Leukemia cell mobilization with G-CSF plus plerixafor during busulfan-fludarabine conditioning for allogeneic stem cell transplantation.

We hypothesized that during conditioning chemotherapy for allogeneic stem cell transplant (allo-SCT), the disruption of stromal-leukemia interactions using G-CSF in combination with the CXCR4-specific inhibitor, plerixafor, may promote the release of leukemic cells from the niche and increase tumor elimination. In a phase 1/2 investigation, we treated 45 AML/myelodysplastic syndrome (MDS)/CML patients (34 AML, 7 MDS and 4 CML) with G-CSF (10 μg/kg daily for 6 days starting on day -9) plus plerixafor (doses of 0, 80, 160 or 240 μg/kg daily for 4 days starting on day -7) along with the busulfan-fludarabine (Bu-Flu) conditioning regimen. In the phase 1 part, we determined that G-CSF plus plerixafor is safe in this setting. We compared the clinical effects and outcomes of AML/MDS study patients (n=40) with 164 patients from a historical data set who received Bu-Flu alone before allo-SCT by stratifying on cytogenetics and disease status to correct for bias. Study patients had increased myeloid chimerism and lower rates of GvHD. There was no significant difference in relapse-free survival or overall survival. The G-CSF plus plerixafor combination increased circulating WBCs, CD34+ cells and CXCR4+ cells, and preferentially mobilized FISH+ leukemic cells.