The AC133+CD38−, but not the rhodamine-low, phenotype tracks LTC-IC and SRC function in human cord blood ex vivo expansion cultures

Phenotypic markers associated with human hematopoietic stem cells (HSCs) were developed and validated using uncultured cells. Because phenotype and function can be dissociated during culture, better markers to prospectively track and isolate HSCs in ex vivo cultures could be instrumental in advancing HSC-based therapies. Using an expansion system previously shown to increase hematopoietic progenitors and SCID-repopulating cells (SRCs), we demonstrated that the rhodamine-low phenotype was lost, whereas AC133 expression was retained throughout culture. Furthermore, the AC133+CD38− subpopulation was significantly enriched in long-term culture-initiating cells (LTC-IC) and SRCs after culture. Preculture and postculture analysis of total nucleated cell and LTC-IC number, and limiting dilution analysis in NOD/SCID mice, showed a 43-fold expansion of the AC133+CD38− subpopulation that corresponded to a 7.3-fold and 4.4-fold expansion of LTC-ICs and SRCs in this subpopulation, respectively. Thus, AC133+CD38− is an improved marker that tracks and enriches for LTC-IC and SRC in ex vivo cultures.