CD34 SELECTION FOR PURGING IN MULTIPLE-MYELOMA AND ANALYSIS OF CD34(+) B-CELL PRECURSORS

Selection of CD34(+) hematopoietic progenitor cells from autografts may be performed in multiple myeloma (MM) to minimize contamination with tumor cells. This approach is based on the assumption that the malignant cells do not express the CD34 antigen. Therefore, we first compared the CD34(+)/CD10(+) and CD34(+)/CD19(+) subpopulations from bone marrow (BM) and peripheral blood (PB) of fourteen MM patients and five normal controls. No difference between the respective early B cell subsets of both groups could be observed. Using tricolor flow cytometry, the CD19 expression on CD34(+)/CD10(+) cells in BM was found to increase continuously from CD19(-) to CD19(dlim). In contrast, circulating CD34(+)/CD10(+) cells did not coexpress the CD19 antigen. This population may contain myeloid progenitor cells or bipotential progenitor cells of the myeloid and lymphoid lineage as suggested by data obtained with fetal liver cells. Further functional studies are required. Enrichment of CD34(+) cells with immunomagnetic beads was performed from BM of three MM patients and four normal donors. The CD34(+) cells were selected with the HPCA-1 antibody and detached from the beads with chymopapain. Compared with the starting cell preparation, a 3.97 +/- 0.48 log (mean +/- SE) reduction of plasma cells could be achieved after CD34 selection. On morphological examination, 84% +/- 4% of the cells in the CD34(+) fraction (MM) were immature blasts. The plating efficiency for hematopoietic colony forming cells was 9.7% +/- 2.8% in the CD34 selected fraction of the MM group, reflecting a 51-fold increase as compared with the starting population. However, the mean recovery of colony forming precursor cells was only 19% +/- 8% in the MM samples and 30% +/- 9% in the control samples. The selection of CD34(+) hematopoietic cells is an effective purging method in MM that may be used for autografts, provided the recovery can be improved.