Yasuhisa Yokoyama

Highly Efficient Ex Vivo Expansion of Human Hematopoietic Stem Cells Using Delta1‐Fc Chimeric Protein

Ex vivo expansion of hematopoietic stem cells (HSCs) has been explored in the fields of stem cell biology, gene therapy, and clinical transplantation. Here, we demonstrate efficient ex vivo expansion of HSCs measured by long‐term severe combined immunodeficient (SCID) repopulating cells (SRCs) from human cord blood CD133‐sorted cells using a soluble form of Delta1. After a 3‐week culture on immobilized Delta1 supplemented with stem cell factor, thrombopoietin, Flt‐3 ligand, interleukin (IL)‐3, and IL‐6/soluble IL‐6 receptor chimeric protein (FP6) in a serum‐ and stromal cell‐free condition, we achieved approximately sixfold expansion of SRCs when evaluated by limiting dilution/transplantation assays. The maintenance of full multipotency and self‐renewal capacity during culture was confirmed by transplantation to nonobese diabetic/SCID/γcnull mice, which showed myeloid, B, T, and natural killer cells as well as CD133+CD34+ cells, and hematopoietic reconstitution in the secondary recipients. Interestingly, the CD133‐sorted cells contained approximately 4.5 times more SRCs than the CD34‐sorted cells. The present study provides a promising method to expand HSCs and encourages future trials on clinical transplantation.

Derivation of functional mature neutrophils from human embryonic stem cells

Human embryonic stem cells (hESCs) proliferate infinitely and are pluripotent. Only a few reports, however, describe specific and efficient methods to induce hESCs to differentiate into mature blood cells. It is important to determine whether and how these cells, once generated, behave similarly with their in vivo-produced counterparts. We developed a method to induce hESCs to differentiate into mature neutrophils. Embryoid bodies were formed with bone morphogenic protein-4, stem cell factor (SCF), Flt-3 ligand (FL), interleukin-6 (IL-6)/IL-6 receptor fusion protein (FP6), and thrombopoietin (TPO). Cells derived from the embryoid bodies were cultured on a layer of irradiated OP9 cells with a combination of SCF, FL, FP6, IL-3, and TPO, which was later changed to granulocyte-colony-stimulating factor. Morphologically mature neutrophils were obtained in approximately 2 weeks with a purity and efficiency sufficient for functional analyses. The population of predominantly mature neutrophils (hESC-Neus) showed superoxide production, phagocytosis, bactericidal activity, and chemotaxis similar to peripheral blood neutrophils from healthy subjects, although there were differences in the surface antigen expression patterns, such as decreased CD16 expression and aberrant CD64 and CD14 expression in hESC-Neus. Thus, this is the first description of a detailed functional analysis of mature hESC-derived neutrophils.

Notch Activation Induces the Generation of Functional NK Cells from Human Cord Blood CD34-Positive Cells Devoid of IL-15

The development of NK cells from hematopoietic stem cells is thought to be dependent on IL-15. In this study, we demonstrate that stimulation of human cord blood CD34+ cells by a Notch ligand, Delta4, along with IL-7, stem cell factor, and Fms-like tyrosine kinase 3 ligand, but no IL-15, in a stroma-free culture induced the generation of cells with characteristics of functional NK cells, including CD56 and CD161 Ag expression, IFN-γ secretion, and cytotoxic activity against K562 and Jurkat cells. Addition of γ-secretase inhibitor and anti-human Notch1 Ab to the culture medium almost completely blocked NK cell emergence. Addition of anti-human IL-15-neutralizing Ab did not affect NK cell development in these culture conditions. The presence of IL-15, however, augmented cytotoxicity and was required for a more mature NK cell phenotype. CD56+ cells generated by culture with IL-15, but without Notch stimulation, were negative for CD7 and cytoplasmic CD3, whereas CD56+ cells generated by culture with both Delta4 and IL-15 were CD7+ and cytoplasmic CD3+ from the beginning and therefore more similar to in vivo human NK cell progenitors. Together, these results suggest that Notch signaling is important for the physiologic development of NK cells at differentiation stages beyond those previously postulated.

Hes1 suppresses acute myeloid leukemia development through FLT3 repression.

In leukemogenesis, Notch signaling can be up and downregulated in a context-dependent manner. The transcription factor hairy and enhancer of split-1 (Hes1) is well-characterized as a downstream target of Notch signaling. Hes1 encodes a basic helix–loop–helix-type protein, and represses target gene expression. Here, we report that deletion of the Hes1 gene in mice promotes acute myeloid leukemia (AML) development induced by the MLL–AF9 fusion protein. We then found that Hes1 directly bound to the promoter region of the FMS-like tyrosine kinase 3 (FLT3) gene and downregulated the promoter activity. FLT3 was consequently upregulated in MLL–AF9-expressing immortalized and leukemia cells with a Hes1- or RBPJ-null background. MLL–AF9-expressing Hes1-null AML cells showed enhanced proliferation and ERK phosphorylation following FLT3 ligand stimulation. FLT3 inhibition efficiently abrogated proliferation of MLL–AF9-induced Hes1-null AML cells. Furthermore, an agonistic anti-Notch2 antibody induced apoptosis of MLL–AF9-induced AML cells in a Hes1-wild type but not a Hes1-null background. We also accessed two independent databases containing messenger RNA (mRNA) expression profiles and found that the expression level of FLT3 mRNA was negatively correlated with those of HES1 in patient AML samples. These observations demonstrate that Hes1 mediates tumor suppressive roles of Notch signaling in AML development, probably by downregulating FLT3 expression.

Disease-specific mutations in mature lymphoid neoplasms: recent advances.

Mature lymphoid neoplasms (MLN) are clinically and pathologically more complex than precursor lymphoid neoplasms. Until recently, molecular characterization of MLN was mainly based on cytogenetics/fluorescence in situ hybridization, allele copy number, and mRNA expression, approaches that yielded scanty gene mutation information. Use of massive parallel sequencing technologies has changed this outcome, and now many gene mutations have been discovered. Some of these are considerably frequent in, and substantially specific to, distinct MLN subtypes, and occur at single or several hotspots. They include the V600E BRAF mutation in hairy cell leukemia, the L265P MYD88 mutation in Waldenström macroglobulinemia, the G17V RHOA mutation in angioimmunoblastic T‐cell lymphoma and peripheral T‐cell lymphoma, not otherwise specified, and the Y640F//D661Y/V/H/I//N647I STAT3 mutations in T‐cell large granular lymphocytic leukemia. Detecting these mutations is highly valuable in diagnosing MLN subtypes. Defining these mutations also sheds light on the molecular pathogenesis of MLN, furthering development of molecular targeting therapies. In this review, we focus on the disease‐specific gene mutations in MLN discovered by recent massive sequencing technologies.

Detection of the G17V RHOA mutation in angioimmunoblastic T-cell lymphoma and related lymphomas using quantitative allele-specific PCR.

Angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) are subtypes of T-cell lymphoma. Due to low tumor cell content and substantial reactive cell infiltration, these lymphomas are sometimes mistaken for other types of lymphomas or even non-neoplastic diseases. In addition, a significant proportion of PTCL-NOS cases reportedly exhibit features of AITL (AITL-like PTCL-NOS). Thus disagreement is common in distinguishing between AITL and PTCL-NOS. Using whole-exome and subsequent targeted sequencing, we recently identified G17V RHOA mutations in 60–70% of AITL and AITL-like PTCL-NOS cases but not in other hematologic cancers, including other T-cell malignancies. Here, we establish a sensitive detection method for the G17V RHOA mutation using a quantitative allele-specific polymerase chain reaction (qAS-PCR) assay. Mutated allele frequencies deduced from this approach were highly correlated with those determined by deep sequencing. This method could serve as a novel diagnostic tool for 60–70% of AITL and AITL-like PTCL-NOS.

Clinical usefulness of WT1 mRNA expression in bone marrow detected by a new WT1 mRNA assay kit for monitoring acute myeloid leukemia: a comparison with expression of WT1 mRNA in peripheral blood.

We have previously shown the clinical usefulness of Wilms’ tumor 1 gene (WT1) mRNA expression in peripheral blood (PB) as a minimal residual disease (MRD) monitoring marker in 191 acute myeloid leukemia (AML) patients using the WT1 mRNA assay kit “Otsuka” (Otsuka Pharmaceutical Co., Ltd.; “former kit”). In contrast, the usefulness of WT1 mRNA expression in bone marrow (BM) has been investigated in only a limited number of subjects using former kit. Following that previous study, a next-generation kit, WT1 mRNA assay kit II “Otsuka” (Otsuka Pharmaceutical Co., Ltd.; “new kit”) has been newly developed. In the present study, we aimed to evaluate the performance of the new kit and to investigate the clinical usefulness of WT1 mRNA expression in BM. The PB and BM were collected on the same day from 164 blood disease patients, including 118 AML patients. WT1 mRNA expression was determined using the new and former kits and the values obtained were compared. The performance of new kit was shown to be equivalent to that of former kit. As reported in PB, WT1 mRNA expression in BM was found to be a useful marker for monitoring disease status as well as for a diagnosis of early stage relapse in AML patients.

Early Pathologic Findings of Bronchiolitis Obliterans after Allogeneic Hematopoietic Stem Cell Transplantation: A Proposal from a Case

Bronchiolitis obliterans (BO) is one of the serious, noninfectious pulmonary complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Early diagnosis of BO is usually difficult because patients are often asymptomatic at an initial stage of the disease and pathologic findings are available mostly at the late stages. Therefore, the diagnosis of the disease is based on the pulmonary function test using the National Institute of Health consensus criteria. Here, we report a case of slowly progressive BO. A biopsy specimen at an early stage demonstrated alveolar destruction with lymphocyte infiltration in bronchial walls and mild narrowing of bronchioles without fibrosis, those were strongly indicative of initial pathologic changes of BO. Definitive BO followed, which was proven by both clinical course and autopsy. While alloreactive lymphocytes associated with chronic graft-versus-host disease are believed to initiate BO, we present a rare case that directly implies such a scenario.

Prognosis Factors in Japanese Elderly Patients with Primary Central Nervous System Lymphoma Treated with a Nonradiation, Intermediate-Dose Methotrexate-Containing Regimen

Background: Nearly half of all patients with primary central nervous system lymphoma (PCNSL) are known to be aged over 60 years. However, clinical factors affecting treatment outcomes in elderly patients are understudied. Methods: We analyzed 38 patients with PCNSL older than 60 years. All patients were treated with a nonradiation, intermediate-dose methotrexate-containing regimen between March 2005 and May 2013 at the University of Tsukuba Hospital. Results: The 3-year overall survival and progression-free survival rates were 56.2% (95% confidence interval (CI) 36.2-76.2%) and 29.8% (95% CI 9-50.6%), respectively, with a median follow-up of 36.5 months. We found that an age > 75 years, a Karnofsky performance score < 70, altered mentation, and a creatinine clearance (CrCl) > 90 ml/min were significant (p < 0.05) factors associated with a worse survival, by univariate analysis. Multivariate analysis revealed that CrCl (p < 0.05; hazard ratio (HR) = 3.39; 95% CI 1.08-10.68) and altered mentation (p < 0.05; HR = 6.27; 95%CI 1.37-28.83) were independent significant association factors. The most frequent adverse event was myelosuppression, with grade 3-4 hematologic toxicities in 28 patients. No delayed neurotoxicities were observed. Conclusion: More intensive therapy may be introduced in selected patients with poor prognosis factors to improve outcomes.

Complete Remission in Systemic Skin Interdigitating Dendritic Cell Sarcoma after ABVD Chemotherapy

Interdigitating dendritic cell sarcoma (IDCS) is a rare and aggressive neoplasm that is thought to arise from dendritic cells. This disease usually involves the lymph nodes and, rarely, extra-nodal sites. We report a 62-year-old man presenting skin nodules in the head, body, and extremities, as well as bone marrow involvement. Morphologic analysis of a biopsied specimen from the skin lesion was consistent with IDCS. Immunohistochemical staining demonstrated that the tumor cells were positive for IDCS-associated antigens such as CD4, CD45, CD68 (KP-1), and S-100 protein. Complete remission was achieved by treatment with 6 cycles of ABVD (adriamycin, bleomycin, vinblastine, and dacarbazine) chemotherapy. Although the optimal treatment of IDSC remains unknown, the experience in the current case supports the notion that ABVD chemotherapy may be effective for IDCS, and further extends this idea to rare patients presenting multiple skin lesions.