Akihisa Sawada

Polycomb Group Gene rae28 Is Required for Sustaining Activity of Hematopoietic Stem Cells

The rae28 gene (rae28), also designated as mph1, is a mammalian ortholog of the Drosophila polyhomeotic gene, a member of Polycomb group genes (PcG). rae28 constitutes PcG complex 1 for maintaining transcriptional states which have been once initiated, presumably through modulation of the chromatin structure. Hematopoietic activity was impaired in the fetal liver of rae28-deficient animals (rae28 −/−), as demonstrated by progressive reduction of hematopoietic progenitors of multilineages and poor expansion of colony forming units in spleen (CFU-S12) during embryonic development. An in vitro long-term culture-initiating cell assay suggested a reduction in hematopoietic stem cells (HSCs), which was confirmed in vivo by reconstitution experiments in lethally irradiated congenic recipient mice. The competitive repopulating units (CRUs) reflect HSCs supporting multilineage blood-cell production. CRUs were generated, whereas the number of CRUs was reduced by a factor of 20 in the rae28 − / − fetal liver. We also performed serial transplantation experiments to semiquantitatively measure self-renewal activity of CRUs in vivo. Self-renewal activity of CRUs was 15-fold decreased in rae28 − / −. Thus the compromised HSCs were presumed to reduce hematopoietic activity in the rae28 − / − fetal liver. This is the first report to suggest that rae28 has a crucial role in sustaining the activity of HSCs to maintain hematopoiesis.

A congenital mutation of the novel gene LRRC8 causes agammaglobulinemia in humans.

A girl with congenital agammaglobulinemia and minor facial anomalies lacked B cells in peripheral blood: karyotypic analysis of white blood cells showed balanced translocation, t(9;20)(q33.2;q12). In the current study, we isolated a novel gene, leucine-rich repeat-containing 8 (LRRC8), at the translocation site on chromosome 9. It has four transmembrane helices with one isolated and eight sequentially located leucine-rich repeats (LRRs) and constitutes a new protein family. It is expressed on T cells as well as on B-lineage cells. Translocation truncates the LRRC8 gene, resulting in deletion of the eighth, ninth, and half of the seventh LRR domains located close to the C-terminal. The truncated form of the LRRC8 gene is transcribed with sequences from the noncoding region adjacent to the truncated seventh LRR. Protein products derived from the truncated gene are coexpressed on white blood cells with the intact LRRC8 protein from the untranslocated allele. Transplantation experiments with murine bone marrow cells that were forced to express the truncated LRRC8 show that expression of the truncated protein inhibited B cell development. These results indicate that LRRC8 is responsible for the B cell deficiency in this patient and is required for B cell development.

Hematopoietic stem cell transplantation for familial hemophagocytic lymphohistiocytosis and Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis in Japan.

Post‐transplant outcomes of hemophagocytic lymphohistiocytosis (HLH) patients were analyzed in Japan where Epstein–Barr virus (EBV)‐associated severe forms are problematic.

Lack of the Polycomb-group gene rae28 causes maturation arrest at the early B-cell developmental stage

The rae28 gene (rae28) is a murine homologue of the Drosophila polyhomeotic gene, which is a member of the Polycomb-group genes. In this study, we examined the role of rae28 in lymphocyte development. Because homozygous rae28-deficient (rae28-/-) mice died in the perinatal period, we examined lymphocyte development by generating chimeric mice reconstituted with green fluorescence protein-labeled mutant fetal liver cells as well as in in vitro culture systems. We further examined RAE28 expression by reverse transcriptase polymerase chain reaction assay in human leukemic cells with B-lineage acute lymphoblastic leukemia (ALL). Severe B-cell maturation arrest was observed in rae28-/- between pro- and pre-B lymphocyte stages. B-cell development was also delayed in heterozygous neonates. Furthermore, interleukin-7-dependent colony-forming ability was impaired not only in homozygous lymphocytes but also in heterozygotes. Its human homologue, RAE28, is located on chromosome 12p13, which frequently is associated with chromosomal abnormalities and loss of heterozygosity in patients with hematologic malignancies. To determine whether a link exists between RAE28 and leukemia, we examined RAE28 expression in leukemic cells from pediatric patients with B-lineage ALL. RAE28 expression was not detected in four B-cell precursor ALL cases of a total of 43 examined, although RAE28 is normally expressed constitutively during the process of B-cell maturation as assessed in isolated cell populations. rae28 plays an important role in the early B-cell developmental stage in a gene dosage-dependent manner. Furthermore, the human RAE28 locus may provide a candidate gene causing the molecular pathogenesis of childhood B-cell precursor ALL.

Defective long-term repopulating ability in hematopoietic stem cells lacking the Polycomb-group gene rae28

Abstract:  The rae28 gene (rae28) is a member of a Polycomb‐group (PcG) complex 1, which is known to help maintain transcription states once these have been initiated, by generating heritable higher‐order chromatin structures. In this study, we examined the capacity of rae28‐deficient (rae28−/−) hematopoietic stem cells (HSCs) to generate long‐term marrow reconstitution. rae28−/− fetal liver cells containing 20 competitive repopulation units (CRUs) were able to support the survival of lethally irradiated congenic mice for as long as 6 months. The marrow reconstituted with the rae28−/− cells, however, could not increase HSCs efficiently. This was evidenced by its inability to reconstitute marrow in serial transplantation experiments, as well as by the reduction in HSC‐enriched Lin− c‐kit+ Sca‐1high+ subpopulation in the bone marrow cells. Moreover, the reconstituted marrow produced less than half of the peripheral blood cells in each of the lineages examined. We also monitored the mean stem cell activity (MAS). MAS of rae28−/− CRUs was progressively reduced after transplantation, and after 12 months it was reduced to one‐tenth of that of the wild‐type. These in vivo results clearly indicate that rae28 is indispensable for the long‐term repopulating ability of HSCs. We further referred to the plausible mechanisms underlying defective long‐term repopulating ability of rae28‐deficient HSCs and argued for its involvement in maintenance of cell proliferation capability as well as that in self‐renewal ability.

Tacrolimus-related encephalopathy following allogeneic stem cell transplantation in children.

Tacrolimus is a potent immunosuppressive drug widely used to prevent and treat graft-versus-host disease (GVHD) in stem cell transplantation (SCT). Among 49 patients receiving tacrolimus who underwent SCT from January 2000 to July 2003, 10 patients (20%) developed encephalopathy. The commonly observed symptoms were convulsions and drowsiness, and most patients complained of signal symptoms such as headache, nausea, and cortical blindness before onset. The most common abnormality on neuroimages was high-intensity lesions in white matter on magnetic resonance imaging T2-weighted or fluid-attenuated inversion recovery images. At onset, all patients were receiving treatment for acute GVHD (grade II/III) or extensive chronic GVHD and demonstrated an abrupt increase in blood pressure from baseline levels. The serum tacrolimus concentration was generally within acceptable levels at onset. Symptoms gradually improved in all patients when the blood pressure was lowered with antihypertensive medication, regardless of continued tacrolimus administration following a short-term suspension. The pathogenesis of tacrolimus-related encephalopathy is multifactorial, although refractory GVHD and a sudden increase in blood pressure seem to be major predisposing factors. Because the withdrawal of tacrolimus or switching to less potent anti-GVHD agents usually worsens the GVHD, the administration of tacrolimus should be managed by closely monitoring serum levels and controlling blood pressure.

Reduced-intensity conditioning in unrelated donor cord blood transplantation for familial hemophagocytic lymphohistiocytosis†

Familial hemophagocytic lymphohistiocytosis (FHL) is a disorder of immune homeostasis characterized by fever, cytopenias, hepatosplenomegaly, and coagulopathy. We studied the outcomes of 13 FHL patients who underwent the first unrelated cord blood transplantation (UCBT) after non‐myeloablative conditionings. The major regimen consisted of fludarabine (FLU; n = 12)+melphalan (MEL; n = 11)±low‐dose total body irradiation (TBI 2‐4 Gy; n = 6). The median age at presentation and period to UCBT were 6 and 5 months, respectively. Central nervous system (CNS) disease developed in one infant at diagnosis, and in two others until UCBT. HLH activity was controlled in all but one at the time of UCBT. Ten patients had early engraftment on median day 21 with no grade >2 treatment‐related toxicity and two controllable grade >2 acute GVHD. Two patients with early rejection successfully underwent subsequent UCBT after myeloablative conditioning. Two others had late graft failure following mixed donor chimerism. Two deaths occurred from HLH; early liver failure and late CNS disease. Of 11 FLU+MEL‐conditioned patients, the frequency of disease‐free complete engraftment was higher for MEL (≥120 mg/m2)+TBI, or high‐dose MEL (180 mg/m2) than for others (83% vs. 25%, p = 0.036). The FLU+MEL‐based non‐myeloablative regimen was acceptable for FHL infants undergoing UCBT, although further studies will be needed for confirmation. Am. J. Hematol. 87:637–639, 2012.

Cytotoxic Chemotherapy Successfully Induces Durable Complete Remission in 2 Patients with Mosquito Allergy Resulting from Epstein-Barr Virus-Associated T-/Natural Killer Cell Lymphoproliferative Disease

Recent findings indicate that Epstein-Barr virus (EBV)-infected T-/natural killer (NK) cells play an important role in the pathogenesis of mosquito allergy, and most patients with mosquito allergy die early in life if not properly treated. Over the last 7 years, we have been using combination chemotherapy and allogeneic stem cell transplantation for the treatment of EBV-associated T-/NK cell lymphoproliferative disease (LPD) in which chronic active EBV infection and mosquito allergy were included. As of this writing, we have successfully treated 2 patients with mosquito allergy with chemotherapy in which EBV-infected T-/NK cells were eradicated. The findings suggest the possible role of chemotherapy in the treatment of EBV-associated T-/NK cell LPD.

Feasibility of HLA-Haploidentical Hematopoietic Stem Cell Transplantation With Post-Transplantation Cyclophosphamide for Advanced Pediatric Malignancies

Background. Patients with advanced malignancies in non-complete remission (CR) have a dismal prognosis after HLA-matched hematopoietic stem cell transplantation (HSCT). T-cell-replete HLA-haploidentical HSCT has remarkable anti-leukemia/tumor effects on these patients, but also a high risk of severe/extensive graft-versus-host disease (GHVD). Post-transplantation cyclophosphamide (PTCY) is regarded as a GVHD-specific immunosuppressant in adults, but its feasibility is unknown in children. Methods. We performed a prospective feasibility study of PTCY at 50 mg/kg on day 3 for children with advanced leukemias or malignant solid tumors: refractory to chemotherapy or relapsed after conventional allogeneic HSCT. Conditioning consisted of fludarabine (180 mg/m2) and melphalan (140–210 mg/m2). Results. Long-term engraftments were achieved in 11 patients (73.3%) after bone marrow transplantation (BMT, n = 13) or peripheral blood (PB) stem cell transplantation (n = 2). The incidence of severe acute GHVD was 25.0% and that of extensive chronic GVHD 0.0% after evaluable BMT. CR was achieved in 6/15 and partial response in 4/15 as the best response. Finally, 11/15 experienced disease progression/relapse, 2/15 suffered treatment-related mortality without evidence of disease, and 2/15 are alive in continuous CR. Conclusions. PTCY is feasible in children; however, for a better outcome in such patients with advanced malignancies, some modifications are anticipated.

Severe persistent bone marrow failure following therapy with 2-chlorodeoxyadenosine for relapsing juvenile xanthogranuloma of the brain†

2‐Chlorodeoxyadenosine (2‐CdA) has been successfully used in children to treat refractory Langerhans cell histiocytosis and juvenile xanthogranuloma (JXG) as salvage therapy. Although 2‐CdA is generally well‐tolerated, with temporary myelosuppression as the primary dose‐limiting toxicity, prolonged myelosuppressive, and immunosuppressive effects have been reported. We describe an adolescent patient with refractory multiple central nervous system JXG, with the lesion size markedly reduced after treatment with 2‐CdA. However, severe transfusion‐dependent bone marrow failure developed after five courses of 2‐CdA. He underwent successful bone marrow transplantation from his HLA compatible sister with reduced intensity conditioning. Pediatr Blood Cancer 2012; 58: 300–302.