No abstract

Pericytes play a crucial role in angiogenesis and vascular maintenance. -selected bmMSCs neither showed these abilities, nor did they attain pericyte function despite progressive CD146 expression once passaged. Thus, cell culture conditions appear to influence expression of this and other reported pericyte markers significantly without correlation to function. The newly developed assays, therefore, promise to close a gap in the in vitro identification of pericytes via function. Indeed, our functional data suggest that pericytes represent a subpopulation of MSCs in bm with a specialized role in vascular biology. However, these functions are not inherent to all MSCs.

To explore the use of stem/progenitor cells from peripheral blood (PB) for allogeneic transplantation, we have studied the mobilization of progenitor cells in normal donors by growth factors. Normal subjects were administered either granulocyte-macrophage colony-stimulating factor (GM-CSF) at 10 micrograms/kg/d, or G-CSF at 10 micrograms/kg/d, or a combination of G- and GM-CSF at 5 micrograms/kg/d each, administered subcutaneously for 4 days, followed by leukapheresis on day 5. Mononuclear cells expressing CD34 (CD34+ cells) were selectively enriched by affinity labeling using Dynal paramagnetic microspheres (Baxter Isolex; Baxter Healthcare Corp, Santa Ana, CA). The baseline CD34+ cells in peripheral blood before mobilization was 0.07% +/- 0.05% (1.6 +/- 0.7/microL; n = 18). On the fifth day after stimulation (24 hours after the fourth dose), the CD34+ cells were 0.99% +/- 0.40% (61 +/- 14/microL) for the 8 subjects treated with G-CSF, 0.25% +/- 0.25% (3 +/- 3/microL, both P < .01 v G-CSF) for the 5 subjects administered GM-CSF, and for the 5 subjects treated with G- and GM-CSF, 0.65% +/- 0.28% (41 +/- 18/microL, P < .5 v GM-CSF). Parallel to this increase in CD34+ cells, clonogenic assays showed a corresponding increase in CFU- GM and BFU-E. The total number of CD34+ cells collected from the G-CSF group during a 3-hour apheresis was 119 +/- 65 x 10(6) and was not significantly different from that collected from the group treated with G- and GM-CSF (101 +/- 35 x 10(6) cells), but both were greater than that from the group treated with GM-CSF (12.6 +/- 6.1 x 10(6); P < .01 for both comparisons). Analysis of the CD34+ subsets showed that a significantly higher percentage of cells with the CD34+/CD38- phenotype is found after mobilization with G- and GM-CSF. In the G-CSF group, immunomagnetic selection of CD34+ cells permitted the enrichment of the CD34+ cells in the apheresis product to 81% +/- 11%, with a 48% +/- 12% yield and to a purity of 77% +/- 21% with a 51% +/- 15% recovery in the G- and GM-CSF group. T cells were depleted from a mean of 4.5 +/- 2.0 x 10(9) to 4.3 +/- 5.2 x 10(6) after selection, representing 99.9% depletion. We conclude that it is feasible to collect sufficient numbers of PB progenitor cells from normal donors with one to two leukapheresis procedures for allogeneic transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

The CD34+ purified grafts were enriched in stem/progenitor cells, with five of these 10 preparations containing > or = 94% CD34+ cells. Engraftment with CD34(+)-purified cell grafts as pure as 99% confirms that autologous CD34+ cells, alone, are sufficient to provide hematopoietic rescue for myeloablated patients. The best purification results were obtained on small marrow harvests from patients with neuroblastoma. The engraftment of highly purified CD34+ cells obtained by this technology and the antitumor effect of the transplant, by which two of 10 poor prognosis patients remain clinically free of tumor, have stimulated further clinical trials.

We have developed a time-lapse camera system to follow the replication history and the fate of hematopoietic stem cells (HSC) at a single-cell level. Combined with single-cell culture, we correlated the early replication behavior with colony development after 14 days. The membrane dye PKH26 was used to monitor cell division. In addition to multiple, synchronous, and symmetric divisions, single-sorted CD34+/CD38− cells derived from fetal liver (FLV) also gave rise to a daughter cell that remained quiescent for up to 8 days, whereas the other daughter cell proliferated exponentially. Upon separation and replating as single cells onto medium containing a cytokine cocktail, 60.6% ± 9.8% of the initially quiescent cells (PKH26 bright) gave rise again to colonies and 15.8% ± 7.8% to blast colonies that could be replated. We have then determined the effects of various regulatory molecules on symmetry of initial cell divisions. After single-cell sorting, the CD34+/CD38− cells derived from FLV were exposed to flt3-ligand, thrombopoietin, stem cell factor (SCF), or medium containing a cytokine cocktail (with SCF, interleukin-3, interleukin-6, granulocyte-macrophage colony-stimulating factor, and erythropoietin). Whereas mitotic rate, colony efficiency, and asymmetric divisions could be altered using various regulatory molecules, the asymmetric division index, defined as the number of asymmetric divisions versus the number of dividing cells, was not altered significantly. This observation suggests that, although lineage commitment and cell proliferation can be skewed by extrinsic signaling, symmetry of early divisions is probably under the control of intrinsic factors.