Peripheral Blood Stem Cells Differ from Bone Marrow Stem Cells in Cell Cycle Status, Repopulating Potential, and Sensitivity Toward Hyperthermic Purging in Mice Mobilized with Cyclophosphamide and Granulocyte Colony-Stimulating Factor

Abstract

Peripheral blood stem cells (PBSCs) are increasingly used in autologous stem cell transplantations. We investigated the mobilizing effect of a combined cyclophosphamide (CTX) and granulocyte colony-stimulating factor (G-CSF) treatment on progenitor cells (STRA) and primitive stem cells (LTRA) in normal and splenectomized CBA/H mice. This combined treatment not only resulted in mobilization but also in expansion of hematopoietic stem cell subsets. The latter phenomenon was somewhat suppressed in splenectomized animals, but in these mice an enhanced mobilization of STRA and LTRA cells into the peripheral blood was observed. Furthermore, we studied the engraftment potential of mobilized PBSCs. Mice transplanted with PBSCs engrafted significantly better compared to mice transplanted with bone marrow stem cells from control and mobilized mice. The repopulation curve was characterized by a less-deep nadir indicating that the differences occur during the initial phase after transplantation. Contamination of autologous PBSC transplants with malignant cells is noticed frequently and is the basis for urging the use of purging modalities. Here we used hyperthermia and found that the mobilized progenitor cells in peripheral blood are more resistant to hyperthermia than those in the bone marrow (i.e., a survival of 11 +/- 5% after 90 min at 43 degrees C for peripheral blood progenitors, compared to 0.5 +/- 0.4% in bone marrow of mobilized animals and 1.6 +/- 0.5% in normal animals, respectively). Hyperthermic purging does not eliminate the superior repopulating features of a PBSC graft, as is demonstrated by an increased median survival time of lethally irradiated mice transplanted with purged PBSCs. In conclusion, our data demonstrate that CTX + G-CSF-mobilized PBSCs have an enhanced engraftment potential concomitantly with a decreased cycling activity and hence a decreased hyperthermic sensitivity. These findings support the use of these mobilized PBSCs for autologous stem cell transplantation and strengthen the basis for using hyperthermia as a purging modality.

Mobilized peripheral blood stem cells provide rapid reconstitution but impaired long-term engraftment in a mouse model

“…2,3,31,32 The observed consistency between clinical and experimental data validates the use of LSK cells in the murine system as a model to study the quality of MPB stem cells. Murine LSK, much like human CD34 þ cells, are predominantly progenitor cells but contain the vast majority of long-term repopulating stem cells.…”

Differential role for very late antigen-5 in mobilization and homing of hematopoietic stem cells

“…33 Briefly, cells were plated out in alpha-medium (StemCell Technologies Inc., Vancouver, BC, Canada) containing 0.8% methylcellulose (Fluka, Bachs SG, Switzerland), 30% FCS (GibcoBRL, Paisley, Scotland) and 10 À4 mol/l 2-mercapthoethanol (Merck, Darmstadt, Germany) at concentrations varying from 10 4 to 5 Â 10 5 nucleated cells/ml. Colony growth was stimulated by granulocyte-macrophage-CSF and stem cell factor.…”

“…29,30 Furthermore, in vitro studies have tried to reveal the involvement of these AMs in the processes of mobilization and homing, 31,32 although the correlation between levels of expression of VLA-5 and homing is not always clear. 16,21 The clinical observations [6][7][8][9][10] and our own experimental data 33 implicating that MPB cells engraft much faster than bone marrow stem cells are difficult to reconcile, assuming an opposite role for AMs in mobilization and homing. 34 If VLA-5 indeed plays an important role in the process of homing and the expression of this AM is downregulated during mobilization, either upregulation of this AM occurs within the first hours after transplantation of MPB cells or selective homing of cells expressing VLA-5 might be possible.…”

“…33 We compared the reconstitution potential of MPB cells with that of normal bone marrow (NBM) and bone marrow from mobilized animals (MBM) and analyzed the expression of various AMs in these cell populations. In particular, the involvement of VLA-5 in the opposing processes of mobilization and homing was determined.…”

Combinatorial and distinct roles of α5 and α4 integrins in stress erythropoiesis in mice

“…Both ␣ 4 and ␣ 5 integrins are widely expressed in hematopoietic cells and have been implicated in several functional aspects, such as proliferation, survival, maturation of erythroid cells, or in homing and proliferation of hematopoietic progenitor cells. [9][10][11][12][13][14][15] However, in vitro and in vivo data have not been consistent, so that the exact role of these 2 integrins has remained inconclusive. For example, adhesion to fibronectin is dependent on both ␣ 4 ␤ 1 and ␣ 5 ␤ 1 , and it was found to influence stem cell homing of hematopoietic progenitors to BM or spleen, but the results have been controversial for ␣ 5 integrin.…”