Phenotypic and functional characterization of mobilized peripheral blood CD34+ cells coexpressing different levels of c-Kit

In this report we evaluated the exact expression pattern of c-Kit on mobilized peripheral blood (PB) CD34(+) cells. Using a monoclonal antibody against CD117 antigen (95C3), flow cytometric analysis revealed that approximately 25% of the mobilized PB CD34(+) cells coexpress c-Kit. This cell fraction showed a considerable heterogeneity with respect to c-Kit expression, consisting of a small fraction with high levels of c-Kit (4.2%) (CD34(+)/CD117(high) fraction) and a larger proportion of cells expressing low levels of this antigen (21.0%) (CD34(+)/CD 117(low) fraction). Clonogenic assays showed that CD34(+)/CD117(high) cell fraction consisted almost exclusively of erythroid progenitors, in contrast to CD34(+)/CD117(low) cell subset which gave rise mostly to granulocyte-monocyte colonies. The majority of CFU-GEMM and the most primitive week 6 cobblestone area forming cells (CAFCs) segregated in the CD34(+)/CD117(low) cell subset, suggesting the highest content of multipotential progenitors within this cell fraction. None of the sorted cell subsets was able to produce reactive oxygen intermediates (ROI). However, ex vivo expansion of the sorted subsets with interleukin 3, stem cell factor and FLT3 ligand for 2 weeks resulted in a significant production of O-2- and H2O2/HOCl by CD34(+)/CD117(low) cell fraction, compared to the same sorted but not expanded counterparts. According to the major content of multipotential hematopoietic progenitors and highest capacity to generate sufficient amounts of ROI after ex vivo expansion, we suggest that CD34(+)/CD117(low) cell subset would be one of the most potential candidates for transplantation in patients with acute lymphoblastic leukemia, which lack c-Kit antigen expression. (C) 1998 Elsevier Science Ltd. All rights reserved.