In multiple myeloma, circulating hyperdiploid B cells have clonotypic immunoglobulin heavy chain rearrangements and may mediate spread of disease

DNA aneuploidy characterizes a proportion of malignant bone marrow (BM)-loc alized plasma cells in multiple myeloma (NM). This analysis shows that for most MM patients, circulating clonotypic B cells in MM are also hyperdiploi d, Although all normal B cells and some malignant B cells are diploid, hype rdiploidy is likely to be exclusive to those that are malignant, Hyperdiplo id MM B cells express CD34 and have clonotypic IgH transcripts, confirming them as part of the malignant clone. For MM, 92% (70/76) of patients had a DNA hyperdiploid subset [5-30% of peripheral blood mononuclear cells (PBMCs )] of CD19(+) B cells. All CD19(+) PBMCs in MM expressed CD19 and IgH varia ble diversity joining (VDJ) transcripts, confirming them as B cells, DNA an euploid cells were undetectable in T or B lymphocytes from normal blood, sp leen or thymus, or in blood from patients with B chronic lymphocytic leukem ia, In MM, untreated patients had the highest DNA index (1.12), DNA hyperdi ploid PBMCs were most frequent among untreated patients and were significan tly reduced after chemotherapy, Diploid B cells were significantly more fre quent after chemotherapy than at diagnosis. Of the hyperdiploid PBMCs, 81 /- 3% expressed CD34 and CD19, In contrast to circulating CD34(+) B cells, CD34(-) B cells in MM are diploid, In MM, unlike hyperdiploid PBMC B cells, hyperdiploid BM plasma cells lack both CD34 and CD19, suggesting that loss of CD34 correlates with differentiation and BM anchoring, Irt situ reverse transcription-PCR of the CD34(+) (hyperdiploid) and CD34(-) (diploid) PBMC B-cell subsets was performed using patient-specific primers to amplify clo notypic IgH VDJ transcripts, Confirming previous work, CD34(+) hyperdiploid MM PBMCs mere clonotypic (86 +/- 5%). In contrast, CD34(-) diploid MM PBMC s had few monoclonal cells (4.8 +/- 2%). The lack of hyperdiploidy, togethe r with the relative absence of cells having clonotypic transcripts, suggest s these polyclonal CD34(-) B cells are normal, After culture in colchicine to arrest mitosis, hyperdiploid B cells were reduced and MRI B cells accumu lated in a diploid G(2)-M suggesting that hyperdiploid in MM may represent a transient S-phase arrest rather than an aneuploid G(0), phase. The DNA hy perdiploidy of CD34(+) clonotypic B cells suggests these cells may be clini cally important constituents of the myeloma clone and that they may play a direct role in the spread of myeloma.