Absence of Rh123 export by MM plasma cells, but the presence of CsA-sensitive Rh123 export by subsets of lymphocytes in myeloma PBMC. MM B cells were defined by staining with CD11B-PE. Previous work shows that all CD11B⁺ PBMC express CD19 and IgH mRNA.20a Plasma cells were defined as CD38^hi cells. Monocytes were identified by their CD14^bright phenotype and their high scatter after P-gp mediated dye export. T cells were defined by staining with CD4-PE or CD8-PE; the Rh123 export values represent the overall mean CsA-sensitive export incuding both PBMC and BM T-cell subsets. All staining was compared to an isotype-matched control MoAb. Files were gated for the indicated subset and the Rh123 dye export ± CsA was plotted as a histogram. CsA-sensitive, P-gp mediated dye export was defined as Rh123 staining in the absence of CsA minus Rh123 staining in the presence of CsA. BMC from 23 MM patients and PBMC from 68 MM patients were analyzed. ***P < .0001 as compared to MM B cells from PBMC.