Abstract 3884: Gene expression profiling and copy number alterations of circulating clonotypic B cells of multiple myeloma newly diagnosed patients reveals pathways potentially involved in the development and in the disease persistence
Authors: Martello Marina , Terragna Carolina , Martinelli Giovanni , Dico Flores , Borsi Enrica , Zamagni Elena , Pantani Lucia , Tacchetti Paola , Zannetti Beatrice , Mancuso Katia , Rocchi Serena , Brioli Annamaria , Guadagnuolo Viviana , Cavo Michele 
Published: May 2015

Abstract
Background Although the advances in Multiple Myeloma (MM) therapy, the disease remains incurable. The existence of Myeloma Propagating Cells (MPCs) is supposed to be one of the major causes of MM drug-resistance, leading to relapse. However, very little is known about the molecular characteristics of MPCs, even if some studies suggested that these cells have phenotypic characteristics resembling the memory B cells.
Aim and methods In order to molecularly characterize the 138+ neoplastic clone and the memory B cells located both in bone marrow (BM) and in peripheral blood (PBL), we collected the 138+ 138- cell fractions of 50 newly diagnosed MM patients (pts). We isolated the B cell population and, when possible, the memory B cell clone. For each cell fraction we performed a VDJ rearrangement analysis. The complete set of genomic aberrations was evaluated by SNP Array 6.0 (Affymetrix). Gene expression profile HG-U133 Plus 2.0 microarray analyses (Affymetrix) were performed according to a standardized protocol.
Results The VDJ rearrangement analyses confirmed the clonal relationship between the 138+ clone and the memory B cells clone.
Both BM and PBL 138+ cell fractions showed exactly the same genomic macro-alterations. In the BM and PBL 138-19+27+ cell fractions any macro-alteration was detected, whereas several micro-alterations (range: 1-350 Kb) unique of the memory B cells clone, were highlighted. These micro-alterations were located out of any genomic variants region and are presumably associated to the MM pathogenesis, as confirmed by the presence of KRAS, WWOX and XIAP genes among the amplified regions. Moreover, the memory B cells were characterized by the presence of several LOH regions, including possibly involved tumor suppressor (TS) genes.
To get insight into the biology of the clonotypic B cell population, we compared the gene expression profile of 7 MM B cells vs 5 donor B cells samples, thus showing a differential expression of 11480 probes (Fold Change: 2;-2; FDR: 0,05; p-value: &lt;0,05) by unsupervised analysis of hierarchical clustering. Among the self-renewal mechanisms, we observed the down-regulation of Hedgehog pathway and the iperactivation of Notch and Wnt signaling. Moreover, these immature cells showed a particular phenotype correlated to resistance to proteasome inhibitors, due to the attenuation of the unfolded protein response (IRE1α-XBP1: -18.0; -19.96. P&lt;0,05).
Conclusions Data suggested that the MM 138+ clone might resume the end of the complex process of myelomagenesis, whereas the memory B cells have some intriguing micro-alterations and a specific transcriptional program, supporting the idea that these post germinal center cells might be involved in the transforming event that originate and sustain the neoplastic clone.
Citation Format: Marina Martello, Carolina Terragna, Giovanni Martinelli, Flores Dico, Enrica Borsi, Elena Zamagni, Lucia Pantani, Paola Tacchetti, Beatrice Zannetti, Katia Mancuso, Serena Rocchi, Annamaria Brioli, Viviana Guadagnuolo, Michele Cavo. Gene expression profiling and copy number alterations of circulating clonotypic B cells of multiple myeloma newly diagnosed patients reveals pathways potentially involved in the development and in the disease persistence. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3884. doi:10.1158/1538-7445.AM2014-3884