Graft source determines human hematopoietic progenitor distribution pattern within the CD34(+) compartment

Exploratory research for optimal GvHD prophylaxis after single unit CBT in adults: short-term methotrexate reduced the incidence of severe GvHD more than mycophenolate mofetil

In order to examine GvHD prophylaxis in umbilical cord blood transplantation (UCBT) in more detail, we compared transplant outcomes after UCBT for acute leukemia among GvHD prophylaxes using registry data. We selected patients transplanted with a calcineurin inhibitor and methotrexate (MTX)/mycophenolate mofetil (MMF) combination. A total of 1516 first myeloablative UCBT between 2000 and 2012 (Cyclosporine A (CyA) plus MTX, 824, Tacrolimus (Tac) plus MTX, 554, Tac plus MMF, 138) were included. With adjusted analyses, Tac plus MMF showed a significantly higher risk for grade II-IV and III-IV acute GvHD than CyA or Tac plus MTX. Although NRM was similar, Tac plus MMF showed a significantly lower risk of relapse than CyA or Tac plus MTX. A significant difference was observed in the risk of overall mortality (OM) between the MTX-containing group and MMF-containing group. In patients with standard-risk disease, there was no significant difference in the risk of OM in any GvHD prophylaxis. However, in patients with advanced-risk disease, Tac plus MMF showed a significantly lower risk of OM. Therefore, MTX-containing prophylaxis is preferred in UCBT for standard-risk disease, whereas MMF-containing prophylaxis is preferred for advanced-risk disease. A prospective study to identify optimal GvHD prophylaxis for UCBT is warranted.

Characterization of the growth modulatory activities of osteoblast conditioned media on cord blood progenitor cells

Engraftment outcomes are strongly correlated with the numbers of hematopoietic stem and progenitor cells (HSPC) infused. Expansion of umbilical cord blood (CB) HSPC has gained much interest lately since infusion of expanded HSPC can accelerate engraftment and improve clinical outcomes. Many novel protocols based on different expansion strategies of HSPC and their downstream derivatives are under development. Herein, we describe the production and properties of serum-free medium (SFM) conditioned with mesenchymal stromal cells derived-osteoblasts (OCM) for the expansion of umbilical CB cells and progenitors. After optimization of the conditioning length, we show that OCM increased the production of human CB total nucleated cells and CD34⁺ cells by 1.8-fold and 1.5-fold over standard SFM, respectively. Production of immature CD34⁺ subpopulations enriched in hematopoietic stem cells was also improved with a shorter conditioning period. Moreover, we show that the growth modulatory activities of OCM on progenitor expansion are regulated by both soluble factors and non-soluble cellular elements. Finally, the growth and differentiation modulatory activities of OCM were fully retained after high dose-ionizing irradiation and highly stable when OCM is stored frozen. In summary, our results suggest that OCM efficiently mimics some of the natural regulatory activities of osteoblasts on HSPC and highlight the marked expansion potentials of SFM conditioned with osteoblasts.

Gene and miRNA expression profiles of hematopoietic progenitor cells vary depending on their origin

Hematopoietic progenitor cells (HPCs) from granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood (G-PB), bone marrow (BM), or umbilical cord blood (CB) have differing biological properties and differing kinetics of engraftment post-transplantation, which might be explained, at least in part, by differing gene and miRNA expression patterns. To assess the differences in gene and miRNA expression, we analyzed whole genome expression profiles as well as the expression of 384 miRNAs in CD34(+) cells isolated from 18 healthy individuals (6 individuals per subtype of HPC source). We identified 43 genes and 36 miRNAs differentially expressed in the various CD34(+) cell sources. We observed that CD34(+) cells from CB and BM showed similar gene and miRNA expression profiles, whereas CD34(+) cells from G-PB had a very different expression pattern. Remarkably, 20 of the differentially expressed genes are targets of the differentially expressed miRNAs. Of note, the majority of genes differentially expressed in CD34(+) cells from G-PB are involved in cell cycle regulation, promoting the process of proliferation, survival, hematopoiesis, and cell signaling, and are targets of overexpressed and underexpressed miRNAs in CD34(+) cells from the same source. These data suggest significant differences in gene and miRNA expression among the various HPC sources used in transplantation. We hypothesize that the differentially expressed genes and miRNAs involved in cell cycle and proliferation might explain the differing kinetics of engraftment observed after transplantation of hematopoietic stem cells obtained from these different sources.

A novel three-dimensional flow chamber device to study chemokine-directed extravasation of cells circulating under physiological flow conditions

Extravasation of circulating cells from the bloodstream plays a central role in many physiological and pathophysiological processes, including stem cell homing and tumor metastasis. The three-dimensional flow chamber device (hereafter the 3D device) is a novel in vitro technology that recreates physiological shear stress and allows each step of the cell extravasation cascade to be quantified. The 3D device consists of an upper compartment in which the cells of interest circulate under shear stress, and a lower compartment of static wells that contain the chemoattractants of interest. The two compartments are separated by porous inserts coated with a monolayer of endothelial cells (EC). An optional second insert with microenvironmental cells of interest can be placed immediately beneath the EC layer. A gas exchange unit allows the optimal CO₂ tension to be maintained and provides an access point to add or withdraw cells or compounds during the experiment. The test cells circulate in the upper compartment at the desired shear stress (flow rate) controlled by a peristaltic pump. At the end of the experiment, the circulating and migrated cells are collected for further analyses. The 3D device can be used to examine cell rolling on and adhesion to EC under shear stress, transmigration in response to chemokine gradients, resistance to shear stress, cluster formation, and cell survival. In addition, the optional second insert allows the effects of crosstalk between EC and microenvironmental cells to be examined. The translational applications of the 3D device include testing of drug candidates that target cell migration and predicting the in vivo behavior of cells after intravenous injection. Thus, the novel 3D device is a versatile and inexpensive tool to study the molecular mechanisms that mediate cellular extravasation.

Endothelial progenitor cell: a blood cell by many other names may serve similar functions

The first reports of circulating cells that displayed the capacity to repair and regenerate damaged vascular endothelial cells as progenitor cells for the endothelial lineage (EPC) were met with great enthusiasm. However, the cell surface antigens and colony assays used to identify the putative EPC were soon found to overlap with those of the hematopoietic lineage. Over the past decade, it has become clear that specific hematopoietic subsets play important roles in vascular repair and regeneration. This review will provide some overview of the hematopoietic hierarchy and methods to segregate distinct subsets that may provide clarity in identifying the proangiogenic hematopoietic cells. This review will not discuss those circulating viable endothelial cells that play a role as EPC and are called endothelia colony-forming cells. The review will conclude with identification of some roadblocks to progress in the field of identification of circulating cells that participate in vascular repair and regeneration.

Is it time to revisit our current hematopoietic progenitor cell quantification methods in the clinic?

In the clinical practice of hematopoietic SCT, the minimum numbers of cells required for a successful engraftment are defined on the basis of their CD45 and CD34 expression profiles. However, the quantity of earlier progenitors or CD34-positive cells at different differentiation stages within stem cell grafts is not generally taken into consideration. During the last decade, various teams have quantified the number of cells expressing various combinations of CD34, CD38, CD133, CD90 co-expression and/or aldehyde dehydrogenase functional capacity using flow cytometry. Some of these studies resulted in the greater appreciation that combinations of these Ags were associated with varied myeloid, erythroid and platelet engraftment rates whereas others showed that the relative absence or presence of these markers could define cells responsible for either short- or long-term engraftment. These findings were also extended to differences between progenitor cell populations found within BM vs peripheral or cord-blood grafts. Cells harvested from donors are also generally frozen and stored; thawed cells have variable levels of viability and functional capacity based on the time tested post thaw, which also can be assessed by flow cytometry. Finally, flow cytometry has the potential for analysis of cells carrying a mesenchymal stem cell phenotype, which may be quiescent within some of the stem cell products. This review will address the need for stem cell subpopulation quantification and summarize existing published data to identify some Ags and functional characteristics that can be applicable to daily clinical practice.