Circulating clonal cells in multiple myeloma do not express CD34 mRNA, as measured by single-cell and real-time RT-PCR assays

The peripheral blood (PB) mononuclear cells in patients with multiple myelo ma (MM) have been reported to include CD34-expressing cells that are clonal ly related to the myeloma cells, To determine whether there were elevated l evels of CD34 mRNA or whether CD34(+) cells in the PB include myeloma-relat ed cells, we developed a quantitative real-time and a competitive CD34 RT-P CR assay working on single now-sorted cells. Myeloma-specific cells were de tected with allele-specific oligonucleotides (ASO) IgH PCR, PBSC products a nd mononuclear cell fractions in blood from normal donors, untreated and tr eated myeloma patients were analysed, When measured by flow cytometry, the numbers of CD34(+)/CD19(+) cells were consistently <0.1% of the mononuclear cells. In addition, no significant di fference was found in the levels of CD34 mRNA between normal subjects and u ntreated MM patients (P=0.935). In the treated group of MM patients the CD3 4 mRNA levels were significantly reduced (P = 0.052) because of the stem fe ll toxicity of melphalan. Further, no cells clonally related to the MM clon e were found within the CD34 compartment, defined by a sort-gate that inclu ded all cells expressing CD34 mRNA, as no cells outside the used CD34 sort- gate had a detectable level of CD34 mRNA. We conclude that in myeloma patie nts, the myeloma clone is not found within the CD34 compartment.