Trascriptome Analysis of Bone Marrow CD14⁺ Monocytes Revealed Differential Expression Profiles in Symptomatic Multiple Myeloma (MM) Compared to Smoldering MM and Monoclonal Gammopathy of Undetermined Significance

Abstract 1811

Symptomatic multiple myeloma (MM), smoldering MM (SMM) and monoclonal gammopathy of uncertain significance (MGUS) are well known different pathological and clinical entities of plasma cell (PC) disorders. Nevertheless molecular studies performed on clonal CD138⁺ PC do not clear distinguished these disorders that share common alterations. Studies focusing on the presence of potential molecular alterations in the microenvironment cells are ongoing. Because monocytes are the cells primarily involved in osteoclastogenesis, angiogenesis and immune system disfuction, that are the hallmark of symptomatic MM compared to SMM and MGUS, in this study we have analyzed the transcriptional profile of the bone marrow (BM) CD14⁺ cells in these settings of patients.

BM CD14⁺ monocytes were purified from a total cohort of 36 patients with PC disorders including 21 patients with symptomatic MM, 8 patients with SMM and 7 patients with MGUS. CD14⁺ cells were isolated from the CD138 negative fraction of BM samples of patients by immunomagnetic method with anti-CD14 monoclonal antibody conjugated with microbeads. The presence of potential haemopoietic and CD138⁺ contaminating cells was excluded by FACS analysis. Only samples with CD14 purity greater than 95% were analyzed by microarrays by GeneChip® HG-U133Plus 2.0 arrays (Affymetrix®) (13 MM, 8 SMM and 7 MGUS). Data obtained were then validated on selected genes by Real-Time quantitative PCR. A multiclass analysis identified 14 differentially expressed genes, which characterized MGUS vs SMM vs symptomatic MM. A supervised analysis between symptomatic MM vs. SMM and MGUS samples identified 101 genes differentially expressed in CD14⁺ (58 genes up-regulated in MM vs SMM and MGUS and 43 genes donwregulated). Interestingly, among the differentially expressed genes we found that cytokines and cytokine receptors (IL21, IL21R, IL15, IL15R), chemokines (CXCL10, CXCL11) and interferon-inducible proteins (IFI27, IFI44) were up-regulated in CD14⁺ of MM patients as compared to SMM and MGUS. A supervised analysis between MM and MGUS identified 6 differentially expressed genes in CD14⁺ whereas 37 genes distinguished MM and SMM patients. Notably the SLAMF7 (CS1) gene recently indentified as a therapeutic target in CD138⁺ MM cells was up-regulated in CD14⁺ monocytes of MM patients as compared either to MGUS alone or to MGUS plus SMM could be a potential candidate gene. Overall our preliminary results indicate that a different transcriptional fingerprint may be identified in BM CD14⁺ cells of patients with symptomatic MM as compared to those with indolent PC disorders such as SMM and MGUS with a greater number of differentially expressed genes between symptomatic MM and SMM patient rather than between MM and MGUS.