Peripheral blood hematopoietic progenitor/stem cells proliferate to form colonies in liquid culture but require contact with vascular endothelial cells and gm‐csf

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Abstract
To test the hypothesis whether peripheral blood hematopoietic progenitor/stem cells (PBSCs) interact with vascular endothelial cells during events leading to extramedullary hematopoiesis, we cocultured T-cell depleted, peripheral blood mononuclear cells obtained from cytokine treated primates in liquid culture containing a monolayer of porcine aortic endothelial cells (PAECs) for 7 days. Recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) added to cocultures of PBSC-PAEC stimulated colony formation, while only a few clusters were observed in cultures without GM-CSF. In contrast, colony formation was not stimulated when either interleukin 1 (IL-1) or IL-3 were added to the cultures. Colony and cluster formation in response to GM-CSF was dose dependent; 20 ±5 colonies/5,000 cells were formed at 3 U/ml, and optimal colony formation of 42 ±11/5,000 cells occurred at 100 U/ml. Colonies formed in the presence of GM-CSF were large, and most contained >200 cells. Morphological and phenotypical characterization of cells from isolated colonies suggested that the majority of cells were predominantly immature myeloid elements. However, there was also a low but consistent frequency of megakaryocytic lineage cells. Thus, PBSCs interact with non-bone marrow- derived vascular endothelial cells and proliferate, but only in the presence of GM-CSF, suggesting that PBSC interaction with vascular endothelial cells in vivo could lead to extramedullary hematopoiesis.