Increased Copy Number of Interleukin-6 Receptor Gene Is Associated with Adverse Survival In Multiple Myeloma Patients Treated with Autologous Stem Cell Transplantation

Interleukin-6 (IL-6) is a potent pleiotropic cytokine that regulates plasma cell (PC) growth via IL-6 receptor (IL-6R). We hypothesized that upregulation of IL-6R in myeloma cells might confer the growth privilege to myeloma cells over bone marrow (BM) hematopoietic cells. We investigated the frequency and prognostic implication of increased copy number of IL-6R gene by fluorescence in situ hybridization (FISH) in patients with newly diagnosed multiple myeloma (MM). To confirm the role of IL-6R, the change of proliferative potentials after blocking of IL-6R by monoclonal antibody was observed in a myeloma cell line.

102 patients with newly diagnosed MM were enrolled. FISH study for IL-6R was performed using home-made probe for the locus. The BAC (bacterial artificial chromosome) clone RP11 350G8 (BACPAC Resources, Oakland, CA) was used as the IL-6R gene-positive clone and the FISH probe was labeled by a nick translation reaction. FISH signals were counted among BM plasma cells sorted by immunoglobulin light chain staining (cIg FISH). U266 myeloma cell line was treated with IL-6R monoclonal antibody (MRA, Chugai, Japan) at concentration of 0.06 to 1.25 μM and then cell viability test were performed.

The amplification of IL-6R was detected in 53/102 patients (52.0%). The 5-year overall survival (OS) rate of patients with IL-6R gene amplification was 41.3% versus 44.8% for those with a normal IL-6R (P = 0.425). In 44 patients treated with high-dose chemotherapy and autologous stem cell transplantation (ASCT), patients with 3.1 or more mean IL-6R gene copy number per PC showed worse 5-year OS compared to those who had less than 2.1 mean copies of IL-6R gene (44.4% versus 78.0%, P = 0.024). In multivariate analysis, the increase of IL-6R copy numbers (mean copy/PC ≥ 3.1) could be considered as an independent prognostic factor for MM patients underwent ASCT (hazard ratio, 30.9; 95% CI, 1.74–548.6; P = 0.020). Treatment of IL-6R monoclonal antibody on the U266 cell line induced marked reduction of cell viability compared with control, ranged from 7.1% to 98.7% according to the increase in treated antibody level.

The gain of IL-6R gene is frequent in myeloma, showing an association with adverse prognosis in MM patients treated with ASCT. In vitro suppression of cell proliferation by IL-6R blocker suggests the potential role of IL-6R in myeloma cell growth and therapeutic implication of IL-6R blocker in the future.

No relevant conflicts of interest to declare.