Evaluation of multiple myeloma cell apoptosis in primary bone marrow samples

Although different approaches have been proposed to selectively determine multiple myeloma (MM) cells in a heterogeneous population of bone marrow (BM) cells, studies on plasma cells from primary samples of MM patients are still challenging. This is partially due to difficulties in obtaining a suitable amount of sample, but even more due to uneven infiltration of BM by MM cells. When the apoptotic effect of different agents on MM plasma cells is studied, evaluation is additionally complicated by morphological changes induced by apoptosis. We introduce a modified gating approach combining specific antibodies and exclusion of cellular interferences.

The extent of apoptosis induced by arsenic trioxide and camptothecin was evaluated by flow cytometry using annexin V and propidium iodide (PI) after selective labelling of plasma cells with CD38 and CD138 antibodies. We selectively analysed MM plasma cell apoptosis combining CD38/CD138-positivity and exclusion of cellular interferences.

Thirty BM samples from newly diagnosed MM patients were analysed. We compared the proportion of cells in different phases of apoptosis obtained by gating on a CD38/CD138-positive population only and by the novel approach. The proportion of cells in early apoptosis evaluated by the modified gating technique was significantly higher for both inductors.

The introduced gating approach can increase the reliability of selective evaluation of MM plasma cell apoptosis in primary samples. The modified method can further be implemented for the analysis of various processes in plasma cells by flow cytometry.