The phenotypic profile of CD34-positive peripheral blood stem cells in different mobilization regimens

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 in dividuals 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 p retreatment (n = 24). Multiparameter flow cytometry was performed for CD34( +) subpopulation analysis and focused on adhesion molecules, differentiatio n markers and megakaryocytic markers relevant for stem cell homing, with sp ecial 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 4 91 x 10(6) CD34(+) cells per leukapheresis procedure respectively) than reg imen IU (mean 41 x 10(6) CD34(+) cells per leukapheresis procedure). Both t he expression of L-selectin and CD54 on CD34(+) cells was significantly low er in group III, as was the percentage of megakaryocytic (CD41(+)) progenit ors. A higher percentage of primitive (CD38(-) and/or HLA DR-) CD34(+) cell s was found in group III, correlating with a higher clonogenicity of the CD 34(+) cells. However, when comparing the CD34(+) subpopulations that were a lso positive for L-selectin, there was no significant difference between th e three regimens. A similar approach for the megakaryocytic CD34(+) populat ion 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 res pectively. We concluded that the phenotypes of the CD34(+) cells in the G-C SF (group I) and G-CSF-chemotherapy (group II) regimens are similar, wherea s the phenotype of the CD34(+) cells mobilized in the high-dose regimen (gr oup III) displayed features that might negatively influence homing of the c ells. Future studies will be directed towards regimens that will lead to th e mobilization of a higher amount of CD34(+) cells with a phenotypically fa vourable phenotype.