Recently, allogeneic peripheral blood stem cell transplantation from human leukocyte antigen (HLA)-haploidentical donors using post-transplantation cyclophosphamide (PTCY-haploPBSCT) has become available in clinical practice. However, the efficacy of PTCY in adult T-cell leukemia (ATL) is not fully established yet. In this study, we retrospectively examined data of seven patients who underwent PTCY-haploPBSCT. The overall survival rate at 100 days after transplantation was 85.7%, and the 1-year overall survival rate was 68.6%. The cumulative incidence of relapse at 1 year was 31.4%, whereas the 1-year nonrelapse mortality was 17.1%. The cumulative incidence of grade III-IV acute graft-versus-host disease (GVHD) on day 100 was 14.3%, and the incidence of chronic GVHD at 1 year was 33.3%. These results suggest that PTCY-haploPBSCT can be a viable option even in patients with ATL. Further accumulation of knowledge and improvement of transplantation outcomes are warranted in the future.

Using post-transplant cyclophosphamide (PTCy-haplo), haploidentical allogeneic hematopoietic stem cell transplantation has shown a surge in popularity in recent years. There are, however, only a few reports of PTCy-haplo being used to treat myelodysplastic syndromes (MDS) that have been complicated by myeloid sarcoma (MS). An immuno-suppressive therapy was given to a 25-year-old man who was diagnosed with low-risk MDS in September 2007. After an ileocecal ulcer biopsy that revealed MS in July 2019, a chromosomal analysis of the bone marrow cells in August 2019 revealed loss of chromosome 7, which is associated with poor prognosis. Because the patient lacked an HLA-matched sibling donor, he underwent PTCy-haplo in December 2019. On day 33, complete remission and donor chimerism was achieved. Ileocecal ulcer scarring was discovered by a colonoscopy on day 54. Grade I cutaneous acute graft-versus-host disease was discovered approximately on day 30 and treated with topical steroids. PTCy-haplo may be an effective treatment for MS.

A 31-year-old man underwent allogeneic bone marrow transplantation (BMT) for the treatment of transfusion-dependent aplastic anemia (AA) after conditioning with a regimen including fludarabine, cyclophosphamide, and antithymocyte globulin. The patient developed a late graft rejection on day 103 and showed autologous hematologic recovery not requiring transfusions on day 76. Peripheral blood leukocytes were of 100% recipient origin on day 103, and paroxysmal nocturnal hematuria (PNH)-type granulocytes were detected 5 months after BMT. The patient suddenly experienced hemolytic symptoms triggered by cold stimulation, and was diagnosed with autoimmune hemolytic anemia (AIHA) 37 months after BMT. Although anemia was ameliorated by prednisolone (PSL), hemolytic attacks repeatedly occurred, which became refractory to corticosteroids. Moreover, the patient underwent a splenectomy for the steroid-resistant AIHA and achieved AIHA remission without the need for PSL at 53 months after BMT. The immune tolerance breakdown to erythrocyte antigens was thought to have occurred due to various factors including immune AA, medication, cold stimulation, and infection, leading to AIHA development in this case.

Recent studies have demonstrated that cancer-specific metabolism plays a crucial role in a variety of malignancies, including acute myeloid leukemia (AML). To identify a novel therapeutic target for AML, we conducted a metabolite screen on AML cells and normal hematopoietic stem/progenitor cells (HSPCs) and detected that the metabolism of glycerol-3-phosphate (G3P) is reprogrammed in AML. Glycerol-3-phosphate acyltransferases (GPATs), the first and rate-limiting enzymes in the lipid biosynthesis pathway, convert G3P into lysophosphatidic acid (LPA). Among various GPAT isozymes, GPAT1 was highly expressed in AML cells and silencing it inhibited the cell growth of AML. GPAT1 is located on the outer membrane of the mitochondria and regulates mitochondrial fusion and oxidative phosphorylation (OXPHOS). Silencing GPAT1 promoted mitochondrial fission and reduced OXPHOS. In AML, the GPAT1 inhibitor also suppressed cell proliferation and mitochondrial metabolism. However, this inhibitor had no effect on normal hematopoiesis in vivo. In conclusion, these findings indicate that targeting GPAT1 may be a promising therapeutic strategy for AML, since it suppresses leukemia-specific metabolism without impairing normal HSPCs.

Histiocytosis is a syndrome characterized by fever, pain, and other symptoms caused by the neoplastic proliferation of atypical cells of the macrophage-dendritic cell lineage and surrounding inflammatory cell infiltration. The diagnosis is confirmed by the immune-histological features of biopsied specimens. From this viewpoint, histiocytosis is divided into Langerhans cell histiocytosis (LCH) (CD1a+/CD207+/CD14±/CD68±) and non-LCH, including Erdheim-Chester disease (ECD), juvenile xanthogranuloma, and Rosai-Dorfman disease (CD1a−/CD207−/CD14++/CD68++). Genetic alterations occur at the cellular level in hematopoietic progenitor cells, and environmental factors are assumed to influence tumor development. The genomic analysis of the lesions involved revealed driver mutations primarily in the MAPK pathway, including BRAF-V600E, and the PI3K pathway. This strongly suggests that abnormalities in these signaling pathways play a role in pathogenesis. Steroids, vinca alkaloids, cytarabine, and cladribine are commonly used to treat histiocytosis. However, efficacy has not been fully confirmed in any of them. In recent years, the efficacy of BRAF inhibitors and MEK inhibitors has been reported mainly in therapy-resistant and refractory cases of LCH and ECD.

Macrophages are historically well appreciated for their functions in host defense and phagocytosis, and they are among the most multifunctional and heterogeneous cell types present in virtually every tissue. Macrophages perform many tissue-specific functions that are essential for the maintenance of tissue homeostasis, and abnormalities in macrophage functions have been linked to various pathologies, including histiocytic syndromes. In this talk, I shall discuss macrophage biology from homeostatic and disease perspectives.

Langerhans cell histiocytosis (LCH) is characterized by immature dendritic cell proliferation, which is currently classified as an inflammatory myeloid neoplasm. Clinical features and outcomes vary from spontaneously regressing isolated bone disease to fatal liver, spleen, or hematopoietic system (risk organ) involvement-positive multisystem disease. LCH cells have the only mutation in the mitogen-activated protein kinase (MAPK) signaling pathway gene, represented by the BRAF V600E mutation, which is the driver mutation. The type of disease depends on the stage of hematopoietic cell differentiation at which the mutation occurs. LCH cells acquire anti-apoptosis and senescence-associated secretory phenotype by oncogene-induced senescence, with migration failure to lymph nodes. These cause LCH cell accumulation and various inflammatory cell recruitment in the lesion, resulting in severe inflammation. Tissue damage in LCH is due to this inflammation, not the LCH cell proliferation. Patients with a risk of organ involvement without the initial treatment response may be rescued by allogeneic hematopoietic stem cell transplantation after reducing the disease activity with MAPK inhibitors. Intravenous zoledronic acid and intrathecal cytarabine injections have been introduced into the ongoing clinical trial in Japan to reduce bone recurrence and prevent neurodegeneration as sequelae.

Histiocytosis is classified based on proliferating histiocyte-like cells. Langerhans cell histiocytosis (LCH) has several subtypes with various outcomes, from spontaneous to fatal regression, and these subtypes had been managed as different diseases. However, these different names of disease were unified to one disease named histiocytosis X since they are pathologically identical. Presently, LCH has been used as a unified name because proliferating cells have the characteristics of Langerhans cells. Since then, clonality and BRAF mutations have been reported, and their neoplastic characteristics has become clear; however, explaining its various subtypes is difficult with only the neoplastic character. Various relationships/correlations are also known between inflammatory factors and LCH subtypes. We have pointed out that the Merkel cell polyomavirus may be involved in LCH development and LCH is a disease with both neoplastic and reactive characters, that is, “a disease in which abnormal Langerhans-like cells with neoplastic character overreact to some triggers.”

A DNA aptamer to the von Willebrand factor (VWF) A1 domain, TAGX-0004, inhibits the binding of VWF to platelets. Nucleic acid aptamers are single-stranded DNA or RNA molecule forming three-dimensional structures that are capable of specifically binding to proteins and are expected to contribute to alternative medicine. ARC1779, an aptamer targeting the VWF A1 domain, had been evaluated in a phase II clinical trial of patients with acquired thrombotic thrombocytopenic purpura (aTTP); however, its development was terminated. Caplacizumab, an anti-VWF A1 domain nanobody, is now increasingly employed as first-line therapy for the treatment of aTTP in Western countries. However, there have been reports regarding adverse bleeding events and the high cost of the treatment. In this study, the inhibitory effects of TAGX-0004 were compared with those of ARC1779 and caplacizumab on in vitro platelet aggregation and thrombus formation. TAGX-0004 had an excellent high affinity to the VWF A1 domain and superior efficacy, such as its potent inhibitory activity in in vitro platelet aggregation and thrombus formation. Therefore, it can potentially overcome the problems associated with caplacizumab and can be developed as a promising drug not only for aTTP treatment but also for the treatment of the various VWF-mediated thrombotic disorders.

The mortality rate due to coronavirus disease 2019 (COVID-19) reached 5.3 million. However, identifying the novel treatment targets that ultimately reduce or prevent disease aggravation will be possible by understanding the mechanism and pathophysiology underlying the COVID-19 aggravation. Authors of previous studies have identified the “cytokine storm” that constitutes the secretion of inflammatory cytokines driven by the coagulation/fibrinolytic system as an inflammatory cytodynamic control mechanism that contributes to the aggravated COVID-19 pathology and the pathophysiology of related diseases. Vasculature-lining endothelial cells are bioreactors that produce or contribute to the modulation status of cytokines and coagulation and fibrinolytic system factors. The key steps in the pathophysiology of organ damage include the destabilization of the angiocrine system triggered by vascular endothelial damage during severe COVID-19. Overproduced or imbalanced angiocrine factors and inflammatory cytokines contribute to major COVID-19 complications. Within its scope, this study outlines the significance of the fibrinolytic system in the pathophysiology of inflammatory diseases, focusing on the research results. The possibility of molecular that target these angiocrine and fibrinolytic factors for inflammatory diseases as novel treatment approaches for inflammatory diseases, such as COVID-19, was discussed.

Antithymocyte globulin (ATG) for graft-versus-host disease (GVHD) prophylaxis has been demonstrated for chronic GVHD inhibition by a series of randomized control trials. The optimal dose of ATG remained unestablished; however, the recommended dose of ATG by the European Group for Blood and Marrow Transplantation has recently decreased. While a lower ATG dose has been used in Japan, ATG usage is recommended in peripheral blood stem cell transplantation or human leukocyte antigens (HLA) 1-locus mismatched bone marrow transplantation with myeloablative conditioning from the nation-wide retrospective studies showing that ATG inhibited chronic GVHD and improved GVHD-free, relapse-free survival. The association of absolute lymphocyte counts (ALC) before ATG administration with transplant outcomes has been reported, which suggests a possible strategy to individualize the ATG dose according to ALC before ATG. Recent studies compared the transplant outcomes using ATG and post-transplant cyclophosphamide, which has rapidly spread in haploidentical transplantation; however, further studies are needed to establish those positioning in HLA-matched/mismatched transplantation.

Graft-versus-host disease (GVHD), which is characterized by T-cell activation following allogeneic hematopoietic cell transplantation (allo-HCT), remains one of the most significant hurdles directly or indirectly affecting transplant outcomes. With improved knowledge, experimental and clinical models have been established over the last two decades to predict the clinical utility of novel therapeutic agents, and clinical care has progressed. In addition, recent advances have revealed mechanisms underlying GVHD that focus on the breakdown of tissue tolerance following allo-HCT, complementing established concepts of immunological intolerance that allo-reactive T cells and antigen-presenting cells contribute to the development and aggravation of GVHD. The pathophysiology of GVHD as influenced by various cells and tissues and therapeutic strategies based on mechanistic findings to advance the understanding of GVHD and individualize allo-HCT have been discussed in this review.

Chronic graft-versus-host disease (GVHD) affects various organs and causes significant morbidity and mortality after allogeneic hematopoietic cell transplantation. The 2005 National Institutes of Health consensus criteria for chronic GVHD have set international standards for endpoints and designing and reporting of clinical trials; these criteria were revised in 2014 to incorporate accumulated evidence and controversies. In addition, preclinical studies of chronic GVHD have identified treatment targets such as regulatory T cells, B-cell signaling, Th17 cells, Tc17 cells, follicular helper T cells, follicular regulatory T cells, and fibrosis-promoting factors. These efforts led to the approval of ibrutinib, belumosudil, and ruxolitinib by the U.S. Food and Drug Administration for treating chronic GVHD after failure of one or more lines of systemic therapy, and an increasing number of investigational agents that target different biological pathways of chronic GVHD are under development in clinical trials. To address challenges in a rapidly evolving field, a third National Institutes of Health consensus project was held in 2020, in which investigators, patient advocacy organizations, and pharmaceutical companies aimed to define basic and clinical research roadmaps that may lead to significant change in chronic GVHD management over the next 5 years.

During the treatment of disseminated intravascular coagulation (DIC) associated with hematopoietic malignancies (particularly, acute leukemia), fatal bleeding, such as cerebral, alveolar, and gastrointestinal hemorrhages at diagnosis or immediately after initiating treatment, determines the patient’s prognosis. DIC should always be suspected in such cases, and the diagnosis should be made on the basis of the former Ministry of Health and Welfare DIC diagnostic criteria or the 2017 Japanese Society on Thrombosis and Hemostasis DIC diagnostic criteria. This treatment requires the use of appropriate anticoagulants and replacement therapies. The anticoagulant should be chosen based on the patient’s risk of bleeding. Here we present the recent evidence of DIC complicating hematopoietic malignancies with antithrombin agents and recombinant human soluble thrombomodulin. Moreover, prognostic markers during the course of therapy have been reported. The effect of treatment, including withdrawal from DIC, should be carefully assessed. In the future, detailed evidence regarding the tumor subtype, tumor burden, and disease severity will be required to ensure appropriate drug choice for the treatment.

Antiplatelet factor 4 (PF4) antibodies, also known as anti-PF4/heparin complex antibodies, are measured to diagnose heparin-induced thrombocytopenia (HIT). In HIT, anti-PF4 antibodies induced by heparin exposure cause thrombocytopenia and thrombosis. However, in recent years, autoimmune HIT (aHIT) that develops without heparin exposure has been getting attention. In 2021, anti-PF4 antibodies were reported to cause the fatal vaccine-induced immune thrombotic thrombocytopenia (VITT) that developed after adenoviral vector vaccination for COVID-19. HIT, aHIT, and VITT are considered to be caused by anti-PF4 antibodies, and their pathological conditions are similar. However, they have different levels of severity, and the detection sensitivity of their antibodies varies depending on the assay. Herein, we review three pathologies, namely, HIT, aHIT, and VITT, associated with anti-PF4 antibodies.

Thrombotic microangiopathy (TMA) is a pathological condition characterized by platelet thrombi-induced generalized microvascular occlusion, thrombocytopenia, and microangiopathic hemolytic anemia. TMA includes the life-threatening diseases thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS). TTP is different from HUS in that it has a severe deficiency in ADAMTS13 activity. Congenital TTP is caused by a lack of plasma ADAMTS13 activity caused by genetic mutations, and acquired TTP is caused by a secondary deficiency caused by autoantibodies. In Japan the only product approved for the treatment of congenital TTP is fresh frozen plasma containing ADAMTS13. Recombinant ADAMTS13 may provide a new treatment option for congenital TTP. The first-line treatment for acquired TTP is plasma exchange. Rituximab treatment should be considered for patients who are refractory or have relapsed. Caplacizumab is a nanobody that specifically targets von Willebrand factor. ISTH recently published guidelines recommending that caplacizumab be added to the initial treatment for acquired TTP. Atypical HUS (aHUS) is related with the dysregulation of the complement alternative pathway. Eculizumab, a monoclonal antibody that inhibits C5, was the first drug approved for aHUS, and it was found to be well-tolerated by patients and effective in clinical use. TMA is classified based on its etiology, and specific treatments for targeting various etiologies are now available.

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 and is known to have thrombotic complications. Various-sized thrombosis occurs in the arteries and veins, especially in lung tissue. The prevention and treatment of thrombosis is an important issue that is directly linked to its prognosis. Additionally, the drastic fibrinolytic enhancement and lethal bleeding in some severe COVID-19 are important issues. The efficacy of antiplatelet for COVID-19 is controversial. Thus, warfarin or tranexamic acid alone should be avoided. Heparin is effective for mild to moderate COVID-19 but is ineffective in severe cases since the anticoagulant activity of heparin is insufficient or heparin increases major bleeding. In severe COVID-19 cases with drastic fibrinolytic enhancement, heparin and nafamostat combination therapy may avoid lethal bleeding. In COVID-19 clinical practice, not only the coagulation activation was evaluated but also the fibrinolytic activation to consider treatment strategies.