LONG-TERM CULTURES TO EVALUATE ENGRAFTMENT POTENTIAL OF CD34(-BLOOD AFTER MOBILIZATION BY CHEMOTHERAPY WITH AND WITHOUT GM-CSF() CELLS FROMPERIPHERAL)

In this study we used a long-term culture system to evaluate engraftme nt potential of human peripheral blood (PB) cells mobilized by chemoth erapy (CT) associated or not with granulocyte-macrophage colony-stimul ating factor (GM-CSF). In six patients who underwent blood cell transp lantation, PB CD34(+) cells were cultured after mobilization and were compared to CD34(+) cells in steady state from PB and bone marrow (BM) . Qualitative differences were shown between PBC samples obtained afte r CT with and without GM-CSF. Despite similar CFU-GM counts at culture initiation, GM-CSF-mobilized CD34(+) cells might contain a lower prop ortion of primitive stem cells, as suggested by the significant decrea se in CFU-GM numbers produced beyond week 5 compared to CT-mobilized C D34(+) cells (p = 0.033). Likewise, the percentage of CFU-GM produced beyond week 5 in relation to initial input was significantly lower tha n steady-state PB (p = 0.039) and than CT-mobilized CD34(+) cells (p = 0.033). However, this CFU-GM production with GM-CSF-mobilized PB CD34 (+) cells was not different from cultures with BMC CD34(+) cells. Thes e results suggest that GM-CSF can mobilize CFU-GM in the blood mainly by differentiation at the expense of the primitive stem cell compartme nt. It appears valuable to define clearly for each mobilizing procedur e a particular threshold of CFU-GM which reflects sufficient numbers o f primitive stem cells to ensure long-term engraftment.