Recent evidence suggests that the targeting of membrane transporters specifically activated in cancer stem cells (CSCs) is an important strategy for cancer therapy. The objectives of the present study were to investigate the ion channel expression profiles in digestive CSCs. Cells strongly expressing CSC markers, such as ALDH1A1 and CD44, were separated from the human esophageal squamous cell carcinoma, gastric cancer, and pancreatic cancer cell lines using fluorescence-activated cell sorting, and CSCs were identified based on tumorsphere formation. Messenger RNA levels of CSC markers were higher in CSCs than in non-CSCs. These CSCs also exhibited resistance to anticancer agents. The microarray analysis revealed that the expression of transient receptor potential vanilloid 2 (TRPV2), voltage-gated calcium channels (VGCCs), and voltage-gated potassium channels (VGKCs) were upregulated in esophageal, gastric, and pancreatic CSCs, respectively, compared with non-CSCs. The TRPV2 inhibitor tranilast, VGCCs inhibitors amlodipine and verapamil, and VGKC inhibitor 4-aminopyridine exhibited greater cytotoxicity in CSCs compared with non-CSCs, and their inhibitory effects were also confirmed in a xenograft model in nude mice. Taking these results, phase I/II study to investigate clinical safety and efficacy of neoadjuvant combination chemotherapy of tranilast in advanced esophageal squamous cell carcinoma (TNAC study) is ongoing. These researches identified a role of ion channels in the persistence of CSCs and suggested that their inhibitors may have potential as a therapeutic agent for digestive cancers.

In acute myeloid leukemia (AML), EVI1 rearrangement represented by inv(3)(q21q26) or t(3;3)(q21;q26) causes EVI1 overexpression via structural rearrangement of an enhancer, and confers poor prognosis. My colleagues and I performed a mutational analysis of EVI1-rearranged myeloid neoplasms and identified SF3B1, a core RNA splicing factor, as the most commonly co-mutated gene. Indeed, latent leukemia development in transgenic mice bearing the humanized inv(3)(q21q26) allele was significantly accelerated by co-occurrence of Sf3b1 mutation. Intriguingly, we found that this SF3B1 mutant induced mis-splicing of EVI1 itself, which generated an aberrant EVI1 isoform with in-frame insertion of 6 amino acids near the DNA-binding domain of EVI1. This aberrant EVI1 isoform exhibited DNA-binding activity different from wild-type EVI1 and significantly enhanced the self-renewal capacity of murine hematopoietic stem cells. We also identified the cryptic branch point and exonic splicing enhancer required for this EVI1 mis-splicing induced by the SF3B1 mutant. These data provide a basis for further elucidation of the molecular mechanism and potential therapeutic candidates for EVI1-rearranged AML.

The treatment outcomes for adult Philadelphia chromosome-negative acute lymphoblastic leukemia (ALL) have improved with the introduction of pediatric protocols. On assessing long-term survivors of chemotherapy who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), it was found that these patients had good performance status and few complications. Therefore, in the first complete remission (1CR) of ALL, allo-HSCT is indicated for patients in whom the results of chemotherapy are predicted to be poor. In adolescent and young adult (AYA) patients with ALL, allo-HSCT is recommended in the 1CR if end of consolidation measurable residual disease (MRD) is positive. In adults with ALL (non-AYA patients), if end of induction MRD is negative, chemotherapy should be continued and allo-HSCT is not recommended. In the future, it is necessary to perform a comprehensive evaluation of individual patients that considers MRD, as well as the initial tumor burden and biological features of leukemic cells.

Primary myelofibrosis (PMF) is characterized by the clonal expansion of megakaryocytes and myeloid cells from stem cells with abnormal cytokine expression, resulting in bone marrow fibrosis, angiogenesis, and osteosclerosis. The use of next-generation sequencing revealed that both genetic and epigenetic changes are important in the pathogenesis of PMF. Several epigenetic regulator genes, including TET2, the polycomb-related gene ASXL1, and the polycomb-group gene EZH2, have been found to be targeted by somatic gene mutations in PMF patients. Among these, loss of Ezh2 has been demonstrated to disrupt the function of the polycomb repressive complex 2, promoting the development of JAK2V617F-induced myelofibrosis in mice. In this analysis, we highlight the role of PRC dysfunction in the pathogenesis of PMF.

Bone marrow (BM) failure is a condition characterized by peripheral pancytopenia due to decreased BM function. It includes conditions such as acquired aplastic anemia (AA), myelodysplastic syndrome (MDS), and paroxysmal nocturnal hemoglobinuria (PNH). AA is characterized by pancytopenia and BM hypoplasia, and is primarily caused by an autoimmune mechanism involving cytotoxic T cells that damage hematopoietic stem cells (HSCs). Recent genomic research has revealed that patients with AA often exhibit clonal hematopoiesis by HSCs with genetic alterations, such as PIGA, DNMT3A, ASXL1, BCOR/BCORL1, copy-number neutral LOH of chromosome 6p (6pLOH), and HLA class I allele mutations. The genomic landscape of AA is distinct from MDS and age-related clonal hematopoiesis. Most notably, the presence of PNH-type cells and HLA class I allele-lacking cells indicates the presence of HSCs that have escaped from autoimmunity. We recently identified a common nonsense mutation at codon19 (c.19C>T, p.R7X) in exon1 (Exon1mut) of different HLA-A and HLA-B alleles, and HLA-DR loss of hematopoietic stem progenitor cells in AA patients carrying HLA-DR15. These results provide important clues for understanding the immune pathophysiology of BM failure.

Hematopoietic cells are a group of cells that first appear in the midembryonic stage of the mouse and are essential for body growth and maintenance. For a long time, their development was widely assumed to be divided into primitive and definitive hematopoiesis. However, erythromyeloid progenitors were identified as the wave between primitive and definitive hematopoiesis, and at least three waves were recognized. An even more multilayered structure of hematopoietic development is becoming evident in recent years, with the progress and spread of lineage tracing experiments. This review will focus on recent advances in the behavior of hematopoietic stem and progenitor cells in the embryo revealed by cell lineage-tracking experiments.

Hematopoietic stem and progenitor cells in mammals primarily reside in the bone marrow after birth. There, the cellular dynamics and subsequent fate of those cells are regulated by the adjacent microenvironment, known as the niche, to sustain lifelong blood cell production. To analyze and study physiological hematopoiesis and various hematopoietic disorders, it is essential to deeply understand how the niche regulates hematopoiesis and how niche dysregulation occurs. However, the dynamics of hematopoietic stem and progenitor cells and their interactions with the niche are dynamic and complex, and our knowledge of the spatial organization of bone marrow cells and niche factors is still limited. In this review, I provide an overview of classical techniques for spatiotemporal understanding of the cellular communities in bone marrow, as well as recent advances in bone marrow imaging techniques and valuable animal models, and discuss future prospects in this field.

Myelopoiesis is a process that produces myeloid cells including granulocytes and mononuclear phagocytes. The differentiation and proliferation of hematopoietic stem and progenitor cells are tightly regulated to meet demands for such myeloid cells both at steady state and under stressed conditions. CCAAT/enhancer-binding protein family transcription factors are involved not only in the appropriate regulation of myelopoiesis but also in dysregulated myelopoiesis. A recent study has revealed that inflammation, in addition to the established concepts or mechanisms of dysregulated myelopoiesis, triggers long-term epigenetic memory in hematopoietic stem/progenitor cells. Further, clonal hematopoiesis develops and impairs host health conditions via inflammatory conditions. Intensive studies covering both the basic and clinical aspects of myelopoiesis are required to establish therapeutic and even prophylactic approaches to different types of human diseases including hematopoietic and nonhematopoietic origins.

Chronic myeloid leukemia (CML) stem cells have been identified to promote CML relapse due to their quiescent cell cycle and tyrosine kinase inhibitor resistance. Therefore, their eradication is important for the cure of CML. We herein identified the quiescent CML stem cell fraction using a G0 marker that can visualize quiescent cells. Whole-transcriptome analysis of imatinib-resistant, quiescent CML stem cells revealed that NF-κB is activated via inflammatory signals in the same cells. The combination of imatinib and an inhibitor of this inflammatory signal (IRAK1/4 inhibitor) effectively eliminated CML stem cells and attenuated PD-L1 expression in CML stem cells. Furthermore, the combination of anti-PD-L1 antibody and imatinib effectively eliminated CML stem cells in the presence of T-cell immunity, indicating the importance of creating an environment in which T cells can attack CML stem cells. Thus, IRAK1/4 inhibitors exert two effects: blocking CML stem cell survival and proliferation signals by inhibiting NF-κB and blocking T cell immune evasion by reducing PD-L1 expression in CML stem cells. Collectively, their combination may be one of the attractive strategies for achieving a radical cure for CML. Discussions regarding the possibility of future medications seem warranted.

Myelodysplastic syndromes (MDS) are a clonal disorder based on genomic mutations in hematopoietic stem cells. They are categorized as lower-risk MDS, characterized by peripheral cytopenia; and higher-risk MDS, characterized by progression to acute myeloid leukemia. Previous studies reported that inflammation and immune activation are deeply involved in the pathogenesis of lower-risk MDS. Recent studies elucidated the molecular basis for the activation of inflammatory pathways via dysregulated innate immune system and the resultant cell-death acceleration in lower-risk MDS. Conversely, immunosuppression and immune escape are substantially involved in the pathogenesis and disease progression of higher-risk MDS. VEXAS syndrome is an autoinflammatory disease characterized by clonal hematopoiesis with somatic mutation of UBA1 in hematopoietic stem and progenitor cells and has attracted broad attention as a lower-risk MDS model caused by systemic inflammation. Although therapeutic effects of immunosuppressants are observed for a limited number of patients with lower-risk MDS with inflammation, an optimal treatment should be developed based on their pathology.

Microglia are the only immune cells in the central nervous system. It has been shown that microglia actively regulate the number of neurons by participating in the cell death of neural stem cells during development and maturation. In addition, recent optical techniques have enabled in vivo imaging, which has revealed the function of microglia on synapses. Microglia regularly monitor synaptic activity and remove synapses that show abnormal activity in the event of brain infarction or other disorders. During development, microglia contribute to the formation of immature synapses by contacting dendrites during early synapse formation, and they are also involved in the de-synaptic process by selectively removing weakly active synapses through the use of classical complement cascade signaling. Furthermore, these abnormalities are known to contribute to the development of autism during development and to the development of Alzheimer's disease during maturation. In addition to this, microglia also contribute to plastic changes in synapses during the learning process in maturation. Furthermore, by modifying synaptic activity, microglia are known to be involved in changes in the activity of neuronal circuits. In addition to these synaptic functions, microglia are also known to be involved in the permeability of the blood-brain barrier. In this chapter, these functions will be summarized and discussed.

Adult T-cell leukemia-lymphoma (ATL) is a highly aggressive peripheral T-cell neoplasm caused by human T-cell leukemia virus type 1 (HTLV-1) infection occurring in approximately 5% of patients after prolonged latent period. ATL relapses within a short period despite its transient response to multiagent chemotherapy and the prognosis is extremely poor due to anticancer drug resistance and immunodeficiency. Although novel agents with different mechanisms, such as molecular targeted agents, have improved the prognosis, the number of cured patients remains limited. Hematopoietic stem cell transplantation resulted in long-term remission, whereas its indication is limited due to treatment-related mortality. As most ATL patients are of advanced age, development of a lesser toxic treatment is necessary. Therefore, we developed a novel therapeutic dendritic cell vaccine targeting the HTLV-1 Tax antigen. The safety profile has been confirmed in a pilot and phase I clinical studies, and a promising long-term clinical efficacy has also been obtained. This novel vaccine is a noninvasive, long-lasting therapy for ATL and can potentially be extended to different applications for low-grade ATL and high-risk HTLV-1 carriers.

By carrying a systemic circulation, hematopoietic and vascular systems coordinately govern the functional organ connections in the body. Blood vessels play an important role in the development, regeneration, and maintenance of organs by acting as conduits for environmental factors in the blood to tissues and secreting organ-specific cytokines as angiocrine signals. Recently, it has become clear that vascular endothelial cells, which are the main constituent cells of the blood vessels and play a role in homeostasis, are diverse. It has also been established that the cells of stem cell fraction exist in endothelial cells. The vascular endothelial cells in various organs are functionally different. For example, it has been discovered that sinusoidal blood vessels in the liver produce coagulation factor VIII as an organ-specific vascular function. Determining how such tissue-/organ-specific function of the endothelial cells is induced is a topic of interest in the vascular field of study.

The unbalanced translocation der (1;7)(q10;p10) is a characteristic cytogenetic abnormality observed in myelodysplastic syndrome (MDS). A 63-year-old man presented to our hospital with fever and lung disease. The chromosomal analysis of bone marrow cells showed 46, XY, +1, der (1;7)(q10;p10) in all four metaphases. The patient was diagnosed with MDS. Bronchoscope examination revealed organizing pneumonia. The patient's eosinophil count rose to 39% after 30 days. His fever and dyspnea worsened, and a skin rash (systemic erythema) appeared simultaneously. Therefore, the patient was commenced on azacitidine and corticosteroids. Although treatment with both drugs could control disease progression transiently, the WT-1 value and the percentage of myeloblasts in the patient's bone marrow increased. Therefore, the patient received hematopoietic stem cell transplantation from his haplo-identical donor daughter. Some reports have demonstrated that patients with MDS with der (1;7)(q10;p10) have better prognosis than those with other abnormalities, such as -7/7q-. However, reported cases with severe complications show very poor prognosis. MDS with der (1;7)(q10;p10) complicated by eosinophilia and organizing pneumonia have not been reported, and its prognosis is expected to be very poor. Our case suggests that such cases might quickly require hematopoietic stem cell transplantation before the disease worsens.

POEMS syndrome is a rare monoclonal plasma cell disorder with unique symptoms distinct from other plasma cell neoplasms. To identify and find the transcriptional features of clonal plasma cells in POEMS syndrome (POEMS clones), single-cell RNA sequencing was performed on patient-derived bone marrow plasma cells. POEMS clones were identified in 5 out of 10 patients, and the proportions of POEMS clones in the plasma cells were markedly smaller than that of other plasma cell malignancies such as multiple myeloma and MGUS. The transcriptional features of POEMS clones differed from those of other plasma cell diseases, and representative MM-related oncogenes were not upregulated in POEMS clones. Notably, POEMS clones are negative for CD19 and express significantly lower MHC-II levels than normal plasma cells; thus, CD19- HLA-DRlo is confirmed as a useful marker to identify POEMS clones in patients. These findings unveil the unique features of POEMS clones and contribute to the understanding of the pathogenesis of POEMS syndrome.

Acute myeloid leukemia (AML) is one of the most common hematologic malignancies derived from self-renewing and highly propagating leukemic stem cells (LSCs). We have previously identified T-cell immunoglobulin mucin-3 (TIM-3) as an AML LSC-specific surface molecule by comparing the gene expression profiles of LSCs and hematopoietic stem cells (HSCs). TIM-3 expression clearly discriminates LSCs from HSCs within the CD34+CD38- stem cell fraction. Furthermore, AML cells secrete galectin-9 (Gal-9, a TIM-3 ligand) in an autocrine manner, resulting in constitutive TIM-3 signaling, which maintains LSC self-renewal capacity through β-catenin accumulation. In this study, we investigated the LSC-specific mechanisms of TIM-3 signaling. We found that TIM-3 signaling drove the canonical Wnt pathway, which was independent of Wnt ligands, to maintain cancer stemness in LSCs. Gal-9 ligation activated the cytoplasmic Src homology 2 (SH2) binding domain of TIM-3 to recruit hematopoietic cell kinase (HCK), a Src family kinase that is highly expressed in LSCs. HCK phosphorylated p120-catenin to promote the formation of the LDL receptor-related protein 6 (LRP6) signalosome, hijacking the canonical Wnt pathway. This TIM-3/HCK/p120-catenin axis was employed principally in immature LSCs compared to TIM-3-expressing exhausted T-cells.

HLA-haploidentical stem cell transplantations using posttransplant cyclophosphamide (PTCy-haplo) rapidly increased worldwide. In Japan, the number of HLA-haploidentical stem cell transplantation cases exceeded related HLA-matched transplants in 2020. Recent retrospective studies using Japanese registry data have reported comparable transplantation outcomes between PTCy-haplo and HLA-matched unrelated and cord blood transplantations. PTCy-haplo was initially developed in the bone marrow transplantation setting after non-myeloablative conditioning but has recently become widely used in peripheral blood stem cell transplantation and myeloablative conditioning. Peripheral blood stem cell transplantation increases the occurrence of graft-versus-host disease but may have more improved transplant outcomes compared with bone marrow transplantation. Other factors, such as the number of infused cluster of differentiation 34-positive cells, donor age, HLA class II mismatch, HLA-B leader, and reduced PTCy dosage, may also contribute to the outcome of PTCy-haplo transplantations. Furthermore, PTCy has been reportedly effective in related/unrelated HLA-matched transplantation and HLA-mismatched unrelated transplantations. A prospective phase II trial using PTCy in patients who underwent HLA-matched and 1-2 allele-mismatched transplantation is ongoing in Japan. Patient enrollment has already been completed, and the results will be revealed soon. Using PTCy to sufficiently reduce the occurrence of graft-versus-host disease will make performing allogeneic transplants with a higher safety level possible.

Large-scale in vitro red blood cell (RBC) production has been attempted in recent years. Potential cell sources for RBC production include hematopoietic stem/progenitor cells, pluripotent stem cells, and immortalized erythroid progenitor cell lines, which can induce enucleated RBCs with characteristics such as oxygen-carrying capacity and deformability. A phase I clinical study of cultured RBCs produced from hematopoietic stem/progenitor cells has revealed a similar in vivo half-life between cultured and native RBCs. Thus, the application of cultured RBCs in blood transfusion is gradually advancing. However, a single transfusion requires a large number of cells, unlike other cell therapies. Therefore, developing a method to mass-produce RBCs from a small culture volume at a low cost is important in the future. This review summarizes the current status and prospects concerning in vitro RBC production using each cell source, which can improve future transfusion medicine.

Aplastic anemia (AA) is a non-neoplastic bone marrow failure syndrome caused by the destruction of hematopoietic stem and progenitor cells by the immune system. However, in some cases of AA, a small number of specific clones with gene mutations are observed without clinical manifestations. Cases with mutated PIG-A, BCOR/BCORL1, or HLA class I allele clones respond better to immunosuppressive therapies (ISTs). Cases with MDS-related clones, such as DNMT3A or ASXL1 mutations, are at a higher risk for secondary MDS. In this review, I will focus on the clonal hematopoiesis (CH) in AA and discuss its clinical significance, including its impact on disease boundaries and transition. I will also discuss the pathophysiology and diagnosis of hypoplastic MDS, a type of MDS that responds to ISTs.