CD34+ Cells in the Blood of Patients With Multiple Myeloma Express CD19 and IgH mRNA and Have Patient-Specific IgH VDJ Gene Rearrangements

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Abstract
Peripheral blood mononuclear cells (PBMC) from patients with multiple myeloma (MM) are here shown to include 23% ± 2% of CD34+ cells, the majority of which coexpress CD19, as identified by a panel of 17 anti-CD34 antibodies. The expression of CD34 mRNA by sorted CD34+ PBMC from MM was confirmed by in situ reverse transcriptase-polymerase chain reaction (RT-PCR) with CD34-specific primers. The majority of CD34+ MM PBMC were CD19+ cells that expressed mRNA for CD19 and for rearranged IgH as identified with consensus IgH VDJ primers, as well as having cytoplasmic Ig, definitively identifying them as B cells, in absolute numbers of 0.06 to 0.69 × 109/L of blood. CD34 is largely absent from normal B cells. To determine the clonal relationship of CD34+ B cells to autologous MM plasma cells, IgH VDJ DNA rearrangements of sorted CD34+ MM blood B cells were amplified by nested PCR using consensus primers followed by Southern blotting with allele-specific oligonucleotides for 7 MM patients, and clonotypic IgH mRNA expression was assessed for 4 MM patients using quantitative patient-specific in situ RT-PCR. For 9 of 11 myeloma patients tested, CD34+ blood B cells included IgH gene rearrangements or expressed IgH mRNA identical to that of autologous bone marrow plasma cells. For 4 of 4 MM patients, 74% to 94% of individual sorted CD34+19+ B cells expressed clonotypic IgH mRNA, as detected by in situ RT-PCR with patient-specific primers. Clonotypic IgH VDJ sequences were absent from B cells of unrelated MM patients and of normal donors. Clonotypic CD34+ B cells were detected before, during, and after treatment, and during relapse. Our results indicate a clonal relationship between CD34+ MM B cells and malignant plasma cells. We speculate that CD34 may play an important role in the biology of myeloma by facilitating extravasation from blood and thus spread of myeloma through the skeletal system.