A Review of Advances in Hematopoietic Stem Cell Mobilization and the Potential Role of Notch2 Blockade

Updates on the mobilization pipeline for hematopoietic stem cell collection

Hematopoetic Stem Cell Transplantation is a life saving procedure which requires mobilization of stem cells for apheresis procedure. In this review we aimed to examine mobilizing agents that are in use and under investigation. Apheresis practitioners who oversee stem cell collections should be familiar with the recent advances in mobilization agents to utilize most up-to-date information for better patient outcomes.

The Effect of Iron Overload on the Mobilization of Peripheral Blood Hematopoietic Stem Cells in Pediatric Patients with Thalassemia Major

INTRODUCTION

The purpose of this study was to examine the effect of iron overload on the mobilization of peripheral blood stem cells (PBSCs) in pediatric patients with β-thalassemia major (TM).

METHODS

We retrospectively reviewed the records of 226 patients with TM from whom PBSCs were collected. Iron overload was based on serum ferritin level, and liver and cardiac iron overload was measured by magnetic resonance imaging (MRI) T2*.

RESULTS

The mean age of the TM patients was 7.35 ± 3.41 years. Of the patients, only 171 received MRI. Of the 171 patients, 35 had normal liver iron levels, 39 mild liver iron overload, 90 intermediate liver iron overload, and 7 severe liver iron overload. The intermediate + severe group was associated with significantly higher age and BMI and lower leukapheresis product white blood cell count and CD34+ cell levels (all, p < 0.05).

CONCLUSION

Leukapheresis indices were similar between patients with different degrees of iron overload according to the ferritin level and cardiac iron overload, in which the later might be due to the small number of patients with cardiac overload. In patients with TM, the intermediate and severe liver iron overload was associated with poorer mobilization of PBSCs.

Take a spin: Apheresis in the care of adult leukaemia patients

Apheresis is an automated process to separate the whole blood of a patient or a donor, collect or remove specific blood components, and return the remaining back to the individual. Apheresis is an integral part of blood and marrow transplantation and has been increasingly utilized in novel cellular therapies for a variety of blood disorders. This review uses clinical cases to highlight the multiple roles of apheresis in the care of adult leukaemia patients, including therapeutic leukapheresis in hyperleukocytosis, mobilized peripheral blood hematopoietic progenitor cell collection in donors, mononucleated cell collection in preparation of donor lymphocyte infusion or chimeric antigen receptor T cells manufacture, and extracorporeal photopheresis in the treatment of graft versus host diseases.

Hematopoietic stem cell mobilization

Hematopoietic stem cell (HSC) transplantation has been used to treat hematopoietic diseases for over 50 years. HSCs can be isolated from bone marrow (BM), umbilical cord blood, or peripheral blood. Because of lower costs, shorter hospitalization, and faster engraftment, peripheral blood has become the predominant source of HSCs for transplantation. The major factors determining the rate of successful HSC transplantation include the degree of human leukocyte antigen matching between the donor and recipient and the number of HSCs for transplantation. Administration of granulocyte colony-stimulating factor (G-CSF) alone or combined with plerixafor (AMD3100) are clinical used methods to promote HSC mobilization from BM to the peripheral blood for HSC transplantations. However, a significant portion of healthy donors or patients may be poor mobilizers of G-CSF, resulting in an insufficient number of HSCs for the transplantation and necessitating alternative strategies to increase the apheresis yield. The detailed mechanisms underlying G-CSF-mediated HSC mobilization remain to be elucidated. This review summarizes the current research on deciphering the mechanism of HSC mobilization.

Notch Signaling in the Bone Marrow Lymphopoietic Niche

Lifelong mammalian hematopoiesis requires continuous generation of mature blood cells that originate from Hematopoietic Stem and Progenitor Cells (HSPCs) situated in the post-natal Bone Marrow (BM). The BM microenvironment is inherently complex and extensive studies have been devoted to identifying the niche that maintains HSPC homeostasis and supports hematopoietic potential. The Notch signaling pathway is required for the emergence of the definitive Hematopoietic Stem Cell (HSC) during embryonic development, but its role in BM HSC homeostasis is convoluted. Recent work has begun to explore novel roles for the Notch signaling pathway in downstream progenitor populations. In this review, we will focus an important role for Notch signaling in the establishment of a T cell primed sub-population of Common Lymphoid Progenitors (CLPs). Given that its activation mechanism relies primarily on cell-to-cell contact, Notch signaling is an ideal means to investigate and define a novel BM lymphopoietic niche. We will discuss how new genetic model systems indicate a pre-thymic, BM-specific role for Notch activation in early T cell development and what this means to the paradigm of lymphoid lineage commitment. Lastly, we will examine how leukemic T-cell acute lymphoblastic leukemia (T-ALL) blasts take advantage of Notch and downstream lymphoid signals in the pathological BM niche.

Current Views on the Roles of O-Glycosylation in Controlling Notch-Ligand Interactions

The 100th anniversary of Notch discovery in Drosophila has recently passed. The Notch is evolutionarily conserved from Drosophila to humans. The discovery of human-specific Notch genes has led to a better understanding of Notch signaling in development and diseases and will continue to stimulate further research in the future. Notch receptors are responsible for cell-to-cell signaling. They are activated by cell-surface ligands located on adjacent cells. Notch activation plays an important role in determining the fate of cells, and dysregulation of Notch signaling results in numerous human diseases. Notch receptors are primarily activated by ligand binding. Many studies in various fields including genetics, developmental biology, biochemistry, and structural biology conducted over the past two decades have revealed that the activation of the Notch receptor is regulated by unique glycan modifications. Such modifications include O-fucose, O-glucose, and O-N-acetylglucosamine (GlcNAc) on epidermal growth factor-like (EGF) repeats located consecutively in the extracellular domain of Notch receptors. Being fine-tuned by glycans is an important property of Notch receptors. In this review article, we summarize the latest findings on the regulation of Notch activation by glycosylation and discuss future challenges.