Update on clinical experience with AMD3100, an SDF-1/CXCL12-CXCR4 inhibitor, in mobilization of hematopoietic stem and progenitor cells

Investigation of the effective action distance between hematopoietic stem/progenitor cells and human adipose-derived stem cells during their in vitro co-culture

The in vitro suitable action distance between umbilical cord blood-derived hematopoietic stem/progenitor cells and its feeder cell, human adipose-derived stem cells, during their co-culture, was investigated through a novel transwell co-culture protocol, in which the distance between the two culture chambers where each cell type is growing can be adjusted from 10 to 450 μm. The total cell number was determined with a hemacytometer, and the cell morphology was observed under an inverted microscope each day. After 7 days of co-culture, the fold-expansion, surface antigen expression of CD34(+) and CFU-GM assay of the hematopoietic mononuclear cells (MNCs) were analyzed. The results showed that there was an optimal communication distance at around 350 μm between both types of stem cells during their in vitro co-culture. By using this distance, the UCB-MNCs and CD34(+) cells were expanded by 15.1 ± 0.2 and 5.0 ± 0.1-fold, respectively. It can therefore be concluded that the optimal action distance between stem cells and their supportive cells, when cultured together for 7 days, is of around 350 μm.

[CXCR4, a therapeutic target in rare immunodeficiencies?]

Currently, more than 200 primary immunodeficiency diseases have been discovered. In most cases, genetic defects affect the expression or the function of proteins involved in immune development and homeostasis. Some orphan immuno-hematological disorders are characterized by an abnormal leukocyte trafficking, a notion predictive of an anomaly of the chemokine/chemokine receptor system. In this review, we focus on recent advances in the characterization of dysfunctions of the CXCL12 (SDF-1)/CXCR4 signaling axis in two rare human immunodeficiencies, one associated with a loss of CXCR4 function, the Idiopathic CD4(+) T-cell Lymphocytopenia, and the other with a gain of CXCR4 function, the WHIM syndrome.

Twenty-five years of peripheral blood stem cell transplantation

Peripheral blood stem cell transplantation (PBSCT) is the most common transplantation procedure performed in medicine. Its clinical introduction in 1986 replaced BM as a stem-cell source to approximately 100% in the autologous and to approximately 75% in the allogeneic transplantation setting. This historical overview provides a brief insight into the discovery of circulating hematopoietic stem cells in the early 1960s, the development of apheresis technology, the discovery of hematopoietic growth factors and small molecule CXCR4 antagonist for stem- cell mobilization, and in vivo experimental transplantation studies that eventually led to clinical PBSCT. Also mentioned are the controversies surrounding the engraftment potential of circulating stem cells before acceptance as a clinical modality. Clinical trials comparing the outcome of PBSCT with BM transplantation, registry data analyses, and the role of the National Marrow Donor Program (NMDP) in promoting unrelated blood stem-cell donation are addressed.

Bone marrow as a source of hematopoietic stem cells for human gene therapy of β-thalassemia

β-Thalassemia is a severe inherited anemia caused by insufficient production of β-globin chains. Allogeneic hematopoietic stem cell (HSC) transplantation is currently the only cure, and is limited by donor availability and regimen-related toxicity and mortality. Gene therapy is a promising therapeutic tool for all thalassemic patients lacking a compatible donor and potentially provides transfusion independence in the absence of transplant-related complications, such as graft rejection and graft-versus-host disease. The issue of HSC procurement is critical in this setting because of the specific features of thalassemic syndromes, which include bone marrow (BM) expansion, ineffective erythropoiesis, and splenomegaly. Little is known about the efficiency of CD34(+) cell yield from steady-state BM harvests from thalassemic patients. We have collected data on safety and cell yield from 20 pediatric patients with β-thalassemia who underwent autologous BM harvest before allogeneic HSC transplantation, and from 49 age-matched sibling donors who also underwent BM harvest. The procedure was safe, as no significant adverse events occurred. In terms of cell yield, no difference was found between patients and normal donors in the number of CD34(+) cells and total nucleated cells harvested. Most importantly, no difference was found in the proportion of myeloid and erythroid progenitors, suggesting a similar repopulating capacity. On the basis of these results, we conclude that steady-state BM can be used as a safe and efficient source of HSC for gene therapy of β-thalassemia.

[Dysfunctions of the CXCL12 (SDF-1)/CXCR4 signaling axis in the WHIM syndrome and the idiopathic CD4(+) T-cell lymphocytopenia]

Chemokines are small cytokine-like secreted proteins that govern migration of leukocytes to their specific niches in lymphoid organs and to inflammatory sites. They mediate their functions by binding to and activating chemokine receptors, which belong to the heptahelical G protein-coupled receptor family. The CXC chemokine Stromal cell Derived Factor-1 (SDF-1/CXCL12) is the sole natural ligand for the broadly expressed CXCR4 receptor and acts as a chemoattractant for many leukocyte subsets. The CXCL12/CXCR4 axis exerts critical activities in homeostatic processes such as organogenesis, hematopoiesis and leukocyte trafficking. Dysregulations of CXCR4 signaling and/or expression are associated with several infectious, inflammatory, autoimmune and malignant conditions. In light of recent data, we review here CXCR4 dysfunctions unveiled in two rare human immunodeficiency disorders, one characterized by a gain of CXCR4 function, the WHIM syndrome, and the other by a loss of CXCR4 function, the idiopathic CD4(+) T-cell lymphocytopenia.

The role of chemokine receptor CXCR4 in the biologic behavior of human soft tissue sarcoma

The molecular basis of sarcoma remains poorly understood. However, recent studies have begun to uncover some of the molecular pathways involved in sarcomagenesis. The chemokine receptor CXCR4 has been implicated in sarcoma development and has been found to be a prognostic marker for poor clinical outcome. There is growing evidence that overexpression of CXCR4 plays a significant role in development of metastatic disease, especially in directing tumor cells towards the preferential sites of metastases in sarcoma, lung and bone. Although further investigation is necessary to validate these pathways, there is potential for clinical application, particularly in the use of pharmacologic inhibitors of CXCR4 as means of preventing sarcoma metastasis.

The brain-bone-blood triad: traffic lights for stem-cell homing and mobilization

Navigation of transplanted stem cells to their target organs is essential for clinical bone marrow reconstitution. Recent studies have established that hematopoietic stem cells (HSCs) dynamically change their features and location, shifting from quiescent and stationary cells anchored in the bone marrow to cycling and motile cells entering the circulation. These changes are driven by stress signals. Bidirectional migrations to and from the bone marrow are active processes that form the basis for HSC transplantation protocols. However, how and why HSCs enter and exit the bone marrow as part of host defense and repair is not fully understood. The development of functional, preclinical, immune-deficient NOD/SCID (non-obese diabetic-severe combined immunodeficiency) mice transplantation models has enabled the characterization of normal and leukemic human HSCs and investigation of their biology. Intensive research has revealed multiple tasks for the chemokine SDF-1 (stromal cell-derived factor-1, also known as CXCL12) in HSC interactions with the microenvironment, as well as the existence of overlapping mechanisms controlling stress-induced mobilization and enhanced HSC homing, sequential events of major physiological relevance. These processes entail dynamically interacting, multi-system aspects that link the bone marrow vasculature and stromal cells with the nervous and immune systems. Neural cues act as an external pacemaker to synchronize HSC migration and development to balance bone remodeling via circadian rhythms in order to address blood and immune cell production for the physiological needs of the body. Stress situations and clinical HSC mobilization accelerate leukocyte proliferation and bone turnover. This review presents the concept that HSC regulation by the brain-bone-blood triad via stress signals controls the bone marrow reservoir of immature and maturing leukocytes.