A RATIONALE FOR POSITIVE SELECTION OF PERIPHERAL-BLOOD STEM-CELLS IN MULTIPLE-MYELOMA - HIGHLY PURIFIED CD34(-FRACTIONS OF LEUKAPHERESIS PRODUCTS DO NOT CONTAIN MALIGNANT-CELLS() CELL)

In multiple myeloma (MM), the presence of tumor cells in leukapheresis products (LP) has been demonstrated with highly sensitive molecular b iological tools in up to 100% of cases. Therefore methods to reduce th e tumor load of LP by CD34(+) selection are envisaged. However, there is controversy as to whether the CD34(+) cell is already involved in t he malignant process. We have established a PCR assay with allele-spec ific oligonucleotide primers (ASO) complementary to the CDR3-hypervari able region of the immunoglobulin heavy chain gene of each patient's m yeloma clone. Using this ASO-PCR, 43 LP of 10 patients with MM eligibl e for high-dose therapy were assessed for malignant cells. Furthermore , in an experimental setting we have examined 10 CD34(+) and four CD19 (+) fractions obtained from PCR-positive LP by sequential preparative magnetic and fluorescence activated cell sorting (purity >96%) for the presence of the tumor-specific CDR3 region. The majority of LP harbor ed cells of the myeloma clone (93%), while all CD34(+) fractions were PCR-negative. In all CD19(+) fractions malignant cells were detected. These results confirm that CD34(+) selection can be considered for LP in MM. The sensitivity of the ASO-PCR (up to 10(-5)) enables us furthe r to monitor the efficacy of CD34(+) enrichment protocols in the clini cal setting.