Quantification of Dendritic Cells and Osteoclasts in the Bone Marrow of Patients with Monoclonal Gammopathy

Microbial antigens-loaded myeloma cells enhance Th2 cell proliferation and myeloma clonogenicity via Th2-myeloma cell interaction

Background

Myeloma cells retain B cell functions, considered to be potential antigen presenting cells, yet there is little information regarding promoting Th2 cell proliferation or the direct effects to myeloma on the Th2 cells stimulated by microbial antigens-loaded myeloma cells.

Methods

Mixed lymphocyte reaction was used colorimetric assays via CCK8-kit. Surface molecular expression was performed by flow cytometry, cells sorting using microbeads. The concentrations of cytokines in serum were assessed using an ELISA kit. Clonogenic assay were performed in a methylcellulose culture system. Statistical analysis was assessed using the Student’s t-test or one-way analysis of variance for multiple comparisons test.

Results

The expression of HLA-DR, CD80 and CD40 on RPMI8266 cell membrane surface was upregulated by interaction with interferon-γ and/or Bacillus Calmette-Guerin Vaccine (BCGV). RPMI8266 cells were able to induce the mixed lymphocyte reaction in a dose-dependent fashion. The Th2 ratio induced by RPMI8266 treated by BCGV and interferon-γ (treated-RPMI8266) cells was only slightly greater than by untreated-tumor cells, but the serum IL-4 level secreted by Th2 cells was markedly higher in treated-RPMI8266 cells group. Th2 cells stimulated by treated-myeloma cells could directly promote treated-myeloma cell clonogenicity in a dose-dependent manner. Anti-HLADR IgG2b completely blocked increased of IL-4 secretion by Th2 cells stimulated by treated-myeloma cells, while also blocked enhancing the clonogenicity of treated tumor cells stimulated by MM-Th2 cells.

Conclusions

These results indicate that a novel mechanism of myeloma pathogenesis in myeloma cells could act as an APC to present microbial Ags to Th2 cells, promoting Th2 cell proliferation, consequently facilitating tumor development by close interaction between Th2 myeloma cells. Taken together, the microbial Ag presenting course of MM-Th2-MM interactions—restricted by MHC class-II—may result in tumor development such that all factors involved in the system could have a potential for myeloma therapeutic intervention.

Lymphocyte Subsets and Inflammatory Cytokines of Monoclonal Gammopathy of Undetermined Significance and Multiple Myeloma

Almost all multiple myeloma (MM) cases have been demonstrated to be linked to earlier monoclonal gammopathy of undetermined significance (MGUS). Nevertheless, there are no identified characteristics in the diagnosis of MGUS that have been helpful in differentiating subjects whose cancer may progress to a malignant situation. Regarding malignancy, the role of lymphocyte subsets and cytokines at the beginning of neoplastic diseases is now incontestable. In this review, we have concentrated our attention on the equilibrium between the diverse lymphocyte subsets and the cytokine system and summarized the current state of knowledge, providing an overview of the condition of the entire system in MGUS and MM. In an age where the therapy of neoplastic monoclonal gammopathies largely relies on drugs capable of acting on the immune system (immunomodulants, immunological checkpoint inhibitors, CAR-T), detailed knowledge of the the differences existing in benign and neoplastic forms of gammopathy is the main foundation for the adequate and optimal use of new drugs.

Contributions of the Bone Microenvironment to Monoclonal Gammopathy of Undetermined Significance Pathogenesis

PURPOSE OF REVIEW

MGUS (monoclonal gammopathy of undetermined significance) is a plasma cell disorder characterized by a moderate increase in serum monoclonal protein (≤ 3 g/dL), an increase in bone marrow plasma cell infiltration (≤ 10%) and the absence of any end-organ damage. Although MGUS is considered a benign condition, evidence for clinical consequences is increasing. In this review, we examine the most recent evidence regarding MGUS manifestations and risks and present an overview of MGUS population studies as related to bone disease. Data reveals important MGUS-related bone alterations that may contribute to disease pathogenesis.

RECENT FINDINGS

MGUS patients present a rate of 1% per year risk of progression to the more aggressive multiple myeloma (MM) and therefore research has focused on the study of risk factors and the events leading to this progression. However, the exact health implications of MGUS itself and the mechanisms behind them remain unclear. It is now evident that the bone microenvironment plays a key role in hematologic cancers and other oncogenic processes leading to bone metastasis.

Impact of sphingolipids on osteoblast and osteoclast activity in Gaucher disease

Gaucher disease (GD) is an inherited disorder in which mutations in the GBA1 gene lead to deficient β-glucocerebrosidase activity and accumulation of its substrate glucosylceramide. Bone disease is present in around 84% of GD patients, ranging from bone loss including osteopenia and osteonecrosis to abnormal bone remodelling in the form of Erlenmeyer flask formation. The range of severity and variety of types of bone disease found in GD patients indicate the involvement of several mechanisms. Here we investigate the effects of exogenous sphingolipids on osteoclasts, osteoblasts, plasma cells and mesenchymal stem cells (MSC) and the interactions between these cell types. Osteoclasts were differentiated from the peripheral blood of Gaucher patients and control subjects. Osteoblasts were differentiated from mesenchymal stem cells isolated from bone marrow aspirates of Gaucher patients and control subjects. The human osteoblast cell line SaOS-2 was also investigated. Osteoclasts, osteoblasts and a human myeloma plasma cell line NCI-H929 were cultured with relevant exogenous sphingolipids to assess effects on cellular viability and function. Calcium deposition by osteoblasts differentiated from Gaucher patient MSC's was on average only 11.4% of that deposited by control subject osteoblasts. Culture with glucosylsphingosine reduced control subject MSC viability by 10.4%, SaOS-2 viability by 17.4% and plasma cell number by 40%. Culture with glucosylceramide decreased calcium deposition by control MSC-derived osteoblasts while increasing control subject osteoclast generation by 55.6%, Gaucher patient osteoclast generation by 37.6% and plasma cell numbers by up to 29.7%. Excessive osteoclast number and activity and reduced osteoblast activity may have the overall effect of an uncoupling between osteoclasts and osteoblasts in the GD bone microenvironment.

Cancer-associated bone disease

Bone is commonly affected in cancer. Cancer-induced bone disease results from the primary disease, or from therapies against the primary condition, causing bone fragility. Bone-modifying agents, such as bisphosphonates and denosumab, are efficacious in preventing and delaying cancer-related bone disease. With evidence-based care pathways, guidelines assist physicians in clinical decision-making. Of the 57 million deaths in 2008 worldwide, almost two thirds were due to non-communicable diseases, led by cardiovascular diseases and cancers. Bone is a commonly affected organ in cancer, and although the incidence of metastatic bone disease is not well defined, it is estimated that around half of patients who die from cancer in the USA each year have bone involvement. Furthermore, cancer-induced bone disease can result from the primary disease itself, either due to circulating bone resorbing substances or metastatic bone disease, such as commonly occurs with breast, lung and prostate cancer, or from therapies administered to treat the primary condition thus causing bone loss and fractures. Treatment-induced osteoporosis may occur in the setting of glucocorticoid therapy or oestrogen deprivation therapy, chemotherapy-induced ovarian failure and androgen deprivation therapy. Tumour skeletal-related events include pathologic fractures, spinal cord compression, surgery and radiotherapy to bone and may or may not include hypercalcaemia of malignancy while skeletal complication refers to pain and other symptoms. Some evidence demonstrates the efficacy of various interventions including bone-modifying agents, such as bisphosphonates and denosumab, in preventing or delaying cancer-related bone disease. The latter includes treatment of patients with metastatic skeletal lesions in general, adjuvant treatment of breast and prostate cancer in particular, and the prevention of cancer-associated bone disease. This has led to the development of guidelines by several societies and working groups to assist physicians in clinical decision making, providing them with evidence-based care pathways to prevent skeletal-related events and bone loss. The goal of this paper is to put forth an IOF position paper addressing bone diseases and cancer and summarizing the position papers of other organizations.

Enhancement of myeloma development mediated though myeloma cell-Th2 cell interactions after microbial antigen presentation by myeloma cells and DCs

Microbial agents are regarded as a potential cause of tumors, but their direct effects on tumors, such as myeloma, are not well studied. Our studies demonstrated that expression of HLA-DR and CD40 on the myeloma cell membrane surface is upregulated by interferon-γ and/or microbial antigens (Ags). Unlike prior studies, our study showed that Th2 cells cannot promote myeloma growth directly. However, Bacillus Calmette–Guerin Vaccine (BCGV)-specific Th2 cells stimulated by BCGV-loaded dendritic cells (DCs) promoted myeloma clonogenicity directly when the myeloma cells expressed major histocompatibility complex Class-II molecules (MHC-II) and took up BCGV Ag. B-cell lymphoma 6 (Bcl-6) protein expression and the proportion of HLA-DR⁺ or CD40⁺ cells were higher in colonies of Th2 cell-stimulated myeloma cells. Furthermore, anti-HLA-DR or neutralizing CD40 antibody could prevent this increase in Bcl-6 expression and colony number. These results indicate that microbes and microbial Ag-specific Th2 cells may directly impact the biology of myeloma and contribute to tumor progression. Activation may be limited to MHC-II⁺ myeloma cells that retain B cell and stem cell characteristics. Taken together, our data suggest that factors involved in microbial Ag presentation, such as DCs, Th2 cells and so on, are potential targets for myeloma therapeutic intervention.

Depth and volume of resorption induced by osteoclasts generated in the presence of RANKL, TNF-alpha/IL-1 or LIGHT

Rheumatoid arthritis (RA) is associated with pathological bone destruction mediated by osteoclasts. Although RANKL has been reported as a crucial factor for osteoclastogenesis, several other factors increased in RA support osteoclast formation and resorption in the absence of RANKL such as TNF-alpha and LIGHT. To date, in vitro bone resorption experiments are reported as the mean area of bone resorption per cortical or dentine slices and do not provide any information about depth and volume of resorption. The aims of this study were to assess these parameters by light microscopy and vertical scanning profilometry (VSP). Peripheral blood mononuclear cells were used as a source of osteoclast precursors and were cultured for up to 21 days in the presence of RANKL, TNF-alpha/IL-1 or LIGHT. Mean area, depth and volume of resorption were assessed by light microscopy and vertical scanning profilometry. As expected, RANKL induced large resorption pits (10,876 ± 2190μm(2)) whereas TNF-alpha/IL-1 and LIGHT generated smaller pits (respectively 1328 ± 210 and 1267 ± 173μm(2)) with no noticeable differences between these two cytokines. Depth and volume of resorption measured by VSP showed that RANKL promoted deep resorption pits resulting in large volume of resorption. Interestingly, although mean area of resorption was similar between TNF-alpha/IL-1 and LIGHT, the depth and volume of resorption of these lacunae were significantly increased by 2-fold with TNF-alpha/IL-1. These results provide evidence that although LIGHT appeared elevated in the synovial fluid of RA patients, its role in bone resorption is less than TNF-alpha/IL-1 or RANKL.

Cell fusion and hyperactive osteoclastogenesis in multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy whose progression may account for uncontrolled osteoclastogenesis promoted by the malignant plasma cells within the marrow microenvironment. Osteoclasts are multinucleated cells derived from the fusion of myeloid progenitors such as monocytes/macrophages, in response to specific differentiation factors released within the marrow niche, that are significantly deregulated in MM. In this malignancy DC-STAMP, a major fusogen protein enrolled by pre-osteoclasts, is highly expressed by peripheral macrophages, whereas dendritic cells and myeloma plasma cells show high fusogenic susceptibility and under specific conditions transdifferentiate to osteoclasts. In particular, the malignant plasma cells, besides altered ploidy, expression of cancer stem cell phenotype and high metastasizing capability, are able to express phenotypic markers of osteclasts, namely the proteolytic enzymes for the bone matrix, and to activate the β3 transcriptional pathway leading to ERK1/2 phosphorylation and initiation of the bone resorbing activity. Thus, based on the imbalanced osteoclast formation and activity that involve cells constitutively uncommitted to osteoclast differentiation, both homotypic and heterotypic cell fusions in myeloma marrow microenvironment represent a major pathogenetic event that drives the development and progression of the skeleton devastation typical of the myeloma bone disease.

Computed microtomography of bone specimens for rapid analysis of bone changes associated with malignancy

Breast and prostate cancers are specially metastasizing to bone. Metastases from breast cancer usually exhibit a mixed osteolytic/osteosclerotic aspect, with osteolysis predominating. Osteosclerosis is a common finding in prostatic cancer although osteolysis occurs within the sclerotic lesions. B-cell malignancies (lymphoma, myeloma) are also associated with marked osteolysis. Histopathological examination of bone biopsies was used for the diagnosis of malignancies and, prior to embedding, microcomputed tomography (microCT) was done on the bone specimens. Patients (247) who presented either a bone metastasis, an overt myeloma, a lymphoma or a monoclonal gammopathy of undetermined significance were studied. All patients had a bone biopsy studied by 2D histomorphometry for the histopathology. During the fixation time, the bone cores were analyzed by microCT. On the 3D reconstructed models provided by microCT, signs of osteolysis/osteosclerosis were searched: excess of bone resorption, focal disorganization of microarchitecture, bone metaplasia, osteosclerosis. A strong agreement was obtained between histomorphometry and microCT results using Cohen's kappa test (kappa = 0.713). MicroCT identified excess bone resorption on trabecular surfaces when eroded surfaces were >10.5% by histomorphometry. MicroCT failed to identify some patients with smoldering myeloma or some lymphomas with microresorption. MicroCT data are obtained within 4 hr and suggest the malignant invasion of bone marrow when excess of bone resorption/formation is obtained. MicroCT can be used in the immediate postbiopsy period making possible a fast identification of malignancy. However these signs are not specific and must be confirmed by histopathological analysis.

The cathepsin K inhibitor AAE581 induces morphological changes in osteoclasts of treated patients

Inhibitors of Cathepsin K (Cat-K) are recognized as an interesting way to inhibit osteoclast (OC) activity. OCs from patients treated with the anticathepsin-K inhibitor AAE581 (balicatib) were found enlarged. They contained numerous vacuoles filled with tartrate resistant acid phosphatase (TRAcP), an intracellular enzyme that terminates the degradation of collagen internalized in OC transcytotic vesicles. In a phase 2 clinical study, 675 patients with postmenopausal osteoporosis received the Cat-K inhibitor AAE581 at 0, 5, 10, 25, or 50 mg/D during 1 year. Eleven patients had a transiliac bone biopsy, studied undecalcified. Histoenzymatic detection of TRAcP was used to identify and count OC number. The histomorphometrist was not aware of the randomization of patients at the time of analysis. OC were unstained in one patient because of a failure in the fixation protocol, but easily observable in the 10 remaining patients. Whatever the received dose, treated patients exhibited a characteristic aspect of the OC cytoplasm which appeared filled of deeply-stained brown vacuoles, making cells looking like bunches of grape. These round vacuoles, evidenced on TRAcP-stained sections, were due to the accumulation of intracytoplasmic TRAcP. This led to a moderate enlargement of the OC size when compared to a series of control osteoporotic patients. AAE581 did not induce OC apoptosis at any dosage but it modified OC morphology. Cat-K inhibition (inhibiting the extracellular collagen breakdown) is associated with a compensatory accumulation of intracellular TRAcP that could not be used to complete protein degradation. TRAcP is also known to be degraded by Cat-K.