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‐Bl 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.