Peripheral blood CD34+ cells differ from bone marrow CD34+ cells in Thy-1 expression and cell cycle status in nonhuman primates mobilized or not mobilized with granulocyte colony-stimulating factor and/or stem cell factor

Abstract

Granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) have been shown to stimulate the circulation of hematopoietic progenitor cells in both mice and nonhuman primates. We evaluated the immunophenotype and cell cycle status of CD34+ cells isolated from the bone marrow (BM) and leukapheresis product of cytokine-mobilized nonhuman primates. CD34+ cells were isolated from rhesus macaques that had received no cytokine therapy, 100 micrograms/kg/d G-CSF, 200 micrograms/kg/d SCF, or a combination of both 100 micrograms/kg/d G-CSF and 200 micrograms/kg/d SCF as a subcutaneous injection for 5 days. BM was aspirated before (day 0) and on the last day (day 5) of cytokine administration. On days 4 and 5, peripheral blood (PB) mononuclear cells were collected using a novel method of leukapheresis. Threefold more PB mononuclear cells were collected from animals receiving G-CSF alone or G-CSF and SCF than from animals that had received either SCF alone or no cytokine therapy. CD34+ cells were positively selected using an immunoadsorptive system from the BM, PB, and/or leukapheresis product. Threefold and 10-fold more CD34+ cells were isolated from the leukapheresis product of animals receiving G-CSF or G-CSF and SCF, respectively, than from animals receiving no cytokine therapy or SCF alone. The isolated CD34+ cells were immunophenotyped using CD34-allophycocyanin, CD38-fluorescein isothiocyanate, and Thy-1-phycoerythrin. These cells were later stained with 4', 6-diamidino-2-phenylindole for simultaneous DNA analysis and immunophenotyping. BM-derived CD34+ cells did not differ significantly in cell cycle status and Thy-1 or CD38 phenotype before or after G-CSF and/or SCF administration. Similarly, CD34+ cells isolated from the leukapheresis product did not differ significantly in immunophenotype or cell cycle status before or after G-CSF and/or SCF administration. However, there were consistent differences in both immunophenotype and cell cycle status between BM- and PB-derived CD34+ cells. CD34+ cells isolated from the PB consistently had a smaller percentage of cells in the S+G2/M phase of the cell cycle and had a higher percentage of cells expressing Thy-1 than did CD34+ cells isolated from the BM. A greater proportion of PB-derived CD34+ cells were in the S+G2/M phase of the cell cycle after culture in media supplemented with interleukin-6 and SCF, However, culturing decreased the proportion of CD34+ cells expressing Thy-1.