The type of regimen used might result in mobilization of phenotypically and functionally different CD34(+) cells. We compared the phenotype of CD34(+) cells in leukapheresis products of three homogeneous groups: I, healthy individuals treated with granulocyte colony-stimulating factor (G-CSF) alone (n = 13); II, patients mobilized with G-CSF following chemotherapy (n = 16); and III, patients mobilized with G-CSF after high-dose chemotherapeutic pretreatment (n = 24). Multiparameter flow cytometry was performed for CD34(+) subpopulation analysis and focused on adhesion molecules, differentiation markers and megakaryocytic markers relevant for stem cell homing, with special reference to the importance of L-selectin expression. Regimens I and II led to higher numbers of mobilized CD34(+) cells (mean 468 x 10(6) and 491 x 10(6) CD34(+) cells per leukapheresis procedure respectively) than regimen III (mean 41 x 10(6) CD34(+) cells per leukapheresis procedure). Both the expression of L-selectin and CD54 on CD34(+) cells was significantly lower in group III, as was the percentage of megakaryocytic (CD41(+)) progenitors. A higher percentage of primitive (CD38(-) and/or HLA(-)DR(-)) CD34(+) cells was found in group III, correlating with a higher clonogenicity of the CD34(+) cells. However, when comparing the CD34(+)_ subpopulations that were also positive for L-selectin, there was no significant difference between the three regimens. A similar approach for the megakaryocytic CD34+ population resulted in an even worse quality of regimen III: 5.1% of CD34(+) being CD41(+)/L-selectin(+) compared with 9.2% and 8.9% in regimens I and II respectively. We concluded that the phenotypes of the CD34(+) cells in the G-CSF (group I) and G-CSF-chemotherapy (group II) regimens are similar, whereas the phenotype of the CD34(+) cells mobilized in the high-dose regimen (group III) displayed features that might negatively influence homing of the cells. Future studies will be directed towards regimens that will lead to the mobilization of a higher amount of CD34(+) cells with a phenotypically favourable phenotype.

Summary. The type of regimen used might result in mobilization of phenotypically and functionally different CD34 1 cells. We compared the phenotype of CD34 1 cells in leukapheresis products of three homogeneous groups: I, healthy individuals treated with granulocyte colony-stimulating factor (G-CSF) alone (n 13); II, patients mobilized with G-CSF following chemotherapy (n 16); and III, patients mobilized with G-CSF after high-dose chemotherapeutic pretreatment (n 24). Multiparameter flow cytometry was performed for CD341 subpopulation analysis and focused on adhesion molecules, differentiation markers and megakaryocytic markers relevant for stem cell homing, with special reference to the importance of L-selectin expression. Regimens I and II led to higher numbers of mobilized CD34 subpopulations that were also positive for L-selectin, there was no significant difference between the three regimens. A similar approach for the megakaryocytic CD34 1 population resulted in an even worse quality of regimen III: 5´1% of CD34 1 being CD41 1 /L-selectin 1 compared with 9´2% and 8´9% in regimens I and II respectively. We concluded that the phenotypes of the CD34 1 cells in the G-CSF (group I) and G-CSF±chemotherapy (group II) regimens are similar, whereas the phenotype of the CD34 1 cells mobilized in the high-dose regimen (group III) displayed features that might negatively influence homing of the cells. Future studies will be directed towards regimens that will lead to the mobilization of a higher amount of CD34 1 cells with a phenotypically favourable phenotype.