A gp130 Interleukin-6 Transducer-Dependent SCID Model of Human Multiple Myeloma

Heparan sulphate proteoglycans are essential for the myeloma cell growth activity of EGF-family ligands in multiple myeloma

The epidermal growth factor (EGF)/EGF-receptor (ErbB1-4) family is involved in the biology of multiple myeloma (MM). In particular, ErbB-specific inhibitors induce strong apoptosis of myeloma cells (MMC) in vitro. To delineate the contribution of the 10 EGF-family ligands to the pathogenesis of MM, we have assessed their expression and biological activity. Comparing Affymetrix DNA-microarray-expression-profiles of CD138-purified plasma-cells from 65 MM-patients and 7 normal individuals to those of plasmablasts and B-cells, we found 5/10 EGF-family genes to be expressed in MMC. Neuregulin-2 and neuregulin-3 were expressed by MMC only, while neuregulin-1, amphiregulin and transforming growth factor-alpha were expressed by both MMC and normal plasma-cells. Using real-time polymerase chain reaction, we found HB-EGF, amphiregulin, neuregulin-1 and epiregulin to be expressed by cells from the bone marrow-environment. Only the EGF-members able to bind heparan-sulphate proteoglycans (HSPGs) - neuregulin-1, amphiregulin, HB-EGF - promote the growth of MMC. Those ligands strongly bind MMC through HSPGs. The binding and the MMC growth activity was abrogated by heparitinase, heparin or deletion of the HS-binding domain. The number of HS-binding EGF ligand molecules bound to MMC was higher than 10(5) molecules/cell and paralleled that of syndecan-1. Syndecan-1, the main HSPG present on MM cells, likely concentrates high levels of HS-binding-EGF-ligands at the cell membrane and facilitates ErbB-activation. Altogether, our data further identify EGF-signalling as promising target for MM-therapy.

Expression of EGF-family receptors and amphiregulin in multiple myeloma. Amphiregulin is a growth factor for myeloma cells

A hallmark of plasma cells is the expression of syndecan-1, which has major functions in epithelial cells, in particular as the coreceptor of heparin-binding growth factors. We previously found that heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a growth factor for malignant plasma cells. As amphiregulin (AREG) is another heparin-binding factor of the EGF family, we investigated its role in multiple myeloma (MM). Using Affymetrix DNA microarrays, we show here that the AREG gene was expressed by purified primary myeloma cells from 65 patients and that the expression was higher than in normal bone marrow (BM) plasma cells or plasmablastic cells. AREG stimulated IL-6 production and growth of BM stromal cells. Using real-time reverse transcriptase-polymerase chain reaction, we found that MM cells expressed ErbB receptors and that AREG promoted their growth. Furthermore, PD169540 (a pan-ErbB inhibitor) and IRESSA (an ErbB1-specific inhibitor) induced apoptosis of primary myeloma cells from 10/14 and 4/14 patients, respectively, and there was a synergistic effect with dexamethasone. Altogether, our data provide strong evidence that AREG plays an important role in the biology of MM and emphasize the advantages of using ErbB inhibitors, which might target myeloma cells as well as the tumor environment.

Cooperation between heparin-binding EGF-like growth factor and interleukin-6 in promoting the growth of human myeloma cells

Interleukin-6 (IL-6) is a major survival and proliferation factor of human malignant plasma cells and IL-6 dependent myeloma cell lines can be obtained from patients with terminal disease. We show here that mutated diphtheria toxin, a specific inhibitor of heparin-binding epidermal growth factor-like growth factor (HB-EGF), blocked the IL-6-induced growth of two myeloma cell lines (XG-1 and XG-14) and did not significantly affect that of two other cell lines (XG-6 and XG-13). The IL-6 mediated growth of myeloma cells was also inhibited by antibodies to ErbB1, a receptor for HB-EGF. The XG-1 and XG-14 cell lines that are sensitive to HB-EGF inhibitors overexpressed HB-EGF and EGF receptor (ErbB1) genes. They also overexpressed CD9, a tetraspanin that binds to the heparin-binding domain of HB-EGF and is critical for promoting ErbB1 activation by HB-EGF. The XG-6 and XG-13 myeloma cells that were not significantly sensitive to HB-EGF antagonists, poorly expressed HB-EGF, ErbB1 and CD9 genes or proteins. We demonstrated that recombinant HB-EGF supported the long-term growth of myeloma cells, as did IL-6. The myeloma cell growth factor activity of HB-EGF was completely inhited by antibodies to ErbB1, but also by antibodies to gp130 IL-6 transducer or to IL-6. These data indicate that in the XG-1 and XG-14 IL-6-dependent myeloma cell lines, the CD9/HB-EGF/erbB1 and the IL-6/IL-6R/gp130 pathways cooperate synergistically to trigger myeloma cell growth. They suggest that inhibitors of the EGF receptor or HB-EGF may be useful for inducing myeloma cell apoptosis in patients with multiple myeloma.

Induced Expression of B7-1 on Myeloma Cells Following Retroviral Gene Transfer Results in Tumor-Specific Recognition by Cytotoxic T Cells

The aim of this study was to evaluate whether tumor cells from patients with multiple myeloma activate allogeneic and autologous T cells. Results showed that myeloma cells expressed few B7-2 and no B7-1 in six cell lines and primary cells from 11 patients. They expressed substantial levels of HLA class I, CD40, and a set of adhesion molecules. In accordance with the low density of B7 molecules on these cells, they were poor allogeneic CD8+ T cell stimulators. Neither IFN-γ plus TNF-α nor CD40 stimulation significantly induced B7-1 or up-regulated B7-2 on human myeloma cell line or primary myeloma cells from six of seven patients. However, such induction was found on autologous bone-marrow nontumoral cells and on autologous dendritic cells following CD40 stimulation. High B7-1 expression was stably obtained on human myeloma cell line using transduction with a B7-1 retrovirus, enabling these cells to stimulate allogeneic CD8+, though not CD4+, T cell proliferation. For one patient with advanced disease, B7-1 gene transfer made it possible to amplify autologous cytotoxic T cells that killed autologous myeloma cells in an HLA class I-restricted manner, but not autologous PHA blasts. These results suggest that B7-1 gene transfer could be a promising immunotherapeutic approach in multiple myeloma.