Isolation Method for Long-Term and Short-Term Hematopoietic Stem Cells.

Self-renewal capacity and multi-lineage differentiation potential are generally regarded as the defining characteristics of hematopoietic stem cells (HSCs). However, numerous studies have suggested that functional heterogeneity exists in the HSC compartment. Recent single-cell analyses have reported HSC clones with different cell fates within the HSC compartment, which are referred to as biased HSC clones. The mechanisms underlying heterogeneous or poorly reproducible results are little understood, especially regarding the length of self-renewal when purified HSC fractions are transplanted by conventional immunostaining. Therefore, establishing a reproducible isolation method for long-term HSCs (LT-HSCs) and short-term HSCs (ST-HSCs), defined by the length of their self-renewal, is crucial for overcoming this issue. Using unbiased multi-step screening, we identified a transcription factor, Hoxb5, which may be an exclusive marker of LT-HSCs in the mouse hematopoietic system. Based on this finding, we established a Hoxb5 reporter mouse line and successfully isolated LT-HSCs and ST-HSCs. Here we describe a detailed protocol for the isolation of LT-HSCs and ST-HSCs using the Hoxb5 reporter system. This isolation method will help researchers better understand the mechanisms of self-renewal and the biological basis for such heterogeneity in the HSC compartment.

Identification of the minimum requirements for successful haematopoietic stem cell transplantation.

Historically, defining haematopoietic subsets, including self-renewal, differentiation and lineage restriction, has been elucidated by transplanting a small number of candidate cells with many supporting bone marrow (BM) cells. While this approach has been invaluable in characterising numerous distinct subsets in haematopoiesis, this approach is arguably flawed. The haematopoietic stem cell (HSC) has been proposed as the critical haematopoietic subset necessary for transplantation. However, due to the presence of supporting cells, the HSC has never demonstrated sufficiency. Utilising the homeobox B5 (Hoxb5)-reporter system, we found that neither long-term (LT) HSCs nor short-term (ST) HSCs alone were sufficient for long-term haematopoietic reconstitution. Critically, reconstitution can be rescued by transplanting combined LT- and ST-HSCs, without supporting cells; a fraction we term the 'Minimum Subset for Transplantation' (MST). The MST accounts for only 0·005% of nucleated cells within mouse BM, and this MST can be cultured, expanded and genetically modified while preserving its rapid haematopoietic engraftment potential. These results support the consideration of an MST approach for clinical translation, especially for gene therapy approaches that require HSC compartment modification.

Hoxb5 defines the heterogeneity of self-renewal capacity in the hematopoietic stem cell compartment.

Self-renewal and multipotency are essential functions of hematopoietic stem cells (HSCs). To maintain homeostatic hematopoiesis, functionally uniform HSCs have been thought to be an ideal cell-of-origin. Recent technological advances in the field have allowed us to analyze HSCs with single cell resolution and implicate that functional heterogeneity may exist even within the highly purified HSC compartment. However, due in part to the technical limitations of analyzing extremely rare populations and our incomplete understanding of HSC biology, neither the biological meaning of why heterogeneity exists nor the precise mechanism of how heterogeneity is determined within the HSC compartment is entirely known. Here we show the first evidence that self-renewal capacity varies with the degree of replication stress dose and results in heterogeneity within the HSC compartment. Using the Hoxb5-reporter mouse line which enables us to distinguish between long-term (LT)-HSCs and short-term (ST)-HSCs, we have found that ST-HSCs quickly lose self-renewal capacity under high stress environments but can maintain self-renewal under low stress environments for long periods of time. Critically, exogeneous Hoxb5 expression confers protection against loss of self-renewal to Hoxb5-negative HSCs and can partially alter the cell fate of ST-HSCs to that of LT-HSCs. Our results demonstrate that Hoxb5 imparts functional heterogeneity in the HSC compartment by regulating self-renewal capacity. Additionally, Hoxb5-positive HSCs may exist as fail-safe system to protect from the exhaustion of HSCs throughout an organism's lifespan.

Impact of the Use and Type of Antibiotics on Acute Graft-versus-Host Disease.

The intestinal microbiota plays an important role in the pathogenesis of acute graft-versus-host disease (aGVHD). During the course of hematopoietic stem cell transplantation (HSCT), the intestinal microbiota is influenced by the use of broad-spectrum antibiotics. However, the impact of the use and type of antibiotics on the microbiota composition and, subsequently, the onset of aGVHD remain poorly understood. We hypothesized that the use and type of antibiotics had an impact on the occurrence of aGVHD. We assessed 275 patients who underwent their first allogeneic HSCT between January 2005 and June 2015 at Kyoto University Hospital. We monitored the 6 most frequently administered antibiotics (fourth-generation cephalosporins, glycopeptides, piperacillin-tazobactam, carbapenems, aminoglycosides, and quinolones) administered between days -14 and +14 relative to HSCT and its duration. The primary endpoint was the cumulative incidence of grades II to IV aGVHD. The cumulative incidence of aGVHD was significantly higher in patients administered fourth-generation cephalosporins than in patients not receiving fourth-generation cephalosporins (grades II to IV: hazard ratio, 1.98; 95% confidence interval, 1.19 to 3.29; P = .0087; grades III to IV: hazard ratio, 8.03; 95% confidence interval, 1.07 to 60.51; P = .043). In contrast, there was no significant association between administration of other antibiotics and aGVHD incidence. As for organ-specific aGVHD, the cumulative incidence of gut aGVHD was significantly higher in patients who received fourth-generation cephalosporins than in those who did not (31% versus 16%, P = .018). In conclusion, we demonstrated that the administration of fourth-generation cephalosporins had a strong impact on the development of aGVHD.

Rapidly progressive autoimmune pancytopenia successfully treated with steroids.

A 73-year-old woman was admitted to our hospital because of pancytopenia. Bone marrow aspiration showed increased cellularity with no dysplastic change. Laboratory tests revealed increased reticulated erythrocytes and reticulated platelets, positive direct Coombs test, and hemolysis. These findings led to the diagnosis of Evans syndrome. Relatively decreased mature neutrophils in the bone marrow aspirate raised the possibility of autoimmune neutropenia. Antineutrophil antibody was detected by the 6 cell-lineage immunofluorescence test, consistent with the diagnosis of autoimmune neutropenia. The patient had no underlying diseases, and was therefore considered to have idiopathic autoimmune pancytopenia. Due to rapid progression of the disease, prednisolone was administered at an initial dose of 0.5 mg/kg per day and the pancytopenia improved promptly.

Successful Treatment of TAFRO Syndrome, a Variant of Multicentric Castleman's Disease, with Cyclosporine A: Possible Pathogenetic Contribution of Interleukin-2.

Multicentric Castleman's disease is a systemic inflammatory disorder characterized by lymphadenopathy and excessive interleukin-6 production. A unique clinicopathologic variant of multicentric Castleman's disease, TAFRO (i.e., thrombocytopenia, anasarca, fever, renal failure or reticulin fibrosis, and organomegaly) syndrome, was recently proposed in Japan. Despite the successful use of anti-interleukin-6 therapy in some patients with TAFRO syndrome, not all patients achieve remission. The pathophysiological etiology of and suitable therapeutic strategies for this variant have not been established. Here, we present our experience of a unique case of TAFRO syndrome in a 78-year-old woman whose symptoms responded differently to several therapies. Tocilizumab, an anti-interleukin-6 receptor antibody, successfully induced remission of fever and lymphadenopathy. However, severe thrombocytopenia persisted and she developed anasarca, ascites, and pleural effusion shortly thereafter. Rituximab, an anti-CD20 antibody, and glucocorticoid therapy provided no symptom relief. In contrast, cyclosporine A, an immunosuppressive agent that blocks T cell function by inhibiting interleukin-2, yielded immediate improvements in systemic fluid retention and a gradual increase in platelet count, with complete resolution of disease symptoms. Excessive serum interleukin-2, when used as an anti-cancer agent, has been reported to cause side effects such as fluid retention, thrombocytopenia, and renal failure. Our case was unique because the anti-interleukin-2 therapy successfully improved symptoms that were not relieved with anti-interleukin-6 therapy. The present report therefore provides insight into the possible role of interleukin-2, in addition to interleukin-6, in TAFRO syndrome. This report will certainly help to clarify the pathogenesis of and optimal treatment strategies for TAFRO syndrome.