G-CSF-MOBILIZED CD34(-BLOOD STEM-CELLS ARE SIGNIFICANTLY LESS APOPTOTIC THAN UNSTIMULATED PERIPHERAL-BLOOD CD34(+) CELLS - ROLE OF G-CSF ASSURVIVAL FACTOR() PERIPHERAL)

The mechanism of release of CD34(+) cells into the peripheral blood (P B) after mobilization treatment with chemotherapy and/or growth factor s is not clearly understood. Growth factors may induce increased proli feration and self renewal within the stem cell compartment. It is poss ible that they alter adhesion molecule profiles or other progenitor:st roma interactions, to allow release of these cells into the periphery. However, CD34(+) cells present in the PB under steady-state condition s, albeit in low number. Growth factors such as granulocyte colony-sti mulating factor (G-CSF) may promote the survival of CD34(+) cells in t he PB by suppressing apoptosis. In order to test this hypothesis, we h ave quantitated apoptotic cells in the CD34(+) fraction of peripheral blood stem cell (PBSC) collections, using two-colour flow cytometry, a fter staining with anti-CD34 antibody and the fluorescent DNA binding agent, 7-amino actinomycin D (7AAD). 7AAD differentially stains live, apoptotic and dead cells, due to the altered accessibility of DNA in e ach subpopulation. We have shown a significant reduction in the propor tion of apoptotic cells in the CD34(+) population mobilized by G-CSF c ompared to CD34(+) cells in unstimulated PB, consistent with the theor y that G-CSF is acting, at least in part, by suppressing apoptosis. In addition, we found that G-CSF mobilized CD34(+) cells are less apopto tic than CD34(+) cells of unstimulated normal bone marrow, indicating that, at the doses used, G-CSF is significantly altering the survival capacity of the mobilized cells.