In vitro culture of primary plasmacytomas requires stromal cell feeder layers

Metabolic, Anti-apoptotic and Immune Evasion Strategies of Primary Human Myeloma Cells Indicate Adaptations to Hypoxia

Multiple Myeloma (MM) is an incurable plasma cell malignancy primarily localized within the bone marrow (BM). It develops from a premalignant stage, monoclonal gammopathy of undetermined significance (MGUS), often via an intermediate stage, smoldering MM (SMM). The mechanisms of MM progression have not yet been fully understood, all the more because patients with MGUS and SMM already carry similar initial mutations as found in MM cells. Over the last years, increased importance has been attributed to the tumor microenvironment and its role in the pathophysiology of the disease. Adaptations of MM cells to hypoxic conditions in the BM have been shown to contribute significantly to MM progression, independently from the genetic predispositions of the tumor cells. Searching for consequences of hypoxia-induced adaptations in primary human MM cells, CD138-positive plasma cells freshly isolated from BM of patients with different disease stages, comprising MGUS, SMM, and MM, were analyzed by proteome profiling, which resulted in the identification of 6218 proteins. Results have been made fully accessible via ProteomeXchange with identifier PXD010600. Data previously obtained from normal primary B cells were included for comparative purposes. A principle component analysis revealed three clusters, differentiating B cells as well as MM cells corresponding to less and more advanced disease stages. Comparing these three clusters pointed to the alteration of pathways indicating adaptations to hypoxic stress in MM cells on disease progression. Protein regulations indicating immune evasion strategies of MM cells were determined, supported by immunohistochemical staining, as well as transcription factors involved in MM development and progression. Protein regulatory networks related to metabolic adaptations of the cells became apparent. Results were strengthened by targeted analyses of a selected panel of metabolites in MM cells and MM-associated fibroblasts. Based on our data, new opportunities may arise for developing therapeutic strategies targeting myeloma disease progression.

Interleukin-36 receptor mediates the crosstalk between plasma cells and synovial fibroblasts

The IL-1 family member IL-36α has proinflammatory and pathogenic properties in psoriasis. IL-36α binds to the IL-36 receptor leading to nuclear factor kappa B/mitogen activated protein kinase mediated cytokine release. The IL-36R antagonist prevents recruitment of IL-1 receptor accessory protein and therefore IL-36-dependent cell activation. In inflamed human tissue, we previously could show that resident B cells and plasma cells (PC) express IL-36α. Further, fibroblast-like synoviocytes (FLS) produced proinflammatory cytokines upon IL-36α-stimulation. We hypothesize an IL-36-specific crosstalk between B cells/PCs and FLS permitting a proinflammatory B cell niche. Here, we firstly demonstrated that B cell lines and B cells from healthy donors express IL-36α and stimulation increased IL-36α in B cells and primary plasmablasts/PCs. Moreover, FLS respond specifically to IL-36α by proliferation and production of matrix metalloproteinases via p38/HSP27 signaling. Importantly, IL-36R-deficiency abrogated IL-36α-induced production of inflammatory mediators in FLS and changed the intrinsic FLS-phenotype. Using an in vitro co-culture system, we could show that IL-36R-deficient FLS had a limited capacity to support PC survival compared to wild-type FLS. Hence, we demonstrated an IL-36R-dependent crosstalk between B cells/PCs and FLS. Our data support the concept of initiation and maintenance of a proinflammatory niche by B cells in the joints.

Stem Cell-Soluble Signals Enhance Multilumen Formation in SMG Cell Clusters

Saliva plays a major role in maintaining oral health. Patients with salivary hypofunction exhibit difficulty in chewing and swallowing foods, tooth decay, periodontal disease, and microbial infections. At this time, treatments for hyposalivation are limited to medications (e.g., muscarinic receptor agonists: pilocarpine and cevimeline) that induce saliva secretion from residual acinar cells as well as artificial salivary substitutes. Therefore, advancement of restorative treatments is necessary to improve the quality of life in these patients. Our previous studies indicated that salivary cells are able to form polarized 3-dimensional structures when grown on growth factor-reduced Matrigel. This basement membrane is rich in laminin-III (L1), which plays a critical role in salivary gland formation. Mitotically inactive feeder layers have been used previously to support the growth of many different cell types, as they provide factors necessary for cell growth and organization. The goal of this study was to improve salivary gland cell differentiation in primary cultures by using a combination of L1 and a feeder layer of human hair follicle-derived mesenchymal stem cells (hHF-MSCs). Our results indicated that the direct contact of mouse submandibular (mSMG) cell clusters and hHF-MSCs was not required for mSMG cells to form acinar and ductal structures. However, the hHF-MSC conditioned medium enhanced cell organization and multilumen formation, indicating that soluble signals secreted by hHF-MSCs play a role in promoting these features.

CD28-mediated pro-survival signaling induces chemotherapeutic resistance in multiple myeloma

Chemotherapeutic resistance remains a significant hurdle in the treatment of multiple myeloma (MM) and is significantly mediated by interactions between MM cells and stromal cells of the bone marrow microenvironment. Despite the importance of these interactions, the specific molecules and downstream signaling components involved remain incompletely understood. We have previously shown that the prototypic T-cell costimulatory receptor CD28, which is also expressed on MM cells, is a key mediator of MM survival and apoptotic resistance. Crosslinking CD28 by agonistic antibodies or myeloid dendritic cells (DC; these express the CD28 ligands CD80/CD86) prevents apoptosis caused by chemotherapy or serum withdrawal. We now report that CD28 pro-survival signaling is dependent upon downstream activation of phosphatidyl-inositol 3-kinase/Akt, inactivation of the transcription factor FoxO3a, and decreased expression of the pro-apoptotic molecule Bim. Conversely, blocking the CD28-CD80/CD86 interaction between MM cells and DC in vitro abrogates the DC's ability to protect MM cells against chemotherapy-induced death. Consistent with these observations, in vivo blockade of CD28-CD80/CD86 in the Vk*MYC murine myeloma model sensitizes MM cells to chemotherapy and significantly reduces tumor burden. Taken together, our findings suggest that CD28 is an important mediator of MM survival during stress and can be targeted to overcome chemotherapy resistance.

Extracellular matrix remodeling by bone marrow fibroblast-like cells correlates with disease progression in multiple myeloma

The pathogenesis of multiple myeloma (MM) is regarded as a multistep process, in which an asymptomatic stage of monoclonal gammopathy of undetermined significance (MGUS) precedes virtually all cases of MM. Molecular events characteristic for the transition from MGUS to MM are still poorly defined. We hypothesized that fibroblast-like cells in the tumor microenvironment are critically involved in the pathogenesis of MM. Therefore, we performed a comparative proteome profiling study, analyzing primary human fibroblast-like cells isolated from the bone marrow of MM, of MGUS, as well as of non-neoplastic control patients. Thereby, a group of extracellular matrix (ECM) proteins, ECM receptors, and ECM-modulating enzymes turned out to be progressively up-regulated in MGUS and MM. These proteins include laminin α4, lysyl-hydroxylase 2, prolyl 4-hydroxylase 1, nidogen-2, integrin α5β5, c-type mannose receptor 2, PAI-1, basigin, and MMP-2, in addition to PDGF-receptor β and the growth factor periostin, which are likewise involved in ECM activities. Our results indicate that ECM remodeling by fibroblast-like cells may take place already at the level of MGUS and may become even more pronounced in MM. The identified proteins which indicate the stepwise progression from MGUS to MM may offer new tools for therapeutic strategies.

Tug of war in the haematopoietic stem cell niche: do myeloma plasma cells compete for the HSC niche?

In the adult mammal, normal haematopoiesis occurs predominantly in the bone marrow, where primitive haematopoietic stem cells (HSC) and their progeny reside in specialised microenvironments. The bone marrow microenvironment contains specific anatomical areas (termed niches) that are highly specialised for the development of certain blood cell types, for example HSCs. The HSC niche provides important cell–cell interactions and signalling molecules that regulate HSC self-renewal and differentiation processes. These same signals and interactions are also important in the progression of haematological malignancies, such as multiple myeloma (MM). This review provides an overview of the bone marrow microenvironment and its involvement in normal, physiological HSC maintenance and plasma cell growth throughout MM disease progression.

Anti-CD47 antibodies promote phagocytosis and inhibit the growth of human myeloma cells

Multiple myeloma is a plasma cell neoplasm residing in bone marrow. Despite advances in myeloma therapies, novel therapies are required to improve patient outcomes. CD47 is highly expressed on myeloma cells and a potential therapeutic candidate for myeloma therapies. Flow cytometric analysis of patient bone marrow cells revealed that myeloma cells overexpress CD47 when compared with non-myeloma cells in 73% of patients (27/37). CD47 expression protects cells from phagocytosis by transmitting an inhibitory signal to macrophages. Here we show that blocking CD47 with an anti-CD47 monoclonal antibody increased phagocytosis of myeloma cells in vitro. In xenotransplantation models, anti-CD47 antibodies inhibited the growth of RPMI 8226 myeloma cells and led to tumor regression (42/57 mice), implicating the eradication of myeloma-initiating cells. Moreover, anti-CD47 antibodies retarded the growth of patient myeloma cells and alleviated bone resorption in human bone-bearing mice. Irradiation of mice before myeloma cell xenotransplantation abolished the therapeutic efficacy of anti-CD47 antibodies delivered 2 weeks after radiation, and coincided with a reduction of myelomonocytic cells in spleen, bone marrow and liver. These results are consistent with the hypothesis that anti-CD47 blocking antibodies inhibit myeloma growth, in part, by increasing phagocytosis of myeloma cells.

Extraosseous (extramedullary) plasmacytomas: a clinicopathologic and immunophenotypic study of 32 Chinese cases

Background

Extraosseous plasmacytoma, so called extramedullary plasmacytoma (EMP) is relatively rare in China. The aim was investigate the clinicopathologic features of EMP and the role of Immunophenotype and genotype detection in diagnosis of EMP.

Methods

Thirty-two cases of EMP were investigated retrospectively by histopathology, immunophenotype, genotype and survival analysis.

Results

Clinically, the mean age of the patients was 53.4. Most of the patients received no treatment after the diagnosis was established, and the prognosis was relatively poor. Histologically, in 40% of the cases, the neoplastic cells were grade II or III. The neoplastic cells expressed one or more PC associated antigens. The immunophenotype of EMP and inflammation of sinonasal regions with numerous PC infiltrations were compared and showed some difference in expression of CD45, CD27, CD44v6 and Bcl-2 as well. Ig light chain restriction was detected in 87.5% of the cases.

Conclusions

we described 32 Chinese cases of EMP, compare with that reported in the literature, some differences are presented, including higher percentage of grade II and III cases, clinically inconsistent treatment and management as well as poor outcome of the disease.

Extracellular matrix in bone marrow can mediate drug resistance in myeloma

Glucocorticoids such as dexamethasone, frequently used for the treatment of multiple myeloma (MM), produce a rapid reduction in tumor mass. However, despite frequent initial complete remission, prolonged dexamethasone treatment results in the appearance of chemoresistant tumor cells and most patients with MM ultimately present relapse of the underlying disease. Accumulating data suggest that bone marrow components such as cytokines, extracellular matrix (ECM) and adjacent stroma cells could cooperate to provide a sanctuary to malignant plasma cells that allow their survival after initial drug exposure. This review focuses on the two major components of the bone marrow ECM that have been identified as mediators for innate or acquired drug resistance in MM, hyaluronan and fibronectin. These two ECM molecules are thought to play a crucial role in the pathogenesis of MM, combining their protective activities to promote optimal conditions for the long life of plasma cells and contribute to de novo drug resistance. They represent promising targets for the development of innovative treatments in order to prevent interactions between tumor cells and their microenvironment and to sensitize cancer cells to chemotherapy before the emergence of acquired mechanisms of chemoresistance.

Fibroblastic reticular cell infection by hemorrhagic fever viruses

Viral hemorrhagic fevers (VHFs) often cause high mortality with high infectivity, multiorgan failure, shock and hemorrhagic diathesis. Fibroblastic reticular cells (FRCs) within secondary lymphoid organs provide a supporting scaffold to T-lymphocyte areas. These cells regulate the movement of various immune cells and soluble molecules that promote T-lymphocyte homeostasis. We previously reported Ebola virus infection of FRCs, but ascribed little significance to this finding. Here, we studied infection of FRCs by Ebola, Marburg and Lassa viruses. We demonstrate that FRCs, or the extracellular ‘conduit’ of the fibroblastic reticulum of nonhuman primates, are targets of Ebola, Marburg and Lassa viruses. Furthermore, we observed that FRC damage correlates temporally and spatially with lymphocyte damage and that FRCs serve as nidi of fibrin deposition. In addition, we show that nonhuman primate FRCs express p75 NGF receptor and tissue transglutaminase. Our data suggest that viral infection of FRCs may be crucial to the immunological dysfunction and coagulopathy characteristic of VHFs. We further propose that p75 NGF receptor and tissue transglutaminase may be involved in FRC-associated dysfunction during the course of infection.

Heterologous tissue culture expression signature predicts human breast cancer prognosis

BACKGROUND

Cancer patients have highly variable clinical outcomes owing to many factors, among which are genes that determine the likelihood of invasion and metastasis. This predisposition can be reflected in the gene expression pattern of the primary tumor, which may predict outcomes and guide the choice of treatment better than other clinical predictors.

METHODOLOGY/PRINCIPAL FINDINGS

We developed an mRNA expression-based model that can predict prognosis/outcomes of human breast cancer patients regardless of microarray platform and patient group. Our model was developed using genes differentially expressed in mouse plasma cell tumors growing in vivo versus those growing in vitro. The prediction system was validated using published data from three cohorts of patients for whom microarray and clinical data had been compiled. The model stratified patients into four independent survival groups (BEST, GOOD, BAD, and WORST: log-rank test p = 1.7x10(-8)).

CONCLUSIONS

Our model significantly improved the survival prediction over other expression-based models and permitted recognition of patients with different prognoses within the estrogen receptor-positive group and within a single pathological tumor class. Basing our predictor on a dataset that originated in a different species and a different cell type may have rendered it less sensitive to proliferation differences and endowed it with wide applicability.

SIGNIFICANCE

Prognosis prediction for patients with breast cancer is currently based on histopathological typing and estrogen receptor positivity. Yet both assays define groups that are heterogeneous in survival. Gene expression profiling allows subdivision of these groups and recognition of patients whose tumors are very unlikely to be lethal and those with much grimmer outlooks, which can augment the predictive power of conventional tumor analysis and aid the clinician in choosing relaxed vs. aggressive therapy.

IL-6 regulates CD44 cell surface expression on human myeloma cells

Multiple myeloma (MM) is a progressive B-lineage neoplasia characterized by the accumulation of slow proliferative malignant plasma cells in the bone marrow compartment where the microenvironment seems to be favorable for their growth and survival. Heparan sulfate proteoglycans such as syndecan-1 and CD44 are thought to play a central role in the survival signals provided by these bone marrow survival niches, which require complex interactions between myeloma cells, extracellular matrix, stromal cells and soluble factors. In this report, we demonstrate that interleukin-6 (IL-6), the main survival and growth factor for myeloma cells, strongly increases CD44 gene expression. In addition, we show that IL-6 modulates CD44 RNA alternative splicing and induces the overexpression of all CD44 variant exons. Finally, we show that IL-6-induced CD44 cell surface molecules have a functional polarized membrane distribution. As IL-6 secretion induced from bone marrow stromal cells by myeloma cells is partly mediated through direct cell-to-cell interaction involving CD44 adhesion molecules, our findings suggest that a CD44/IL-6 amplification loop plays a crucial role in myeloma cell survival.

Selection of a highly aggressive myeloma cell line by an altered bone microenvironment in the C57BL/KaLwRij mouse

In multiple myeloma (MM), bone marrow microenvironment has an important role for the survival and growth of plasma cells. We previously showed that a high bone turnover, induced by ovariectomy, increased MM cells growth in the 5T2MM model. The present study characterized a new plasma cell line (5THL) which was isolated from 5T2MM mice previously ovariectomized. Cells were propagated unchanged in normal C57BL/KaLwRij mice during six generations. 5THL was compared to the original 5T2MM phenotype. Paraproteinemia was detected 6 weeks post injection in 5THL mice and after 8 weeks in 5T2MM mice. All 5THL mice developed a hind-limb paralysis after 10 weeks. 5T2MM mice were euthanized at 16 weeks, due to a more progressive development of the disease. In 5THL mice, osteolytic lesions were observed after 8 weeks and severe bone destruction was evidenced at 10 weeks. In 5T2MM mice, minimal lesions were observed only after 10 weeks. Like in 5T2MM mice, no extra osseous lesions were observed in 5THL mice. The 5THL MM model closely mimics human myeloma with higher and faster bone aggressiveness. This new aggressive cell line, with a preserved phenotype, was selected by an altered microenvironment due to an increased bone turnover.

Plasma cell survival is mediated by synergistic effects of cytokines and adhesion-dependent signals

Recent results suggest that plasma cell longevity is not an intrinsic capacity, but depends on yet unknown factors produced in their environment. In this study, we show that the cytokines IL-5, IL-6, TNF-alpha, and stromal cell-derived factor-1alpha as well as signaling via CD44 support the survival of isolated bone marrow plasma cells. The cytokines IL-7 and stem cell factor, crucially important for early B cell development, do not mediate plasma cell survival, indicating that plasma cells and early B cells have different survival requirements. As shown in IL-6-deficient mice, IL-6 is required for a normal induction, but not for the maintenance of plasma cell responses in vivo, indicating that the effects of individual survival factors are redundant. Optimal survival of isolated plasma cells requires stimulation by a combination of factors acting synergistically. These results strongly support the concept that plasma cell survival depends on niches in which a combination of specific signals, including IL-5, IL-6, stromal cell-derived factor-1alpha, TNF-alpha, and ligands for CD44, provides an environment required to mediate plasma cell longevity.

Neoplastic development in plasma cells

An increasing number of model systems of plasma cell tumor (PCT) formation have been and are being developed. Discussed here are six models in mice and multiple myeloma (MM) in humans. Each model illustrates a unique set of biological factors. There are two general types of model systems: those that depend upon naturally arising mutagenic changes (pristane-induced PCTs, 5TMM, and MM) and those that are associated with oncogenes (Emu-v-abl), growth factors [interleukin-6 (IL-6)], and anti-apoptotic factors (Bcl-xL/Bcl-2). PCTs develop in several special tissue microenvironments that provide essential cytokines (IL-6) and cell-cell interactions. In mice, the activation and deregulation of c-myc by chromosomal translocations is a major feature in many of the models. This mechanism is much less a factor in MM and the 5T model in mice. Genetically determined susceptibility is involved in many of the mouse models, but only a few genes have been implicated thus far.

Circulating immunoglobulin A- and immunoglobulin G-secreting hybridoma cells in peripheral blood preferably migrate to female genital tracts. The role of sex hormones

Antigen-specific circulating immunoglobulin-secreting cells (ISC) migrate to various secondary and tertiary lymphoid tissues. To understand the migration of the cells into the genital tract and its regulation by sex hormones, spleen-derived SG2 hybridoma cells secreting immunoglobulin G2b (IgG2b) and Peyer's patch-derived PA4 hybridoma cells secreting polymer IgA were labelled with 3H-TdR, and intravenously injected into syngeneic mice of both sexes. Using flow cytometry, surface molecular markers of plasma cells, CD38 and CD138, and adhesion molecules, CD49d, CD162, and CD11a were found to be positive in SG2 and PA4 cells, but CD62L, alpha4beta7 and CD44 were not expressed on these cells. The relative distribution indexes (RDIs) of the cells in genital tract and other tissues were measured. The means of RDIs of SG2 and PA4 cells in female genital tissues were 6.5 and 4.5 times as many as the means in male genital tissues, respectively. The treatment of ovariectomized mice with beta-oestradiol significantly increased the RDIs of PA4 cells in cervix and vagina, but decreased the RDIs of SG2 cells in vagina, horn of uterus, uterus and rectum (P<0.05). Progesterone treatment increased the RDIs of PA4 cells in vagina and rectum (P<0.05). The treatment with testosterone significantly increased the RDIs of SG2 and PA4 cells in epididymis and accessory sex glands (P<0.05). These results demonstrate that the female genital tract is the preferable site for the migration of circulating hybridoma cells to the male genital tract, and sex hormones play an important role in regulation of the migration of circulating ISC to genital tracts.

IL-6 transgenic mouse model for extraosseous plasmacytoma

Plasma cell neoplasms in humans comprise plasma cell myeloma, otherwise known as multiple myeloma, Ig deposition and heavy chain diseases, and plasmacytoma (PCT). A subset of PCT, designated extramedullary PCT, is distinguished from multiple myeloma and solitary PCT of bone by its distribution among various tissue sites but not the bone marrow. Extramedullary (extraosseus) PCT are rare spontaneous neoplasms of mice but are readily induced in a susceptible strain, BALB/c, by treatment with pristane. The tumors develop in peritoneal granulomas and are characterized by Myc-activating T(12;15) chromosomal translocations and, most frequently, by secretion of IgA. A uniting feature of human and mouse plasma cell neoplasms is the critical role played by IL-6, a B cell growth, differentiation, and survival factor. To directly test the contribution of IL-6 to PCT development, we generated BALB/c mice carrying a widely expressed IL-6 transgene. All mice exhibited lymphoproliferation and plasmacytosis. By 18 months of age, over half developed readily transplantable PCT in lymph nodes, Peyer's patches, and sometimes spleen. These neoplasms also had T(12;15) translocations, but remarkably, none expressed IgA. Unexpectedly, approximately 30% of the mice developed follicular and diffuse large cell B cell lymphomas that often coexisted with PCT. These findings provide a unique model of extramedullary PCT for studies on pathogenesis and treatment and suggest a previously unappreciated role for IL-6 in the genesis of germinal center-derived lymphomas.

CD44 isoforms are differentially regulated in plasma cell dyscrasias and CD44v9 represents a new independent prognostic parameter in multiple myeloma

To evaluate the role of CD44 variant isoforms (CD44v) in plasma cell dyscrasias, CD44v expression was analysed in bone marrow (BM) biopsies of multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS) patients, in biopsies of soft tissue infiltration by MM and in extramedullary plasmacytoma samples. Expression of CD44 isoforms containing the 3v, 4v, 6v or 10v domain was observed in 15, 7, 13 and 5% of 87 samples from 49 consecutive MM cases, but could not be detected in ten normal persons or 11 MGUS patients. In contrast, CD44v9 revealed a broader pattern of expression and was observed in plasma cells in three out of ten normal persons and in three out of 11 MGUS cases. In MM, CD44v9 was detected in 32 out of 87 samples (37%) of BM infiltrates and was associated with an advanced Durie and Salmon stage (P<0.03), a progressive disease (P<0.01) and an IgA subtype (P<0.01). Furthermore, CD44v9 expression was observed in three out of five cases of MM soft tissue infiltrates, was often upregulated during disease progression, was significantly correlated with a shorter overall survival (P<0.03) and emerged as an independent prognostic factor in multivariate analysis (stage: relative risk 1.36, P<0.02; CD44v9 expression: relative risk 1.45, P<0.04). These results substantiate the clinical relevance of CD44v domains in plasma cell disorders and establish CD44v9 as a new independent prognostic parameter in MM.

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)

Autocrine interleukin-6 production and highly malignant multiple myeloma: relation with resistance to drug-induced apoptosis

In this study, flow cytometry was used to evaluate interleukin-6 (IL-6) production by bone marrow mononuclear cells from 47 patients with multiple myeloma (MM) in different clinical stages and 15 patients with monoclonal gammopathy of undetermined significance. In patients with MM, autocrine IL-6 production paralleled the clinical disease stage. The largest proportion of syndecan-1(+)/IL-6(+) cells was detected in patients with resistant relapse or primary refractory disease, suggesting that tumor progression involves expansion of myeloma cells producing IL-6. The authors assessed autocrine IL-6 production and in vitro proliferation and apoptosis of myeloma cells in 6 myeloma cell clones (MCCs) and in 2 myeloma cell lines, namely IM-9 and U-266-1970, which showed different sensitivities to the addition of exogenous IL-6. Autocrine IL-6 production was observed in IL-6-independent MCC-2, MCC-3, and MCC-5 cloned from patients with aggressive disease and in the IM-9 cell line. In contrast, IL-6-dependent MCC-1, MCC-4, and MCC-6 were syndecan-1(+) and IL-6(-). Blocking experiments with anti-IL-6 monoclonal antibody from clone AH65, which binds IL-6-IL-6Ralpha complexes, prevented cell proliferation of IL-6(+) MCCs. Flow cytometry evaluations after propidium iodide staining revealed different susceptibilities of MCCs to cell death. IL-6-producing MCCs showed minimal spontaneous and dexamethasone-induced apoptosis, whereas a regular amplitude of apoptosis occurred in the IL-6(-) MCCs. These data provide evidence that autocrine IL-6 reflects a highly malignant phenotype of myeloma cells. In fact, autocrine IL-6 production and deregulated apoptosis may induce expansion of selective IL-6(+) myeloma cells resistant to spontaneous and drug-induced cell death.

CD44v10 in hematopoiesis and stem cell mobilization

Transplantation of hematopoietic progenitor cells provides in many instances of malignant tumors an ultimate chance of curative therapy, whereby the transfer of peripheral blood stem cells (PBSC) may even be advantageous as compared to bone marrow cells. Yet, the transfer of PBSC requires mobilization of stem cells into the periphery, which is mostly achieved via hematopoietic growth factors like G-CSF. Although G-CSF has been found to efficiently mobilize stem cells in most instances, some patients do not or insufficiently respond to G-CSF treatment In addition, G-CSF treatment may by accompanied by maturation of the most primitive progenitors and this may have an impact on stem cell homing and recovery of hemopoiesis. Therefore, additional approaches for stem cell mobilization have been searched for, in particular mobilization via a blockade of an adhesion molecule expressed by CD34-positive cells, like VLA-4 (CD49d) and the hematopoietic isoform of CD44 (CD44s). We recently described that in the mouse one of the CD44 variant isoforms, CD44v10, is expressed on a subpopulation of bone marrow cells, whereas a CD44v10 receptor-globulin only binds to stromal elements. These features appeared promising for anti-CD44v10 as a means of stem cell mobilization. Indeed, treatment with anti-CD44v10 revealed promising results concerning the recovery of multilineage colony forming units in the spleen and the peripheral blood. We here summarize features of expression and function of CD44 in hematopoiesis an provide further evidence for anti-CD44v10 as a means to mobilize hematopoietic progenitor cells.

Lymph nodes and Peyer's patches of IL-6 transgenic BALB/c mice harbor T(12;15) translocated plasma cells that contain illegitimate exchanges between the immunoglobulin heavy-chain mu locus and c-myc

Hyperplastic plasmacytotic lymph nodes and Peyer's patches of 12 of 25 (48%) BALB/c mice that carried a human IL-6 transgene under the transcriptional control of the histocompatibility H-2L(D) promoter (BALB/c.IL-6 mice) were found to harbor 15 cell clones that contained in their T(12;15) translocation breakpoint regions illegitimate genetic recombinations between the upstream flank of the immunoglobulin heavy-chain C mu locus (5'-C mu) and c-myc (5'-C mu/c-myc+ clones). Similar 5'-C mu/c-myc+ clones were also detected in pristane-induced peritoneal granulomata (a significant source of IL-6 in situ) of three of 13 (13%) conventional BALB/c mice, but not in lymphoid tissues of pristane-treated BALB/c mice, nor in any tissue of untreated BALB/c mice. These findings provided strong evidence that IL-6 may be able to promote the growth and/or survival of clones that contained rearrangements between 5'-C mu and c-myc. Taken in conjunction with our previous observation that 5'-C mu/c-myc+ clones are the precursors for pristane-induced BALB/c plasmacytomas, the findings further suggested that IL-6 may play a pivotal role in the early stage of plasmacytoma development, by promoting tumor precursor cells. The BALB/c.IL-6 model of plasmacytomagenesis may be superior to the conventional BALA/c model because the putative plasmacytoma precursors appear to be more prevalent and in their development independent of treating the mice with inflammation-inducing plasmacytomagenic agents, such as pristane or silicone polymers.

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.

Interleukin-1 in multiple myeloma: producer cells and their role in the control of IL-6 production

We studied the role of interleukin (IL)-1beta in patients with multiple myeloma. By in situ hybridization and immunochemistry, myeloid and megakaryocytic cells expressed high levels of the IL-1beta gene and produced IL-1beta. Myeloma cells less potently expressed the IL-1beta gene and IL-1beta protein. IL-1beta gene expression was not constitutive since it was detected in the bone marrow myeloma cells of two patients, unlike circulating tumoural cells. In addition, nine myeloma cell lines failed to express the IL-1beta gene and this expression could not be induced by 12 different cytokines. We demonstrated that IL-1 was mainly responsible for IL-6 production in the tumoural environment through a PGE2 loop. In fact, an IL-1 receptor antagonist (IL-1RA) blocked PGE2 synthesis and IL-6 production by 80%; this blockage could be reversed by adding synthetic PGE2. Similar findings were found with indomethacin, an inhibitor of cyclooxygenase that blocks PGE2 synthesis. Taken together, these data emphasize the possibility of blocking IL-1 by using IL-1RA or other antagonists in order to block IL-6 production, which is a major tumoural survival and proliferation factor.

Both Stroma and Stem Cell Factor Maintain Long-Term Growth of ELM Erythroleukemia Cells, but Only Stroma Prevents Erythroid Differentiation in Response to Erythropoietin and Interleukin-3

Defining how the stromal requirements of hematopoietic progenitors change during leukemia progression is an important topic that is not well understood at present. The murine ELM erythroleukemia is an interesting model because the erythroid progenitors retain dependence on bone marrow-derived stromal cells for long-term growth in vitro, and they also undergo erythroid differentiation in the presence of erythropoietin (EPO) and interleukin-3 (IL-3). In this report, we have shown using neutralizing antibodies that stem cell factor (SCF), insulin-like growth factor (IGF)-1, and integrin signaling pathways are all involved. We then determined whether ELM cells can be maintained long-term without stroma in various combinations of growth factors produced by stroma cells or growth factors for which ELM cells have receptors. This showed that ELM cells could be maintained with high efficiency in SCF alone; furthermore, the cells remained absolutely SCF-dependent and did not become more tumorigenic than cells maintained on stroma. In contrast, ELM cells underwent clonal extinction when serially cloned in IGF1; any cells that survived long-term growth in IGF-1 were found to be IGF1-independent. One important difference between maintaining ELM cells on stroma and growth in SCF is that stroma reversibly inhibits their differentiation in response to EPO and IL-3, whereas SCF does not.

Both Stroma and Stem Cell Factor Maintain Long-Term Growth of ELM Erythroleukemia Cells, but Only Stroma Prevents Erythroid Differentiation in Response to Erythropoietin and Interleukin-3

Defining how the stromal requirements of hematopoietic progenitors change during leukemia progression is an important topic that is not well understood at present. The murine ELM erythroleukemia is an interesting model because the erythroid progenitors retain dependence on bone marrow-derived stromal cells for long-term growth in vitro, and they also undergo erythroid differentiation in the presence of erythropoietin (EPO) and interleukin-3 (IL-3). In this report, we have shown using neutralizing antibodies that stem cell factor (SCF), insulin-like growth factor (IGF)-1, and integrin signaling pathways are all involved. We then determined whether ELM cells can be maintained long-term without stroma in various combinations of growth factors produced by stroma cells or growth factors for which ELM cells have receptors. This showed that ELM cells could be maintained with high efficiency in SCF alone; furthermore, the cells remained absolutely SCF-dependent and did not become more tumorigenic than cells maintained on stroma. In contrast, ELM cells underwent clonal extinction when serially cloned in IGF1; any cells that survived long-term growth in IGF-1 were found to be IGF1-independent. One important difference between maintaining ELM cells on stroma and growth in SCF is that stroma reversibly inhibits their differentiation in response to EPO and IL-3, whereas SCF does not.

Long-term bone marrow cultured stromal cells regulate myeloma tumour growth in vitro: studies with primary tumour cells and LTBMC-dependent cell lines

Long-term bone marrow cultured stromal cells (LTBMC) produce IL-6 after contact with tumour cells from multiple myeloma patients. We found that LTBMC could substitute for exogenous IL-6 in the stimulation of bone marrow plasma cells from myeloma patients with active disease in short-term cultures. In addition, tumour cells of some patients with inactive disease, which were unresponsive to exogenous IL-6, were induced to IL-6-dependent growth after LTBMC co-culture. To study the role of LTBMC in myeloma tumour growth in vitro, plasma cell lines UM-2 and UM-3 were selected. UM-2 and UM-3 grew in contact with LTBMC and proliferation was blocked by antibodies against IL-6, IL-6 receptor (IL-6R, gp80, CD126) or the common signal transducing unit, gp130 (CD130). Culture with IL-6 alone or combined with GM-CSF resulted in cell death via apoptosis. The combination of IL-6 with soluble gp80, however, maintained in vitro proliferation of UM-2 and UM-3 cells. These data imply that LTBMC regulate myeloma growth in vitro via production of IL-6, possibly via induction of a functional IL-6 receptor on the tumour cells.

Characterization of C57BL/6 plasmacytomas lacking a c-myc translocation

BALB/c peritoneal plasmacytomas induced by a variety of agents are invariably associated with a c-myc translocation. In contrast, naturally arising bone marrow plasma cell tumors in C57BL/KaLwRij mice lack this translocation. This difference has led to the suggestion that these are 2 fundamentally different plasma cell diseases. Herein, we have analyzed 2 rare C57BL/6 peritoneal plasmacytomas in terms of characteristics associated with the bone marrow-derived lines. Like the bone marrow lines, these peritoneal plasmacytomas do not exhibit c-myc translocations, indicating that c-myc translocation is not an obligatory event in the development of all murine extramedullary plasmacytomas. However, myc is dysregulated at the mRNA level, indicating that myc overexpression may be fundamental to most plasma cell diseases but that dysregulation can occur by alternative mechanisms possibly reflecting different genetic backgrounds.

Defective development of pristane-oil-induced plasmacytomas in interleukin-6-deficient BALB/c mice

Interleukin (IL)-6 is known to be an essential growth factor for myeloma cells, both in vitro and in vivo. In mice, IL-6 is required for development of B cell tumors upon infection with a retrovirus expressing the myc/raf oncogenes. In the present study, we used the pristane-oil-induced plasmacytoma model, which more closely mimics tumor transformation and progression in human multiple myeloma. Also using this system, we found that IL-6-deficient BALB/c mice are protected against tumor development. Although the pristane-induced inflammatory reaction was less pronounced in IL-6-deficient mice versus their wild-type littermates, both B cell differentiation and plasma cell formation took place, and even morphological evidence of plasma cell transformation was detected, albeit at a low frequency. However, in the absence of IL-6, there were never signs of uncontrolled proliferation of either normal B lymphocytes or tumor cells, suggesting that the role of IL-6 in murine plasmacytoma and possibly also in human multiple myeloma is to ensure abnormal survival and proliferation of previously transformed tumor cells and therefore tumor development and progression.

Indomethacin Is a Potent Inhibitor of Pristane and Plastic Disc Induced Plasmacytomagenesis in a Hypersusceptible BALB/c Congenic Strain

Continuous indomethacin (INDO) administration in the drinking water (10 to 20 μg/mL) profoundly inhibited plasmacytoma (PCT) development initiated by three 0.2- or 0.5-mL intraperitoneal (i.p.) injections of pristane in hypersusceptible BALB/c.DBA/2-Idh1-Pep3 congenic mice. The most effective inhibitions were obtained with continuous INDO treatment. When treatment was delayed until 50 to 60 days after the first pristane injection, there was approximately a 50% reduction in PCT incidence. The primary action of pristane is the induction of a chronic inflammation in the peritoneal connective tissues and the formation of a microenvironment where PCTs develop. INDO, a powerful inhibitor of prostaglandin synthases (cyclooxygenases 1 and 2), did not inhibit the formation of mesenteric oil granuloma nor the appearance of cells in this chronic inflammatory tissue carrying c-myc illegitimately joined to an Ig heavy chain switch region, ie, the t(12; 15) chromosomal translocation. INDO inhibited PCT induction by the i.p. implantation of 21 × 2 mm polycarbonate discs. These solid objects predominantly induce the formation of a patchy fibroplastic tissue on contacting peritoneal surfaces. These and previous data indicate that indomethacin inhibits an intermediate stage in PCT development after the arrival of cells bearing the T(12; 15) translocation in the oil granuloma and before these cells acquire transplantability to a pristane-conditioned host. The biological mechanism that explains how INDO inhibits PCT development is not yet established but appears to result from decreased production of prostaglandins in chronic inflammatory tissues (oil granuloma, fibroplasia), suggesting that prostaglandins play an active role in oil and solid plastic induced PCT formation.

Indomethacin Is a Potent Inhibitor of Pristane and Plastic Disc Induced Plasmacytomagenesis in a Hypersusceptible BALB/c Congenic Strain

Continuous indomethacin (INDO) administration in the drinking water (10 to 20 μg/mL) profoundly inhibited plasmacytoma (PCT) development initiated by three 0.2- or 0.5-mL intraperitoneal (i.p.) injections of pristane in hypersusceptible BALB/c.DBA/2-Idh1-Pep3 congenic mice. The most effective inhibitions were obtained with continuous INDO treatment. When treatment was delayed until 50 to 60 days after the first pristane injection, there was approximately a 50% reduction in PCT incidence. The primary action of pristane is the induction of a chronic inflammation in the peritoneal connective tissues and the formation of a microenvironment where PCTs develop. INDO, a powerful inhibitor of prostaglandin synthases (cyclooxygenases 1 and 2), did not inhibit the formation of mesenteric oil granuloma nor the appearance of cells in this chronic inflammatory tissue carrying c-myc illegitimately joined to an Ig heavy chain switch region, ie, the t(12; 15) chromosomal translocation. INDO inhibited PCT induction by the i.p. implantation of 21 × 2 mm polycarbonate discs. These solid objects predominantly induce the formation of a patchy fibroplastic tissue on contacting peritoneal surfaces. These and previous data indicate that indomethacin inhibits an intermediate stage in PCT development after the arrival of cells bearing the T(12; 15) translocation in the oil granuloma and before these cells acquire transplantability to a pristane-conditioned host. The biological mechanism that explains how INDO inhibits PCT development is not yet established but appears to result from decreased production of prostaglandins in chronic inflammatory tissues (oil granuloma, fibroplasia), suggesting that prostaglandins play an active role in oil and solid plastic induced PCT formation.

Stromal cell organisation in the mouse lymph node. A light and electron microscopic investigation using the zinc iodide-osmium technique

The organisation of the stromal cell compartment in the mouse lymph node was studied by light and electron microscopy after tissue impregnation by the zinc iodide-osmium (ZIO) method. Fibroblastic reticular cells (FRCs) represented the main stromal cell population. These cells were located both in the cortical region and in the medulla and exhibited various configurations. In the cortex, FRCs were fusiform in shape and came into close proximity with the floor of the subcapsular sinus. In the medulla, the FRCs were shaped like irregular dendritic cells which formed a complex 3-dimensional network. The FRCs surrounded vascular structures such as capillaries and/or high endothelial venules; in these instances they were organised in a discontinuous sheath-like fashion around the vessel wall. By light and electron microscopy, FRCs have been observed to come in close spatial relationship with a number of cells in the lymph node, including sinus endothelial cells, the endothelium of high endothelial venules and capillaries, various types of lymphocytes, follicular dendritic cells and interdigitating cells. These microanatomical features are consistent with the proposal that FRCs may be involved in the communicative networks between the different lymph node compartments. In particular, the FRCs may be involved in the transport of molecules from the sinus compartment to the high endothelial venules or to the distinct cell populations in the lymphoid parenchyma.

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.

Induction of IL-6 production by bone marrow stromal cells on the adhesion of IL-6-dependent hematopoietic cells

Cellular interactions between hematopoietic cells and stromal cells play crucial roles in the proliferation and differentiation of the hematopoietic cells. Interleukin-6 (IL-6)-dependent 7TD1 cells markedly proliferated without IL-6 when they were co-cultured with hematopoietic-supportive bone marrow stromal cells, HESS-5 cells and HESS-1 CL.3 cells, which can support long-term hematopoiesis in vitro with but not without direct cell contact, cell contact being prevented with a microporous membrane. The production of IL-6 and the amount of IL-6 mRNA in hematopoietic-supportive stromal cells but not 7TD1 cells significantly increased only when the stromal cells were co-cultured in direct contact with 7TD1 cells. Furthermore, the amount of IL-6 mRNA increased according to the number of 7TD1 cells co-cultured. These inductions were not observed on co-culture with a murine myeloid cell line, M1 cells, or on the addition of the co-culture supernatant. These results suggest that 7TD1 cells transmit the signal to stromal cells that enhances IL-6 production by stromal cells via direct cell contact. A certain specific molecule for transduction of the signals may exist on the surface membrane of stromal cells and hematopoietic cells.

Distinct tumorigenic potential of abl and raf in B cell neoplasia: abl activates the IL-6 signaling pathway

The development of murine plasma cell tumors induced by raf/myc containing retroviruses is facilitated by T cells and completely dependent on IL-6. To determine whether kinases with differing specificities reflect alternative biochemical pathways in B cell tumorigenesis, we have employed an abl/myc containing retrovirus to assess neoplastic development. In contrast with raf/myc, abl/myc disease is T cell and IL-6 independent. An examination of the IL-6 signal transduction pathway reveals that this pathway, as defined by activation of Stat3, is inducible by IL-6 in raf/myc tumors but constitutively activated in abl/myc tumors. These findings provide a mechanism for the derivation of cytokine-independent plasma cell tumors and suggest that both IL-6-dependent and independent tumors may arise in vivo depending on the particular mutational events incurred during tumorigenesis.

CD40 and the effect of anti-CD40-binding on human multiple myeloma clonogenicity

CD40 is a 48 kDa glycosylated phospoprotein that is a member of the tumor necrosis factor receptor (TNF-R) superfamily. CD40 was originally identified in B lymphocytes, and is found on monocytes, dendritic cells, some carcinoma cell lines, and the thymic epithelium. CD40 is expressed on normal pre-B through mature B stages of differentiation. For normal B cells, the cross-linking of CD40 induces cell cycle progression, long-term proliferation in vitro, IgE secretion, increased adhesion molecule (LFA-1) expression, and low level IL-6 secretion. The natural ligand of CD40 (CD40L, gp39, or T-BAM, for T-B cell activating molecule) was recently identified as an inducible molecule expressed transitionally on activated T cells. Although originally believed to be absent in normal and malignant plasma cells, CD40 has been demonstrated on the majority of myeloma cell lines and myeloma cells from plasma cell dyscrasia (PCD) patient specimens tested. CD40 activation modulated myeloma cell proliferation and clonogenicity in vitro, suggesting that the CD40 pathway is active in myeloma cell growth. For the IL-6 dependent cell line ANBL-6, CD40 activation was associated with autocrine IL-6 production. However, the IL-6 pathway does not appear to play a predominant role in CD40 activation of non-IL-6-dependent MM cell lines and patient primary bone marrow cultures. The possible pathophysiologic role of the CD40 receptor in human multiple myeloma is discussed.

Adhesion molecules involved in the binding of murine myeloma cells to bone marrow stromal elements

In previous work, we reported the development of the B9/BMI syngeneic murine bone marrow metastasis model. Interleukin (IL)-6-dependent, IL-I-producing B9/BMI cells, which preferentially home to and colonise the vertebral and femoral marrow after i.v. injection, exhibit striking similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-I. Because the haematopoietic microenvironment consists of different cell types, such as endothelial cells, fibroblasts, adipocytes and macrophages, we investigated the functional significance of these adhesion molecules in heterotypic binding assays between B9/BMI cells and a newly established bone marrow-derived endothelial cell line (BMEC), a fibroblastoid pre-adipocyte cell line (BMS2.2) and primary bone marrow-derived macrophages. B9/BMI cells adhered well to all stromal elements: a combination of monoclonal antibodies (MAbs) against CD44 and VLA-4 significantly inhibited the adherence of B9/BMI cells to BMEC and BMS2.2 cells, whereas binding of B9/BMI cells to macrophages was partially blocked with an anti-ICAM-I MAb. Our results implicate multiple recognition mechanisms, including those involving CD44, VLA-4 and ICAM-I, in the retention of B9/BMI cells in the bone marrow.

CD44: physiological expression of distinct isoforms as evidence for organ-specific metastasis formation

Continuous progress has been achieved during recent decades in the therapy of metastasizing malignancies by improving chemotherapeutic strategies and new approaches in radiation therapy. Genetic manipulation of tumor cells and of the tumor fighting immune system is hoped to add significant contributions to curative interventions in disseminated tumors. That we are still far from eradicating death by malignant growth is due ultimately to our limited understanding of the cascade of events resulting in metastasis formation, which until recently was believed to rely on multiple rounds of mutation and selection processes. This implies an individually specific history of each metastatic tumor, which would rule out uniform diagnostic and therapeutic concepts. When it was noted in a rat tumor model that the transfer of cDNA of a single gene, a CD44 variant isoform (CD44v) covering the exons v4-v7, sufficed to initiate metastasis formation of a locally growing tumor, hope was created that a "metastogene" may have been identified. Although the idea of CD44v expression as a unifying concept for tumor progression was not sustained, the discovery of CD44v-initiated metastatic spread allowed a conceptually new hypothesis on tumor progression as a consequence of the reactivation of genetic programs of ontogeny, stem cell differentiation, and/or lymphocyte activation. Since distinct CD44 isoforms play an important role in these processes, unraveling the functions of this family of molecules can indeed provide a cornerstone in the understanding of tumor progression. This article summarizes briefly the present knowledge on known functions of CD44 isoforms with particular focus on parallels between physiological programs and tumor progression.

Interleukin 6 is essential for in vivo development of B lineage neoplasms

Interleukin (IL) 6 has been suggested to be the major cytokine responsible for proliferation of neoplastic plasma cells in both human myeloma and mouse plasmacytoma. Much of the evidence supporting this suggestion is derived from in vitro studies in which the survival or proliferation of some plasma cell tumors has been found to be IL-6 dependent. However, it remains unclear whether this dependency is the consequence of in vivo or in vitro selective pressures that preferentially expand IL-6-responsive tumor cells, or whether it reflects a critical in vivo role for IL-6 in plasma cell neoplasia. To address this question, we have attempted to induce plasma cell tumors in normal mice and in IL-6-deficient mice generated by introduction of a germline-encoded null mutation in the IL-6 gene. The results demonstrate that mice homozygous (+/+) or heterozygous (+/-) for the wild-type IL-6 allele yield the expected incidences of plasma cell tumors. In contrast, mice homozygous for the IL-6-null allele (-/-) are completely resistant to plasma cell tumor development. These studies define the essential role of IL-6 in the development of B lineage tumors in vivo and provide experimental support for continued efforts to modulate this cytokine in the treatment of appropriate human B cell malignancies.

T cells induce terminal differentiation of transformed B cells to mature plasma cell tumors

Major interest in the analysis of mature plasma cell neoplasias of mice and humans has focused on identification of precursor cells that give rise to mature malignant plasma cells. Although several laboratories have recently suggested that such cells are present in the granulomas of pristane-treated mice and the bone marrow of some multiple myeloma patients, the in vivo cellular interactions required for their differentiation into mature plasma cell tumors remains unclear. Given the extensive interactions of peripheral T cells and normal B cells, we assessed the potential role of T cells in plasma-cell tumor development, by using a myc, raf-containing retrovirus, J3V1, to induce plasmacytomas in normal BALB/c mice, T-cell-deficient nude mice, and T-cell-reconstituted nude mice. The B-lineage tumors arising in normal BALB/c mice were uniformly mature plasmacytomas, most of which secreted immunoglobulin. In contrast, nude mice yielded predominantly non-immunoglobulin-secreting B-cell lymphomas with a phenotype characteristic of peripheral B cells. T-cell reconstitution of nude mice prior to tumor induction resulted in a shift from B-cell lymphomas to plasmacytomas. These results imply that transformation can occur prior to terminal differentiation of B cells and that such transformed cells can be driven to terminal differentiation by peripheral T cells. These findings further suggest that, in human multiple myeloma, the ability of T cells to influence the differentiation state of transformed B cells may provide a mechanism by which malignant plasma cells found in the bone marrow could arise from clonotypically related less-mature B cells found in both the bone marrow and periphery.

Generation of a fusion partner to sample the repertoire of splenic B cells destined for apoptosis

B cells proliferate and diversify in germinal centers in response to antigen. Only a small percentage of these B cells will emerge to form the serum antibody response. Other B cells making lower affinity antibodies, acquiring nonsense mutations, or expressing autoreactivity as a result of somatic mutation undergo an apoptotic cell death and are not efficiently sampled in current analyses of B-cell hybridomas. We have demonstrated that expression of bcl-2 in the NSO myeloma fusion partner leads to a higher yield of viable hybridomas, with a selective increase in hybridomas from B cells that produce autoantibodies and are seldom recovered when spleen cells from non-autoimmune mice are fused to the conventional NSO cell line. Using this fusion partner, we have generated hybridomas from anti-DNA antibody-producing transgenic B cells that are anergic in vivo and destined for apoptosis. These studies provide a strategy to sample the repertoire of B cells that arise in vivo but are not selected to contribute to the expressed antibody response. Furthermore, they demonstrate that restricted expression of bcl-2 in B cells contributes to the maintenance of self-tolerance in secondary lymphoid organs.