Successful mobilization of peripheral blood stem cells after addition of ancestim (stem cell factor) in patients who had failed a prior mobilization with filgrastim (granulocyte colony-stimulating factor) alone or with chemotherapy plus filgrastim

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 × 106/kg BW) with filgrastim-alone or chemotherapy-plus-filgrastim. The same mobilization regimen was used with the addition of rHuSCF. In the filgrastim-alone group (n=13), rHuSCF 20 μg/kg was started 3 days before filgrastim and continued for the duration of filgrastim. In the chemotherapy-plus-filgrastim group (n=31), rHuSCF 20 μg/kg/day plus filgrastim 5–10 μg/kg/day were administered concurrently. Leukaphereses were continued to a maximum of four procedures or a target of ⩾3 × 106 CD34+ cells/kg. In both groups, CD34+ yield (× 106/kg BW) of the study mobilization was higher than that of the prior mobilization (median: 2.42 vs 0.84 P=0.002 and 1.64 vs 0.99 P=<0.001, 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 × 106/kg. The probability of a successful mobilization was the same in those with a CD34+ yield of 0.5–0.75 × 106/kg BW in the prior mobilization as in those with 0.76–1.99 × 106/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.