Gene Expression Profiling of B-Lymphocyte and Plasma Cell Populations from Waldenström’s Macroglobulinemia. Comparison with Expression Patterns of the Same Cell-Counterparts from Other B-Cell Neoplasms.

The tumoral clone of Waldenström’s macroglobulinemia (WM) shows a wide morphological heterogeneity which ranges from B lymphocytes (BL) to plasma cells (PC), including a lymphoplasmacytic population that defines the disease. The differences between these cell compartments and their cell-counterpart in other lymphoproliferative disorders have not yet been sufficiently explored. We compared the gene expression profiling (GEP) of BL and PC from patients diagnosed with WM, with clonal BL and PC from patients with chronic lymphocytic leukemia (CLL) and multiple myeloma (MM) respectively. Bone marrow samples from 10 WM and 10 MM patients and peripheral blood from 10 CLL patients were used for the analysis. The isolation of the different cell populations was carried out by multiparameter flow cytometry sorting with the following monoclonal antibodies combination: Kappa or Lambda-FITC, CD10-PE, CD38-PerCP-Cy5.5, CD19-PE-Cy7, CD34-APC and CD45-APC-Cy7. Total RNA (100–500 ng) was amplified and labeled using the “GeneChip Two-Cycle cDNA Synthesis Kit” and hybridized to “Human Genome U133A” microarray (Affymetrix). Processing of genechip data was carried out using the Robust Multi-chip Average (RMA) and the Affymetrix Microarray Suite v.5 (MAS5) gene expression algorithms. Two-way hierarchical cluster analysis showed that GEP was able to classify PC from WM and PC from MM in two different groups. In a similar way, BL from WM and CLL were grouped in different clusters. The Significance Analysis of Microarrays (SAM) algorithm identified gene expression changes in a total of 163 genes (103 up and 60 down-regulated) when MW PC were compared with MM PC. Some of these genes were related to regulation of PC development: PAX5 was overexpressed and IRF4 infraexpressed in WM PC. PC from WM displayed high expression levels of MYB and DEK oncogenes while MM PC showed an elevated expression level of v-MAF oncogene. Regarding gene functional categories, “immune response” and “signal transduction” were the biological process more active in WM PC. Comparison between BL from WM and BL from CLL revealed that 31 genes were differentially expressed: IL4 receptor, LEF1 (WNT/b-catenin pathway), fibromodulin (modulator of TGF-b activity) and FGR oncogene (tyrosine kinase protein) showed very low expression levels in WM BL compared to CLL BL. In contrast, the growth factor IL6 was over-expressed in WM BL. These results indicate that both PC and BL from WM are genetically different from the MM and CLL cell-counterpart. The differentially expressed genes have important functions in the B-cell differentiation and oncogenesis. Supported by Spanish Myeloma Network (G03/136) and “Ministerio de Ciencia y Tecnología” (SAF04/06587) and “Junta de Castilla y León” grants (SA032/04)