Non-Invasive Imaging Provides Spatiotemporal Information on Disease Progression and Response to Therapy in a Murine Model of Multiple Myeloma

Background

Multiple myeloma (MM) is a B-cell malignancy, where malignant plasma cells clonally expand in the bone marrow of older people, causing significant morbidity and mortality. Typical clinical symptoms include increased serum calcium levels, renal insufficiency, anemia, and bone lesions. With standard therapies, MM remains incurable; therefore, the development of new drugs or immune cell-based therapies is desirable. To advance the goal of finding a more effective treatment for MM, we aimed to develop a reliable preclinical MM mouse model applying sensitive and reproducible methods for monitoring of tumor growth and metastasis in response to therapy.

Material and Methods

A mouse model was created by intravenously injecting bone marrow-homing mouse myeloma cells (MOPC-315.BM) that expressed luciferase into BALB/c wild type mice. The luciferase in the myeloma cells allowed in vivo tracking before and after melphalan treatment with bioluminescence imaging (BLI). Homing of MOPC-315.BM luciferase+ myeloma cells to specific tissues was examined by flow cytometry. Idiotype-specific myeloma protein serum levels were measured by ELISA. In vivo measurements were validated with histopathology.

Results

Strong bone marrow tropism and subsequent dissemination of MOPC-315.BM luciferase⁺ cells in vivo closely mimicked the human disease. In vivo BLI and later histopathological analysis revealed that 12 days of melphalan treatment slowed tumor progression and reduced MM dissemination compared to untreated controls. MOPC-315.BM luciferase⁺ cells expressed CXCR4 and high levels of CD44 and α4β1 in vitro which could explain the strong bone marrow tropism. The results showed that MOPC-315.BM cells dynamically regulated homing receptor expression and depended on interactions with surrounding cells.

Conclusions

This study described a novel MM mouse model that facilitated convenient, reliable, and sensitive tracking of myeloma cells with whole body BLI in living animals. This model is highly suitable for monitoring the effects of different treatment regimens.     

The allogeneic effect on tumor growth. II. Suppression of both ascitic and solid MOPC 315 plasmacytoma by the graft-vs-host reaction, with pathologic correlation.

The growth of an ascitic murine plasmacytoma, MOPC 315, can be retarded in CAF1 hybrid host mice by the i.p. injection of donor lymphoid cells. The graft-vs-host reaction can be established by a variety of donor cells, including parental BALB/c and A/J and congenic inbred B10.D2 which share the major histocompatibility locus with BALB/c(H-2d). Optimal results are consistently obtained when parental BALB/c spleen cells are injected before tumor inoculation, and a second dose of donor spleen cells injected 1 week later. This aloogeneic effect on tumor growth is manifested by delayed appearance of the tumor and prolonged host survival. Pathologic studies on the ascites tumor indicated that the allogeneic effect suppresses the initial appearance and early growth of the plasmacytoma. However, once established, MOPC 315 grows rapidly and fatally in both control mice and recipients of donor lymphoid cells. Further, a subcutaneous implant of MOPC 315 is suppressed by an allogeneic effect established either i.v. with BALB/c spleen cells before tumor inoculation or by BALB/c spleen cells administered subcutaneously at the time of MOPC 315 implant. Thirty percent of mice treated by i.v. or subcutaneous donor lymphoid cells were tumor free at 150 days after tumor inoculation.     

Eosinophils and Megakaryocytes Support the Early Growth of Murine MOPC315 Myeloma Cells in Their Bone Marrow Niches

Multiple myeloma is a bone marrow plasma cell tumor which is supported by the external growth factors APRIL and IL-6, among others. Recently, we identified eosinophils and megakaryocytes to be functional components of the micro-environmental niches of benign bone marrow plasma cells and to be important local sources of these cytokines. Here, we investigated whether eosinophils and megakaryocytes also support the growth of tumor plasma cells in the MOPC315.BM model for multiple myeloma. As it was shown for benign plasma cells and multiple myeloma cells, IL-6 and APRIL also supported MOPC315.BM cell growth in vitro, IL-5 had no effect. Depletion of eosinophils in vivo by IL-5 blockade led to a reduction of the early myeloma load. Consistent with this, myeloma growth in early stages was retarded in eosinophil-deficient ΔdblGATA-1 mice. Late myeloma stages were unaffected, possibly due to megakaryocytes compensating for the loss of eosinophils, since megakaryocytes were found to be in contact with myeloma cells in vivo and supported myeloma growth in vitro. We conclude that eosinophils and megakaryocytes in the niches for benign bone marrow plasma cells support the growth of malignant plasma cells. Further investigations are required to test whether perturbation of these niches represents a potential strategy for the treatment of multiple myeloma.     

Normalizing the bone marrow microenvironment with p38 inhibitor reduces multiple myeloma cell proliferation and adhesion and suppresses osteoclast formation

The multiple myeloma (MM) bone marrow (BM) microenvironment plays a critical role in supporting tumor growth and survival as well as in promoting formation of osteolytic lesions. Recent results suggest that the p38 mitogen-activated protein kinase (MAPK) is an important factor in maintaining this activated environment. In this report, we demonstrate that the p38alpha MAPK inhibitor, SCIO-469, suppresses secretion of the tumor-supportive factors IL-6 and VEGF from BM stromal cells (BMSCs) as well as cocultures of BMSCs with MM cells, resulting in reduction in MM cell proliferation. Additionally, we show that SCIO-469 prevents TNFalpha-induced adhesion of MM cells to BMSCs through an ICAM-1- and VCAM-1-independent mechanism. Microarray analysis revealed a novel set of TNFalpha-induced chemokines in BMSCs that is strongly inhibited by SCIO-469. Furthermore, reintroduction of chemokines CXCL10 and CCL8 to BMSCs overcomes the inhibitory effect of SCIO-469 on TNFalpha-induced MM adhesion. Lastly, we show that SCIO-469 inhibits secretion and expression of the osteoclast-activating factors IL-11, RANKL, and MIP-1alpha as well as prevents human osteoclast formation in vitro. Collectively, these results suggest that SCIO-469 treatment can suppress factors in the bone marrow microenvironment to inhibit MM cell proliferation and adhesion and also to alleviate osteolytic activation in MM.     

Requirement for NK cells in CD40 ligand-mediated rejection of Philadelphia chromosome-positive acute lymphoblastic leukemia cells.

We have previously developed a murine model of Philadelphia chromosome-positive acute lymphoblastic leukemia by i.v. injection of a pre-B ALL cell line (BM185) derived from Bcr-Abl-transformed BALB/c bone marrow. We are studying the potential to elicit autologous antileukemic immune responses by introducing genes encoding immunomodulators (CD40 ligand (CD40L), CD80, and GM-CSF) into leukemia cells. BM185 cells expressing CD40L or CD80 alone, when injected into BALB/c mice, were rejected in approximately 25% of mice, whereas cohorts receiving BM185 cells expressing two or more immunomodulator genes rejected challenge 50-76% of the time. The greatest protection was conferred in mice receiving BM185 cells expressing all three immunomodulators. Addition of murine rIL-12 treatments in conjunction with BM185/CD80/CD40L/GM-CSF vaccination allowed rejection of preestablished leukemia. BM185 cell lines expressing CD40L were rejected in BALB/c nu/nu (nude) mice, in contrast to cell lines expressing CD80 and/or GM-CSF. Nude mice depleted of NK cells were no longer protected when challenged with BM185/CD40L, demonstrating a requirement for NK cells. Similarly, NK cell depletion in immunocompetent BALB/c mice resulted in a loss of protection when challenged with BM185/CD40L, confirming the data seen in nude mice. The ability of CD40L to act in a T cell-independent manner may be important for clinical applications in patients with depressed cellular immunity following chemotherapy.     

Antisera to the secretory component recognize the murine Fc receptor for IgA

Studies were undertaken to determine a possible structural relationship between the secretory component (SC) and the receptor for IgA (Fc alpha R). An IgA-mediated rosetting technique was used to assess the presence of Fc alpha R+ cells in various lymphoid tissues from normal BALB/c mice and mice bearing an IgA plasmacytoma (MOPC 315). Tissues from the MOPC 315-bearing BALB/c mice were found to have a significantly higher percentage of Fc alpha R+ cells; thus, nonadherent spleen cells from MOPC 315-bearing mice were used as a source of Fc alpha R+ cells in these studies. The cells were preincubated with anti-SC and then assayed for the ability of IgA to bind to the Fc alpha R. Antisera to SC from various species inhibited the formation of IgA-mediated rosettes, although preincubation of the Fc alpha R+ cells with antisera directed against other cell surface molecules (e.g., Thy1.2, Lyt1, Lyt2, Fc gamma R, MHC class I and II) or preimmune sera had no significant effect on IgA-mediated rosette formation. Preabsorption of the anti-SC with secretory IgA or with free SC removed the inhibitory effect; preabsorption with myeloma IgA had no effect. These data suggest that SC and Fc alpha R are related serologically and may be structurally related, possible in the IgA-binding region.     

Neovascular niche for human myeloma cells in immunodeficient mouse bone

The interaction with bone marrow (BM) plays a crucial role in pathophysiological features of multiple myeloma (MM), including cell proliferation, chemoresistance, and bone lesion progression. To characterize the MM-BM interactions, we utilized an in vivo experimental model for human MM in which a GFP-expressing human MM cell line is transplanted into NOG mice (the NOG-hMM model). Transplanted MM cells preferentially engrafted at the metaphyseal region of the BM endosteum and formed a complex with osteoblasts and osteoclasts. A subpopulation of MM cells expressed VE-cadherin after transplantation and formed endothelial-like structures in the BM. CD138(+) myeloma cells in the BM were reduced by p53-dependent apoptosis following administration of the nitrogen mustard derivative bendamustine to mice in the NOG-hMM model. Bendamustine maintained the osteoblast lining on the bone surface and protected extracellular matrix structures. Furthermore, bendamustine suppressed the growth of osteoclasts and mesenchymal cells in the NOG-hMM model. Since VE-cadherin(+) MM cells were chemoresistant, hypoxic, and HIF-2α-positive compared to the VE-cadherin(-) population, VE-cadherin induction might depend on the oxygenation status. The NOG-hMM model described here is a useful system to analyze the dynamics of MM pathophysiology, interactions of MM cells with other cellular compartments, and the utility of novel anti-MM therapies.     

Cancer Cell Expression of Autotaxin Controls Bone Metastasis Formation in Mouse through Lysophosphatidic Acid-Dependent Activation of Osteoclasts

Background

Bone metastases are highly frequent complications of breast cancers. Current bone metastasis treatments using powerful anti-resorbtive agents are only palliative indicating that factors independent of bone resorption control bone metastasis progression. Autotaxin (ATX/NPP2) is a secreted protein with both oncogenic and pro-metastatic properties. Through its lysosphospholipase D (lysoPLD) activity, ATX controls the level of lysophosphatidic acid (LPA) in the blood. Platelet-derived LPA promotes the progression of osteolytic bone metastases of breast cancer cells. We asked whether ATX was involved in the bone metastasis process. We characterized the role of ATX in osteolytic bone metastasis formation by using genetically modified breast cancer cells exploited on different osteolytic bone metastasis mouse models.

Methodology/Principal Findings

Intravenous injection of human breast cancer MDA-B02 cells with forced expression of ATX (MDA-B02/ATX) to inmmunodeficiency BALB/C nude mice enhanced osteolytic bone metastasis formation, as judged by increased bone loss, tumor burden, and a higher number of active osteoclasts at the metastatic site. Mouse breast cancer 4T1 cells induced the formation of osteolytic bone metastases after intracardiac injection in immunocompetent BALB/C mice. These cells expressed active ATX and silencing ATX expression inhibited the extent of osteolytic bone lesions and decreased the number of active osteoclasts at the bone metastatic site. In vitro, osteoclast differentiation was enhanced in presence of MDA-B02/ATX cell conditioned media or recombinant autotaxin that was blocked by the autotaxin inhibitor vpc8a202. In vitro, addition of LPA to active charcoal-treated serum restored the capacity of the serum to support RANK-L/MCSF-induced osteoclastogenesis.

Conclusion/Significance

Expression of autotaxin by cancer cells controls osteolytic bone metastasis formation. This work demonstrates a new role for LPA as a factor that stimulates directly cancer growth and metastasis, and osteoclast differentiation. Therefore, targeting the autotaxin/LPA track emerges as a potential new therapeutic approach to improve the outcome of patients with bone metastases.     

The allogeneic effect on tumor growth. I. Inhibition of a murine plasmacytoma, MOPC 315, by the graft-vs-host reaction.

The allogeneic effect has been employed as a potent immunopotentiator in preventing the growth of a murine plasmacytoma and prolonging host survival. Parental BALB/c spleen cells were passively transferred to (BALB/c x A/H)F1 hybrid mice, who were then given a highly lethal dose of MOPC 315 plasmacytoma, a tumor of BALB/c origin. The resultant graft-vs-host reaction protected the recipient mice against growth of the tumor and significantly prolonged survival. This phenomenon was dependent upon the dose of BALB/c lymphoid cells employed, the route of administration, and the time interval between lymphoid cell transfer and tumor inoculation. A wide range of lymphoid cell doses and time intervals were effective, and repeated doses of allogeneic cells provided better protection than a single dose.     

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.     

Activation of immunoglobulin allotype-specific T cells by B cells

To investigate the role of Ia and immunoglobulin (Ig) molecules of B cells in alloantigen-specific and nominal antigen-specific T-cell activations, the ability of B cells to stimulate Ig allotype-specific T cells was examined. T15-primed B10.BR T cells responded to MOPC 315 (IgA myeloma protein derived from BALB/c) as well as T15 but not to MOPC31c (IgG, myeloma protein). These T cells were stimulated by papain-digested Fc fragment of T15. Thus, T15-primed B10.BR T cells were shown to be specific for Ig allotype of T15, that is, Igh-2a. T15-specific B10.BR T cells were selected by 10-day cultures with T15 in vitro. They responded to BALB.K spleen cells without addition of soluble T15 antigen to the assay culture. Stimulator cells in this mixed lymphocyte reaction (MLR)-like response between T15-specific B10.BR T cells and BALB.K spleen cells were Thy-1⁻, Ia⁺ cells and these responses were blocked by anti-Ia^κ antibodies. Furthermore, Sephadex G-10-passed BALB.K B cells stimulated the proliferation of T15-specific B10.BR T cells, while they failed to stimulate allogeneic BALB/c spleen cells. The stimulating ability of B cells in this MLR-like response of T15-specific B10.BR T cells was shown to be genetically restricted, namely, both H-2 and non-H-2 genes are involved in the manifestation of the stimulating ability. This system will provide a useful model for studying the role of B-cell surface Ig and Ia molecules in the activation of antigen-specific T cells and alloreactive T cells.     

Sex and Genetic Factors Determine Osteoblastic Differentiation Potential of Murine Bone Marrow Stromal Cells

Sex and genetic factors determine skeletal mass, and we tested whether bone histomorphometric parameters were sexually dimorphic in femurs from 1 to 6 month old C57BL/6 mice. Trabecular bone volume declined more rapidly in female mice than in male littermates because of enhanced bone resorption. Although bone formation was not different between sexes, female mice exhibited a higher number of osteoblasts than male littermates, suggesting that osteoblasts from female mice may have a reduced ability to form bone. To determine the impact of sex on osteoblastogenesis, we investigated the potential for osteoblastic differentiation of bone marrow stromal cells from C57BL/6, Friend leukemia virus-B (FVB), C3H/HeJ and BALB/c mice of both sexes. Bone marrow stromal cells from female FVB, C57BL/6 and C3H/HeJ mice exhibited lower Alpl and Osteocalcin expression and alkaline phosphatase activity, and formed fewer mineralized nodules than cells from male littermates. Proliferative capacity was greater in cells from male than female C57BL/6, but not FVB, mice. Sorting of bone marrow stromal cells from mice expressing an α-Smooth muscle actin-green fluorescent protein transgene, revealed a higher yield of mesenchymal stem cells in cultures from male mice than in those from female littermates. Sex had a modest impact on osteoblastic differentiation of mesenchymal stem cells. To determine the influence of sex and genetic factors on osteoblast function, calvarial osteoblasts were harvested from C57BL/6, FVB, C3H/HeJ and BALB/c mice. Alpl expression and activity were lower in osteoblasts from C57BL/6 and C3H/HeJ, but not FVB or BALB/c, female mice than in cells from littermates. Sex had no effect on osteoclastogenesis of bone marrow cultures of C57BL/6 mice, but osteoblasts from female mice exhibited higher Rankl and lower Opg expression than cells from male littermates. In conclusion, osteoblastogenesis is sexually dimorphic and influenced by genetic factors.     

Properties of Immature Myeloid Progenitors with Nitric-Oxide-Dependent Immunosuppressive Activity Isolated from Bone Marrow of Tumor-Free Mice

Myeloid derived suppressor cells (MDSCs) from tumor-bearing mice are important negative regulators of anti-cancer immune responses, but the role for immature myeloid cells (IMCs) in non-tumor-bearing mice in the regulation of immune responses are poorly described. We studied the immune-suppressive activity of IMCs from the bone marrow (BM) of C57Bl/6 mice and the mechanism(s) by which they inhibit T–cell activation and proliferation. IMCs, isolated from BM by high-speed FACS, inhibited mitogen-induced proliferation of CD4⁺ and CD8⁺ T-cells in vitro. Cell-to-cell contact of T-cells with viable IMCs was required for suppression. Neither neutralizing antibodies to TGFβ1, nor genetic disruption of indolamine 2,3-dioxygenase, abrogated IMC-mediated suppressive activity. In contrast, suppression of T-cell proliferation was absent in cultures containing IMCs from interferon-γ (IFN-γ) receptor KO mice or T-cells from IFN-γ KO mice (on the C57Bl/6 background). The addition of NO inhibitors to co-cultures of T-cells and IMC significantly reduced the suppressive activity of IMCs. IFN-γ signaling between T-cells and IMCs induced paracrine Nitric Oxide (NO) release in culture, and the degree of inhibition of T-cell proliferation was proportional to NO levels. The suppressive activity of IMCs from the bone marrow of tumor-free mice was comparable with MDSCs from BALB/c bearing mice 4T1 mammary tumors. These results indicate that IMCs have a role in regulating T-cell activation and proliferation in the BM microenvironment.     

Soluble rank ligand produced by myeloma cells causes generalised bone loss in multiple myeloma

Patients with multiple myeloma commonly develop focal osteolytic bone disease, as well as generalised osteoporosis. The mechanisms underlying the development of osteoporosis in patients with myeloma are poorly understood. Although disruption of the RANKL/OPG pathway has been shown to underlie formation of focal osteolytic lesions, its role in the development of osteoporosis in myeloma remains unclear. Increased soluble RANKL in serum from patients with myeloma raises the possibility that this molecule plays a key role. The aim of the present study was to establish whether sRANKL produced by myeloma cells contributes directly to osteoporosis. C57BL/KaLwRij mice were injected with either 5T2MM or 5T33MM murine myeloma cells. 5T2MM-bearing mice developed osteolytic bone lesions (p<0.05) with increased osteoclast surface (p<0.01) and reduced trabecular bone volume (p<0.05). Bone volume was also reduced at sites where 5T2MM cells were not present (p<0.05). In 5T2MM-bearing mice soluble mRANKL was increased (p<0.05), whereas OPG was not altered. In contrast, 5T33MM-bearing mice had no changes in osteoclast surface or trabecular bone volume and did not develop osteolytic lesions. Soluble mRANKL was undetectable in serum from 5T33MM-bearing mice. In separate experiments, RPMI-8226 human myeloma cells were transduced with an human RANKL/eGFP construct, or eGFP alone. RPMI-8226/hRANKL/eGFP cells, but not RPMI-8226/eGFP cells, stimulated osteoclastic bone resorption (p<0.05) in vitro. Sub-cutaneous injection of NOD/SCID mice with RPMI-8226/hRANKL/eGFP or RPMI-8226/eGFP cells resulted in tumour development in all mice. RPMI-8226/hRANKL/eGFP-bearing mice exhibited increased serum soluble hRANKL (p<0.05) and a three-fold increase in osteoclast number (p<0.05) compared to RPMI-8226/eGFP-bearing mice. This was associated with reduced trabecular bone volume (27%, p<0.05), decreased trabecular number (29%, p<0.05) and increased trabecular thickness (8%, p<0.05). Our findings demonstrate that soluble RANKL produced by myeloma cells causes generalised bone loss, suggesting that targeting RANKL may prevent osteoporosis in patients with myeloma.     

RANKL from bone marrow adipose lineage cells promotes osteoclast formation and bone loss

Receptor activator of NF‐κB ligand (RANKL) is essential for osteoclast formation and bone remodeling. Nevertheless, the cellular source of RANKL for osteoclastogenesis has not been fully uncovered. Different from peripheral adipose tissue, bone marrow (BM) adipose lineage cells originate from bone marrow mesenchymal stromal cells (BMSCs). Here, we demonstrate that adiponectin promoter‐driven Cre expression (Adipoq^Cre ) can target bone marrow adipose lineage cells. We cross the Adipoq^Cre mice with rankl^fl/fl mice to conditionally delete RANKL from BM adipose lineage cells. Conditional deletion of RANKL increases cancellous bone mass of long bones in mice by reducing the formation of trabecular osteoclasts and inhibiting bone resorption but does not affect cortical bone thickness or resorption of calcified cartilage. Adipoq^Cre; rankl^fl/fl mice exhibit resistance to estrogen deficiency and rosiglitazone (ROS)‐induced trabecular bone loss but show bone loss induced by unloading. BM adipose lineage cells therefore represent an essential source of RANKL for the formation of trabecula osteoclasts and resorption of cancellous bone during remodeling under physiological and pathological conditions. Targeting bone marrow adiposity is a promising way of preventing pathological bone loss.     

Induction of B-Cell Lymphoma in BALB/c Nude Mice with an Ecotropic, B-Tropic Helper Virus Present in the Murine AIDS Virus Stock

The pathogenicities of the murine AIDS (MAIDS) virus complex (LP-BM5) and ecotropic helper virus (BM5eco) isolated from the complex to BALB/c nude mice were studied to elucidate the possible role of replication-competent helper virus in inducing the monoclonal outgrowth of lymphoid cells. Neither LP-BM5 nor BM5eco was pathogenic in adult BALB/c nude mice. However, B-cell lymphoma developed with a very high frequency when either virus was inoculated into newborn BALB/c nude (nu/nu) mice. The cells from the B-cell lymphoma were easily transplanted into nude mice. These results suggested that ecotropic helper virus in the MAIDS virus complex plays an important role in inducing the monoclonal outgrowth of lymphoid cells under immunodeficient conditions caused by defective virus.     

Serglycin Proteoglycan Is Required for Multiple Myeloma Cell Adhesion,in Vivo Growth,and Vascularization

Recently, it was discovered that serglycin, a hematopoietic cell proteoglycan, is the major proteoglycan expressed and constitutively secreted by multiple myeloma (MM) cells. High levels of serglycin are present in the bone marrow aspirates of at least 30% of newly diagnosed MM patients. However, its contribution to the pathophysiology of MM is unknown. Here, we show that serglycin knockdown (by ∼85% compared with normal levels), using lentiviral shRNA, dramatically attenuated MM tumor growth in mice with severe combined immunodeficiency. Tumors formed from cells deficient in serglycin exhibited diminished levels of hepatocyte growth factor expression and impaired development of blood vessels, indicating that serglycin may affect tumor angiogenesis. Furthermore, knockdown of serglycin significantly decreased MM cell adhesion to bone marrow stromal cells and collagen I. Even though serglycin proteoglycan does not have a transmembrane domain, flow cytometry showed that serglycin is present on the MM cell surface, and attachment to the cell surface is, at least in part, dependent on its chondroitin sulfate side chains. Co-precipitation of serglycin from conditioned medium of MM cells using a CD44-Fc chimera suggests that CD44 is the cell surface-binding partner for serglycin, which therefore may serve as a major ligand for CD44 at various stages during myeloma progression. Finally, we demonstrate that serglycin mRNA expression in MM cells is up-regulated by activin, a predominant cytokine among those increased in MM patients with osteolytic lesions. These studies provide direct evidence for a critical role for serglycin in MM pathogenesis and show that targeting serglycin may provide a novel therapeutic approach for MM.     

A Dominant Trait Linked to Chromosome 1 in DBA/2 Mice for the Resistance to Autoimmune Gastritis Appears in Bone Marrow Cells

Neonatal thymectomy (NTx) induces autoimmune gastritis (AIG) in BALB/c mice, a model for human type A chronic atrophic gastritis, but not in DBA/2 mice and rarely in CDF1 mice (a hybrid of BALB/c and DBA/2 mice). The aim of this study was to clarify the mechanisms of AIG-resistance in mice bearing the dominant trait of DBA/2. Linkage groups associated with, and cells related to AIG resistance were examined with CDF1-BALB/c backcrosses. Intracellular staining and flow-cytometric bead array for several cytokines were performed on NTx BALB/c mice and NTx DBA/2-chimeric BALB/c mice receiving DBA/2-bone marrow cells. In NTx BALB/c mice, IFN-γ-secreting CD4⁺ T cells were increased, but not in NTx DBA/2 mice. Because Vβ6⁺ T cell-bearing mice of half of their backcrosses developed AIG, but the other half of Vβ6⁺ T cell-negative mice developed scarcely, resistance for AIG generation is associated with the presence of the Mls-1a locus on chromosome 1 in DBA/2 mice, which deletes Vβ6⁺ T cells. NTx DBA/2-chimera BALB/c mice showed dominant production of IL-10 and resistance for AIG, although the deletion of Vβ6⁺ T cells was found not to be a cause of AIG-resistance from Mls-1a locus segregation experiments. Although NTx DBA/2-chimeric BALB/c mice did not suffer from AIG, they brought immediate precursors of T cells for AIG. It is concluded that DBA/2 mice generate bone marrow-derived cells that produce anti-inflammatory cytokines to prevent the activation of AIG-T cells.     

Comparison of the ease of tolerance induction in thymus and bone marrow of three strains of mice

Three strains of mice which vary in their susceptibility to induction of immune tolerance with human gamma-globulin were studied to evaluate the cellular basis for their sensitivity to induction of the unresponsive state. Tolerance induction in BALB/c mice was difficult to establish, while tolerance induction was easily achieved in C57BL/6 and CBF₁ (BALB/c × C57BL/6) mice. The degree of unresponsiveness obtained with various tolerogen doses in intact C57BL/6 and CBF₁ mice was reflected in the sensitivity of their thymocytes to the production of the unresponsive state. In the BALB/c mouse strain slight immune suppression observed at low tolerogen doses was correlated with bone marrow cell unresponsiveness while significant levels of tolerance observed at a high tolerogen dose was due to suppression of thymus cells. It was apparent that CBF₁ mice had inherited both thymus cells and bone marrow cells which exhibited the sensitivity to induction of immune tolerance characteristic of those same cells of their C57BL/6 parent.