Homotypic cell aggregations of human myeloma cells with ICAM-1 and LFA-1 molecules

Modeling Myeloma Dissemination In Vitro with hMSC-interacting Subpopulations of INA-6 Cells and Their Aggregation/Detachment Dynamics

Multiple myeloma involves early dissemination of malignant plasma cells across the bone marrow; however, the initial steps of dissemination remain unclear. Human bone marrow-derived mesenchymal stromal cells (hMSC) stimulate myeloma cell expansion (e.g., IL6) and simultaneously retain myeloma cells via chemokines (e.g., CXCL12) and adhesion factors. Hence, we hypothesized that the imbalance between cell division and retention drives dissemination. We present an in vitro model using primary hMSCs cocultured with INA-6 myeloma cells. Time-lapse microscopy revealed proliferation and attachment/detachment dynamics. Separation techniques (V-well adhesion assay and well plate sandwich centrifugation) were established to isolate MSC-interacting myeloma subpopulations that were characterized by RNA sequencing, cell viability, and apoptosis. Results were correlated with gene expression data (n = 837) and survival of patients with myeloma (n = 536). On dispersed hMSCs, INA-6 saturate hMSC surface before proliferating into large homotypic aggregates, from which single cells detached completely. On confluent hMSCs, aggregates were replaced by strong heterotypic hMSC-INA-6 interactions, which modulated apoptosis time dependently. Only INA-6 daughter cells (nMA-INA6) detached from hMSCs by cell division but sustained adherence to hMSC-adhering mother cells (MA-INA6). Isolated nMA-INA6 indicated hMSC autonomy through superior viability after IL6 withdrawal and upregulation of proliferation-related genes. MA-INA6 upregulated adhesion and retention factors (CXCL12), that, intriguingly, were highly expressed in myeloma samples from patients with longer overall and progression-free survival, but their expression decreased in relapsed myeloma samples. Altogether, in vitro dissemination of INA-6 is driven by detaching daughter cells after a cycle of hMSC-(re)attachment and proliferation, involving adhesion factors that represent a bone marrow-retentive phenotype with potential clinical relevance.

SIGNIFICANCE

Novel methods describe in vitro dissemination of myeloma cells as detachment of daughter cells after cell division. Myeloma adhesion genes were identified that counteract in vitro detachment with potential clinical relevance.

Adhesion molecules in multiple myeloma oncogenesis and targeted therapy

Every day we march closer to finding the cure for multiple myeloma. The myeloma cells inflict their damage through specialized cellular meshwork and cytokines system. Implicit in these interactions are cellular adhesion molecules and their regulators which include but are not limited to integrins and syndecan-1/CD138, immunoglobulin superfamily cell adhesion molecules, such as CD44, cadherins such as N-cadherin, and selectins, such as E-selectin. Several adhesion molecules are respectively involved in myelomagenesis such as in the transition from the precursor disorder monoclonal gammopathy of undetermined significance to indolent asymptomatic multiple myeloma (smoldering myeloma) then to active multiple myeloma or primary plasma cell leukemia, and in the pathological manifestations of multiple myeloma.

Analysis of cell-cell contact mediated by Ig superfamily cell adhesion molecules

Cell-cell adhesion is a fundamental requirement for all multicellular organisms. The calcium-independent cell adhesion molecules of the immunoglobulin superfamily (IgSF-CAMs) represent a major subgroup. They consist of immunoglobulin folds alone or in combination with other protein modules, often fibronectin type-III folds. More than 100 IgSF-CAMs have been identified in vertebrates and invertebrates. Most of the IgSF-CAMs are cell surface molecules that are membrane-anchored either by a single transmembrane segment or by a glycosylphosphatidylinositol (GPI) anchor. Some of the IgSF-CAMs also occur in soluble form, e.g., in the cerebrospinal fluid or in the vitreous fluid of the eye, due to naturally occurring cleavage of the GPI anchor or the membrane-proximal peptide segment. Some IgSF-CAMs, such as NCAM, occur in various forms that are generated by alternative splicing. This unit contains a series of protocols that have been used to study the function of IgSF-CAMs in vitro and in vivo.

Zoledronic acid exerts its antitumor effect in multiple myeloma interfering with the bone marrow microenvironment

Multiple myeloma (MM) is a B-cell malignancy characterized by an excess of monotypic plasma cells which localize almost exclusively in the bone marrow provoking bone destruction via the activation of the osteoclasts. The bone marrow microenvironment, mainly through stromal cells, is strictly involved in the evolution of the disease supporting MM cell growth and survival [1]. MM plasma cells reside in the bone marrow by binding to adhesion molecule of extracellular matrix (ECM) and stromal cells. The activation of some signaling pathways within the stromal cells increases the production of several cytokines which in turn favors the myeloma cell proliferation and survival [2-6], and enhance the drug resistance by anti-apoptotic mechanisms [1,7-9]. Novel therapeutic agents target not only the myeloma cells but also the interaction between MM cells and the bone marrow microenvironment [8]. Bisphosphonates (Bps) interfere as well with bone microenvironment inhibiting the survival of stromal cells and hampering the contact between plasma and stromal cells. In this review we will revise preclinical evidences, and the potential mechanisms of the antitumor activity of zoledronic acid.

Zoledronic acid down-regulates adhesion molecules of bone marrow stromal cells in multiple myeloma

BACKGROUND

Myeloma plasma cells interact with the bone marrow microenvironment which, in turn, supports their growth and protects them from apoptosis. In vitro studies have demonstrated the antitumor potential of zoledronic acid (ZOL) on myeloma cell lines, but few data are available on its effects on bone marrow stromal cells (BMSCs). The aim of the current study was to evaluate the antiproliferative and apoptotic effect of ZOL on BMSCs, as well as its effect on the expression of adhesion molecules.

METHODS

BMSCs, obtained from bone marrow mononucleated cells of 8 patients with multiple myeloma, were treated with increasing concentrations of ZOL for 3 days. Cytotoxic effect was analyzed by 3-(4-5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide; thiazolyl blue (MTT) assay whereas the induction of apoptosis was evaluated by flow cytometric detection of fluorescein isothiocyanate-labeled annexin V, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, and nuclear changes. Moreover, expression of CD106, CD56, CD50, CD49d, CD44, and CD40 was analyzed by flow cytometry. Data were evaluated by the Friedman test.

RESULTS

After 3 days of exposure at concentrations of 10(-4) to 10(-5) M, ZOL induced a decrease in proliferation (P < 0.0001) and an increase in apoptosis (P < 0.002). Analysis of culture supernatants showed that myeloma BMSCs expressed interleukin (IL)-6, negligible levels of tumor necrosis factor-alpha, and no IL-1beta. In vitro exposure to the lowest concentrations of ZOL decreased IL-6 production by BMSCs. Among the adhesion molecules, CD106, CD54, CD49d, and CD40, which were strongly expressed at baseline, showed a statistically significant reduction compared with controls after exposure to ZOL.

CONCLUSIONS

ZOL interfered with myeloma BMSCs by reducing proliferation, increasing apoptosis, and modifying the pattern of expression of adhesion molecules, especially those involved in plasma cell binding. These effects on BMSCs might explain the antitumor activity of ZOL.

Apoptotic signaling in multiple myeloma: therapeutic implications

Fifteen thousand new cases of multiple myeloma (MM) will occur in the United States in 2003, and the disease remains incurable. Diverse classes of chemotherapeutic agents induce cell death or apoptosis in MM cells; however, prolonged drug exposures ultimately induce chemoresistance. The mechanisms whereby MM cells resist drugs include alterations in intracellular signaling as well as adherence and cytokines in the bone marrow (BM) microenvironment. Novel agents that target the MM cell in its BM microenvironment are needed to both enhance anti-MM activity and prevent development of drug resistance. Delineation of cellular growth and apoptotic signaling pathways in MM cells may identify molecules that serve as novel therapeutic targets on the basis of interruption of MM cell growth or triggering of MM cell death.

Selective in vivo growth of lymphocyte function- associated antigen-1-positive murine myeloma cells. Involvement of function-associated antigen-1-mediated homotypic cell-cell adhesion

OBJECTIVES

Lymphocyte function-associated antigen-1 (LFA-1) expression on multiple myeloma cells and its potential role in myeloma biology have been the subject of conflicting literature reports. In this study we used the 5T experimental mouse model to analyze the involvement of LFA-1 in myeloma cell bone marrow homing, survival, and growth.

MATERIALS AND METHODS

The 5T33MM vitro (5T33MMvt) myeloma line was used. LFA-1 and intercellular adhesion molecule-1 (ICAM-1) expression were analyzed by flow cytometry. A small molecule antagonist of LFA-1/ICAM interactions, BIRT 377, was used to block LFA-1 in vitro. Transendothelial migration was assessed by measuring migration through Transwells coated with bone marrow endothelial cells. Immediate in vivo homing was analyzed by tracing 51Cr-labeled cells. Invert microscopic cell counting was used to analyze homotypic cell adhesion. Cell cycle analysis was used to analyze apoptosis. S+G(2)/M phase analysis and 3H-thymidine incorporation were used to assess proliferation. Cells were separated into LFA-1(+) and LFA-1(-) fraction by magnetic activated cell sorting.

RESULTS

5T33MMvt cells had a heterogeneous LFA-1 expression and all cells were positive for the LFA-1 ligand ICAM-1. LFA-1 inhibition with BIRT 377 did not affect transendothelial migration of the 5T33MMvt cells; however, it did result in cell cluster scattering, indicating LFA-1 involvement in homotypic cell-cell adhesion. No effect was observed on apoptosis, but the percentage of cells in S+G(2)/M phase was decreased by 39%. 3H-thymidine incorporation confirmed this effect on 5T33MMvt cell proliferation (38% reduction). When 5T33MMvt cells were injected into animals, all myeloma cells isolated at the end stage of the disease were LFA-1(+) in contrast to the situation before injection. LFA-1(+) and LFA-1(-) MM cells had similar in vivo bone marrow homing capacities. Mice injected with LFA-1(+) 5T33MMvt cells developed myeloma (5/5) within 12 weeks after injection. In contrast, LFA-1(-) recipients did not develop the disease (0/5), even 1 year after tumor inoculation.

CONCLUSIONS

Our data suggest that LFA-1-mediated homotypic cell-cell adhesion is involved in myeloma cell proliferation and raises the possibility that this interaction may have a crucial role in in vivo myeloma cell growth. LFA-1 does not appear to play a role in the bone marrow homing of these cells.

Syndecan-1 is targeted to the uropods of polarized myeloma cells where it promotes adhesion and sequesters heparin-binding proteins

Syndecan-1 (CD138) is a heparan sulfate-bearing proteoglycan present on the surface of myeloma cells where it mediates myeloma cell-cell and cell-extracellular matrix adhesion. In this study, we examined myeloma cell lines for cell membrane localization of syndecan-1. On some cells we note a striking localization of syndecan-1 to a single small membrane protrusion, with the remainder of the cell surface being mostly negative for syndecan-1. Examination of cell morphology reveals that a proportion of cells from myeloma cell lines, as well as primary myeloma cells, are polarized, with a uropod on one end and lamellipodia on the other end. On these polarized cells, syndecan-1 is specifically targeted to the uropod, but in contrast, on nonpolarized cells syndecan-1 is evenly distributed over the entire cell surface. In addition to syndecan-1, several other cell surface molecules localize specifically to the uropod, including CD44 and CD54. Functional assays reveal that myeloma cell lines with a high proportion of polarized cells have a much higher migratory potential than cell lines with few polarized cells. Moreover, the uropod is the cell pole preferentially involved in aggregation of myeloma cells and in adhesion of myeloma cells to osteoblast-like cells. When polarized myeloma cells are incubated with heparin-binding proteins, like hepatocyte growth factor or osteoprotegerin, they concentrate in the uropod. These data indicate that syndecan-1 is targeted to the uropod of polarized myeloma cells and that this targeting plays a role in promoting cell-cell adhesion and may also regulate the biological activity of heparin-binding cytokines.

Syndecan-1 is targeted to the uropods of polarized myeloma cells where it promotes adhesion and sequesters heparin-binding proteins

Syndecan-1 (CD138) is a heparan sulfate-bearing proteoglycan present on the surface of myeloma cells where it mediates myeloma cell-cell and cell-extracellular matrix adhesion. In this study, we examined myeloma cell lines for cell membrane localization of syndecan-1. On some cells we note a striking localization of syndecan-1 to a single small membrane protrusion, with the remainder of the cell surface being mostly negative for syndecan-1. Examination of cell morphology reveals that a proportion of cells from myeloma cell lines, as well as primary myeloma cells, are polarized, with a uropod on one end and lamellipodia on the other end. On these polarized cells, syndecan-1 is specifically targeted to the uropod, but in contrast, on nonpolarized cells syndecan-1 is evenly distributed over the entire cell surface. In addition to syndecan-1, several other cell surface molecules localize specifically to the uropod, including CD44 and CD54. Functional assays reveal that myeloma cell lines with a high proportion of polarized cells have a much higher migratory potential than cell lines with few polarized cells. Moreover, the uropod is the cell pole preferentially involved in aggregation of myeloma cells and in adhesion of myeloma cells to osteoblast-like cells. When polarized myeloma cells are incubated with heparin-binding proteins, like hepatocyte growth factor or osteoprotegerin, they concentrate in the uropod. These data indicate that syndecan-1 is targeted to the uropod of polarized myeloma cells and that this targeting plays a role in promoting cell-cell adhesion and may also regulate the biological activity of heparin-binding cytokines.

The role of adhesion receptors in the pathogenesis of multiple myeloma

There is now an improved understanding of the types of adhesion receptors present on normal and malignant plasma cells. This knowledge has been helpful in identifying plasma cells and in beginning to understand the pathogenesis of myeloma. Future research is needed to delineate the signaling pathways used by the plasma cell after the adhesion receptor binds to its ligands. This information should help in designing more effective therapy for this fatal disease.

Homing behaviour of the malignant cell clone in multiple myeloma

Multiple myeloma (MM) represents a B cell malignancy characterised by the presence of a monoclonal population of end-stage B cells in the bone marrow. Although fully matured bone marrow plasma cells are the predominant cell type in MM, there is much evidence that also more immature B cells are included in the malignant cell clone which are considered to be the myeloma precursor cells. The fact that these cells are detectable in the blood circulation and that their number increases with disease progression, makes it very likely that they represent the component of the tumour clone that mediates disease dissemination. This implies that these cells must have the potential to extravasate and home to the bone marrow environment. Like the migration mechanisms used by normal leukocytes and/or metastatic tumour cells of non-haematopoietic origin, it can be assumed that this bone marrow homing process is mediated by adhesive interactions and chemotactic signals provided by the microenvironment of the tumour. Once in the bone marrow compartment, myeloma cells will receive the appropriate signals to grow and survive. This aspect of tumour-homing is found to be the result of a functional interplay between the myeloma cells and the surrounding microenvironment, involving the action of several cytokines and adhesion molecules. In the end phase of the disease, myeloma cells can lose their stroma-dependency resulting in extramedullary tumour growth. We review normal B cell homing and discuss molecular mechanisms that determine the homing behaviour of the malignant cell clone in MM.

Interaction of tumor and host cells with adhesion and extracellular matrix molecules in the development of multiple myeloma

Adhesion molecules play an important role in the growth regulation and migration of multiple myeloma (MM) cells. They mediate homing of MM cells to the bone marrow and MM cell to bone marrow stromal cell adhesion, with resultant interleukin-6 related autocrine and paracine growth and antiapoptotic affects. Their pattern of expression on tumor cells correlates with the development of plasma cell leukemia or extramedullary disease. Clinically, expression of adhesion molecules on tumor cells or in the serum has already shown prognostic utility. Finally, since adhesion molecules are involved at multiple steps in the pathogenesis of MM, therapeutic studies may target these molecules.

Organ involvement and phenotypic adhesion profile of 5T2 and 5T33 myeloma cells in the C57BL/KaLwRij mouse

The aim of this study was to evaluate the tissue infiltration and phenotypic adhesion profile of 5T2 multiple myeloma (MM) and 5T33 MM cells and to correlate it with that observed in human disease. For each line, 30 mice were intravenously inoculated with myeloma cells and at a clear-cut demonstrable serum paraprotein concentration; mice were sacrificed and a number of organs removed. The haematoxylin-eosin stainings on paraffin sections were complemented with immunohistochemistry using monoclonal antibodies developed against the specific MM idiotype. When analysed over time, 5T2 MM cells could be observed in bone marrow samples from week 9 after transfer of the cells. For the 5T33 MM, a simultaneous infiltration was observed in bone marrow, spleen and liver 2 weeks after inoculation. Osteolytic lesions consistently developed in the 5T2 MM, but this was not consistent for 5T33 MM. PCNA staining showed a higher proliferative index for the 5T33 MM cells. The expression of adhesion molecules was analysed by immunohistochemistry on cytosmears: both 5T2 MM and 5T33 MM cells were LFA-1, CD44, VLA-4 and VLA-5 positive. We conclude that both lines have a phenotypic adhesion profile analogous to that of human MM cells. As the 5T2 MM cells are less aggressive than the 5T33 MM cells, their organ distribution is more restricted to the bone marrow and osteolytic lesions are consistently present, the former cell line induces myeloma development similar to the human disease.

Bone marrow of patients with active multiple myeloma: angiogenesis and plasma cell adhesion molecules LFA-1, VLA-4, LAM-1, and CD44

Bone marrow plasma cells and stromal cells in multiple myeloma (MM) have been shown to be capable of releasing cytokines with angiogenic properties. Plasma cells can also express adhesion molecules controlling their adhesive interactions with endothelial cells. In the present study, we have evaluated by immunohistochemistry the extent of angiogenesis in the bone marrow of: a) 51 patients with active and non-active MM; b) 25 patients with monoclonal gammopathy of undetermined significance (MGUS). Plasma cells were investigated by flow cytometry for the expression of the adhesion molecules LFA-1, VLA-4, LAM-1, and CD44. The results showed that, while angiogenesis was very low or absent in patients with MGUS and non-active MM, it increased markedly in those with active MM. The highest detectability of plasma cell adhesion molecules, except LAM-1, was also found in these patients. The functional significance of these findings is unknown. Their consistent occurrence in the bone marrow of active myeloma patients, however, strongly suggests that more frequent adhesive interactions between plasma cells and their microvasculature underlie tumor dissemination.

Oncostatin M, leukemia inhibitory factor, and interleukin 6 induce the proliferation of human plasmacytoma cells via the common signal transducer, gp130

We analyzed the stimulatory effect of oncostatin M (OSM), leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and the inhibitory effect of anti-IL-6 antibody (Ab), anti-IL-6 receptor monoclonal antibody (mAb), and anti-gp130 mAb on the growth of human plasmacytoma cells freshly isolated from a patient with multiple myeloma. The purified cells showed a plasmacytoid morphology and expressed CD38, CD54, and CD56 antigens but no CD3, CD5, CD10, CD19, CD20, or very late antigen 5. IL-6 receptor (IL-6R) and its signal transducer, gp130, were expressed on their cell surface at a low level. Dose-dependent proliferation of the cells in response to OSM, LIF, and IL-6, but not to IL-11, was observed using [3H]TdR incorporation in vitro. Both anti-IL-6 Ab and anti-IL-6R mAb inhibited the growth of the cells in the presence or absence of exogenous IL-6. These cells release IL-6 but not OSM or LIF into the culture supernatant during short-term culture. Therefore, an autocrine growth mechanism mediated by IL-6, but not by OSM or LIF, was confirmed. Furthermore, anti-gp130 mAb completely inhibited the proliferation of the cells induced by OSM, LIF, as well as IL-6. These data indicate that OSM, LIF, and IL-6 can act as growth factors of human plasmacytoma cells through a common signal transducer, gp130, on their cell surface, and also suggest the potential therapeutic application of anti-gp130 mAb, as well as anti-IL-6R mAb against myeloma/plasmacytomas.

Involvement of adhesion molecules LFA-1 and ICAM-1 in osteoclast development

We report here that leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) are involved in osteoclast development. Osteoclast development was observed on co-culture of mouse spleen cells and mouse bone marrow derived clonal stromal cells, TMS-14, in the presence of 1 alpha, 25-dihydroxyvitamin D-3 (1 alpha, 25-(OH)2D3) for 8 days, and quantified with respect to tartrate-resistant acid phosphatase (TRACP) activity. When either one of the monoclonal antibodies (MAbs) to mouse LFA-1 and mouse ICAM-1 was added to the co-culture system, the TRACP activity was significantly inhibited. The experiment in which one-day treatment with each of these MAbs was performed during the 8 days of cultivation showed that the inhibitory effects of both MAbs on the TRACP activity at 8 days were observed from an early stage of the culture, but were more notable at a later stage (days 4-6). As the expression of ICAM-1 was observed on both spleen cells and TMS-14, we next examined whether the interaction between stromal cells and osteoclast progenitors or among osteoclast progenitors was more important for osteoclast development. To determine this, rat spleen cells and a MAb to rat ICAM-1 were used instead of those of mouse. When MAb to rat ICAM-1 or mouse ICAM-1 was added to the co-culture system of rat spleen cells and TMS-14, the inhibitory effect of the MAb to rat ICAM-1 was mainly observed at a later stage of the culture period and that of anti-mouse ICAM-1 antibody was only observed at an earlier stage. These results indicate that adhesion molecules LFA-1 and ICAM-1 may play a role in osteoclast development via interaction between stromal cells and osteoclast progenitors as well as among osteoclast progenitors.

Homologous C3 deposition and homotypic cell adhesion in a human myeloid cell line, P39

It has been accepted that decay-accelerating factor (DAF) and membrane cofactor protein (MCP) on human cells block C3 deposition, thereby preventing homologous complement attack. In this study, we discovered that a human myeloid cell line, P39, was a target for human C3 even though it expressed normal DAF and MCP. This homologous C3 deposition was induced by serum containing Mg2+ and EGTA (Mg(2+)-EGTA serum) selectively on a P39 subline [P39(+)cells] having the capacity to form cell aggregates. Another P39 subline [P39(-)cells] growing as a separated form did not induce homologous C3 deposition. Multiple C3 fragments, C3b and C3bi, were fixed on P39(+) cells and a significant amount of C5a was released. Several distinct C3 fragment-membrane acceptor molecule complexes were immunoprecipitated with anti-C3c antibody from surface-labeled P39(+) cells treated with Mg(2+)-EGTA serum and from unlabeled cells incubated with 125I-labeled C3 and Mg(2+)-EGTA serum. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed 90, 60 and < or = 40 kDa C3 acceptors on P39(+) cells. On these cells, some of the C3 bound to these acceptors remained in the form of C3b, which can form C3/C5 convertases. P39(+) cells differed phenotypically from P39(-) cells in that P39(+) cells expressed intercellular adhesion molecule-1 (ICAM-1), whereas P39(-) cells did not. Both cells were lymphocyte function-associated antigen 1 (LFA-1)+/CR3- counter-receptors for ICAM-1. However, homotypic cell adhesion was not completely inhibited by antibodies against ICAM-1 and LFA-1, suggesting that the homotypic cell aggregation of P39(+) cells is due only in part to ICAM-1 and LFA-1. In addition, C3 deposition, the expression of ICAM-1, and cell aggregation were enhanced by both tumor necrosis factor-alpha and interferon-gamma. Although the principal causative mechanisms remain obscure, C3 deposition and cell adhesion appear in parallel in this cell line and may be involved in the modulation of cell-mediated immune reactions.

A novel flow cytometric assay for the quantification of adhesion of subsets within a heterogeneous cell population; analysis of lymphocyte function-associated antigen-1 (LFA-1)-mediated binding of bone marrow-derived primary tumour cells of patients with multiple myeloma

In a previous study the expression of the adhesion molecule LFA-1 on tumour cells in patients suffering from multiple myeloma (MM) was correlated with growth of the malignant plasma cells in vivo. Here we describe a novel in vitro flow cytometric adhesion assay (FCAA) which, based on scatter and fluorescence properties, was used to analyse the contribution of the LFA-1/intercellular adhesion molecule-1 (ICAM-1) adhesion pathway in the binding of bone marrow (BM)-derived LFA-1-positive primary tumour cells of patients with MM to interferon-gamma (IFN-gamma)-activated, ICAM-1-positive, human venous umbilical endothelial cells (huVEC) in vitro. To validate the FCAA, cells from different myeloma cell lines were labelled with the fluorescent dye CFDA or stained for CD38 expression, and LFA-1-mediated adhesion to IFN-gamma-activated endothelial cells was quantified. Results obtained with the FCAA were compared with a conventional adhesion assay employing 51Cr-labelled cells. Statistical analysis revealed that both assays gave similar results. This allowed analysis of the contribution of LFA-1 to the adhesive potential of malignant plasma cells in bone marrow mononuclear cells (BMMC) from MM patients to IFN-gamma-activated endothelial cells. The results prove that LFA-1 expressed on bone marrow-derived plasma cells from MM patients can be used for cellular adhesion to ICAM-1 expressed on adherent growing cells, and are suggestive for a role of the LFA-1/ICAM-1 adhesion pathway in the pathophysiology of MM. The FCAA described in this study is a generally applicable assay, allowing analysis of the interaction of distinct subpopulations with in vitro grown adherent cells of different origin.

The involvement of adhesion molecules in the biology of multiple myeloma

Multiple myeloma represents a B cell malignancy characterized by a monoclonal proliferation of plasma cells. A striking feature of the disease is the tendency of the malignant plasma cells to affect mainly the bone marrow environment and to invade the peripheral blood only in the terminal stage. The growth of myeloma plasma cells is believed to be regulated by a functional interplay between the tumor cells and the bone marrow stroma, involving the action of various cytokines. This growth control is most probably mediated by close cellular contact of the myeloma cells and marrow stromal components. Therefore it can be assumed that myeloma plasma cells possess the ability to interact with the bone marrow stroma. Until now the adhesive mechanisms that may underlie this interaction, remain undetermined. We investigated the expression of several adhesion molecules on bone marrow plasma cells in myeloma patients and normal controls. Normal as well as malignant plasma cells were found to be strongly positive for the intercellular adhesion molecule ICAM-1, the fibronectin receptor VLA-4 and the lymphocyte homing receptor CD44. In addition, a much weaker expression of the second fibronectin receptor VLA-5, the laminin receptor VLA-6 and the vitronectin receptor CD51 was demonstrated. In contrast to normal plasma cells, myeloma cells can also express the neural cell adhesion molecule N-CAM. In this report we discuss the possible role of adhesion molecules in the pathogenesis and clinical evolution of multiple myeloma.

Multiple myeloma: the biology of malignant plasma cells

Multiple myeloma remains a difficult disorder to treat and cures are virtually unknown. Most modalities of treatment have been tried on an empirical basis, and a greater understanding of the nature of myeloma progenitors may lead to more specific therapies. In the past few years interest in the biology of myeloma plasma cells has increased and the current state of knowledge is summarised in this review. Myeloma clonogenic, or colony, assays have been attempted by many groups. Despite this, no direct equivalent is available of the CFU-GM assay for granulocyte-macrophage progenitors in normal marrow. No published methods have been exported widely to other laboratories. Recently, myeloma plasma cells were found to express a wide range of adhesion molecules permitting cell to cell and cell to stroma interactions. This finding may explain the difficulty of myeloma colony assays, since adhesive clumping must be prevented. The observation that interleukin (IL)-6 can stimulate myeloma plasma cells led to further work with other cytokines such as IL-3 and GM-CSF. The precise role of IL-6 in the usual case of bone marrow myeloma remains unclear however.

The role of adhesion molecules in multiple myeloma

Human myeloma plasma cells had been considered to express few surface antigens until recently. The past two International Workshops on Leucocyte Differentiation Antigens have shown that myeloma cells can express a range of surface molecules, and it has become clear that many of these have adhesive functions. The identification of ICAM-1 (CD54) and H-CAM (CD44) on human plasma cells was the initial observation, and other antigens such as N-CAM (CD56) and LFA-3 (CD58) have been confirmed as features of malignant plasma cells in particular. The degree of expression of LFA-1 (CD11a) remains to be characterised fully. It seems probable that the loss of some adhesion structures may be associated with increased malignancy and plasma cell leukaemia. At the present time there are few studies relating to the function of these molecules, although homotypic adhesion appears to occur, and it is likely that such studies will shed light on the pathogenesis of myeloma.