Abstract 1521: High-throughput molecular profiling of Multiple Myeloma clonotypic CD19+ B cells highlights pathways potentially involved in the disease endurance

The bulk of current knowledge on Multiple myeloma (MM) disease is mainly based on the molecular characterization of 138+ plasma cells, but we become aware that MM heterogeneity has more deepen roots. Recent studies support that Myeloma Propagating Cells (MPCs) might be responsible of relapses and they residing in the 138- compartment. In order to molecularly characterize mature and precursor cell fractions, we collected the 138+ and 138-19+27+ cell fractions from bone marrow (BM) and peripheral blood (PBL) of 50 newly diagnosed MM patients (pts). Clonogenic assays were performed by plating cell fractions of MM cell lines. The molecular characterization included: IgH rearrangement sequencing, analysis of genomic aberrations and gene expression profiling by Affymetrix 6.0 SNPs array and HG-U133 Plus 2.0 microarray. Clonogenic assays showed that 138- cells were able to form colonies more efficiently than 138+ cells. By VDJ gene rearrangement sequencing, a clonal relationship between the 138+ clone and precursor ones was confirmed. SNPs arrays showed that both BM and PBL 138+ cell fractions carried the same genomic macro-alterations. On the contrary, in the 138-19+27+ cell fractions from BM and PBL any macro-alteration was detected, whereas several micro-alterations unique of the memory B cells clone were highlighted. An enrichment analysis revealed that genes are involved in DNA repair mechanisms, transcriptional regulation, negative regulation of apoptosis and angiogenesis. Interestingly, KRAS, WWOX and XIAP genes are located in the amplified regions of immature cells. Moreover, we observed several LOH regions that covered important tumor suppressor genes, including TP53, CDKN2C and RASSF1A. The involvement of immature cells in MM pathogenesis was confirmed by the analysis of the 19+ cells’ transcriptome profiles. 20 MM 19+ cells samples (12 from PBL, 8 from BM) were compared both to their normal counterpart and to the mature 138+ cell fractions. In particular, unsupervised analysis by hierarchical clustering discriminated the differential expression of 11480 and 11360 probes in the PBL and BM 19+ clones, respectively (2; FDR = 0,05; p