Flow cytometric and functional characterization of AC133(+) cells from human umbilical cord blood

AC133(+) cells may represent an alternative source of transplantable haemop oietic progenitor cells to CD34(+) cells. Here, we have addressed the chara cterization of umbilical cord blood (UCB) AC133(+) cells and compared their immunophenotypic and functional features with those of UCB CD34(+) cells. UCB AC133(+) and CD34(+) cell fractions were purified by magnetic cell sort ing, analysed by flow cytometry, tested For their content in blast cell col ony-forming units (CFU-Bl), erythroid and granulocyte-macrophage colony-for ming units before and after expansion in the presence of various haemopoiet ic growth factor combinations. Median AC133(+) cell yield was 62.3%, and me dian AC133(+) population purity was 97.9%. AC133(+) cells were found to con tain significantly more CFU-Bl than CD34(+) cells: furthermore, the replati ng efficiency, i.e. the number of CFU-Bl capable of generating secondary co lonies, was higher in the former than in the latter cells. Both AC133(+) an d CD34(+) cells displayed an increased ability to give rise to committed pr ogenitors after 7-day expansion in liquid cultures. These data suggest that the AC133(+) cell subset is a heterogeneous pool of immature and more diff erentiated cells that can be maintained and expanded in well-defined cultur e conditions. In comparison with CD34(+) cells, UCB AC133(+) cells appear t o contain a higher number of early haemopoietic progenitors.