Immunophenotyping of plasma cells in multiple myeloma.

Multiparametric immunophenotyping of multiple myeloma (MM) and other plasma cell (PC) dyscrasias represents an attractive approach not only for research purposes but also in clinical practice. Based on well-established antigenic patterns, discrimination between myelomatous and normal PCs can be easily achieved in various types of samples, and this can be particularly valuable for the differential diagnosis between MGUS and MM and for monitoring residual disease in the latter. In addition, immunophenotyping may be an alternative and more reproducible method than morphology for evaluating PC infiltration, as well as for specifically analyzing DNA content and the cell-cycle distribution of different subsets of PCs. Despite the widespread use, standardization of methods and protocols still remains a challenge. In this chapter, we describe in detail the protocols and precise instructions for specimen collection, sample preparation, together with the methods for staining PCs and flow cytometry, data acquisition, and data analysis, including the more recent developments in the field. We highlight the most frequent limitations, and provide troubleshooting and practical recommendations that could help to solve them. The goal of this chapter is to emphasize the relevance of methodological issues in order to obtain reproducible and high-quality results regarding the phenotypic analysis of PCs.