Muse cells are non-tumorigenic reparative endogenous stem cells identified by SSEA-3+. They are pluripotent and are stably mobilized from the bone marrow to the peripheral blood and distribute to organ connective tissue, where they contribute to daily minute repair of damaged/lost cells by spontaneous differentiation into tissue-constituent cells. Muse cells specifically home to damaged site to repair the tissue by simultaneous differentiation into multiple tissue-constituent cells. When the number of endogenous Muse cells is not sufficient, administration of exogenous Muse cells delivers robust functional recovery. Muse cells do not need to be "induced" or genetically manipulated. Intravenous drip is the main method of administration, making surgical operation unnecessary. Because Muse cells have an immunomodulatory system similar to the placenta, donor-derived Muse cells can be directly administered to patients without HLA-matching or immunosuppression therapy. Allogeneic Muse cells remain in the host tissue as differentiated cells for more than half a year. Clinical trials for the treatment of myocardial infarction, stroke and epidermolysis bullosa with intravenous injection of donor-derived Muse cells are currently conducted by the Life Science Institute Inc. Muse cells may safely provide clinically relevant effects compatible with the 'body's natural repair systems' by a simple cost-effective strategy.

Parkinson's disease (PD), a common neurodegenerative disorder, is characterized by selective degeneration of dopaminergic neurons in the substantia nigra. There is no effective treatment to delay or halt the progression of PD. The establishment of disease models, based on human biology, is therefore important for developing effective disease-modifying therapies. The recent progress of human induced pluripotent stem cell-associated technologies provides an opportunity to understand disease etiology, discover new drugs, and develop novel therapeutic interventions.

Current research on stem cells and regenerative medicine indicates new perspectives on the relationship between differentiation and gene information. Induced pluripotent stem (iPS) cells need the artificial gene expression of the somatic cell, which is related to initialization. Paradoxically, that means that cell differentiation depends on almost all the gene information stored precisely in the nucleus of a somatic cell, plus the transformation of gene expression. Our research team tried to identify the culture conditions in the transdifferentiation of human leiomyoma cells, closely similar to the early embryonal stage, composed of various factors (hypoxia, non-serum, and regulation of cell adhesion molecules such as Wnt/β-catenin signaling). As a result, inhibition of Wnt/β-catenin signaling under serum starvation and hypoxia induces adipocytic transdifferentiation in human leiomyoma cells. Here we explain this unique culture system, referring to the components of intracellular mechanisms and the extracellular microenvironment in embryo development.

Recent progress in whole genome sequencing has identified recurrent somatic mutations in the additional sex combs like 1 (ASXL1) gene in a variety of hematological disorders and even in premalignant conditions. However, the molecular mechanisms regarding the contribution of ASXL1 mutation to the pathogenesis of premalignant conditions remain largely unelucidated. Thus, we investigated the biological effects of mutant Asxl1 using newly-generated knock-in (KI) mice. Heterozygous mutant KI mice developed phenotypes resembling human low-risk myelodysplastic syndromes (MDS), and some of them developed an MDS/myeloproliferative neoplasm-like disease after a long latency. The H2AK119ub1 level around the promoter region of p16Ink4a was significantly decreased in KI hematopoietic stem cells (HSCs), suggesting perturbation of Bmi1-driven H2AK119ub1 histone modification by mutant Asxl1. The mutant Asxl1 failed to interact with Bmi1, although wild type ASXL1 protein did not. When p16Ink4a expression was depleted in Asxl1 KI mice, the HSC pool was restored, and apoptosis was ameliorated in HSCs. These findings demonstrate that the loss of protein interaction between mutant Asxl1 and Bmi1 affected the activity of Prc1. The subsequent derepression of p16Ink4a by aberrant histone ubiquitination could induce cellular senescence, resulting in low-risk MDS-like phenotypes in heterozygous Asxl1 KI mice.

Genetic abnormalities of acute myeloid leukemia (AML) include chromosomal translocations and gene mutations. Commonly observed chromosomal abnormalities in AML are t (8;21), t (15;17), inv (16), and 11q23-related translocations. These aberrations produce RUNX1-RUNX1T1, PML-RARA, CBF-MYH11, and MLL-fusion genes, respectively, which promote leukemic stem cell formation by interfering with hematopoietic differentiation and enhancing the self-renewal capacity of hematopoietic cells. Gene mutations recurrently occur in transcription factors, signaling molecules, tumor suppressor genes, epigenetic regulators, RNA splicing factors, and cohesion complexes, with FLT3, NPM1, and DNMT3A being the most frequently mutated genes in AML. Recent studies disclosed the biological function of mutated genes and their correlation with prognosis. Based on these findings, development of novel therapeutic drugs targeting mutated genes or dysregulated genetic pathways is underway.

Immune checkpoint inhibitors(ICIs)have provided great success in cancer treatment field, and immunotherapies using ICIs have become standard therapy for several cancers. Cancer stem-like cells(CSCs)are defined by their higher tumorigenicity and resistance to chemotherapy and radiotherapy, thus they are supposed to be responsible for recurrence and distant metastasis. Therefore, control of CSCs is a key factor to improve patients' prognosis. In this review article, we summarize the expression of PD-L1, a molecular target of ICIs, in CSCs, and discuss the possibility of CSC-targeting immunotherapy using ICIs.

Hematopoietic stem cells (HSCs) reside at the top of the differentiation hierarchy and differentiate into multiple hematopoietic cell lineages via a finely-tuned process. HSCs have been shown to locate in a specific microenvironment (niche) that integrates HSC function, including self-renewal, and differentiation. Accumulating evidence has revealed that various types of cells in and around the bone marrow participate in HSC function regulation as niche-comprising cells. Furthermore, recent studies have identified the stromal cells closely associated with bone marrow vasculatures as HSC niche components. The remarkable advances in experimental technologies have enabled the identification of functional differences among distinct niche cell types in the bone marrow. In this article, we review recent evidence regarding the HSC niche by focusing on the cell types associated with bone marrow vasculatures and discuss future research directions.

Differentiation of hematopoietic stem/progenitor cells should be tightly regulated depending on the environmental changes to maintain homeostasis. For example, erythropoiesis repression and myelopoiesis induction are widely recognized as infectious/inflammatory conditions. Transcription factors are expected to play significant roles in achieving such alterations. However, the precise mechanism by which the differentiation trajectory shift is controlled under environmental changes has not fully been elucidated. In this study, we showed that Bach transcription factors organize the erythro-myeloid differentiation in hematopoietic stem/progenitor cells in response to the environmental changes. Under the steady state, Bach transcription factors support erythroid differentiation and repress myeloid differentiation by regulating the expression of their target genes. In contrast, the functions of Bach transcription factors were repressed, which induced myelopoiesis and repressed erythropoiesis, under emergency conditions, such as infection/inflammation. Competitive roles of Bach transcription factors and C/EBP, the key regulator of myelopoiesis, might be important for tuning erythro-myeloid differentiation trajectory and its shift in response to infection/inflammation. Disfunction of Bach transcription factors was considered to be related to anemia in chronic inflammation and myelodysplastic syndromes. In addition, considering previous findings, Bach2 might possess important roles in the conditioning of the hematopoietic system for subsequent emergency conditions.

Acquired aplastic anemia (AA) is a hematopoietic disorder caused by an immunologic attack on hematopoietic stem cells (HSCs). The presence of cells with a paroxysmal nocturnal hemoglobinuria (PNH) phenotype or with copy-number neutral loss of heterozygosity of chromosome 6p (6pLOH) suggests an immune-mediated pathophysiology underlying AA. Recently, genomic studies have revealed clonal hematopoiesis by HSCs with altered genes. PIGA, DNMT3A, ASXL1, BCOR, 6pLOH, and HLA class I allele mutations are common in patients with AA. The genomic landscape of AA is distinct from that of the myelodysplastic syndrome or age-related clonal hematopoiesis. This suggests that escape from an autoimmune attack is strongly associated with clonal hematopoiesis in AA. Eltrombopag (EPAG), a thrombopoietin receptor agonist, has recently emerged as a novel therapeutic agent for AA. Further studies are needed to clarify whether EPAG induces clonal expansion of these clones.

Here, we report the case of a 9-year-old girl with acute myeloid leukemia (AML) developed from systemic mastocytosis (SM). She experienced bladder and rectal disturbance due to an extramedullary nodule in the paraspinal region of the sacrum. Cytogenetic and genetic analyses of leukemic cells revealed the KIT D816Y mutation besides t (8;21) (q22:q22) /RUNX1-RUNX1T1. Despite receiving proton beam therapy after conventional chemotherapy, the patient relapsed after 2 months. As SM-AML with the KIT D816 mutation in adults exhibits a poor prognosis, hematopoietic stem cell transplantation is recommended. Owing to a few reports of SM-AML in children, the standard therapy for pediatric cases has not been established to date. Based on our experience and the related literature, the prognosis of childhood SM-AML could be as poor as in adults. Hence, further investigation, including mutational analyses of the KIT gene, is warranted to establish a risk-oriented strategy for managing childhood SM-AML.

The mesenchymal stem cell (MSC) is a type of tissue stem cell. In clinical studies, cultured MSCs have shown important therapeutic effects on diseases via both the reduction of neurological defects and the regulation of immune responses. However, in vivo MSC localization, function, and properties are poorly understood; therefore, the molecular understanding of MSC hierarchy is less advanced compared to hematopoietic stem cell hierarchy. Runt-related transcription factor 2 (Runx2) is an essential transcriptional regulator of osteoblast differentiation from MSCs. Runx2 deficiency in Paired-related homeobox 1 (Prrx1)-derived cells (Runx2Prrx1-/- mice) results in defective intramembranous ossification. Double-positive cells for Prrx1-GFP, and stem cell antigen-1 (Sca1) (Prrx1+Sca1+ cells) in the calvaria, express Runx2 at lower levels, and are more homogeneous and primitive compared with Prrx1+Sca1- cells. Our results suggest that osteoblast differentiation in vivo may begin at the Prrx1+Sca1+ MSC stage, with sequential progression to Prrx1+Sca1- cells, followed by Osterix+Prrx1-Sca1- osteoblast precursors, which eventually form mature α1(I)-collagen+ osteoblasts. This research will enable us to better understand the in vivo molecular biology features of MSCs, leading to their therapeutic applications for tissue repair and regeneration.

In most mammalian species, adult neurogenesis appears to occur only in the olfactory bulb and hippocampal dentate gyrus, where neural stem/progenitor cells exist to create new neurons. The discovery of multi-potential neural stem/progenitor cells (NPCs) in the adult brain has precipitated a novel therapeutic strategy for harnessing these endogenous cells to aid in recovery from neurodegenerative disorders. During neurodegeneration, a plethora of endogenous factors, including cytokines, chemokines, neurotransmitters, blood-derived factors, and reactive oxygen species, are released by the activation of resident microglia, astrocytes, and infiltrating peripheral macrophages. It is interesting that these endogenous factors affect the proliferation, migration, differentiation, and survival of newly generated cells involved in the incorporation of newly generated neurons into the brain's circuitry. The unique profile of these endogenous factors can vary the degree of neuroregeneration after neurodegeneration. We show that adult neurogenesis-activating signals are regulated by endogenous factors produced during neurodegeneration.

Neurons differentiated from neural stem cells mature to form a neuronal network. Neuronal maturation enables neurotransmission that regulates brain function. Therefore, abnormal neuronal differentiation causes dysfunction in neurotransmission, and is involved in the onset of various neuropsychiatric disorders. Most of the drugs currently available for the treatment of neuropsychiatric disorders act on membrane receptors and reuptake transporters of neurotransmitters, and control neurotransmission. These membrane proteins have a high affinity for a specific neurotransmitter, and are highly expressed in synapses. By contrast, xenobiotic transporters have a relatively lower affinity for neurotransmitters, but widely recognize various organic compounds, and are also expressed in brain neural cells. It has remained largely unknown why such xenobiotic transporters are expressed in neural cells that play a key role in neurotransmission. We have therefore attempted to clarify the physiological roles of organic cation transporters (OCTs) in neural stem cells in order to obtain new insight into the treatment of neuropsychiatric disorders. The carnitine/organic cation transporter OCTN1/SLC22A4 is expressed at much higher levels in neural stem cells compared with other OCTs, and promotes their differentiation into neurons through the uptake of the food-derived hydrophilic antioxidant ergothioneine after oral administration. In this review, we introduce current topics on the physiological/pathophysiological roles of OCTs in neural stem cells, and discuss their possible application to the treatment of neuropsychiatric disorders.

Langerhans cell sarcoma (LCS) is a rare neoplastic proliferation of Langerhans cells with a poor prognosis. Owing to its rarity, standard treatment for LCS has not been established to date. Here, we report a case of LCS occurring in multiple lymph nodes in the right cervix in which remission is maintained by autologous hematopoietic stem cell transplantation (auto-HSCT) after surgical resection. A 58-year-old male presented with enlarged right submandibular lymph nodes. Positron-emission tomography/computed tomography (PET/CT) revealed multiple lymphadenopathies in his right cervix. We performed a lymph node biopsy, and he was diagnosed with LCS. We selected the CHOP regimen as the first-line chemotherapy; however, rapid disease progression was observed soon after the first cycle of the therapy. The neck dissection was performed on day 16 of the CHOP therapy. As the residual tumor was suspected, we started the second-line chemotherapy with a combination of etoposide, cisplatin, ifosfamide, and gemcitabine; complete remission was confirmed by PET/CT. Subsequently, the patient was administered high-dose chemotherapy with auto-HSCT. After 2 years of auto-HSCT, complete remission has been maintained. Although there is no report of auto-HSCT for LCS, it could be an effective therapeutic tool for the disease.

Failure of autologous peripheral blood stem cell collection (PBSCH) can affect the treatment modality for patients with hematological malignancies. The clinical efficacy of plerixafor in PBSCH was analyzed in our institution. The medical records of 61 patients were retrospectively reviewed. The use of plerixafor was determined according to the CD34+ cell count in the peripheral blood (PB CD34+) on day 4 of G-CSF administration and patients' backgrounds. A total of 47 patients received G-CSF plus plerixafor: 31 with multiple myeloma, 8 with AL amyloidosis or POEMS syndrome, and 8 with non-Hodgkin lymphoma. The median fold increase in PB CD34+ following the first dose of plerixafor was 7.18 times. The median number of collected CD34+ cells on day 5 was 4.1×106/kg and 5.3×106/kg in total. Among the 47 patients, 44 (93.6%) yielded the minimum required cell collection of 2.0×106/kg within an average of 1.3 days. Plerixafor enables rapid and efficient mobilization, and sufficient numbers of CD34+ cells were successfully collected.

Human hepatocytes possess a wider range of phase I and II drug-metabolizing enzyme activities than other liver tissue-derived products, such as human liver microsomes. Thus, hepatocytes may be useful for predicting the in vivo metabolic fate of new drugs of abuse in humans. Recently, new types of human hepatocytes have been made commercially available for use in drug metabolism studies, such as a liver tumor-derived cell line (HepaRG), and a human induced pluripotent stem cell-derived hepatocyte (h-iPS-HEP). In our laboratory, HepaRG has been used to elucidate the metabolic pathways of XLR-11, a synthetic cannabinoid, and its thermal degradant. In addition, the potential of h-iPS-HEP to metabolize drugs was assessed using fentanyl as a model drug, and indeed, h-iPS-HEP exhibited a pattern for fentanyl metabolite formation similar to that observed in vivo. In addition, the phase I and II drug-metabolizing enzyme activities of HepaRG, h-iPS-HEP, liver-humanized mouse-derived hepatocytes (PXB-cellsTM), and human primary hepatocytes were evaluated and compared. HepaRG showed high phase I and II drug metabolism activities; however, the CYP2D6 activity in these cells was quite low, and therefore h-iPS-HEP lacked O-methylation and conjugation activities. PXB-cells provided optimal results, i.e., these cells are extremely easy to use, and they possess higher phase I and II drug-metabolizing enzyme activities than the other cells tested. Although PXB-cells are contaminated with mouse-derived cells up to a concentration of several percent, this cell system appears to be promising for the prediction of in vivo human metabolism of new drugs of abuse.

Cell therapy for Parkinson's disease has a history of being applied clinically with aborted embryos as donor source. Efficacy of the therapy under the appropriate condition has been reported. Based on this experience and the advancement of stem cell technology, clinical trials of cell therapy with embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) are going to start soon in several countries. In Japan a physician-initiated clinical trial of iPSC-based therapy for Parkinson's disease has launched since 2018. This trial adopts allogeneic transplantation with a cell line from iPSC stock. This article discusses patient selection, procedure, and risk of the therapy. It also introduces the world's current situation of the cell therapy for Parkinson's disease.

Over the past 15 years, many studies have revealed that Wnt signaling has a strong impact on hematopoietic stem cell fate. After a controversy over the interpretation of some results, the current understanding is that an appropriate degree of canonical Wnt signaling induces hematopoietic stem cell self-renewal and that noncanonical Wnt signaling keeps the quiescence. It is also likely that the balance between canonical and noncanonical Wnt pathways regulates the stress response and aging of hematopoietic stem cells.

Mesenchymal stem cell (MSC) is a type of tissue stem cell. In clinical studies, cultured MSCs have shown important therapeutic effects on diseases via the reduction of neurological defects and regulation of immune responses. However, in vivo MSC localization, function, and properties are poorly understood; therefore, the molecular understanding of MSCs hierarchy is less advanced compared to hematopoietic stem cell hierarchy. To address these issues, we developed a method that enables us to visualize MSCs, manipulate their function, and analyze their molecular biology in vivo. Paired-related homeobox 1 (Prrx1)-positive cells are transiently observed during limb skeletal development in mice. Prrx1-positive cells form heterogeneous populations comprising multiple mesenchymal progenitors with different lineages that are developing into osteoblasts, chondrocytes, adipocytes, fibroblasts, and tendon and ligament cells. Our results suggest that osteoblast differentiation in the calvaria begins at the Prrx1+Sca1+ MSC stage with sequential progression to Prrx1+Sca1- cells, then Osterix+Prrx1-Sca1- osteoblast precursors, which eventually form mature α1(I)-collagen+ osteoblasts. Using Runt-related transcription factor 2 (Runx2) conditional knockout mice, furthermore, we found that the essential period of Runx2 function in intramembranous ossification likely begins at the Prrx1+Sca1+ MSC stage and ends at the Osterix+Prrx1-Sca1- osteoblast precursor stage (before mature the α1(I)-collagen+ osteoblasts appear). This approach will enable us to understand the in vivo molecular biology features of MSCs, leading to their therapeutic applications for tissue repair and regeneration. This development can also contribute to the field of pluripotent stem cell by enabling the transplantation of lineage-restricted mesenchymal progenitors.