Mobilized peripheral blood SSCloALDHbr cells have the phenotypic and functional properties of primitive haematopoietic cells and their number correlates with engraftment following autologous transplantation

We have developed an approach for identifying primitive mobilized peripheral blood cells (PBSC) that express high levels of aldehyde dehydrogenase (ALDH). PBSC were stained with a fluorescent ALDH substrate, termed BODIPY(TM)-aminoacetaldehyde (BAAA), and then analysed using flow cytometry. A population of cells with a low side scatter (SSC) and a high level of BAAA staining, termed the SSClo ALDH(br) population, was readily discriminated and comprised a mean of 3 +/- 5% of leukapheresis samples. A mean of 73 +/- 11% of the SSClo ALDH(br) population expressed CD34 and 56 +/- 25% of all the mobilized CD34(+) cells resided within the SSClo ALDH(br) population. The SSClo ALDH(br) population was largely depleted of cells with mature phenotypes and enriched for cells with immature phenotypes. Sorted SSClo ALDH(br) and SSClo ALDH(br) CD34(+) PBSC were enriched for progenitors with the ability to (1) generate colony-forming units (CFU) and long-term culture (LTC)-derived CFU, (2) expand in primary and secondary LTC, and (3) generate multiple cell lineages. In 21 cancer patients who had undergone autologous PBSC transplantation, the number of infused SSClo ALDH(br) cells/kg highly correlated with the time to neutrophil and platelet engraftment (P < 0.015 and P < 0.003 respectively). In summary, peripheral blood SSClo ALDH(br) cells have the phenotypic and functional properties of primitive haematopoietic cells and their number correlates with engraftment following autologous transplantation.