Application of an immune-magnetic cell sorting method for CD138-positive plasma cells in FISH analysis of multiple myeloma

Introduction: Interphase fluorescence in situ hybridization (FISH) analysis of multiple myeloma (MM) may indiscriminately count signals of nonplasma cells, thus decreasing specificity and sensitivity. We aimed to evaluate the usefulness of an immune-magnetic sorting method for plasma cells in FISH analysis of MM and define optimal sample preparation conditions. Methods: Plasma cells were purified using EasySep (R) CD138 Positive Selection Cocktail and Magnetic Nanoparticles (Invitrogen). We compared FISH results with and without plasma cell purification for three sample preparation methods: direct harvest, 24-h culture, and 96-h culture with interleukin-4 in five newly diagnosed MM patients. Archived fixed bone marrow cells of 17 MM patients were also studied. Results: The percentage of abnormal cells identified was significantly higher with plasma cell purification than without purification (median, 88.0%; range, 84.0-100.0%vs. 15.0%, 12.5-29.5%, respectively). The three sample preparation methods showed comparable results. Immune-magnetic sorting also significantly increased the percentage of abnormal cells identified in FISH analysis of archived fixed bone marrow cells (P < 0.001). Conclusions: Immune-magnetic CD138-positive cell sorting significantly increased the percentage of abnormal cells identified in FISH analysis of MM samples for all sample preparation methods. This method could also be applied for retrospective FISH analysis of archived fixed bone marrow cells.