Biological characterization of stem cell present in mobilized peripheral blood of CML patients.

Peripheral blood stem cell grafts are now frequently used for autologous transplantation of patients with malignancies. In this report we address the question of whether true long-term repopulating pluripotent hematopoietic stem cells (PHSC) are mobilized into peripheral blood and whether stem cells isolated from CML patients are depleted of Philadelphia chromosome positive cells. The presence of stem cells in mobilized peripheral blood (MPB) was examined by staining the CD34+Lineage- (Lin-) population for the expression of the Thy-1 antigen. The extent and kinetics of mobilization of CD34+Thy-1+ Lin- cells into peripheral blood were studied. In our analysis the percentage of these cells was found to vary widely depending on the day of leukapheresis and the individual patient. Fluorescence activated cell sorting (FACS) was used to isolate Thy-1 subsets from MPB which were analyzed for activity in in vitro long term cultures and in two in vivo models in which SCID-hu mice were implanted with human fetal bone or thymus grafts. The long term culture assay shows that the cells which express Thy-1 are enriched for cobblestone area forming activity (CAFC), an assay which can be used as a measure of detecting PBSC's in vitro. This CD34+Thy-1+ Lin- cell population was capable of producing both B and myeloid cells, and maintaining CD34+Lin- cells in these long term cultures. Moreover, the CD34+Thy-1+Lin- cell subset possessed a higher ability to engraft and to produce multilineage hematopoietic lineages in the SCID-hu bone assay and T cells in the SCID-hu thymus assay.(ABSTRACT TRUNCATED AT 250 WORDS)