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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 trade mark -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 SSCloALDHbr population, was readily discriminated and comprised a mean of 3 +/- 5% of leukapheresis samples. A mean of 73 +/- 11% of the SSCloALDHbr population expressed CD34 and 56 +/- 25% of all the mobilized CD34+ cells resided within the SSCloALDHbr population. The SSCloALDHbr population was largely depleted of cells with mature phenotypes and enriched for cells with immature phenotypes. Sorted SSCloALDHbr and SSCloALDHbr 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 SSCloALDHbr cells/kg highly correlated with the time to neutrophil and platelet engraftment (P < 0.015 and P < 0.003 respectively). In summary, peripheral blood SSCloALDHbr cells have the phenotypic and functional properties of primitive haematopoietic cells and their number correlates with engraftment following autologous transplantation.

Background: A proportion of candidates for high-dose chemotherapy with autologous PBPC support (HDC-PBPCS) will not provide an adequate PBPC yield from their first mobilization. The value of re-mobilization and the best regimen for re-mobilization in these patients is unclear., Methods: In 23 patients who failed to provide > or = 3 x 10(6) CD34+ cells/kg after their first mobilization, PBPC were re-mobilized using a regimen of simultaneous administration of G-CSF and GM-CSF (10 microg/kg/day each) with leukaphereses (LP) starting Day 4 or 5 of CSF administration. Yields of WBC/kg, MNC/kg and CD34+ cells/kg/L of processed blood were compared between the first and second mobilization in each patient. The ability of the combined yield from the two mobilizations to achieve the desired threshold PBPC yield and the tolerability of the re-mobilization were determined., Results: The re-mobilization regimen was well-tolerated and no patient discontinued the regimen because of toxicity. Median collected WBC/kg/L (1.37 x 10(7) versus 2.62 x 10(7), p = 0.0065), MNC/kg/L (0.77 x 10(7) versus 1.97 x 10(7), p = 0.0003), CD34+ cells/kg/L (1.64 x 10(7) versus 4.18 x 10(7), p = 0.001) were significantly higher after the second mobilization (G-CSF/GM-CSF combination). Percentage of CD34+ cells in the leukapheresis was also significantly higher after the second mobilization (median 0.104% versus 0.195%, p = 0.036). Twelve of 22 patients achieved the target PBPC dose (> 3 x 10(6)/CD34+ cells/kg) after two mobilizations (six patients achieved the target from the second mobilization alone). A further eight underwent HDC-PBPCS without achieving the target PBPC dose. These patients experienced a significant delay in neutrophil and platelet engraftment when compared with those patients achieving the target dose., Discussion: This study demonstrates that the combination of G-CSF and GM-CSF is an effective and tolerable method for re-mobilization of PBPC in patients who fail to provide an adequate yield from their first mobilization.