome analysis showed the Ph chromosome as well as other changes. The patient was diagnosed with the accelerated-phase CML because FISH and RT-PCR disclosed BCR/ABL fusion signals and minor BCR/ABL, respectively. Imatinib was administered, but the CML was resistant to this treatment. We gave him nilotinib employing a reduced and intermittent administration protocol because of the progression of anemia and heart failure. The patient achieved PCyR in 8 months, but, 12 months later, his WBC count increased and 83% of the cells were blasts. Because the probable diagnosis was the blast crisis of CML, we switched from nilotinib to dasatinib. However, leukocytosis worsened and he died of pneumonia. It was later revealed that he had a normal karyotype and both FISH and RT-PCR analysis of BCR/ABL were negative. His final diagnosis was Ph negative AML developing from Ph positive CML in PCyR. Since there were no dysplastic changes indicative of MDS, it was assumed that the AML was not secondary leukemia caused by the tyrosine kinase inhibitor but, rather, de novo AML.

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The number of reported cases of bacteremia due to Rothia mucilaginosa (R. mucilaginosa), a component of the normal flora of human gastrointestinal tract mucosa, is limited. We encountered three cases of bacteremia due to R. mucilaginosa during neutropenia after chemotherapy for myeloid malignancies. Although all three patients were successfully treated with antimicrobial agents, one patient developed disseminated lesions in the lungs and soft tissue. The portal of R. mucilaginosa bacteremia is reportedly mucositis or dental disorders; however, no such complications were identified in our patients. Even in the absence of a preexisting portal, R. mucilaginosa should be recognized as a potential causative pathogen of bacteremia during neutropenic periods. Accumulations of cases and isolates are required to further elucidate the risk factors for developing R. mucilaginosa bacteremia, its clinical course, and the optimal antimicrobial treatment.

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A 75-year-old male presented with progressive lower abdominal discomfort. CT scan demonstrated hypertrophy of the intestinal wall, small bowel dilatation, and masses in the descending colon. Biopsy specimens of the jejunum and descending colon revealed widespread distribution of medium-sized atypical lymphocytes with an immunophenotype, positivity for CD3, CD8, CD56, TAI-1, granzyme B and TCRβ, but negativity for CD4, CD5, CD20, CD30 and EBER-ISH. Type II enteropathy-associated T cell lymphoma (EATL; Lugano, stage IIE) was diagnosed. Subsequently, he received 6 cycles of chemotherapy with 2/3 dose CHOP and obtained complete remission. However, 18 months after the initial presentation, he presented with rapidly progressive mental deterioration. Gadolinium enhanced T1-weighted brain MR images showed multiple masses with mild heterogeneous enhancement. Brain biopsy revealed necrotic tumors composed of medium-sized atypical lymphocytes, positive for CD3, CD8, CD56, TIA-1, granzyme B and TCRβ, but negative for CD4, CD20, and EBER-ISH. CT scan disclosed no evidence of systemic lymphoma relapse, indicating central nervous system relapse of EATL. Despite immediate high-dose chemotherapy with methotrexate, he died of disease progression. EATL is a rare disease with a very poor outcome, for which a validated standard treatment is still lacking. Further studies are needed to identify innovative therapies for treating EATL.

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We report a 26-year-old man with primary refractory nodular sclerosis Hodgkin lymphoma against ABVD, ICE and autologous peripheral blood stem cell transplantation (auto-PBSCT), presenting with multiple epidural spinal cord compressions, paraplegia, and generalized lymphadenopathy. We administrated four cycles of brentuximab vedotin to achieve a complete response, and then conducted cord blood transplantation. This case raises the possibility of a new strategy for refractory Hodgkin lymphoma showing residual lesions after auto-PBSCT.

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A 67-year-old woman was diagnosed with chronic lymphocytic leukemia (CLL) in October 2001. In August 2004, she received chemotherapy consisting of fludarabine and cyclophosphamide (FC therapy). After three cycles of FC therapy, the number of tumor cells was markedly decreased. However, anemia progressed. She was diagnosed with pure red cell aplasia (PRCA) by bone marrow examination and was successfully treated with cyclosporin A (CsA). In October 2008, anemia progressed with the exacerbation of CLL and she received three cycles of fludarabine therapy. Although the number of tumor cells diminished, the anemia did not improve. She was diagnosed with PRCA recurrence and was again successfully treated with CsA. PRCA is a rare complication in patients with CLL and has been attributed to T cell-mediated mechanisms. Six cases with PRCA that developed after fludarabine therapy for CLL have already been reported. Fludarabine therapy may be toxic to Treg, resulting in the loss of self-tolerance. It is important to consider the possibility of PRCA in patients with progressive anemia after fludarabine therapy for CLL.

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A 32-year-old woman with acute myeloid leukemia failed to achieve remission with two courses of induction chemotherapy, and she received cord blood transplantation (CBT) in a non-remission state, using an HLA-matched cord blood (CB) graft after a conditioning regimen of fludarabine (Flu) at 125 mg/m²+ melphalan at 140 mg/m²+ total body irradiation (TBI) at 4 Gy. Chimerism analysis of the bone marrow (BM) cells performed on day 21 after CBT revealed 99% of these cells to be the recipient type. We diagnosed the patient as having graft failure (GF), and then carried out a second CBT using an HLA-matched male CB graft on day 29 after the first CBT. The conditioning regimen (modified ‘one-day’-based regimen) consisted of Flu at 30 mg/m² (3 days) + cyclophosphamide (CY) at 2 g/m² (1 day) + TBI 2 Gy. She achieved neutrophil engraftment on day 18. FISH analysis of BM cells on day 13 showed 96% to be of male origin. She has remained in complete remission for 18 months, to date, since the salvage CBT. This case suggests that salvage CBT following a modified ‘one-day’-based regimen may preserve a strong graft versus leukemia effect.

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