The Use of MAGE C1 and Flow Cytometry to Determine the Malignant Cell Type in Multiple Myeloma

The malignant cell phenotype of Multiple Myeloma (MM) remains unclear with studies proposing it to be either clonotypic B or proliferating plasma cells. Cancer/testis antigen MAGE C1 is being extensively studied in MM and it has been suggested that it is involved in the pathogenesis of the cancer. Therefore, we report on the use of MAGE C1 to determine the malignant cell phenotype in MM using flow cytometry. Bone marrow aspirate (BM) and peripheral blood (PB) was collected from twelve MM patients at diagnosis, as well as three MM disease-free controls. Mononuclear cells were isolated using density-gradient centrifugation, and stabilized in 80% ethanol, before analysis via flow cytometry using relevant antibodies against B cell development cell-surface markers and nuclear MAGE C1. MAGE C1 expression was observed consistently in the early stem cells (CD34 + ) and early pro-B to pre-B cells (CD34 +/− /CD19 + ), as well as the proliferating plasma cells in both the MM PB and BM, while no expression was observed in the corresponding control samples. Monoclonality indicated a common origin of these cell types suggesting that the CD34 + /MAGE C1 + are the primary malignant cell phenotype that sustains the downstream B cell maturation processes. Furthermore, this malignant cell phenotype was not restricted to the BM but also found in the circulating PB cells.