Gilteritinib fumarate (Xospata® tablets 40 mg) is a novel, highly selective, oral FMS-like tyrosine kinase 3 (FLT3) inhibitor used for the treatment of patients with relapsed or refractory FLT3-mutated acute myeloid leukemia (AML), and it was approved in Japan in September 2018. Preclinical studies demonstrated that gilteritinib inhibited FLT3 and showed antiproliferative activity against Ba/F3 cells expressing mutated FLT3. In addition, gilteritinib inhibited tumor growth, induced tumor regression, and prolonged survival in mice xenografted with MV4-11 cells endogenously expressing FLT3-internal tandem duplication. In clinical trials conducted in the United States, Europe, and Japan, plasma concentrations after administration of gilteritinib 20 to 450 mg/day were generally dose proportional, and gilteritinib was well tolerated. Multiple clinical trials, including a global Phase III study, in patients with relapsed or refractory FLT3-mutated AML treated with gilteritinib demonstrated higher response rates of complete remission or complete remission with partial hematologic recovery and longer overall survival compared with patients treated with salvage chemotherapy. Some clinical trials are ongoing in patients with FLT3-mutated AML at various treatment stages, such as induction therapy, maintenance therapy, and treatment after hematopoietic stem cell transplantation. In conclusion, in vitro, in vivo, and clinical data indicate that gilteritinib fumarate is an effective treatment option in adult patients with relapsed or refractory FLT3-mutated AML in Japan.

Glaucoma, the leading cause of blindness in adults, is a progressive neurodegenerative disease characterized by retinal ganglion cell (RGC) death. Currently, many intraocular pressure (IOP)-lowering drugs known to affect this disease progression have been developed as therapeutic agents. However, there are many cases of disease progression, even with sufficient IOP reduction. Therefore, newer therapeutic approaches other than IOP-lowering drugs are needed. To elucidate the pathogenesis of glaucoma and to develop therapeutic agents, the evaluation of RGCs is imperative, as their degeneration is the main cause of this disease. However, it is difficult to obtain RGCs from healthy individuals, let alone glaucoma patients. Therefore, research on the pathophysiology of glaucoma and drug discovery has not progressed sufficiently. Recent developments have made it possible to generate induced pluripotent stem (iPS) cells from the blood or skin of glaucoma patients and induce them to differentiate into RGCs to study the pathogenesis of glaucoma. In addition, drug repositioning for ophthalmological diseases such as glaucoma is one of the most active fields. Many of these repositioned drugs have found therapeutic applications in ophthalmology. Here, we introduce the current status of the pharmacological treatment of glaucoma and its prospects.

The eye is a complex organ with highly specialized constituent tissues derived from different primordial cell lineages. The retina develops from neuroectoderm via the optic vesicle, the corneal epithelium is descended from surface ectoderm, while the iris and corneal stroma have a neural crest origin. Recent work with pluripotent stem cells (PSCs) in culture has revealed a previously under-appreciated level of intrinsic cellular self-organization, with a focus on the retina and retinal cells. We recently demonstrated the generation from human induced pluripotent stem cells (iPSCs) of a self-formed ectodermal autonomous multi-zone (SEAM) of ocular cells. The concentric SEAM mimics whole-eye development because cell location within different zones is indicative of ocular cell lineage, spanning the ocular surface ectoderm, lens, neuro-retina, and retinal pigment epithelium. Therefore, SEAM represents a promising resource for new research of ocular morphogenesis and development. Moreover, we successfully isolated corneal epithelial progenitor cells and fabricated corneal epithelial tissue from PSCs. This approach has translational potential for treating severe corneal epithelial disease by transplantation of PSC-derived corneal epithelial tissue. To evaluate the efficacy and safety of the corneal epithelial tissue, we have started a first-in-human clinical study for patients with corneal epithelial stem cell deficiency, which began last year.

Plerixafor is increasingly used in combination with granulocyte-colony-stimulating factor (G-CSF) for peripheral blood stem cell collection. Although it is an expensive drug, its cost-benefit performance is not well investigated. Thus, we analyzed its cost-effectiveness in our hospital. A retrospective observational analysis was performed in patients who underwent stem cell collection between December 2013 and November 2018. A total of 203 patients were investigated and classified into three groups according to their pre-mobilization regimen: G-CSF alone, G-CSF and cyclophosphamide (G+CY), and G-CSF and plerixafor (G+plerixafor). The cost-effectiveness of apheresis of the collected cluster of differentiation (CD) 34+ cells was assessed based on two viewpoints: cost of drugs and cost of equipment. Due to the high cost of plerixafor, the cost of apheresis was higher in patients who received G+plerixafor. However, the difference narrowed when we calculated the cost to collect 2.0×106 CD34+ cells/kg body weight required for a single transplant. The number of stem cells collected from patients who received G+plerixafor was higher than those who received other regimens (median CD34+ cells harvested/day were 2.90 for G-CSF, 2.13 for G+CY, and 4.63 for G+plerixafor, ×106/kg body weight, P<0.01). Our results show that plerixafor enables efficient apheresis.

Angiogenesis is the process of new vascular formation from preexisting blood vessels, and the contribution of endothelial stem cell population to this process has been elucidated. Vascular endothelial growth factor (VEGF) promotes not only the proliferation of endothelial cells (ECs) but also the vascular permeability by inducing cell-to-cell dissociation between ECs. Chronic hyper vascular leakage induces intra-tumoral interstitial hypertension resulting in disturbed vascular perfusion. Hypoxia in the nonfunctional vasculatures causes chromosomal instability of cancer cells resulting in the development of malignant cancer cells, such as cancer stem cells. Hypoxia also induces exhaustion of immune cells. Moreover, the blood vessel structures in tumors are abnormal and nonfunctional, and the infiltration of leukocytes are suppressed. Moreover, drug delivery, including anti-cancer drugs and immune checkpoint inhibitors, is limited. A drug inducing normalization or maturation of abnormal blood vessels in tumor is warranted for the improvement of malignant tumor microenvironment.

Graft-versus-host disease (GVHD) is one of the most important complications after an allogeneic hematopoietic stem cell transplantation (allo-SCT). The current National Institutes of Health's (NIH) consensus is that clinical manifestations, and not the time to symptomatic onset after transplantation, determine whether the clinical syndrome of GVHD is considered acute or chronic. In the past decade, peripheral blood stem cell transplantation from an unrelated donor can be performed in Japan. Furthermore, poor-risk patients without human leukocyte antigen (HLA)-matched donor can receive allo-SCT from HLA haploidentical donor. Therefore, severe or steroid-refractory GVHD would be increased. Corticosteroid, at a dose of 2 mg/kg, is a standard first-line therapy for acute GVHD. If there is no improvement after the first-line therapy, second-line therapy should be administered immediately. Although anti-thymocyte globulin and mesenchymal stem cells are covered by health insurance in Japan, another treatment options should be determined for steroid-refractory acute GVHD. Furthermore, severe chronic GVHD increases patients' mortality and decreases their quality of life. A number of novel drugs targeting specific biological pathways for GVHD are under development. Currently, more than 60 clinical trials are carried out for the treatment of steroid-refractory GVHD worldwide for drug approval. The accumulation of novel evidence for GVHD treatment is expected to be established.

The treatment paradigm in multiple myeloma (MM) together with the introduction of novel agents have resulted in a considerably improved survival. However, the disease is still considered incurable. One of the factors of its recurrence was that acquired genomic events associated with the progression of MM lead to inter- and intrapatient clonal heterogeneities. Also, just like many other cancers, MM contains cancer stem cells, a rare subpopulation of MM cells that exhibit the capacity for self-renewal and differentiation, but also pronounced drug resistance. Furthermore, a growing body of evidence suggests the role of tumor microenvironment and anti-myeloma immune status in the progression and maintenance of MM. Despite much progress in MM pathology, there are still several issues left unsolved. In this review, we will discuss the recent advances in our understanding of the pathology of MM from the perspective of tumor cell-of-origin and how these advances can lead to more effective therapies targeting MM.

Myelodysplastic syndromes (MDS) are neoplastic diseases of the hematopoietic stem cells, caused by genetic mutations. The clinical courses of MDS are highly variable based on the underlying genetic aberrations, ranging from slowly progressing cytopenia to rapidly-manifesting fatal diseases, including the development of acute myelogenous leukemia. The management of lower-risk MDS, which is risk-stratified based on the revised International Prognostic Scoring System (IPSS-R), mainly consists of a supportive therapy, including blood transfusion to treat anemia and thrombocytopenia. Recently, three novel drugs were approved, which became available in Japan. These include darbepoetin alfa, an erythropoiesis-stimulating agent; lenalidomide, which is specifically active for anemia of 5q- syndrome; and deferasirox, an oral iron-chelating agent. Decision analyses also provide evidence in determining the optimal timing for the potentially curative allogeneic hematopoietic stem cell transplantation for lower-risk MDS. Thus, the management of lower-risk MDS should be optimized using these novel agents and newly available evidence.

Evidence of human leukemia stem cells (LSCs) in acute myeloid leukemia (AML) was first reported nearly a quarter century ago through the identification of rare engrafting cell subpopulations in patient-derived xenograft assays. Since then, studies have revealed diverse characteristics of AML stem cells. Initiating mutations convert normal hematopoietic stem cells (HSCs) to pre-leukemic HSCs. The repopulation advantage of pre-leukemic HSCs over normal HSCs leads to clonal evolution. Acquisition of additional mutations in pre-leukemic HSCs results in the development of AML composed of genetically distinct subclones. Each subclone contains LSCs with unique characteristics, and these LSCs contribute to therapeutic resistance and relapse. Interestingly, some LSCs can escape from antitumor immune responses, thereby survive the treatment. This article summarizes recent advances in the field of LSC biology from genomic and immunological perspectives.

Through intensive efforts of genome sequencing of myeloid malignancies, a comprehensive registry of driver mutations has been revealed, virtually providing us with a complete spectrum of driver mutations in these diseases. Importantly, there have been significant correlations between driver mutations, which suggests that some combinations of genetic events confer strong selective advantage on mutated stem cells. Next-generation sequencing technology have also revealed that clonal hematopoiesis is a common, age-related process in which a somatically mutated hematopoietic precursor gives rise to a genetically distinct subpopulation in the blood. Furthermore, novel germline mutations were identified, indicating that mutated stem cells appear long before myelodysplastic syndrome (MDS) presentation. Such founding mutations are thought to be acquired and positively selected in a well-organized manner to allow for expansion of the initiating clone to compromise normal hematopoiesis, ultimately giving rise to MDS and subsequent transformation to acute myeloid leukemia (AML) in many patients.

GATA1-deficient mice die in utero on 12.5 embryonic day (E12.5) due to a complete block of primitive erythropoiesis in the yolk sac, while GATA2-deficient mice die on E10.5 due to severe anemia and hemorrhage, since GATA2 is essential for the development of hemangioblasts, which are common precursor cells of hematopoietic stem cells and endothelial cells. In contrast, GATA3 is critical to the development of Th2 cells. However, GATA3-deficient mice die in utero before the particular phenotype of hematopoietic system emerges, which is caused by a defect in the development of nervous and renal urinary systems. It has been well elucidated that defects in the hematopoietic GATA factors disturb hematopoietic homeostasis. However, details on how GATA factor dysfunction leads to human hematopoietic diseases remain to be clarified. At the end of the twentieth century, several mutations in GATA1 gene were identified as the cause of familial thrombocytopenia. Since then, various types of hematopoietic diseases elicited by GATA1 and GATA2 dysfunctions have been reported. This review summarizes recent topics of GATA factor-related hematopoietic diseases.

Inflammation is a physiological process that primarily occurs as a way to help protect the host against tissue damage and invasion by pathogens. During inflammation, erythropoiesis is suppressed and, if it lasts, anemia develops. The mechanisms underlying this are complex and not fully understood, but various cytokines, such as tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-1β (IL-1β), and IL-6, are involved. TNF-α upregulates PU.1, which is a crucial transcription factor in granulocytic differentiation, and downregulates GATA-1, a master transcription factor for erythroid differentiation, in hematopoietic stem cells. TNF-α and IL-1β suppress erythropoietin production in the kidney, whereas IFN-γ downregulates the expression of erythropoietin receptors in erythroid precursor cells. Moreover, IL-6 upregulates the production of hepcidin, the master regulator of systemic iron metabolism, in the liver. Hepcidin reduces the iron available for erythropoiesis by downregulating the rate of iron release from macrophages. Activated macrophages may also contribute to the development of anemia by shortening the erythrocyte lifespan. Proper management of the underlining conditions is necessary in treating anemia associated with inflammation. Erythropoiesis-stimulating agents may be administered to patients with chronic kidney disease, whereas anti-IL-6 agents may be beneficial for anemic patients with rheumatoid arthritis and idiopathic multicentric Castleman disease.

Acquired pure red cell aplasia (PRCA) is characterized by normocytic anemia, reticulocytopenia, and a marked decrease in erythroid cell count in the bone marrow. PRCA develops in the context of various backgrounds, including recently recognized immune checkpoint inhibitor-associated PRCA, that need careful differential diagnoses. Besides humoral abnormalities such as major ABO-incompatible allogeneic hematopoietic stem cell transplantation-related PRCA, dysregulations of T cells have been shown. STAT3 gene mutations of cytotoxic T cells were identified in 40% of PRCA patients, which might suggest their use as novel molecular markers for PRCA. As initial management options for PRCA, red blood cell transfusion and immunosuppressive therapy (IST) drugs, such as cyclosporin, are usually selected. Roughly 80% of patients respond to IST; however, some relapse afterward or are refractory to IST. When patients with PRCA become refractory to two or three lines of IST, allogeneic hematopoietic stem cell transplantation (HCT) would become an appropriate choice, although the optimal procedures for allogeneic HCT have not been determined. A prospective study of PRCA in Japan has been ongoing since 2016 to solve the myriad clinical issues of PRCA.

Paroxysmal nocturnal hemoglobinuria (PNH) causes clonal expansion of hematopoietic stem cells with abnormal GPI-anchor biosynthesis. The major pathological condition of PNH is that the erythrocytes lacking the complement regulatory factors CD55 and CD59, which are GPI-anchored proteins, lead to intravascular hemolysis through complement activation. Clonal expansion has been assumed to be involved in an immunological attack on hematopoietic stem cells, and the bone marrow failure associated therewith modifies the pathology to varying degrees. The introduction of eculizumab made complement control possible; however, the problems associated with it became apparent as the treatment progressed. Additionally, the PNH Reference Guide was significantly revised in 2016, partly because PNH was designated as a Japanese medical subsidy. With the revised edition of 2020, minor revisions have been added to reflect further advances in treatment and understanding of the disease, while mainly dealing with the clinical introduction of eculizumab derivative, ravulizumab, which uses recycling antibody technology. This review outlines the points of the 2020 revision, including the important points of the previous revision.

Aplastic anemia is a syndrome characterized by the decrease in hematopoietic stem cells along with bone marrow hypoplasia and pancytopenia, which is likely to be a T cell-mediated autoimmune disease. Since the response rate to immunosuppressive therapy is higher if started ahead of time, early initiation of treatment is recommended even in non-severe cases. Among treatment approaches in severe cases, immunosuppressive therapy with anti-thymocyte globulin (ATG) plus cyclosporin is the basic approach. However, the effectiveness of thrombopoietin receptor agonists has also been reported, with recovery of hematopoiesis in three blood lineages observed in some patients. Despite no evidence of increased incidence of genetic mutations with thrombopoietin receptor agonist treatment, bone marrow testing is recommended after three to six months of long-term treatment to detect the presence of chromosomal abnormalities. With regard to hematopoietic stem cell transplantation for aplastic anemia, cyclophosphamide is reduced as a pretreatment therapy, and instead, fludarabine is used in combination in order to reduce cardiotoxicity. Since HLA haploidentical hematopoietic stem cell transplantation has been developed and is being reportedly used in patients with no suitable donors, this transplantation approach might also be extended to aplastic anemia patients who were not considered eligible for transplantation in the past.

Expansion of stem cell numbers without reduction in their regenerative potential is crucial for therapeutic applications. However, the repeated cell divisions and aging impair stem cell function. We found that Pot1a, a component of the shelterin that protects telomeres, involves the maintenance of hematopoietic stem cell (HSC) activity during aging. Pot1a maintained the self-renewal activity of HSCs through the prevention of DNA damage responses in HSCs and suppression of the production of reactive oxygen species. Furthermore, the exogenous Pot1a expanded the HSC number and rejuvenated aged HSCs function upon ex vivo culture. Consistent with these results, treatment with exogenous human POT1 protein maintains human HSC activity in culture. Collectively, these results show that Pot1a or POT1 sustains HSC activity and can be used to expand HSC numbers ex vivo.

Mammals have developed bone marrow (BM) inside the bone tissue because of evolution. Now, it appears that bone tissue displays functional communication with the hematopoietic system. Osteoblast lineage cells serve as a part of the microenvironment for immature hematopoietic cells, whereas mature hematopoietic cells play important roles in regulating osteoblast activity. The nervous system maintains the balance between the hematopoietic and skeletal systems. An understanding of the multiple-organ network that exists between the BM and other systems is useful to elucidate phenomena in clinical hematology and even in other fields, an area which I propose to call "marrowlogy."

Lymphocytes play pivotal roles in innate and adaptive immunity. The differentiation process by which hematopoietic stem cells (HSCs) acquire specific functions has been extensively investigated and is considered the paradigm of cell differentiation. It has been widely accepted that highly enriched HSCs are heterogeneous with respect to their lymphopoietic potential, and aged or stressed HSCs are skewed to the myeloid lineage. Several transcription factors and cytokine signaling pathways have been reported as essential to lymphocyte differentiation. However, the molecular mechanism that modulates the earliest stage remains unclear. Furthermore, the origin and characteristics of early T-lymphoid progenitors that migrate from the bone marrow to the thymus are still unknown in this field. Epigenetic mechanisms likely influence early lineage specification through the regulation of mitochondrial function and modification of nuclear chromatin structure. This review summarizes previous and recent findings on the processes involved in early lymphocyte differentiation. Thus, it provides a foundation for the understanding of the physiology of HSC aging and the pathology of intractable acute lymphocytic leukemia.

An 18-year-old woman presented with fever and liver dysfunction. Computed tomography showed lymphadenopathy, hepatosplenomegaly, and vascular lesions such as aneurysms and irregularities at multiple arteries, including coronary arteries. Based on the high copy number of Epstein-Barr virus (EBV)-DNA in the peripheral blood, EBV-infected CD4+T cells, and the proliferation of EBER-positive cells in the bone marrow, chronic active EBV infection (CAEBV) was diagnosed. Although the fever and liver dysfunction improved as a result of the initial immunosuppressive therapy and multiagent chemotherapy, EBV-DNA remained high. Moreover, she experienced repeated episodes of angina pectoris due to coronary arterial lesions. Therefore, cord blood transplantation was performed after reduced-intensity conditioning. EBV-DNA decreased quickly after initiating the conditioning and became undetectable at day 7 after the transplant. Vascular lesions did not progress after the transplant, and the patient's angina pectoris resolved. At 2.5 years after the transplant, she is alive without disease recurrence. The prognosis of CAEBV with vascular lesions is especially poor. Although the indication for allogeneic hematopoietic stem cell transplantation (HSCT) is difficult to determine in such cases, the clinical course of our case suggests that allogenic HSCT could be safely performed under appropriate management and could successfully control not only CAEBV but also vascular lesions.

A 45-year-old man initially diagnosed with aplastic anemia had been receiving treatment for >4 years when he visited our hospital for a detailed examination. On admission, bone marrow (BM) aspiration showed erythroid dysplasia and chromosomal abnormalities, including trisomy 3 in 1/20 cells. After 3 months of observation, BM aspiration showed the involvement of 5% abnormal lymphocytes, and flow cytometry revealed a monoclonal B-cell phenotype. After a further 5 months of observation, his blood test showed a sudden elevation in white blood cell (WBC) count and the presence of villous lymphocytes. Fluorodeoxyglucose-positron emission tomography (FDG-PET) only revealed strong uptake by systemic BM, and BM aspiration showed the involvement of 76.4% abnormal lymphocytes, which were positive for CD19 and dim CD11c; negative for CD25, CD103, cyclin D1, and BRAF-V600E; and exhibited light chain restriction. The patient was diagnosed with marginal zone lymphoma-like primary bone marrow (BM) lymphoma. Treatment with R-CHOP and R-cladribine failed. He then underwent an allogeneic peripheral blood stem cell transplantation from a human leucocyte antigen (HLA)-identical sibling, and he has since remained in good health and without relapse for 9 years. Further clinical and biological analyses are necessary to establish an optimal treatment strategy for this disease.