Cancer has been viewed as a heterogeneous population of cells.While the large majority of cells that constituting tumors are differentiated, and eventually stop dividing, only a minority population of cells, termed cancer stem cells, is capable of unlimited self-renewal and multi-differentiation, just like somatic stem cells in normal tissues.Cancer stem cells have been identified in a variety of cancers of the blood, brain, stomach, colon, and pancreas.In this review we present current evidence supporting the cancer stem cell model of tumor progression, and discuss the experimental and therapeutic implications.

Granulocyte colony stimulating factor (G-CSF) plays important roles in treating hematologic malignancies including hematopoietic stem cell transplantation (HCT) and intensive chemotherapy. In the situation of peripheral blood cell transplantation (PBSCT), G-CSF mobilizes hematopoietic stem cells and progenitor cells into peripheral blood and thereby accelerates recovery from neutropenia and thus prevents serious infections after transplantation. In the setting of chemotherapy administration for leukemia and lymphoma, G-CSF can be given to prevent febrile neutropenia (FN) in order to maintain drug intensity and thus improve therapeutic outcomes. Based upon the guidelines abroad and in our country, G-CSF should be used as primary or secondary prophylaxis according to the risk of developing FN during chemotherapy. Patients with acute leukemia who received extremely high-risk chemotherapy benefitted from prophylactic treatment with G-CSF, especially those with acute lymphoblastic leukemia. In treating lymphomas for patients given a regimen with a high risk for FN (>20%), administration of G-CSF as primary prophylaxis is recommended. In addition, administration of primary prophylactic G-CSF is also recommended for patients given a regimen with an intermediate risk for FN (10-20%), if they have risk factors for worsening FN or infection.

Hematopoietic stem cells (HSCs) have played a major role in stem cell biology, providing many conceptual ideas and models. Among them is the concept of the "niche", a special bone-marrow microenvironment that by exchanging cues regulates stem-cell fate. The HSC niche also plays an important role in HSC transplantation. Successful engraftment of donor HSCs depends on myeloablative pretreatment to empty the niche. The concept of the stem-cell niche has now been extended to the generation of organs. We postulated that an empty "organ niche" exists in a developing animal when development of an organ is genetically disabled. This organ niche should be developmentally compensated by blastocyst complementation using wild-type primary stem cells (PSCs). We proved the principle of organogenesis from xenogeneic PSCs in an embryo unable to form a specific organ, demonstrating the generation of functionally normal rat pancreas by injecting rat PSCs into pancreatogenesis-disabled mouse embryos. This principle has held in pigs. When pancreatogenesis-disabled pig embryos underwent complementation with blastomeres from wild-type pig embryos to produce chimeric pigs, the chimeras had normal pancreata and survived to adulthood. Demonstration of the generation of a functional organ from PSCs in pigs is a very important step toward generation of human cells, tissues, and organs from individual patients' own PSCs in large animals.

Human mesenchymal stromal/stem cells (MSCs) show a variety of biological characteristics. The clinical trials database provided by the National Institutes of Health, USA, contains about 400 clinical trials of MSCs for a wide range of therapeutic applications internationally (http://www.clinicaltrials.gov, key words "mesenchymal stem cells", as of April, 2015). Encouraging results from these clinical trials include evidence of efficacy against graft versus host disease (GVHD) in hematopoietic stem cell transplantation. Treatment for and/or prevention of engraftment failure and insufficient hematopoietic recovery have also been explored. Herein, we will address the basic principles of MSCs and the current status of clinical studies using MSCs. Future prospects for MSC-based therapy will also be discussed.

Graft-versus-host disease (GVHD) is an important complication in allogeneic hematopoietic stem cell transplantation. The standard regimen for GVHD prophylaxis in bone marrow transplantation and peripheral blood stem cell transplantation from human leukocyte antigen-matched donors is a combination of a calcineurin inhibitor, such as cyclosporin or tacrolimus, and short-term methotrexate. This regimen is well researched and has been nearly optimized in terms of infusion methods and the target blood concentration. The use of mycophenolate mofetil instead of methotrexate has the advantage of a lower incidence and severity of oropharyngeal mucositis. The addition of anti-thymocyte globulin significantly decreases the incidences of severe acute GVHD and extensive chronic GVHD, but does not lead to a significant improvement in overall survival. The GVHD prophylaxis regimens in cord blood transplantation and HLA-haploidentical donor transplantation have not been standardized. The efficacy of other immunosuppressive drugs, regulatory T lymphocytes, and mesenchymal stem cells are currently under investigation. Establishment of new evidence for GVHD prophylaxis from Japan is expected.

Human immune responses are principally characterized by the human leukocyte antigen (HLA) system, a diverse set of cell surface molecules encoded by the major histocompatibility complex gene cluster on the short arm of chromosome 6. Among various members of the HLA family, the best characterized are the classic highly polymorphic class I and class II molecules that are responsible for antigen presentation to T cells and regulation of NK cell functions. In allogeneic hematopoietic cell transplantation, sophisticated approaches to donor-recipient allele-level matching at 3 class I (HLA-A/B/C) and 3 class II (HLA-DRB1/DQB1/DPB1) loci have been proven to lower the risk of immunologic complications such as graft failure and graft-versus-host disease, and possibly to confer effective graft-versus-malignancy effects. Future areas of research include clarifying the role of relatively non-polymorphic non-classical HLA molecules (HLA-E/F/G, HLA-DM/DO) and polymorphic/non-polymorphic class I-related molecules (MICA, MICB, HFE, MR1, CD1, FcRn) in the immune regulation that follows hematopoietic cell transplantation.

Myeloproliferative neoplasms (MPNs) arise from hematopoietic stem cells (HSCs) with genetic abnormalities in combination with mutations in JAK2, MPL or CALR, which induce autosomal JAK-STAT pathway activation, and mutations in epigenetic regulator genes such as TET2 or DNMT3A. The prognosis of patients with polycythemia vera (PV) or essential thrombocythemia (ET) is relatively good, and the therapeutic goal in cases with PV or ET is to prevent thrombohemorrhagic complications. PV or ET patients at least 60 years of age or with a history of thrombosis are in a high-risk category, and are managed with low dose aspirin and cytoreductive therapy. Phlebotomy to maintain Ht<0.45 is also used to manage PV patients. The median survival for Japanese primary myelofibrosis (MF) patients is 3.9 years. Several factors including age>65 years, Hb<10 g/dl, the presence of constitutional symptoms, and the presence of blasts in blood were identified as being associated with shorter survival in MF patients. Those patients in the high-risk category are candidates for allogenic HSC transplantation (allo-HSCT), which is potentially curative but is also associated with higher therapy-related mortality. High-risk MF patients without indications for allo-HSCT are treated with JAK inhibitors, which can markedly ameliorate constitutional symptoms and splenomegaly, and might thereby lead to a degree of improvement in survival.

Myelodysplastic syndromes (MDS) are myeloid clonal disorders presumably induced by genetic mutations in immature hematopoietic cells. According to the international prognostic scoring system (IPSS or IPSS-R), patients are classified into two groups: lower-risk MDS (LR-MDS) and higher-risk MDS (HR-MDS). A majority of LR-MDS patients manifest refractory cytopenias due to inefficient hematopoiesis, and patients in this group are principally treated with agents stimulating hematopoiesis or differentiation. On the other hand, patients with HR-MDS are at much higher risk of developing leukemia, and thus require prompt hematopoietic stem cell transplantation or chemotherapy. In this section, I will discuss current treatment strategies for MDS in Japan, including future perspectives.

Somatic stem cells self-renew to maintain tissue homeostasis for the lifetime of organisms through tightly controlled proliferation and differentiation. Hematopoietic stem cells (HSCs) are essentially required for hematopoietic homeostasis. Therefore, they not only ensure lifelong replenishment of all blood lineages, but also maintain a constant pool. Cell cycle quiescence is a critical feature contributing to stem cell maintenance. Recent studies have highlighted the importance of bone marrow (BM) microenvironments that regulate HSC functions (HSC niches). In the HSC field, there has been considerable interest and debate regarding whether or not quiescence and proliferation of HSCs is regulated by distinct niches. Previous reports suggest that quiescent HSCs reside near osteoblasts in the BM whereas actively cycling HSCs are found near sinusoids. However, this popular concept has not been supported by rigorous analyses. To gain more insight into the spatial localization of HSCs, we have developed a whole-mount staining technique that allows precise measurements of 3D distances of HSCs from structures and allows computational simulation to define the significance of these interactions. This novel approach has allowed us to uncover two distinct types of vessels associated with quiescent and proliferating HSCs and to underscore the importance of arteriolar vessels for stem cell quiescence. We will discuss the crosstalk between the two hematopoietic and mesenchymal stem cells with a review of the recent literature.

Stem cells activate various metabolic programs and acquire ATP and metabolites to maintain self-renewal and multi-differentiation capacities. Pluripotent stem cells and hematopoietic stem cells have recently been shown to have specific metabolic features different from those of differentiated cells. These metabolic features themselves drive stem cell-specific characteristics. Thus, integrative understandings of metabolic regulation of stem cells are essential for the development of technologies for ex vivo expansion of stem cells, efficient induction of differentiated cells from stem cells and targeted therapies aimed at controlling and eliminating tumor-initiating cells.

Leukemic stem cells (LSCs) were originally identified in acute myeloid leukemia (AML) cases by using xenograft models, as a distinct cell population that can initiate leukemia in immunodeficient mice. Since then, many efforts have been made to clarify the identities of LSCs and other cancer stem cells in various cancer types, to both understand their biology and determine the most suitable targets for anti-cancer therapies. LSCs were identified as existing in the immature CD34+CD38- leukemic population in most AML cases, and these cells were found to share some features with normal hematopoietic stem cells. On the other hand, recent studies have shown that in childhood acute lymphoblastic leukemia (ALL), LSCs exist among B-lineage-committed progenitors expressing CD19. In contrast to AML, in which LSCs generate leukemic cells in a hierarchical order with LSCs at the top, leukemia propagation in childhood ALL is better explained by a stochastic model. In B-precursor ALL, LSCs form via acquisition of additional genetic change(s) in CD19+ B-lineage progenitor cells with self-renewing capacity. These LSCs possess a growth advantage and the capacity to produce progeny with the same ability as the LSCs. Identification of genetic and cellular targets in leukemic transformation is necessary to develop improved anti-cancer therapies.

Hematopoietic stem cells give rise to various blood cell types with diverse functions, although these different cell types harbor essentially identical genome sequences. The basis for this cell type diversity is the establishment of specific gene expression patterns through transcription factor regulation. Transcription factors recognize and bind to specific nucleotide sequences in target genes and recruit chromatin modifiers to alter the epigenetic status of these genes, thereby controlling their expression. Dysregulation of these processes can cause diseases such as leukemia. Due to rapid advances in high-throughput experimental techniques including chromatin immunoprecipitation-sequencing (ChIP-seq) and RNA-seq, the study of transcription factors is now entering a new era. In this review, we update the current knowledge of developmental pathways in myeloid cells, particularly mononuclear phagocytes (i.e., monocytes/macrophages and dendritic cells), and the transcription factors known to be required for their development. We subsequently provide an overview of the cooperative and antagonistic mechanisms by which the myeloid transcription factors regulate their target genes, with an emphasis on chromatin biology.

The prevailing view is that both glutamic (Glu) and gamma-aminobutyric (GABA) acids play a role as an amino acid neurotransmitter released from neurons. However, little attention has been paid to the possible expression and functionality of signaling machineries required for amino acidergic neurotransmission in cells other than central neurons. In line with our first demonstration of the presence of Glu receptors outside the brain, in this review I will outline our recent findings accumulated since then on the physiological and pathological significance of neuronal amino acids as an extracellular signal essential for homeostasis in a variety of phenotypic cells. In undifferentiated neural progenitor cells, for instance, functional expression is seen with different signaling machineries used for glutamatergic and GABAergic neurotransmission in neurons. Moreover, Glu plays a role in mechanisms underlying suppression of proliferation for self-replication in undifferentiated mesenchymal stem cells. There is more accumulating evidence for neuronal amino acids playing a role as an extracellular autocrine or paracrine signal commonly used in different phenotypic cells. Evaluation of drugs currently used could be thus beneficial for the efficient prophylaxis and/or the therapy of a variety of diseases relevant to disturbance of amino acid signaling in diverse organs.

As part of our continuing studies on neurotrophin-mimic active compounds in natural products, we investigated the chemical constituents of the pericarps of Illicium jiadifengpi and the roots of Indonesian ginger Zingiber purpureum, resulting in the isolation of new seco-prezizaane-type sesquiterpenoid 1 and phenylbutenoid dimer 3-4 and two new curcuminoids 5-6. The MeOH extract of I. jiadifengpi was fractionated, leading to the isolation of compound 1. Compound 1 significantly enhanced neurite outgrowth in primary cell cultures of fetal rat cortical neurons. It is noteworthy that compound 1 has potential significantly to promote differentiation of multipotent neural stem cell line (MEB5 cells) into neurons. Additionally, we investigated the MeOH extract of the root of Bangle (Z. purpureum) that exhibited neuritogenesis activity in PC12 cells at 25 μg/mL, resulting in the isolation of neurotrophic phenylbutenoid dimers 3-4 and new compounds 5-6. Compounds 3 and 4 were found not only significantly to induce neurite sprouting of PC12 cells but also to increase the neurite length and number of neurites in primary cultured rat cortical neurons, and also showed protective activity against cell death caused by deprivation of serum. Furthermore, chronic treatment with these compounds enhanced hippocampal neurogenesis in dementia model olfactory bulbectomized (OBX) mice. Compounds 5 and 6 had significant NGF-potentiating effects on PC12 cells whereas compound 5 enhanced prevention of amyloid β (Aβ) 42 aggregation.

Hepatocyte-like cells differentiated from human pluripotent stem cells (such as human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells) are expected to be utilized in drug screening. However, the hepatocyte differentiation efficiency and hepatic functions of hepatocyte-like cells were not sufficient to perform ES/iPS cell-based drug discovery. Therefore, we decided to improve the method of hepatocyte differentiation from human ES/iPS cells. To enhance this hepatocyte differentiation efficiency, hepatocyte-related transcription factors, such as forkhead box protein A2 (FOXA2) and hepatocyte nuclear factor 1 alpha (HNF1α), were overexpressed during the hepatocyte differentiation process. In addition, to enhance the functions of hepatocyte-like cells, these cells were cultured in three dimensional (3D) conditions using a Nanopillar plate. By FOXA2 and HNF1α overexpression, human ES/iPS cells could efficiently (more than 80%) differentiate into albumin-positive hepatocyte-like cells. Various hepatic functions, including albumin secretion and drug metabolism capacities, of the hepatocyte-like cells were significantly enhanced by performing 3D cell culture. These results suggest that the method of hepatocyte differentiation could be improved by using gene transfer and 3D cell culture technologies. We believe that these new hepatocyte-like cells would be useful tools in drug development.