Linear reduction of clonal cells in stem cell enriched grafts in transplanted multiple myeloma

In 30 patients with multiple myeloma who were scheduled for peripheral bloo d stern-cell transplantation, a quantitative analysis of the stem cells fol lowing enrichment by anti-CD34 was carried out. To detect the cells of the specific myeloma clone, polymerase chain reaction (PCR) was performed using unique allele-specific oligo primers for the immunoglobulin heavy chain re arrangement. The clonogenic cells before and after stem-cell enrichment, we re quantified by a limiting dilution assay and a highly sensitive semi-nest ed PCR combined with a real-time quantitative PCR. In order to accomplish a statistically adequate end-point analysis, a large number of PCR analyses (40 per sample) were performed. By this technique the lowest detection limi t observed was one myeloma cell per 10(6) cells. Myeloma cells were detecte d in 29/30 samples from the CD34-enriched fraction. The CD34 selection proc edure resulted in a median 28-fold enrichment of CD34(+) haemopoietic precu rsor cells, The stem-cell selection reduced the median concentration of clo nal cells per million total cells by half, with a highly significant linear relationship between the number of myeloma cells before and after stem cel l enrichment. The median depletion of clonal cells by the overall procedure was 2.15 log units, corresponding to a reduction of the total quantity of clonal cells reinfused into the patients by at least 99.3%. We conclude tha t CD34(+) cell enrichment led to a reliable tumour cell depletion of the or der of 2 log, which may not be sufficient since the total number of tumour cells in the leukapheresis product was 7.2 log (median).