Leukapheresis products in multiple myeloma: lower tumor load after mobilization with cyclophosphamide plus granulocyte colony-stimulating factor (G-CSF) compared with G-CSF alone.

High-dose therapy with autografting of peripheral blood stem cells (PBSCs) has become an accepted treatment modality. However, gene-marking studies in patients with acute myeloid leukemia and neuroblastoma have revealed that malignant cells reinfused along with leukapheresis products (LPs) contribute to relapse. Thus, a reduction in the number of malignant cells in autografts is desirable. We analyzed the percentage of malignant cells and the number of CD34(+) PBSCs in LPs mobilized by granulocyte colony-stimulating factor (G-CSF) alone (LP-S) compared with high-dose cyclophosphamide plus G-CSF (LP-CY) in patients with multiple myeloma (MM). A quantitative polymerase chain reaction assay involving CDR3-specific primers based on the method of limiting dilutions was used to determine the tumor loads of LPs. Sixteen LPs from eight patients with MM were analyzed intraindividually in matched pairs. The percentage of malignant cells was lower in LP-CY (p = 0.017; median 0.0067 vs. 0.009%), whereas the number of CD34(+) cells was higher (p = 0.012; median 0.3 vs. 0.095%). The calculated number of malignant cells per CD34(+) cell was significantly lower in LP-CY as well (p = 0.017). We conclude that mobilization by cyclophosphamide plus G-CSF leads to a lower number of malignant cells per CD34(+) cell in LPs compared with G-CSF alone.