PHENOTYPIC AND FUNCTIONAL-CHARACTERIZATION OF MOBILIZED PERIPHERAL-BLOOD CD34(-KIT() CELLS COEXPRESSING DIFFERENT LEVELS OF C)

In this report we evaluated the exact expression pattern of c-Kit on m obilized peripheral blood (PB) CD34(+) cells. Using a monoclonal antib ody against CD117 antigen (95C3), flow cytometric analysis revealed th at 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 o f 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) cel l fraction consisted almost exclusively of erythroid progenitors, in c ontrast to CD34(+)/CD117(low) cell subset which gave rise mostly to gr anulocyte-monocyte colonies. The majority of CFU-GEMM and the most pri mitive week 6 cobblestone area forming cells (CAFCs) segregated in the CD34(+)/CD117(low) cell subset, suggesting the highest content of mul tipotential 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, s tem 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 t o the major content of multipotential hematopoietic progenitors and hi ghest capacity to generate sufficient amounts of ROI after ex vivo exp ansion, we suggest that CD34(+)/CD117(low) cell subset would be one of the most potential candidates for transplantation in patients with ac ute lymphoblastic leukemia, which lack c-Kit antigen expression. (C) 1 998 Elsevier Science Ltd. All rights reserved.