Quantitative comparison of multiple myeloma tumor contamination in bone marrow harvest and leukapheresis autografts.

Autologous transplantation is increasingly being used to treat patients with multiple myeloma (MM). Recently, peripheral blood progenitor cell (PBPC) harvest have been preferred over autologous bone marrow (BM) harvests due to reduced engraftment time, ease of attainment, and presumptive reduction of occult tumor involvement. To resolve this latter assumption quantitatively, we have used the unique immunoglobulin (Ig) heavy chain variable region sequence of the patient's myeloma cell as a marker of clonality. Samples from PBPC collections and 'back-up' BM harvests were obtained from 13 patients with MM and analyzed for tumor contamination using patient-specific oligonucleotide primers and the polymerase chain reaction. As expected, the percentage of tumor cells contaminating the BM harvest (median, 0.74%) was higher than in the PBPC specimens (median, 0.0024%). Because of the increased total number of cells required for PBPC transplantation, the increase in total number of contaminating cells in the BM vs PBPC autografts was less pronounced, (BM:PBPC tumor contamination ratios ranging from 0.9 to > 4500; median, 14). This confirms that in most but not all cases unmanipulated PBPC products are preferable over BM harvests as a method of reducing myeloma autograft tumor contamination.