Atsuo Okamura

Role for vitamin D receptor in the neuronal control of the hematopoietic stem cell niche

Hematopoietic stem/progenitor cells (HSPCs) are released from the bone marrow to the circulation by the cytokine, granulocyte colony-stimulating factor, via sympathetic nervous system (SNS)-mediated osteoblast suppression. Because the orientation of HSPCs in their osteoblastic niche is reported to be guided by [Ca(2+)], we speculated on a cooperation between the calcium-regulating hormones and SNS in the regulation of HSPC trafficking. Here, we present the severe impairment of granulocyte colony-stimulating factor-induced osteoblast suppression and subsequent HSPC mobilization in vitamin D receptor (VDR)-deficient mice. In osteoblasts, functional VDR possessing, at least in part, a transcriptional activity, was specifically induced by β2-adrenergic receptor (AR) agonists. While β2-AR agonists transiently increased mRNA expression of Vdr and its downstream gene, Rankl, 1α,25-dihydroxyvitamin-D(3) sustained the β2-AR-induced Rankl expression at high level by stabilizing VDR protein. These data suggest that VDR is essential for durable β2-AR signaling in the stem cell niche. Our study demonstrates not only a novel function of VDR as a critical modulator of HSPC trafficking, but also the presence of a SNS-mediated, bone-remodeling mechanism through VDR. VDR contributes to brain-bone-blood integration in an unanticipated way distinct from other classical calcium-regulating hormones.

Developmental expression of EphB6 in the thymus: lessons from EphB6 knockout mice ☆

A member of the largest family of receptor protein kinases, EphB6, lacks its intrinsic kinase activity, but it is expressed in normal human tissues. To investigate the physiological function of EphB6, we generated EphB6 deficient mice. EphB6(-/-) mice developed normally, revealed no abnormality in general appearance, and were fertile. Although a developmental increase of EphB6 in the fetal thymus was confirmed, T-cell development in various lymphoid organs of EphB6(-/-) mice was comparable to those of EphB6(+/+). Even in fetal thymus organ cultures, any developmental differences of EphB6(-/-) and EphB6(+/+) thymocytes were undetectable. The different binding characteristics to ephrin-Fc proteins between EphB6(-/-) and EphB6(+/+) thymocytes demonstrated that ephrin-B2 is the unique ligand for EphB6 among eight known ephrins. While EphB6 was a dominant receptor that binds to ephrin-B2 in adult thymocytes, fetal ones also expressed another EphB that binds to ephrin-B2. Overlapping expression of the EphB subfamily in the fetal thymus might compensate for the loss of EphB6 during the thymic development.

Methotrexate-associated lymphoproliferative disorders: management by watchful waiting and observation of early lymphocyte recovery after methotrexate withdrawal

No optimum treatment of iatrogenic immunodeficiency-associated lymphoproliferative disorders due to methotrexate in patients with rheumatoid arthritis (MTX-LPD) has yet been established, although MTX withdrawal is known to have a substantial effect on tumor regression. Here, we retrospectively analyzed 20 cases of MTX-LPD. Tumor shrinkage occurred in 18 of 20 cases, but only following MTX withdrawal. This tumor regression ratio was considerably better than in previous reports, and appeared due to longer “watchful waiting.” Lymphocyte recovery at 2 weeks after MTX withdrawal was significantly higher in cases with tumor regression in 1 month than in those without tumor regression (p = 0.001). Median time to maximal efficacy after MTX cessation in cases without chemotherapy was 12 weeks (range 2–76). In conclusion, watchful waiting for a longer period after MTX cessation with observation of early lymphocyte recovery and uninterrupted continuation of other anti-rheumatoid drugs may be an acceptable management plan for MTX-LPD.

The role of transcriptional coactivator TRAP220 in myelomonocytic differentiation

The TRAP220 subunit of the thyroid hormone receptor‐associated polypeptide transcription coactivator complex (TRAP/Mediator complex), mammalian counterpart of the yeast Mediator complex, is proposed to act on a variety of major and specific biological events through physical interactions with nuclear receptors. The vitamin D receptor (VDR) and retinoic acid receptor (RAR), coupled with retinoid X receptor (RXR), are nuclear receptors which have important roles for monopoiesis and granulopoiesis, respectively. In this study, we present the functional role of TRAP220 in nuclear receptor‐mediated monopoiesis and granulopoiesis. The mouse Trap220−/– yolk sac hematopoietic progenitor cells were resistant to 1,25‐dihydroxyvitamin D3‐stimulated differentiation into monocytes/macrophages. Furthermore, flow cytometric analyses showed that HL‐60 cells, human promyelocytic leukemia cell line, wherein TRAP220 was down‐regulated, did not differentiate efficiently into monocytes and granulocytes by stimulation with 1,25‐dihydroxyvitamin D3 and all‐trans retinoic acid, correspondingly. The expression of direct target genes of VDR or RAR, as well as the differentiation marker genes, was low in the knockdown cells. These results indicated a crucial role of TRAP220 in the optimal VDR‐ and RAR‐mediated myelomonocytic differentiation processes in mammalian hematopoiesis.

A biphenotypic transformation of 8p11 myeloproliferative syndrome with CEP1/FGFR1 fusion gene

Abstract:  We describe here the first case of 8p11 myeloproliferative syndrome (EMS) with t(8;9)(p11;q33), who unusually demonstrated B‐lymphoblastic/monoblastic biphenotypic transformation. A 57‐year‐old woman was admitted because of leukocytosis and diagnosed as EMS. Bone marrow was infiltrated with myeloperoxidase (MPO)‐, CD10+, CD19+, CD20+, CD34+, HLA‐DR+ small lymphoblasts and MPO+, CD2+, CD4+, CD13+, CD14+, CD33+, HLA‐DR+ large monoblasts. The karyotype was 46,XX,t(8;9)(p11;q33)[20] and the CEP1/FGFR1 fusion transcript between CEP1 exon 38 and FGFR1 exon 9 was detected. This case clearly indicates that the blastic transformation in EMS with t(8;9) could arise in the stem cells, which differentiate into not only myelomonocytic but also B‐lymphocytic lineages.

The Impact of Early Rehabilitation on the Duration of Hospitalization in Patients After Allogeneic Hematopoietic Stem Cell Transplantation

BACKGROUND We examined the relationship between the improved physical activity by early rehabilitation and the duration of hospitalization among patients after allogeneic hematopoietic stem cell transplantation (allo-HSCT). METHODS Thirteen allo-HSCT patients with myeloablative conditioning regimens (group A) and 13 patients with nonmyeloablative conditioning regimens (group B) were assessed retrospectively in this study. All patients received physical exercise immediately after neutrophil engraftment at the class 10,000 bioclean room (class 10,000). The mean daily steps at class 10,000 were measured as a substitute for the amount of physical activity, and the duration of hospitalization as one of the clinical outcomes. RESULTS The degree of physical activity showed a negative correlation with the duration of hospitalization in group A (r = -.71; P = .0071), regardless of complications such as acute graft-versus-host disease, infections, and cytomegalovirus reactivation. However, there was no significant association in group B (r = .09; P = .77). CONCLUSION The improved physical activity through early rehabilitation may be an independent, favorable prognostic factor for allo-HSCT patients with myeloablative conditioning regimens.

Extended Mycophenolate Mofetil Administration Beyond Day 30 in Allogeneic Hematopoietic Stem Cell Transplantation as Preemptive Therapy for Severe Graft-Versus-Host Disease

To prevent acute graft-versus-host disease (GVHD), mycophenolate mofetil (MMF) combined with calcineurin inhibitors have been used in allogeneic hematopoietic stem cell transplantation (allo-SCT). Previous studies commonly utilize MMF treatment until day 30 after allo-SCT. However, the feasibility of continuous administration after day 30 has not been well evaluated. We retrospectively assessed the safety and efficacy of extended drug administration. Twenty-five patients ceased MMF at day 30 (group A); whereas, 16 patients (group B) received extended regimens depending on individual risk factors for GVHD. No severe adverse events were observed in either group. Although the cumulative incidence (CI) of grade I to IV GVHD at day 100 was comparable between the 2 groups, the CI of grade II to IV GVHD was less among group B (12.5%) compared with group A (42.3%). Extended MMF administration may be safe and beneficial as preemptive therapy to reduce the development of moderate-to-severe acute GVHD.

Inhibition of G1 to S Phase Progression by a Novel Zinc Finger Protein P58TFL at P-bodies

We recently reported the translocation of the immunoglobulin (Ig) light chain κ locus gene with a possible tumor suppressor gene, TFL, in transformed follicular lymphoma. However, the functional significance in cell transformation remains to be elucidated. Here, we first identified two gene products, P58TFL and P36TFL, derived by alternative splicing. The expression was prominent in normal human lymphocytes but defective in some leukemia/lymphoma cell lines. Overexpression of either protein in a mouse pro-B cell line, Ba/F3, and a human leukemia cell line, Jurkat, inhibited G1 to S phase progression through suppression of retinoblastoma protein (Rb) phosphorylation. The dominant gene product, P58TFL, colocalized with mRNA-processing body markers, eukaryotic translation initiation factor 2C and DCP1 decapping-enzyme homolog A, but not with a stress granule maker, T-cell intracellular antigen 1, in the cytoplasm. Taken together with the unique CCCH-type zinc finger motif, the present study suggests that P58TFL could play an important role in the regulation of cell growth through posttranscriptional modification of cell cycle regulators, at least partially, upstream of Rb. (Mol Cancer Res 2009;7(6):880–9)

Use of mycophenolate mofetil in patients received allogeneic hematopoietic stem cell transplantation in Japan

We evaluated the use of mycophenolate mofetil (MMF) after hematopoietic stem cell transplantation (HSCT) in Japan from 1999 to 2008. MMF was administered to 301 patients, including 157 for the prevention of graft-versus-host disease (GVHD), 94 for the treatment of acute GVHD and 50 for the treatment of chronic GVHD. The three most common doses were 500 mg twice daily, 250 mg three times daily and 1,000 mg twice daily, given to 63, 54 and 45 patients, respectively. The incidence of grade II–IV acute GVHD was 30.0% and grade III–IV was 20.0% in the GVHD prevention group. Among treated patients, disappearance or improvement of subjective symptoms occurred in 57.0% of acute GVHD patients and in 52.0% of chronic GVHD patients. With regard to safety, the following major adverse events (grade 3 or more) were recorded: 31 infections, 31 neutropenia, 28 thrombocytopenia, 25 diarrhea and 1 renal disorder. A total of 116 patients developed grade 3 or 4 adverse events, but 79 were successfully treated with supportive treatment. Thus, our findings suggest that MMF is safe and effective for the prevention and treatment of GVHD in patients who have received an allogeneic stem cell transplant.

Deregulation of a possible tumour suppressor gene, ZC3H12D, by translocation of IGK@ in transformed follicular lymphoma with t(2;6)(p12;q25).

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