Adhesion molecule immunophenotype of bone marrow multiple myeloma plasma cells impacts the presence of malignant circulating plasma cells in peripheral blood.

INTRODUCTION: Multiple myeloma (MM) patients with malignant plasma cells (MMPCs) in their bone marrow (BM) and malignant circulating plasma cells (MMCPCs) in the peripheral blood (PB) are an independent marker of a clinically aggressive disease, and it reflects a poor prognosis defined by a short time to progression and overall survival. We hypothesized that changes in ADM expression on BM MMPCs might contribute to MMCPC presence in the PB of relapsed/refractory multiple myeloma (RRMM) patients. METHODS: We assessed the difference in expression of adhesion molecules and receptors related to cell-cell interaction: integrins, hyaluronic acid receptors, chemokine receptors and other proteins on healthy donor PCs, RRMM BM and PB MMPCs. RESULTS: Adhesion immunophenotype showed a significant loss of many adhesion molecules when comparing BM MMPCs of MMCPC- and MMCPC+ MM patients (CD49d, CD49e, CD56, CD138). Further decrease of adhesion molecules was shown in MMCPCs (CD49d, CD49e, CD56, CD138, CD58), suggesting that loss of these molecules may allow cells to leave the BM. CONCLUSIONS: Loss of adhesion molecule expression enables MMPCs to leave the BM milieu and enter the PB. These changes can be seen in both the PB and BM of MMCPC+ MM patient.