FIRST AND 2ND APHERESIS IN PATIENTS WITH MULTIPLE-MYELOMA - NO DIFFERENCES IN TUMOR LOAD AND HEMATOPOIETIC STEM-CELL YIELD

Autologous peripheral blood stem cells (PBSC) are now widely used to s upport myeloablative therapy in patients with multiple myeloma (MM), T he presence of malignant cells in these autografts has been demonstrat ed. Characteristic kinetics with differential and concomitant mobiliza tion of CD34(+) and malignant cells after high-dose (HD) chemotherapy and hematopoietic growth factor administration have been reported. We determined the amounts of tumor cells and PBSC in leukapheresis produc ts (LP) collected on day 1 (LP1) and 2 (LP2) from 16 MM patients harve sted after HD chemotherapy and G-CSF. Furthermore, LP from six patient s collected on day 5 (LP5) could be examined. The content of clonotypi c cells was quantitated by an allele-specific oligonucleotide (ASO)-PC R assay based on limiting dilutions. CD34(+) PBSC were determined by f low cytometry, The percentages of malignant cells in the leukapheresis products were in the range of 0% to 0.713% (mean 0.047%). CD34(+) cel ls ranged between 0.06% and 5.4% (mean 1.23%). Comparing LP1 with LP2, no differences in the quantity of tumor cells (mean 0.0538% vs 0.0448 %; P = 0.96) and CD34(+) cells (mean 1.49% vs 1.33%; P = 0.50) were se en. The calculated number of tumor cells per CD34(+) cell did not diff er significantly (mean 0.0420 vs 0.0249; P = 0.65). Analyzing LP5 reve aled no changes in the number of tumor cells per CD34(+) cell (0.0511 vs 0.1044; P = 0.46) indicating a relatively constant ratio of PBSC to tumor cells during the course of PBSC harvesting. These results offer the possibility of combining LP harvested over several days without i ncreasing the tumor load per CD34(+) cell.