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

AC133⁺ cells may represent an alternative source of transplantable haemopoietic progenitor cells to CD34⁺ cells. Here, we have addressed the characterization 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 sorting, analysed by flow cytometry, tested for their content in blast cell colony-forming units (CFU-Bl), erythroid and granulocyte-macrophage colony- forming units before and after expansion in the presence of various haemopoietic growth factor combinations. Median AC133⁺ cell yield was 62.3%, and median AC133⁺ population purity was 97.9%. AC133⁺ cells were found to contain significantly more CFU-Bl than CD34⁺ cells; furthermore, the replating efficiency, i.e. the number of CFU-BI capable of generating secondary colonies, was higher in the former than in the latter cells. Both AC133⁺ and CD34⁺ cells displayed an increased ability to give rise to committed progenitors after 7-day expansion in liquid cultures. These data suggest that the AC133⁺ cell subset is a heterogeneous pool of immature and more differentiated cells that can be maintained and expanded in well-defined culture conditions. In comparison with CD34⁺ cells UCB AC133⁺ cells appear to contain a higher number of early haemopoietic progenitors.