Selection of candidate marker genes. To identify markers for further testing, we compared 1285 gene expression profiles of MMPCs with 3164 gene expression profiles of a wide range of hematologic disorders. Through this process, we identified large numbers of strongly differentially expressed genes (supplemental Table 1). Integrating the differential expression data with information about gene function, protein structure, and antibody availability, we selected 7 candidates for further testing: TNFRSF17 (CD269), SLAMF7 (CD319/CS1), GPRC5D, FKBP11, LAMP3 (CD208), ITGA8, and FCRL5 (CD307e). (A) Expression of 3 of our candidate marker genes, SLAMF7 (CD319), FCRL5 (CD307e), and TNFRSF17 (CD269) vs expression of SDC1 (CD138) in MM and leukemia (red, myeloma samples; black, control samples). All genes were more highly expressed in MMPCs and coexpressed with SDC1 (CD138). The results for GPRC5D, FKBP11, LAMP3, and ITGA8 are not shown, as their protein products could not be detected on MMPCs in the subsequent experiments. All genes were specifically expressed in MMPCs, except for FCRL5, which was also expressed in chronic lymphocytic leukemias (bottom-right cluster in middle panel). (B) Expression of our candidate genes in MMPCs and different normal hematopoietic cell types, represented here by gene expression profiles from the DMAP compendium. The selected genes were more highly expressed in MMPCs than in normal hematopoietic cells from different lineages. FCRL5 was not represented in DMAP.