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.
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