Large scale and clinical grade purification of syndecan-1+ malignant plasma cells

Robust isolation of malignant plasma cells in multiple myeloma

Molecular characterization of myeloma requires isolation of malignant plasma cells, which is currently hampered by the instability of CD138. We identified CD319 and CD269 as robust replacements for CD138, facilitating molecular diagnostics in myeloma.

In vitro expansion of gamma delta T cells with anti-myeloma cell activity by Phosphostim and IL-2 in patients with multiple myeloma

T-cell-mediated immunotherapy is a promising therapeutic option for multiple myeloma (MM). Gamma-delta T cells (gammadelta T cells) recognize phosphoantigens and display strong anti-tumour cytotoxicity. The synthetic agonist Phosphostim (bromohydrin pyrophosphate, BrHPP) has been shown to selectively activate Vgamma9Vdelta2 T cells. This study aimed to evaluate the expansion capacity and anti-myeloma cell cytotoxicity of circulating gammadelta T cells from MM patients at different time points throughout the disease, using Phosphostim and interleukin 2 (IL-2). Circulating gammadelta T cell counts in patients with newly diagnosed MM or in relapse did not differ from those in healthy donors. A 14-d culture of peripheral blood mononuclear cells with Phosphostim and IL-2 triggered a 100-fold expansion of gammadelta T cells in 78% of newly diagnosed patients. Gammadelta T cells harvested at the time of haematopoietic progenitor collection or in relapsing patients expanded less efficiently. Expanded gammadelta T cells killed 13/14 myeloma cell lines as well as primary myeloma cells, but not normal CD34 cells. Their killing efficiency was not affected by 2-d IL-2 starvation. This study demonstrated the ability of Phosphostim and IL-2 to expand gammadelta T cells from MM patients, and the efficient and stable killing of human myeloma cells by gd T cells.

B7-1 and 4-1BB ligand expression on a myeloma cell line makes it possible to expand autologous tumor-specific cytotoxic T cells in vitro

OBJECTIVE

The aim of this study was to confer an antigen-presenting cell (APC) ability on multiple myeloma cell lines (HMCLs) using B7-1 and/or 4-1BBL gene transfer.

MATERIALS AND METHODS

HMCLs were retrovirally transduced with B7-1 and/or 4-1BBL cDNAs. Allogeneic or autologous T cells were stimulated by coculture with B7-1- and/or 4-1BBL-transduced HMCLs in the presence of interleukin-2. T cell clones were obtained by limiting dilution. T-cell activation was assessed by interferon-gamma Elispot assays and cytotoxicity by (51)Cr release assays.

RESULTS

Neither primary multiple myeloma cells (MMCs) nor HMCLs expressed B7-1 or 4-1BBL, and these molecules could not be induced by CD40 triggering. HMCLs failed to stimulate allogeneic or autologous T cells. Transduction of HMCLs with B7-1 and/or 4-1BBL retroviruses induced a high expression of B7-1 and 4-1BBL molecules and a strong T-cell activation ability. Long-term cultured CD8(+) T-cell lines could be obtained by stimulation with the autologous B7-1/4-1BBL XG-19 HMCL. These cytotoxic T lymphocytes (CTL) efficiently killed the autologous parental XG-19 HMCL as well as autologous primary MMCs and allogeneic HMCLs. They did not kill autologous CD34 cells and autologous EBV cell line or natural killer target K562 cells. Cloned CTL could recognize allogeneic HMCLs, demonstrating that a shared anti-MMC repertoire was expanded.

CONCLUSION

Transduction with B7-1 and 4-1BBL retroviruses turned HMCLs into efficient APCs. It permitted the long-term expansion of autologous anti-tumor CTL with a shared anti-MMC repertoire, for one HMCL. These data suggest developing an immunotherapy using modified tumor cells in patients with 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.

Microarray-based understanding of normal and malignant plasma cells

Plasma cells (PCs) develop from B lymphocytes following stimulation by antigen and express a genetic program aimed at the synthesis of immunoglobulins. This program includes the induction of genes coding for transcription factors such as PRDM1, X-box-binding protein 1 and BHLHB3, cell-surface molecules such as CD138/syndecan-1, and for the unfolded protein response. We review how the microarray technology has recently contributed to the understanding of the biology of this rare but essential cell population and its transformation into premalignant and malignant PCs.

Adenoviral-mediated transfer of human wild-type p53, GM-CSF and B7-1 genes results in growth suppression and autologous anti-tumor cytotoxicity of multiple myeloma cells in vitro

Multiple myeloma (MM) remains incurable despite the use of high-dose chemotherapy and stem cell transplantation. However, immunotherapy is expected to offer long-term disease control, or even possibly a cure. We have previously demonstrated the suppressive effect of a recombinant adenovirus carrying human wild-type p53, granulocyte-macrophage colony-stimulating factor, and B7-1 genes (Ad-p53/GM-CSF/B7-1) on the growth of laryngeal cancer cells. In the present study, we evaluated the effects of an Ad-p53/GM-CSF/B7-1-modified myeloma cell vaccine strategy aimed to induce apoptosis and to augment the immunogenicity of MM cells. Both MM cell lines and purified primary myeloma cells were infected with Ad-p53/GM-CSF/B7-1. High expression levels of these three genes were confirmed separately by Western blot, enzyme-linked immunosorbent assay (ELISA), and flow cytometry. When wild-type p53, GM-CSF and B7-1 genes were introduced, the growth of MM cells was inhibited via enhanced apoptosis and the immunogenicity of tumor cells was augmented. The combinatorial effect of these three genes on inducing cytotoxic T lymphocytes (CTLs) was more evident than that of p53 individually or any combinations of two (p53 plus GM-CSF or p53 plus B7-1). Furthermore, significant proliferation of autologous peripheral blood lymphocytes (PBLs) and specific cytotoxicity against autologous primary MM cells were induced in vitro. These results suggest that myeloma cell vaccination co-transferred with p53, GM-CSF and B7-1 genes may be a promising immunotherapeutic approach against MM.

An inhibitor of the EGF receptor family blocks myeloma cell growth factor activity of HB-EGF and potentiates dexamethasone or anti-IL-6 antibody-induced apoptosis

We previously found that some myeloma cell lines express the heparin-binding epidermal growth factor-like growth factor (HB-EGF) gene. As the proteoglycan syndecan-1 is an HB-EGF coreceptor as well as a hallmark of plasma cell differentiation and a marker of myeloma cells, we studied the role of HB-EGF on myeloma cell growth. The HB-EGF gene was expressed by bone marrow mononuclear cells in 8 of 8 patients with myeloma, particularly by monocytes and stromal cells, but not by purified primary myeloma cells. Six of 9 myeloma cell lines and 9 of 9 purified primary myeloma cells expressed ErbB1 or ErbB4 genes coding for HB-EGF receptor. In the presence of a low interleukin-6 (IL-6) concentration, HB-EGF stimulated the proliferation of the 6 ErbB1+ or ErbB4+ cell lines, through the phosphatidylinositol 3-kinase/AKT (PI-3K/AKT) pathway. A pan-ErbB inhibitor blocked the myeloma cell growth factor activity and the signaling induced by HB-EGF. This inhibitor induced apoptosis of patients'myeloma cells cultured with their tumor environment. It also increased patients' myeloma cell apoptosis induced by an anti-IL-6 antibody or dexamethasone. The ErbB inhibitor had no effect on the interaction between multiple myeloma cells and stromal cells. It was not toxic for nonmyeloma cells present in patients' bone marrow cultures or for the growth of hematopoietic progenitors. Altogether, these data identify ErbB receptors as putative therapeutic targets in multiple myeloma.

Generation of polyclonal plasmablasts from peripheral blood B cells: a normal counterpart of malignant plasmablasts

A new way to identify tumor-specific genes is to compare gene expression profiles between malignant cells and their autologous normal counterparts. In patients with multiple myeloma, a major plasma cell disorder, normal plasma cells are not easily attainable in vivo. We report here that in vitro differentiation of peripheral blood B lymphocytes, purified from healthy donors and from patients with multiple myeloma, makes it possible to obtain a homogeneous population of normal plasmablastic cells. These cells were identified by their morphology, phenotype, production of polyclonal immunoglobulins, and expression of major transcription factors involved in B-cell differentiation. Oligonucleotide microarray analysis shows that these polyclonal plasmablastic cells have a gene expression pattern close to that of normal bone marrow–derived plasma cells. Detailed analysis of genes statistically differentially expressed between normal and tumor plasma cells allows the identification of myeloma-specific genes, including oncogenes and genes coding for tumor antigens. These data should help to disclose the molecular mechanisms of myeloma pathogenesis and to define new therapeutic targets in this still fatal malignancy. In addition, the comparison of gene expression between plasmablastic cells and B cells provides a new and powerful tool to identify genes specifically involved in normal plasma cell differentiation.

Expression of transcription factors Pu.1, Spi-B, Blimp-1, BSAP and oct-2 in normal human plasma cells and in multiple myeloma cells

Differentiation of B lymphocytes into plasma cells is regulated by the interaction of distinct transcription factors (TFs) which activate gene expression in a lineage- and stage-specific pattern. Using reverse transcription polymerase chain reaction, we studied the expression of five TFs (octamer binding factor oct-2, ets family members PU.1 and Spi-B, pax gene family member BSAP, and Blimp-1) in (1) human cell lines with a plasma cell phenotype, (2) primary malignant plasma cells [obtained from patients with plasma cell leukaemia (PCL) and multiple myeloma], and (3) normal human plasma cells generated in vitro or isolated from normal bone marrows. The expression pattern was compared with TFs expressed by normal CD19+ B lymphocytes and by B cells from chronic lymphocytic leukaemia patients. Our results showed that plasma cells expressed a restricted set of TFs compared with CD19+ B lymphocytes, with continued expression of Spi-B and oct-2, increased Blimp-1 expression, and downregulation of BSAP and PU.1. Cells from PCL lost Spi-B and PU.1 expression completely and expressed only oct-2 and Blimp-1, and thus resembled plasma cell lines. Human plasma cell differentiation therefore seems to be positively regulated by Blimp-1; whether this TF has any oncogenic potential will have to be analysed in future studies.

Identifying intercellular signaling genes expressed in malignant plasma cells by using complementary DNA arrays

In multiple myeloma (MM), the growth of primary plasma cells depends not only on interleukin-6 (IL-6), but also on additional unidentified signals delivered by the bone marrow environment. Using Atlas complementary DNA (cDNA) arrays comprising 268 genes coding for intercellular signaling molecules, this study identified genes that are overexpressed in myeloma cells compared to autologous B-lymphoblastoid cell lines. These genes encode the oncogenic Tyro3 tyrosine kinase receptor, the heparin-binding epidermal growth factor-like growth factor (HB-EGF) that is an epithelial autocrine tumor growth factor, the thrombin receptor (TR) that is linked to HB-EGF and syndecan-1 processing and to cell invasion, chemokine receptors CCR1 and CCR2, the Wnt pathway actor Frizzled-related protein (FRZB), and the Notch receptor ligand Jagged 2. These data, obtained with the Atlas cDNA array, were confirmed by reverse transcriptase-polymerase chain reaction or protein analysis or both. Furthermore, Tyro3, HB-EGF, TR, and FRZB gene expression was documented in purified primary malignant plasma cells from patients with plasma cell leukemia or MM. HB-EGF and FRZB were poorly expressed in purified polyclonal plasma cells. Finally, HB-EGF was proved to be an essential autocrine growth factor for the XG-1 myeloma cells. This study shows the potency and the biologic relevance of cDNA arrays used to analyze simultaneously a large panel of intercellular signaling genes and, by identifying several genes overexpressed in malignant plasma cells, opens new fields of investigation in MM biology. (Blood. 2001;98:771-780)

Adenovector engineered interleukin-2 expressing autologous plasma cell vaccination after high-dose chemotherapy for multiple myeloma - a phase 1 study

Eight multiple myeloma patients participated in a phase I trial evaluating the feasibility and safety of subcutaneous vaccination with adenovirus engineered, autologous plasma cells after high-dose therapy. Plasma cells were concentrated from bone marrow harvests by negative selection and high gradient magnetic separation. The mean plasma cell yield was 2.61 x 10(8). Transgene expression measured 48 h after plasma cell infection with an IL-2 expressing adenovirus averaged 2.95 ng/ml/10(6) cells. Vaccine production was successful for 88% of patients. Two months after high-dose therapy, six patients received from one to five injections of 3.5-9.0 x 10(7) cells/vaccine. Vaccines were well tolerated with only minor systemic symptoms reported. Injection with tumor cells induced a local inflammatory response consisting predominantly of CD8+ and/or TIA-1+ T-lymphocytes. Myeloma specific anti-tumor responses, assessed by interferon-gamma (IFN-gamma) release and cytotoxic T cell killing of autologous tumor cells, were not enhanced after vaccination in one evaluable patient. Clinical response, manifested as a decrease in serum paraprotein, was not observed in the one patient who had measurable disease at the time of vaccination. These results demonstrate that the generation of adenovector modified plasma cell vaccines is technically feasible and can be safely administered post-transplant. Further studies of immunlogic and clinical efficacy are required.

Ku86 variant expression and function in multiple myeloma cells is associated with increased sensitivity to DNA damage

Ku is a heterodimer of Ku70 and Ku86 that binds to double-stranded DNA breaks (DSBs), activates the catalytic subunit (DNA-PKcs) when DNA is bound, and is essential in DSB repair and V(D)J recombination. Given that abnormalities in Ig gene rearrangement and DNA damage repair are hallmarks of multiple myeloma (MM) cells, we have characterized Ku expression and function in human MM cells. Tumor cells (CD38(+)CD45RA(-)) from 12 of 14 (86%) patients preferentially express a 69-kDa variant of Ku86 (Ku86v). Immunoblotting of whole cell extracts (WCE) from MM patients shows reactivity with Abs targeting Ku86 N terminus (S10B1) but no reactivity with Abs targeting Ku86 C terminus (111), suggesting that Ku86v has a truncated C terminus. EMSA confirmed a truncated C terminus in Ku86v and further demonstrated that Ku86v in MM cells had decreased Ku-DNA end binding activity. Ku86 forms complexes with DNA-PKcs and activates kinase activity, but Ku86v neither binds DNA-PKcs nor activates kinase activity. Furthermore, MM cells with Ku86v have increased sensitivity to irradiation, mitomycin C, and bleomycin compared with patient MM cells or normal bone marrow donor cells with Ku86. Therefore, this study suggests that Ku86v in MM cells may account for decreased DNA repair and increased sensitivity to radiation and chemotherapeutic agents, whereas Ku86 in MM cells confers resistance to DNA damaging agents. Coupled with a recent report that Ku86 activity correlates with resistance to radiation and chemotherapy, these results have implications for the potential role of Ku86 as a novel therapeutic target.

Agonist anti-gp130 transducer monoclonal antibodies are human myeloma cell survival and growth factors

We have previously reported obtaining two monoclonal antibodies (mAb) against the human gp130 interleukin-6 (IL-6) transducer which made possible the dimerization of gp130 and the activation of several IL-6-driven functions when used together. We report here that these mAb induce gp130-mediated signaling in human myeloma cells and support the survival and the long-term growth of five IL-6-dependent human myeloma cell lines. Their agonist activity is not affected by neutralizing antibodies to IL-6 or IL-6R. These mAb induce a transient proliferation of primary myeloma cells from most patients with multiple myeloma. Again, IL-6 inhibitors do not affect this agonist activity. By using highly purified primary myeloma cells, we found that these anti-gp130 mAb supported the long-term survival of primary myeloma cells from five patients with primary plasma cell leukemia but failed to induce their long-term growth. For patients with fulminant disease and secondary extramedullary proliferation, the antibodies supported a long-term survival and growth, and anti-gp130 mAb-dependent cell lines were obtained. For patients with medullary involvement only, a co-stimulatory signal is necessary, together with gp130 activation, to trigger cell survival and cycling. Leukemia (2000) 14, 188-197.

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.

Syndecan-1 (CD 138) in myeloma and lymphoid malignancies: a multifunctional regulator of cell behavior within the tumor microenvironment

Syndecan-1 is a transmembrane proteoglycan expressed on the surface of tumor cells of various origins including myeloma, Hodgkin's disease, and certain human immunodeficiency virus (HIV) associated lymphomas. Functional studies in myeloma reveal that syndecan-1 may act as a multifunctional regulator of cell behavior in the tumor microenvironment; it mediates cell-cell adhesion, binding of myeloma cells to type I collagen, and inhibits tumor cell invasion into collagen gels. In addition, syndecan-1 is released from the surface of myeloma cells and this shed form of the molecule inhibits growth and induces apoptosis of myeloma cells and may modulate myeloma bone disease by inhibiting osteoclast formation and promoting osteoblast formation. In view of its effects on tumor cell growth, survival, adhesion and invasion and on bone cell differentiation, syndecan-1 may be an important potentially beneficial regulator of myeloma pathobiology. Further studies are needed to define the clinical significance of syndecan-1 in myeloma and to examine its functional significance in other lymphoid malignancies.

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

Agonist antihuman gp130 transducer monoclonal antibodies (MoAbs) were used in SCID mice to grow myeloma cells whose survival and proliferation is dependent on gp130 transducer activation. The agonist anti-gp130 MoAbs neither bound to murine gp130 nor activated murine cells and, as a consequence, did not induce interleukin-6 (IL-6)–related toxicities in mice. They have a 2-week half-life in vivo when injected in the peritoneum. The agonist antibodies made possible the in vivo growth of exogenous IL-6–dependent human myeloma cells as well as that of freshly explanted myeloma cells from 1 patient with secondary plasma cell leukemia. Tumors occurred 4 to 10 weeks after myeloma cell graft and weighed 3 to 5 g. They grew as solid tumors in the peritoneal cavity and metastasized to the different peritoneal organs: liver, pancreas, spleen, and intestine. Tumoral cells were detected in blood and bone marrow of mice grafted with the XG-2 myeloma cells. Tumoral cells grown in SCID mice had kept the phenotypic characteristics of the original tumoral cells and their in vitro growth required the presence of IL-6 or agonist anti-gp130 MoAbs. Myeloma cells from 4 patients with medullary involvement persisted for more than 1 year as judged by detectable circulating human Ig. However, no tumors were detected, suggesting a long-term survival of human myeloma cells without major proliferation. These observations paralleled those made in in vitro cultures as well as the tumor growth pattern in these patients. This gp130 transducer-dependent SCID model of multiple myeloma should be useful to study various therapeutical approaches in multiple myeloma in vivo.

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

Agonist antihuman gp130 transducer monoclonal antibodies (MoAbs) were used in SCID mice to grow myeloma cells whose survival and proliferation is dependent on gp130 transducer activation. The agonist anti-gp130 MoAbs neither bound to murine gp130 nor activated murine cells and, as a consequence, did not induce interleukin-6 (IL-6)–related toxicities in mice. They have a 2-week half-life in vivo when injected in the peritoneum. The agonist antibodies made possible the in vivo growth of exogenous IL-6–dependent human myeloma cells as well as that of freshly explanted myeloma cells from 1 patient with secondary plasma cell leukemia. Tumors occurred 4 to 10 weeks after myeloma cell graft and weighed 3 to 5 g. They grew as solid tumors in the peritoneal cavity and metastasized to the different peritoneal organs: liver, pancreas, spleen, and intestine. Tumoral cells were detected in blood and bone marrow of mice grafted with the XG-2 myeloma cells. Tumoral cells grown in SCID mice had kept the phenotypic characteristics of the original tumoral cells and their in vitro growth required the presence of IL-6 or agonist anti-gp130 MoAbs. Myeloma cells from 4 patients with medullary involvement persisted for more than 1 year as judged by detectable circulating human Ig. However, no tumors were detected, suggesting a long-term survival of human myeloma cells without major proliferation. These observations paralleled those made in in vitro cultures as well as the tumor growth pattern in these patients. This gp130 transducer-dependent SCID model of multiple myeloma should be useful to study various therapeutical approaches in multiple myeloma in vivo.

Normal and clonal B lineage cells can be distinguished by their differential expression of B cell antigens and adhesion molecules in peripheral blood from multiple myeloma (MM) patients--diagnostic and clinical implications

Human MM is a haematologic disorder characterized by the accumulation of malignant plasma cells (PC), primarily in the bone marrow (BM). Although these cells characteristically home to the BM, in recent years several groups have detected the presence of related malignant B cells in the peripheral blood (PB) which could be implicated in the progression and spread of the disease. However, the proportion and origin of these clonotypic circulating B cells is still controversial. In this study, using a triple-staining flow cytometric procedure and a whole blood lysis method, PB B lineage cells could be divided into two populations according to their distinct repertoires of cell adhesion molecules and B cell antigens in untreated MM patients. The results show that: (i) the percentage and the absolute number of PB CD19+ B cells were decreased in MM patients compared with controls; (ii) the quantity and percentage of B cell antigens (CD20, CD22, CD24, DR, CD138) and adhesion molecules (beta1- and beta2-integrins, CD44, CD54, CD56, CD61 and CD62L) expressed by these PB CD19+ cells of MM patients and healthy subjects were similar and all of them were virtually polyclonal cells; (iii) a very minor circulating CD19-CD38++CD45-/dim subset was also detected which expressed CD138 (B-B4) (high intensity), monoclonal cytoplasmic immunoglobulin (cIg), and was negative for pan-B antigens (CD19, CD20, CD24, DR), surface immunoglobulin (sIg) and several adhesion molecules such as CD62L, CD18 and CD11a; this CD19-CD38++CD45-/dim CD138++ subset was not found in normal blood and exhibited a phenotypic profile which was closely related to that of malignant BM plasma cells, with the exception of the CD56 antigen. Polymerase chain reaction (PCR) analysis of IgH clonotypic rearrangements confirmed these results. We postulate that, in MM patients, circulating B lineage cells may be divided into two different categories: polyclonal CD19+ B cells and a very minor proportion of clonal CD138++ PC that escape from the BM.

Identification and location on syndecan-1 core protein of the epitopes of B-B2 and B-B4 monoclonal antibodies

Using a phage display peptide library, we characterized the epitope of two monoclonal antibodies reacting with syndecan-1: B-B2 and B-B4. The identified epitopes QDIT, for B-B2, and LPEV, for B-B4, were found to align with residues 36-39 and 90-93 of the mature protein, respectively. In contrast to B-B4, the B-B2 epitope is close to a potential glycosaminoglycan attachment site. Since syndecan-1 is heavily glycosylated and post-translational modifications are cell type specific, these results might explain the differences observed in the reactivity pattern of B-B2 and B-B4 and suggest that these monoclonal antibodies are useful probes to study cell surface exposed syndecan-1.

The myeloma cell antigen syndecan-1 is lost by apoptotic myeloma cells

Syndecan-1 is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. It is expressed only on malignant plasma cells in bone marrow samples from patients with multiple myeloma (MM). Several reports have suggested that syndecan-1 was present only on a part of the myeloma cells. By using either IL-6-dependent myeloma cell lines or primary myeloma cells stained by annexin V, we report here that syndecan-1 was rapidly lost by myeloma cells undergoing apoptosis. In the same experimental conditions, expression of other cell membrane antigens such as CD38, HLA class-I or CD49d on apoptotic myeloma cells was not affected. In addition, we show that syndecan-1 loss was independent of activation of the gp130 IL-6 transducer. Dexamethasone induced a strong apoptosis of myeloma cells associated with the loss of syndecan-1. Finally, by using freshly-explanted tumoural samples, we show that syndecan-1 rapidly disappeared from myeloma cells in association with induction of apoptosis. In conclusion we showed that syndecan-1 is a marker for viable myeloma cells which is rapidly lost by apoptotic cells. These results emphasize the usefulness of anti-syndecan-1 antibodies to purge tumoural cells from haemopoietic grafts or to purify these cells for further manipulations for immuno or gene therapies.