Immunoglobulin VH gene sequence analysis of spontaneous murine immunoglobulin-secreting B-cell tumours with clinical features of human disease

Involvement of activation induced cytidine deaminase in malignant B-cells expressing two distinct M-components as an etiology of biclonal gammopathy

Biclonal gammopathy (BG) is a rare phenomenon in which 2 M proteins are detected in the same patient, with 2 major hypotheses regarding its etiology. One potential explanation is that completely different malignant B-cell clones produce different M proteins, while the other is that there is a malignant clone that produces both M proteins simultaneously. In this study, we examined 2 cases of B-cell malignancy with BG and found that some cells were double positive for both M proteins by immunofluorescence and flow cytometry. However, most of the remaining cells were single positive cells that produced only one of the M proteins. We hypothesized that double positive cells were in the process of transitioning from 1 single positive cell to another single positive cell, and that class switch recombination (CSR) would be involved as a mechanism. We then examined the expression of activation induced cytidine deaminase (AICDA), which is responsible for CSR, and found that lymphoma/myeloma cells in 2 BG patients were positive for AICDA by immunostaining. Our study is the first report suggesting that AICDA may be involved in the pathogenesis of BG.

Runx2 Suppression by miR-342 and miR-363 Inhibits Multiple Myeloma Progression

In multiple myeloma, abnormal plasma cells accumulate and proliferate in the bone marrow. Recently, we observed that Runx2, a bone-specific transcription factor, is highly expressed in multiple myeloma cells and is a major driver of multiple myeloma progression in bone. The primary goal of the present study was to identify Runx2-targeting miRNAs that can reduce tumor growth. Expression analysis of a panel of miRNAs in multiple myeloma patient specimens, compared with healthy control specimens, revealed that metastatic multiple myeloma cells express low levels of miR-342 and miR-363 but high levels of Runx2. Reconstituting multiple myeloma cells (CAG) with miR-342 and miR-363 reduced the abundance of Runx2 and the expression of metastasis-promoting Runx2 target genes RANKL and DKK1, and suppressed Runx2 downstream signaling pathways Akt/β-catenin/survivin, which are required for multiple myeloma tumor progression. Intravenous injection of multiple myeloma cells (5TGM1), stably overexpressing miR-342 and miR-363 alone or together, into syngeneic C57Bl/KaLwRij mice resulted in a significant suppression of 5TGM1 cell growth, decreased osteoclasts and increased osteoblasts, and increased antitumor immunity in the bone marrow, compared with mice injected with 5TGM1 cells expressing a miR-Scramble control. In summary, these results demonstrate that enhanced expression of miR-342 and miR-363 in multiple myeloma cells inhibits Runx2 expression and multiple myeloma growth, decreases osteolysis, and enhances antitumor immunity. Thus, restoring the function of Runx2-targeting by miR-342 and miR-363 in multiple myeloma cells may afford a therapeutic benefit by preventing multiple myeloma progression.Implications: miR-342 and miR-363-mediated downregulation of Runx2 expression in multiple myeloma cells prevents multiple myeloma progression. Mol Cancer Res; 16(7); 1138-48. ©2018 AACR.

Myeloma cell-derived Runx2 promotes myeloma progression in bone

The progression of multiple myeloma (MM) is governed by a network of molecular signals, the majority of which remain to be identified. Recent studies suggest that Runt-related transcription factor 2 (Runx2), a well-known bone-specific transcription factor, is also expressed in solid tumors, where expression promotes both bone metastasis and osteolysis. However, the function of Runx2 in MM remains unknown. The current study demonstrated that (1) Runx2 expression in primary human MM cells is significantly greater than in plasma cells from healthy donors and patients with monoclonal gammopathy of undetermined significance; (2) high levels of Runx2 expression in MM cells are associated with a high-risk population of MM patients; and (3) overexpression of Runx2 in MM cells enhanced tumor growth and disease progression in vivo. Additional studies demonstrated that MM cell-derived Runx2 promotes tumor progression through a mechanism involving the upregulation of Akt/β-catenin/Survivin signaling and enhanced expression of multiple metastatic genes/proteins, as well as the induction of a bone-resident cell-like phenotype in MM cells. Thus, Runx2 expression supports the aggressive phenotype of MM and is correlated with poor prognosis. These data implicate Runx2 expression as a major regulator of MM progression in bone and myeloma bone disease.

Mouse models of human myeloma

Multiple myeloma (MM) remains incurable despite high-dose chemotherapy with stem cell support. There is need, therefore, for continuous efforts directed toward the development of novel rational-based therapeutics for MM, which requires a detailed knowledge of the mutations driving this malignancy. In improving the success rate of effective drug development, it is equally imperative that biologic systems be developed to better validate these target genes. Here we review the recent developments in the generation of mouse models of MM and their impact as preclinical models for designing and assessing target-based therapeutic approaches.

Detection of myeloma in skeleton of mice by whole-body optical fluorescence imaging

Development of new therapies for myeloma has been hindered by the lack of suitable preclinical animal models of the disease in which widespread tumor foci in the skeleton can be detected reliably. Traditional means of detecting skeletal tumor infiltration such as histopathology are cumbersome and labor-intensive and do not allow temporal monitoring of tumor progression or regression in response to therapy. To resolve this problem, we modified the Radl 5TGM1 model of myeloma bone disease such that fluorescent myeloma tumors can be optically imaged in situ. Here, we show that murine myeloma 5TGM1 tumor cells, engineered to express enhanced green fluorescent protein (eGFP; 5TGM1-eGFP cells), can be imaged in a temporal fashion using a fluorescence illuminator and a charge-coupled device camera in skeletons of live C57BL/KaLwRij mice. High-resolution, whole-body images of tumor-bearing mice revealed that myeloma cells homed almost exclusively to the skeleton, with multiple focal tumor foci in the axial skeleton, consistent with myeloma tumor distribution in humans. Finally, the tested antitumor treatment effect of Velcade (bortezomib), a proteasome inhibitor used clinically in myeloma, was readily detected by GFP imaging, suggesting the power of the technique in combination with the Radl 5TGM1-eGFP model for rapid preclinical assessment and sensitive monitoring of novel and potential therapeutics. Whole-body GFP imaging is practical, convenient, inexpensive, and rapid, and these advantages should enable a high throughput when evaluating in vivo efficacy of new potential antimyeloma therapeutics and assessing response to treatment.

Endothelial cell-driven regulation of CD9 or motility-related protein-1 expression in multiple myeloma cells within the murine 5T33MM model and myeloma patients

The cell surface expression of CD9, a glycoprotein of the tetraspanin family influencing several processes including cell motility and metastasis, inversely correlates with progression in several solid tumors. In the present work, we studied the expression and role of CD9 in multiple myeloma (MM) biology using the 5T33MM mouse model. The 5T33MMvitro cells were found to be CD9 negative. Injection of these cells in mice caused upregulation of CD9 expression, while reculturing them resulted in downregulation of CD9. Coculturing of CD9-negative 5T33MMvitro cells with BM endothelial cells (BMECs) resulted in a partial retrieval of CD9. Laser microdissection followed by real-time polymerase chain reaction and immunohistochemistry performed on bone sections of 5T33MMvivo diseased mice demonstrated strong local expression of CD9 on MM cells in contact with BMEC compared to MM cells further away. These findings were also confirmed by immunohistochemistry in MM patients. Neutralizing anti-CD9 antibodies inhibited transendothelial invasion of CD9-expressing human MM5.1 and murine 5T33MMvivo cells. In conclusion, we provide evidence that CD9 expression by the MM cells is upregulated in vivo by close interaction of the cells with BMEC and that CD9 is involved in transendothelial invasion, thus possibly mediating homing and/or spreading of the MM cells.

Inhibition of a vaccine-induced anti-tumor B cell response by soluble protein antigen in the absence of continuing T cell help

DNA vaccination can elicit the production of anti-tumor antibodies, thus obviating the need to continuously administer passive antibody. This vaccination strategy is particularly important where antibodies have proven to be effective anti-tumor agents. To amplify antibody responses against weak tumor antigens, we previously designed DNA-fusion vaccines incorporating tumor sequences linked to microbial genes. By using a safe idiotypic (Id) antigen from a B cell tumor fused to a fragment C (FrC) sequence from tetanus toxin, we induced both anti-Id and anti-FrC antibodies. It was important to determine whether the antigen itself, either injected or released from residual tumor cells, would boost the antibody response. Id protein not only failed to boost the response, but permanently and rapidly inhibited it by ablating Id-specific memory B cells. In contrast, an Id protein-FrC conjugate boosted both Id-specific and FrC-specific responses. Strikingly, the depletion of CD4+ T cells converted the Id protein-FrC conjugate vaccine into an inhibitor. These findings support the hypothesis that the activation of memory B cells by a DNA vaccine encoding a protein antigen, in the presence of the protein itself, depends completely on T cell help. Furthermore, by using knockout mice, we have shown that inhibition of the Id-specific memory B cells by the Id protein is largely independent of the FcgammaRIIB and, hence, independent of immune complexes. The principles revealed by using a DNA vaccine have implications for all cancer vaccines designed to induce and maintain antibody responses against weak autologous tumor antigens.

Deregulated expression of the Myc cellular oncogene drives development of mouse “Burkitt-like” lymphomas from naive B cells

Chromosomal translocations juxtaposing immunoglobulin (Ig) and MYC genes are the hallmarks of human Burkitt lymphoma (BL), with deregulated MYC expression being a critical factor in pathogenesis. By inserting an intact mouse Myc gene into the mouse genome, proximal to the Ig enhancer Eμ, the effect of a precise mimic of the major t(8;14) translocation of human endemic BL (eBL) could be investigated. Knock-in mice developed IgM-positive B-cell tumors, with most being typical of eBL by histology and immunophenotype, including expression of the germinal center (GC)–associated protein, BCL6. Unlike eBL, however, analysis of Ig VH sequences revealed no significant level of somatic mutation. Thus, constitutive expression of Myc in the knock-in mice is apparently able to induce “Burkitt-like” lymphomas before antigen stimulation and formation of a GC. In contrast, human eBL development occurs in a GC or post-GC site with a likely contribution to pathogenesis from Epstein-Barr virus (EBV) and other epigenetic factors.

Visualization of 5T33 myeloma cells in the C57BL/KaLwRij mouse: establishment of a new syngeneic murine model of multiple myeloma

OBJECTIVE

Lack of good models for in vivo detection of multiple myeloma (MM) cells hampers our understanding of the disease. Our objective was to establish a murine model for MM, allowing sensitive and labor-free tracing and quantification of MM cells in an immunocompetent host.

METHODS

5T33MM cells were retrovirally transduced, expressing enhanced green fluorescent protein (eGFP) and/or herpes simplex virus thymidine kinase (HSV-tk) as a control. Flow cytometric eGFP detection accuracy and sensitivity were assessed. Functional characteristics of transduced cells, including growth rate and production of IgG2b paraprotein and interleukin-6, were compared to those of nontransduced cells in vitro. For induction of MM, C57BL/KaLwRij mice were injected intravenously with transduced and nontransduced cells. Survival kinetics and distribution of eGFP cells in tissues were evaluated.

RESULTS

Flow cytometric eGFP detection was accurate at 1:1000 transduced/nontransduced cell ratio. Transduced and nontransduced 5T33MM cells exhibited similar growth rates, producing comparable IgG2b and interleukin-6 levels. Intravenous injection of both nontransduced and eGFP-transduced MM cells to C57BL/KaLwRij mice resulted in paraplegia. At the time of paraplegia, eGFP-transduced MM cells were detected substantially in the bone marrow, spleen, and liver, less in lymph nodes, but not in the thymus. The bone marrow of paraplegic mice contained higher eGFP-transduced MM cells compared to that of nonparaplegic animals.

CONCLUSIONS

In the established eGFP-5T33 MM model, MM cells are easily traced in an immunocompetent host. This model simplifies the analysis of homing pattern studies, the evaluation of therapeutic effects of various treatment approaches and contributes towards better understanding of MM.

Dual effects of macrophage inflammatory protein-1alpha on osteolysis and tumor burden in the murine 5TGM1 model of myeloma bone disease

Recent data have implicated macrophage inflammatory protein-1alpha (MIP-1alpha) in multiple myeloma (MM)-associated osteolysis. However, it is unclear whether the chemokine's effects are direct, to enhance osteolysis, or indirect and mediated through a reduction in tumor burden, or both. It is also unclear whether MIP-1alpha requires other factors such as receptor activator of nuclear factor-kappaB ligand (RANKL) for its effects on bone. In murine 5TGM1 (Radl) myeloma-bearing mice, administration of neutralizing anti-MIP-1alpha antibodies reduced tumor load assessed by monoclonal paraprotein titers, prevented splenomegaly, limited development of osteolytic lesions, and concomitantly reduced tumor growth in bone. To determine the effects of MIP-1alpha on bone in vivo, Chinese hamster ovary (CHO) cells secreting human MIP-1alpha (CHO/MIP-1alpha) were inoculated into athymic mice. Mice bearing intramuscular CHO/MIP-1alpha tumors developed lytic lesions at distant skeletal sites, which occurred earlier and were larger than those in mice with CHO/empty vector (EV) tumors. When experimental metastases were induced via intracardiac inoculation, mice bearing CHO/MIP-1alpha tumors developed hypercalcemia and significantly more osteolytic lesions than mice bearing CHO/EV tumors, with intramedullary CHO/MIP-1alpha tumors associated with significantly more tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts. Injection of recombinant MIP-1alpha over calvariae of normal mice evoked a striking increase in osteoclast formation, an effect dependent on RANK/RANKL signaling because MIP-1alpha had no effect in RANK-/- mice. Together, these results establish that MIP-1alpha is sufficient to induce MM-like destructive lesions in bone in vivo. Because, in the 5TGM1 model, blockade of osteoclastic resorption in other situations does not decrease tumor burden, we conclude that MIP-1alpha exerts a dual effect in myeloma, on osteoclasts, and tumor cells.

Acquisition of potential N-glycosylation sites in the immunoglobulin variable region by somatic mutation is a distinctive feature of follicular lymphoma

Most patients with follicular lymphoma (FL) have somatically mutated V genes with intraclonal variation, consistent with location in the germinal center site. Using our own and published sequences, we have investigated the frequency of potential N-glycosylation sites introduced into functional V(H) genes as a consequence of somatic mutation. FL cells were compared with normal memory B cells or plasma cells matched for similar levels of mutation. Strikingly, novel sites were detected in 55 of 70 (79%) patients with FL, compared to 7 of 75 (9%) in the normal B-cell population (P <.001). Diffuse large B-cell lymphoma (DLCL) showed an intermediate frequency (13 of 32 [41%] patients). Myeloma and the mutated subset of chronic lymphocytic leukemia showed frequencies similar to those of normal cells in 5 of 64 (8%) patients and 5 of 40 (13%) patients, respectively. In 3 of 3 random patients with FL, immunoglobulin was expressed as recombinant single-chain Fv in Pichia pastoris, and glycosylation was demonstrated. These findings indicate that N-glycosylation of the variable region may be common in FL and in a subset of DLCL. Most novel sites are located in the complementarity-determining regions. V(H) sequences of nonfunctional V(H) genes contained few sites, arguing for positive selection in FL. One possibility is that the added carbohydrate in the variable region contributes to interaction with elements in the germinal center environment. This common feature of FL may be critical for tumor behavior.

The occurrence and significance of V gene mutations in B cell-derived human malignancy

The classification of B cell tumors has relevance for refining and improving clinical strategies. However, consensus has been difficult to establish, and although a scheme is now available, objective criteria are desirable. Genetic technology will underpin and extend current knowledge, and it is certain to reveal further subdivisions of current tumor categories. The Ig variable region genes of B cell tumors present a considerable asset for this area of investigation. The unique sequences carried in neoplastic B cells are easily isolated and sequenced. In addition to acting as clone-specific markers of each tumor, they indicate where the cell has come from and track its history following transformation. There is emerging clinical value in knowing whether the cell of origin has encountered antigen and has moved from the naive compartment to the germinal center, where somatic mutation is activated. This is amply illustrated by the subdivision of chronic lymphocytic leukemia into two subsets, unmutated or mutated, each with very different prognosis. Other tumors may be subdivided in a similar way. Microarray technology is developing rapidly to probe gene expression and to further divide tumor categories. All these genetic analyses will provide objective data to enhance both our understanding of B cell tumors and our ability to treat them.

Multiple myeloma: evolving genetic events and host interactions

Multiple myeloma is a neoplasm of terminally differentiated B cells (plasma cells) in which chromosome translocations frequently place oncogenes under the control of immunoglobulin enhancers. Unlike most haematopoietic cancers, multiple myeloma often has complex chromosomal abnormalities that are reminiscent of epithelial tumours. What causes full-blown myeloma? And can our molecular understanding of this common haematological malignancy be used to develop effective preventive and treatment strategies?

Plant viral genes in DNA idiotypic vaccines activate linked CD4+ T-cell mediated immunity against B-cell malignancies

DNA delivery of tumor antigens can activate specific immune attack on cancer cells. However, antigens may be weak, and immune capacity can be compromised. Fusion of genes encoding activating sequences to the tumor antigen sequence facilitates promotion and manipulation of effector pathways. Idiotypic determinants of B-cell tumors, encoded by the variable region genes, are clone-specific tumor antigens. When assembled as single-chain Fv (scFv) alone in a DNA vaccine, immunogenicity is low. Previously, we found that fusion of a sequence from tetanus toxin (fragment C; FrC) promoted anti-idiotypic protection against lymphoma and myeloma. We have now investigated an alternative fusion gene derived from a plant virus, potato virus X coat protein, a primary antigen in humans. When fused to scFv, the self-aggregating protein generates protection against lymphoma and myeloma. In contrast to scFv-FrC, protection against lymphoma is mediated by CD4+ T cells, as is protection against myeloma. Plant viral proteins offer new opportunities to activate immunity against linked T-cell epitopes to attack cancer.

Myeloma isotype-switch variants in the murine 5T myeloma model: evidence that myeloma IgM and IgA expressing subclones can originate from the IgG expressing tumour

Isotype-switch variants can easily be detected in a significant proportion of multiple myeloma (MM) patients. The biological significance of these isotype-switch variants remains obscure. Therefore, we studied the appearance of these isotype-switch variants in two murine MM models, 5T2MM and 5T33MM, both of IgG isotype. With a MM-specific PCR assay we could detect isotype-switch variants in the bone marrow of both the 5T2MM and the 5T33MM bearing mice, reflecting again the close resemblance of this mouse model to the human MM. These isotype-switch variants were not found in an in vitro stroma-independent variant of the 5T33MM line. However, when this 5T33MMvitro line was injected into young syngeneic mice, isotype-switch variants appeared thereafter in the isolated tumour cells. These isotype-switch variants could only originate from the MM-IgG expressing cell since IgG subclones from the 5T33MMvitro line again gave rise to isotype-switch variants. The appearance of IgA cells can be explained by down-stream switching of IgG to IgA, while the emergence of IgM cells have to occur via trans-switching to the sister chromatid as the Cmu region is deleted from the CIS-chromosome. This study demonstrates that isotype-switch variants originate from the major tumour clone suggesting no role for the MM-IgM expressing cell as a pre-switch precursor MM cell. The appearance of isotype-switch variants should be considered as a rare but normal event now becoming visible due to the high number of clonal cells present in MM.

Overpassing an aberrant V(kappa) gene to sequence an anti-idiotypic abzyme with (beta)-lactamase-like activity that could have a linkage with autoimmune diseases

A monoclonal antibody 9G4H9 that exhibits a beta-lactamase-like activity was previously obtained in accordance with the idiotypic network theory. This abzyme presents the most catalytic efficiency in amidase activity described in literature (kcat = 0.9 min-1). Some reports have demonstrated that functionality as complex as catalysis may be mimicked in this way. Comparison of the catalytic properties of both enzyme and abzyme previously allowed us to obtain better knowledge about 9G4H9 abzymatic machinery. In attempt to characterize this abzyme, the variable regions of kappa and heavy chain were cloned. We present a 'universal' method to clone the correct Vkappa gene to bypass aberrant Vkappa (abVkappa) produced by MOPC-21-derived hybridomas. Sequences obtained are compared in the GenBank database. The VH and Vkappa genes present some important sequence homology with autoantibodies suggesting a direct relationship between catalytic anti-idiotypic antibody and autoimmunity.

Absence of herpesvirus DNA sequences in the 5T murine model of human multiple myeloma

Kaposi's sarcoma-associated herpesvirus (KSHV, also known as HHV-8) has been found in patients with multiple myeloma (MM) and postulated to be aetiologically associated with the development of this common plasma cell malignancy. A murine model of MM was previously established in which intravenous transfer of 5T myeloma cells into C57BL/KaLwRij mice resulted in characteristic features of human MM. In the present study, we sought to identify herpesvirus DNA sequences in this murine model of MM through polymerase chain reaction (PCR) analysis using primers specific for KSHV, murine herpesvirus 68 (MHV68) and murine cytomegalovirus (MCMV) as well as consensus primers designed from the highly conserved DNA polymerase genes of the Herpesviridae family. None of the DNA samples from whole bone marrow (n = 6) or dendritic cells enriched by long-term culture (n = 8) of 5T myeloma-bearing mice as well as the 5T myeloma cell lines (n = 3) maintained in long-term culture yielded specific amplification products in any of the PCR assays. Two KSHV-specific serological assays measuring antibodies to KSHV latent and lytic antigens also failed to detect the presence of anti-KSHV antibodies in mice that developed MM. These results suggest that the development of 5T murine MM is unlikely to be involved with KSHV or a KSHV-like murine herpesvirus.

Selective initial in vivo homing pattern of 5T2 multiple myeloma cells in the C57BL/KalwRij mouse

One of the main characteristics of multiple myeloma cells is their predominant localization in the bone marrow. It is, however, unclear whether this is due to a selective initial entry, or whether this entry is more random and other processes like survival and/or growth stimulation, only present in the medullar microenvironment, are unique. To investigate this, in vivo homing kinetics of murine 5T2MM cells shortly after injection were assessed in bone marrow, liver, spleen, lungs, heart, intestines, kidney and testis by tracing of radiolabelled cells, by immunostaining of isolated cells and by polymerase chain reaction analysis. We demonstrated the presence of 5T2MM cells in bone marrow, spleen and liver with all other organs being negative. Adhesion assays of 5T2MM cells to different types of endothelial cells demonstrated a selective adhesion of 5T2MM cells to bone marrow and liver and not to lung endothelial cells. We here demonstrate that the specific in vivo localization of the 5T2MM cells is a result of the combination of a selective entry/adhesion of the 5T2MM cells in the bone marrow, spleen and liver, and a selective survival and growth of these tumour cells in the bone marrow and spleen but not in the liver.

DNA vaccines with single-chain Fv fused to fragment C of tetanus toxin induce protective immunity against lymphoma and myeloma

Vaccination with idiotypic protein protects against B-cell lymphoma, mainly through anti-idiotypic antibody. For use in patients, DNA vaccines containing single-chain Fv derived from tumor provide a convenient alternative vaccine delivery system. However, single-chain Fv sequence alone induces low anti-idiotypic response and poor protection against lymphoma. Fusion of the gene encoding fragment C of tetanus toxin to single-chain Fv substantially promotes the anti-idiotypic response and induces strong protection against B-cell lymphoma. The same fusion design also induces protective immunity against a surface Ig-negative myeloma. These findings indicate that fusion to a pathogen sequence allows a tumor antigen to engage diverse immune mechanisms that suppress growth. This fusion design has the added advantage of overcoming potential tolerance to tumor that may exist in patients.