No detectable malignant B cells in the peripheral blood of patients with multiple myeloma

Previous studies have reported the presence of idiotypic B lymphocytes in the peripheral blood of patients with multiple myeloma (MM), suggesting that they may belong to the malignant clone. This led us to investigate by Southern blot analyses the presence of tumour-specific immunoglobulin-gene (Ig-gene) rearrangements in the peripheral-blood mononuclear cells of 21 MM patients. This method was shown to detect clonal cells when they represent as little as 2% of the cell population. B-cell-enriched fractions were also studied in nine cases. An occasional contamination by circulating malignant plasma cells was carefully evaluated using immunofluorescence. Clonal rearrangements were observed in only two cases, in which a contamination by myeloma cells was evident. In these cases the use of different endonucleases clearly demonstrated that these Ig-clonal rearrangements involved post-switched cells. No clonal rearrangement was found when contamination by myeloma cells was absent. Our results demonstrate the absence of detectable B cells involved in the myeloma clone in the peripheral blood of patients with MM.