Summary:This study assessed the ability of recombinant human stem cell factor (rHuSCF) to mobilize stem cells in 44 patients who had failed a prior mobilization (CD34 + yield 0.5-1.9 Â 10 6 /kg BW) with filgrastim-alone or chemotherapyplus-filgrastim. The same mobilization regimen was used with the addition of rHuSCF. In the filgrastim-alone group (n ¼ 13), rHuSCF 20 lg/kg was started 3 days before filgrastim and continued for the duration of filgrastim. In the chemotherapy-plus-filgrastim group (n ¼ 31), rHuSCF 20 lg/kg/day plus filgrastim 5-10 lg/ kg/day were administered concurrently. Leukaphereses were continued to a maximum of four procedures or a target of X3 Â 10 6 CD34 + cells/kg. In both groups, CD34 + yield ( Â 10 6 /kg BW) of the study mobilization was higher than that of the prior mobilization (median: 2.42 vs 0.84 P ¼ 0.002 and 1.64 vs 0.99 P ¼ o0.001, respectively). In all 54 and 45% of patients in the filgrastim-alone group and chemotherapy-plus-filgrastim group, respectively, reached the threshold yield of 2 Â 10 6 / kg. The probability of a successful mobilization was the same in those with a CD34+ yield of 0.5-0.75 Â 10 6 /kg BW in the prior mobilization as in those with 0.76-1.99 Â 10 6 /kg BW. Downmodulation of c-kit expression and a lower percentage of Thy-1 positivity in the mobilized CD34 + cells were noted in the successful mobilizers compared with those in the poor mobilizers. This study shows that rhuSCF is effective in approximately half the patients who had failed a prior mobilization and allows them to proceed to transplant. It also points to the likely role of the SCF/c-kit ligand pair in mobilization.

Summary:For 10 consecutive patients in our unit who did not show a significant rise in blood progenitor cells within 14 days following chemotherapy and G-CSF, we increased the G-CSF dose from 5 to 10 g/kg/day (n = 9) or from 10 to 15 g/kg/day (n = 1). As a result, there were significant increases in total yield as well as yield per apheresis of mononuclear cells, CD34 + cells and CFU-GM (P Ͻ 0.025, Ͻ0.01 and Ͻ0.005, respectively). After G-CSF dose escalation, six of the 10 patients had sufficient CD34 + cells for performing transplantation. These results demonstrate a dose-dependent response of progenitor cell mobilization by G-CSF when used in combination with chemotherapy. Moreover, increasing the dose of G-CSF as late as the third week of mobilization may still provide sufficient cell yield even with patients who did not show a significant mobilization with conventional doses of G-CSF. Keywords: stem cell mobilization; chemotherapy; G-CSF; CD34; CFU-GM With the discovery that the number of circulating hematopoietic progenitor cells dramatically increases during the recovery phase of myelo-suppressive chemotherapy, 1 various chemotherapy regimens were employed to mobilize peripheral blood stem cells (PBSC) for transplant. 2-4 However, the cytopenic phase following myelo-suppressive chemotherapy is often associated with significant morbidity or even mortality. 3,5 With the advent of hematopoietic growth factors (HGF), the use of combined chemotherapy and HGF in mobilizing PBSC results in a shorter cytopenic phase, reduction of infection risks and duration of hospital stay and enhances PBSC yield compared to mobilization with chemotherapy alone. 4,[6][7][8][9][10] Nevertheless, the dosages and scheduling of chemotherapy and HGF to optimize the cell yield, and hence the successful outcome of mobilization, remain to be studied.

Between April 1988 and March 1994 a total of 23 patients with haematological or non-haematological malignancies received serial peripheral blood stem cell (PBSC) mobilization to attain sufficient harvest for PBSC transplant at our institution. There was no improvement in yield with the second mobilization for group A patients (n = 12) who had the same dose of cyclophosphamide twice as mobilizing agent. For group B patients (n = 6). who had a higher dose of cyclophosphamide with the second mobilization, there was significant increase in CFU-GM yield. CD34+ cell yield was not measured. For group C patients, who received interleukin-3 plus granulocyte-macrophage colony-stimulating factor (GM-CSF) with the first mobilization and chemotherapy plus GM-CSF with the second, there was significant increase in CFU-GM as well as CD34+ cell yield. Our results demonstrate that, at the doses studied, chemotherapy dose escalation and combining haemopoietic growth factor with chemotherapy improve progenitor cell yield in PBSC mobilization.

The colony-forming unit-granulocyte-macrophage (CFU-GM) assay is used commonly to assess adequacy of progenitor number in bone marrow transplantation. The assay is poorly standardized, resulting in variability of results between and within laboratories. We assessed three variables that contribute to the lack of standardization. The colony-stimulating activity of human placental-conditioned medium (HPCM) was compared with combinations of recombinant hematopoietic growth factors (HGF) in 5 normal bone marrow donors. A protocol for batch testing of fetal calf serum (FCS) is described. In addition, a rigid training program has been introduced to minimize interstaff and intrastaff variability in the counting of colonies. We show that a five-factor combination of interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), and stem cell factor (SCF) produces a mean increase of 85% in colony number. Some combinations of three HGF produce similar growth to HPCM, and all four HGF combinations are equivalent or superior to HPCM. Batch testing of FCS shows variability between batches. We show significant interstaff and intrastaff variability between a new and experienced staff member that improves following a period of training. In summary, the use of recombinant HGF in association with a rigorous program of batch testing of FCS and staff training results in a CFU-GM assay that can be standardized between laboratories.