Immature dendritic cells in multiple myeloma are prone to osteoclast-like differentiation through interleukin-17A stimulation

Advancements in microenvironment-based therapies: transforming the landscape of multiple myeloma treatment

Multiple myeloma (MM) is the most prevalent malignant monoclonal disease of plasma cells. There is mounting evidence that interactions with the bone marrow (BM) niche are essential for the differentiation, proliferation, survival, migration, and treatment resistance of myeloma cells. For this reason, gaining a deeper comprehension of how BM microenvironment compartments interact with myeloma cells may inspire new therapeutic ideas that enhance patient outcomes. This review will concentrate on the most recent findings regarding the mechanisms of interaction between microenvironment and MM and highlight research on treatment targeting the BM niche.

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

Langerhans cell histiocytosis: current advances in molecular pathogenesis

Langerhans cell histiocytosis (LCH) is a rare and clinically heterogeneous hematological disease characterized by the accumulation of mononuclear phagocytes in various tissues and organs. LCH is often characterized by activating mutations of the mitogen-activated protein kinase (MAPK) pathway with BRAFV600E being the most recurrent mutation. Although this discovery has greatly helped in understanding the disease and in developing better investigational tools, the process of malignant transformation and the cell of origin are still not fully understood. In this review, we focus on the newest updates regarding the molecular pathogenesis of LCH and novel suggested pathways with treatment potential.

Single-cell transcriptomics suggest distinct upstream drivers of IL-17A/F in hidradenitis versus psoriasis

BACKGROUND

On the basis of the mounting evidence that type 17 T (T17) cells and increased IL-17 play a key role in driving hidradenitis suppurativa (HS) lesion development, biologic agents used previously in psoriasis that block signaling of IL-17A and/or IL-17F isoforms have been repurposed to treat HS.

OBJECTIVE

Our research aimed to characterize the transcriptome of HS T17 cells compared to the transcriptome of psoriasis T17 cells, along with their ligand-receptor interactions with neighborhood immune cell subsets.

METHODS

Single-cell data of 12,300 cutaneous immune cells from 8 deroofing surgical HS skin samples including dermal tunnels were compared to single-cell data of psoriasis skin (19,525 cells from 11 samples) and control skin (11,920 cells from 10 samples). All single-cell data were generated by the same protocol.

RESULTS

HS T17 cells expressed lower levels of IL23R and higher levels of IL1R1 and IL17F compared to psoriasis T17 cells (P < .05). HS Treg cells expressed higher levels of IL1R1 and IL17F compared to psoriasis Treg cells (P < .05). Semimature dendritic cells were the major immune cell subsets expressing IL1B in HS, and IL-1β ligand-receptor interactions between semimature dendritic cells and T17 cells were increased in HS compared to psoriasis (P < .05). HS dermal tunnel keratinocytes expressed inflammatory cytokines (IL17C, IL1A, IL1B, and IL6) that differed from the HS epidermis keratinocytes (IL36G) (P < .05). IL6, which synergizes with IL1B to maintain cytokine expression in T17 cells, was mainly expressed by fibroblasts in HS, which also expressed IL11+ inflammatory fibroblast genes (IL11, IL24, IL6, and POSTN) involved in the paracrine IL-1/IL-6 loop.

CONCLUSION

The IL-1β-T17 cell cytokine axis is likely a dominant pathway in HS with HS T17 cells activated by IL-1β signaling, unlike psoriasis T17 cells, which are activated by IL-23 signaling.

New insights into inflammatory osteoclast precursors as therapeutic targets for rheumatoid arthritis and periodontitis

Rheumatoid arthritis (RA) and periodontitis are chronic inflammatory diseases leading to increased bone resorption. Preventing this inflammatory bone resorption is a major health challenge. Both diseases share immunopathogenic similarities and a common inflammatory environment. The autoimmune response or periodontal infection stimulates certain immune actors, leading in both cases to chronic inflammation that perpetuates bone resorption. Moreover, RA and periodontitis have a strong epidemiological association that could be explained by periodontal microbial dysbiosis. This dysbiosis is believed to be involved in the initiation of RA via three mechanisms. (i) The dissemination of periodontal pathogens triggers systemic inflammation. (ii) Periodontal pathogens can induce the generation of citrullinated neoepitopes, leading to the generation of anti-citrullinated peptide autoantibodies. (iii) Intracellular danger-associated molecular patterns accelerate local and systemic inflammation. Therefore, periodontal dysbiosis could promote or sustain bone resorption in distant inflamed joints. Interestingly, in inflammatory conditions, the existence of osteoclasts distinct from "classical osteoclasts" has recently been reported. They have proinflammatory origins and functions. Several populations of osteoclast precursors have been described in RA, such as classical monocytes, a dendritic cell subtype, and arthritis-associated osteoclastogenic macrophages. The aim of this review is to synthesize knowledge on osteoclasts and their precursors in inflammatory conditions, especially in RA and periodontitis. Special attention will be given to recent data related to RA that could be of potential value in periodontitis due to the immunopathogenic similarities between the two diseases. Improving our understanding of these pathogenic mechanisms should lead to the identification of new therapeutic targets involved in the pathological inflammatory bone resorption associated with these diseases.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

The origins and formation of bone-resorbing osteoclasts

Osteoclasts (OCLs) are hematopoietic cells whose physiological function is to degrade bone. OCLs are key players in the processes that determine and maintain the mass, shape, and physical properties of bone. OCLs adhere to bone tightly and degrade its matrix by secreting protons and proteases onto the underlying surface. The combination of low pH and proteases degrades the mineral and protein components of the matrix and forms a resorption pit; the degraded material is internalized by the cell and then secreted into the circulation. Insufficient or excessive activity of OCLs can lead to significant changes in bone and either cause or exacerbate symptoms of diseases, as in osteoporosis, osteopetrosis, and cancer-induced bone lysis. OCLs are derived from monocyte-macrophage precursor cells whose origins are in two distinct embryonic cell lineages - erythromyeloid progenitor cells of the yolk sac, and hematopoietic stem cells. OCLs are formed in a multi-stage process that is induced by the cytokines M-CSF and RANKL, during which the cells differentiate, fuse to form multi-nucleated cells, and then differentiate further to become mature, bone-resorbing OCLs. Recent studies indicate that OCLs can undergo fission in vivo to generate smaller cells, called "osteomorphs", that can be "re-cycled" by fusing with other cells to form new OCLs. In this review we describe OCLs and discuss their cellular origins and the cellular and molecular events that drive osteoclastogenesis.

High serum IL-17A is associated with bone destruction in newly diagnosed multiple myeloma patients

Background

Multiple myeloma (MM) is a malignant proliferative disease of the blood system, characterized by the abnormal growth of clonal plasma cells in the bone marrow. The bone marrow microenvironment (BMM) is highly critical in the pathological process of MM. Many studies have shown that serum interleukin-17A (IL-17A) plays a key role in various infectious diseases, autoimmune diseases, and cancers. However, more clinical studies need to be performed to further prove the influence of serum IL-17A levels on multiple myeloma patients.

Methods

Among a total of 357 participants in our institution’s MM cohort, 175 were eligible for the retrospective study. Multivariate regression models adjusted by potential confounding factors, the violin plots, the generalized additive model and smooth curve fittings, receiver operating characteristic (ROC) curve, and Kaplan–Meier (K-M) curve analysis were applied to the research.

Results

A total of 175 patients with newly diagnosed MM were enrolled in this study. The multivariate linear regression analysis showed that serum IL-17A level in MM patients correlated with the degree of bone lesions and fracture incidence (fully adjusted model, p_{bone lesion} < 0.0001, p_fracture < 0.0001). The violin plot showed that MM patients with higher serum IL-17A levels had more severe bone lesions and higher fracture incidence than those with lower serum IL-17A levels. A total of 171 patients were included in the study of the relationship between serum IL-17A and best overall effect (BOE). We found that serum IL-17A levels were independently related to the best inductive therapeutic efficacy (fully adjusted model, p = 0.037), and the relationship was especially obvious in the light chain group (fully adjusted model, p = 0.009) and IgA group (fully adjusted model, p = 0.0456). It could be deduced from the smooth curve that the higher the serum IL-17A level, the worse the BOE (p = 0.0163). The ROC prediction curve suggested that serum IL-17A could predict the BOE to a certain extent (area under the curve (AUC) = 0.717, p = 0.0327). A total of 148 MM patients were observed in the longitudinal study of the relationship between serum IL-17A and progression-free survival/overall survival (PFS/OS). The K-M curve analysis indicated that serum IL-17A levels in MM patients were not significantly correlated with PFS and OS. However, in the light chain subgroup, MM patients with high serum IL-17A had worse PFS (p = 0.015) and OS (p = 0.0076) compared to those with low serum IL-17A. In the IgA type subgroup, the higher IL-17A level was related to worse OS (p = 0.0061).

Conclusion

This retrospective study found that higher levels of serum IL-17A were independently correlated with higher severity of bone disease and fracture incidence in newly diagnosed MM patients. High serum IL-17A level was related to poor best overall efficacy in the light chain type. High serum IL-17A was also associated with poor PFS and OS in the light chain type and OS in the IgA type subgroup.

Higher proportion of non-classical and intermediate monocytes in newly diagnosed multiple myeloma patients in Egypt: A possible prognostic marker

Background

Interaction between multiple myeloma (MM) cells and proximal monocytes is expected during plasma cell proliferation. However, the role of monocyte subsets in the disease progression is unknown.

Objective

This study evaluated circulating monocyte populations in MM patients and their correlation with disease severity.

Methods

Peripheral monocytes from 20 patients with MM attending Assiut University Hospital in Assiut, Egypt, between October 2018 and August 2019 were processed using a flow cytometry procedure and stratified using the intensity of expression of CD14 and CD16 into classical (CD16^-CD14⁺⁺), intermediate (CD16⁺CD14⁺⁺), and non-classical (CD16⁺⁺CD14⁺) subsets. The data were compared with data from 20 healthy control participants with comparable age and sex.

Results

In patients with MM, the percentage of classical monocytes was significantly lower (mean ± standard error: 77.24 ± 0.66 vs 83.75 ± 0.5), while those of non-classical (12.44 ± 0.5 vs 8.9 ± 0.34) and intermediate (10.3 ± 0.24 vs 7.4 ± 0.29) monocytes were significantly higher when compared with those of controls (all p < 0.0001). Proportions of non-classical and intermediate monocytes correlated positively with serum levels of plasma cells, M-protein, calcium, creatinine and lactate dehydrogenase, and correlated negatively with the serum albumin level. Proportions of classical monocytes correlated positively with albumin level and negatively correlated with serum levels of M-protein, plasma cells, calcium, creatinine, and lactate dehydrogenase.

Conclusion

Circulating monocyte subpopulations are skewed towards non-classical and intermediate monocytes in MM patients, and the intensity of this skewness increases with disease severity.

Current Overview of Treatment for Metastatic Bone Disease

The number of patients with bone metastasis increases as medical management and surgery improve the overall survival of patients with cancer. Bone metastasis can cause skeletal complications, including bone pain, pathological fractures, spinal cord or nerve root compression, and hypercalcemia. Before initiation of treatment for bone metastasis, it is important to exclude primary bone malignancy, which would require a completely different therapeutic approach. It is essential to select surgical methods considering the patient’s prognosis, quality of life, postoperative function, and risk of postoperative complications. Therefore, bone metastasis treatment requires a multidisciplinary team approach, including radiologists, oncologists, and orthopedic surgeons. Recently, many novel palliative treatment options have emerged for bone metastases, such as stereotactic body radiation therapy, radiopharmaceuticals, vertebroplasty, minimally invasive spine stabilization with percutaneous pedicle screws, acetabuloplasty, embolization, thermal ablation techniques, electrochemotherapy, and high-intensity focused ultrasound. These techniques are beneficial for patients who may not benefit from surgery or radiotherapy.

The Immune Microenvironment in Multiple Myeloma: Friend or Foe?

Simple Summary

The crosstalk between multiple myeloma and immune cells within the bone marrow niche has been identified as an emerging hallmark of this hematological disease. As our knowledge on this interplay increases, it becomes more evident that successful treatment approaches need to boost the body’s natural defenses through immunotherapy. The present review will focus on the mechanisms by which myeloma cancer cells turn immune populations into their “partners in crime”. Additionally, we will provide an overview of currently ongoing pre-clinical studies targeting the bone marrow immune microenvironment.

Abstract

Multiple myeloma (MM) is one of the most prevalent hematological cancers worldwide, characterized by the clonal expansion of neoplastic plasma cells in the bone marrow (BM). A combination of factors is implicated in disease progression, including BM immune microenvironment changes. Increasing evidence suggests that the disruption of immunological processes responsible for myeloma control ultimately leads to the escape from immune surveillance and resistance to immune effector function, resulting in an active form of myeloma. In fact, one of the hallmarks of MM is the development of a permissive BM milieu that provides a growth advantage to the malignant cells. Consequently, a better understanding of how myeloma cells interact with the BM niche compartments and disrupt the immune homeostasis is of utmost importance to develop more effective treatments. This review focuses on the most up-to-date knowledge regarding microenvironment-related mechanisms behind MM immune evasion and suppression, as well as promising molecules that are currently under pre-clinical tests targeting immune populations.

Perspective on skeletal health in inflammatory bowel disease

Osteopenia and osteoporosis are common features in inflammatory bowel disease (IBD), comprising both Crohn's disease and ulcerative colitis. Moreover, Crohn's disease is associated with increased fracture risk. The etiology of bone loss in IBD is multifactorial. It includes insufficient intake or absorption of calcium, vitamin D, and potassium; smoking; a low peak bone mass; a low body mass index; and decreased physical activity. In several studies, it has been shown that elevated concentrations of systemic and local pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interferon-γ (IFNγ), interleukin (IL)-1β, IL-4, IL-5, IL-6, IL-13, and IL-17, present in IBD patients are potentially detrimental for bone metabolism and may be responsible for bone loss and increased fracture risk. This perspective aims to review the current literature on the role of inflammatory factors in the pathophysiology of skeletal problems in IBD and to suggest potential treatment to improve bone health, based on a combination of evidence and clinical and pathophysiological reasoning.

Aspirin inhibits RANKL-induced osteoclast differentiation in dendritic cells by suppressing NF-κB and NFATc1 activation

Background

Aspirin has been demonstrated to promote osteoblast-mediated bone formation and inhibit osteoclast (OC)-mediated bone resorption. However, it remains unclear whether aspirin influences other immune cells during bone resorption. Dendritic cells (DCs), the most potent antigen-presenting cells, can also transdifferentiate into active OCs in the presence of receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). The effects of aspirin on DC-derived OCs (DDOCs) were investigated in the current study.

Methods

Flow cytometry and mixed lymphocyte reaction (MLR) assays were used for DC identification. The proliferative capacity of DCs was determined by BrdU assays. Apoptosis was examined by flow cytometry. The osteoclastic potential of DCs was tested using tartrate-resistant acid phosphatase (TRAP) staining, western blotting, and reverse transcription polymerase chain reaction (RT-PCR). Western blotting was also used to examine signaling pathways. A mandibular bone defect model was established to assess the effect of aspirin on bone resorption.

Results

Aspirin had no influence on the surface phenotype, proliferation, or apoptosis of DCs, though aspirin significantly inhibited osteoclast differentiation in RANKL-stimulated DCs. DC osteoclast differentiation was modulated by aspirin via the nuclear factor kappa B (NF-κB)/nuclear factor of activated T cell, cytoplasmic 1 (NFATc1) signaling pathway. Aspirin treatment also had favorable therapeutic effects on bone regeneration in the bone defect model, and the number of osteoclasts was decreased.

Conclusions

Aspirin inhibited RANKL-induced OC differentiation in DCs via the NF-κB pathway, downregulating expression of NFATc1. Aspirin treatment promoted bone regeneration by inhibiting DDOC activation in the early stages of inflammation in a rat mandibular bone defect model.

Immune Function and Diversity of Osteoclasts in Normal and Pathological Conditions

Osteoclasts (OCLs) are key players in controlling bone remodeling. Modifications in their differentiation or bone resorbing activity are associated with a number of pathologies ranging from osteopetrosis to osteoporosis, chronic inflammation and cancer, that are all characterized by immunological alterations. Therefore, the 2000s were marked by the emergence of osteoimmunology and by a growing number of studies focused on the control of OCL differentiation and function by the immune system. At the same time, it was discovered that OCLs are much more than bone resorbing cells. As monocytic lineage-derived cells, they belong to a family of cells that displays a wide heterogeneity and plasticity and that is involved in phagocytosis and innate immune responses. However, while OCLs have been extensively studied for their bone resorption capacity, their implication as immune cells was neglected for a long time. In recent years, new evidence pointed out that OCLs play important roles in the modulation of immune responses toward immune suppression or inflammation. They unlocked their capacity to modulate T cell activation, to efficiently process and present antigens as well as their ability to activate T cell responses in an antigen-dependent manner. Moreover, similar to other monocytic lineage cells such as macrophages, monocytes and dendritic cells, OCLs display a phenotypic and functional plasticity participating to their anti-inflammatory or pro-inflammatory effect depending on their cell origin and environment. This review will address this novel vision of the OCL, not only as a phagocyte specialized in bone resorption, but also as innate immune cell participating in the control of immune responses.

Immunotherapeutics in Multiple Myeloma: How Can Translational Mouse Models Help?

Multiple myeloma (MM) is usually diagnosed in older adults at the time of immunosenescence, a collection of age-related changes in the immune system that contribute to increased susceptibility to infection and cancer. The MM tumor microenvironment and cumulative chemotherapies also add to defects in immunity over the course of disease. In this review we discuss how mouse models have furthered our understanding of the immune defects caused by MM and enabled immunotherapeutics to progress to clinical trials, but also question the validity of using immunodeficient models for these purposes. Immunocompetent models, in particular the 5T series and Vk^⁎MYC models, are increasingly being utilized in preclinical studies and are adding to our knowledge of not only the adaptive immune system but also how the innate system might be enhanced in anti-MM activity. Finally we discuss the concept of immune profiling to target patients who might benefit the most from immunotherapeutics, and the use of humanized mice and 3D culture systems for personalized medicine.

Metastatic bone disease: Pathogenesis and therapeutic options: Up-date on bone metastasis management

Bone metastases (BM) are a common complication of cancer, whose management often requires a multidisciplinary approach. Despite the recent therapeutic advances, patients with BM may still experience skeletal-related events and symptomatic skeletal events, with detrimental impact on quality of life and survival. A deeper knowledge of the mechanisms underlying the onset of lytic and sclerotic BM has been acquired in the last decades, leading to the development of bone-targeting agents (BTA), mainly represented by anti-resorptive drugs and bone-seeking radiopharmaceuticals. Recent pre-clinical and clinical studies have showed promising effects of novel agents, whose safety and efficacy need to be confirmed by prospective clinical trials. Among BTA, adjuvant bisphosphonates have also been shown to reduce the risk of BM in selected breast cancer patients, but failed to reduce the incidence of BM from lung and prostate cancer. Moreover, adjuvant denosumab did not improve BM free survival in patients with breast cancer, suggesting the need for further investigation to clarify BTA role in early-stage malignancies. The aim of this review is to describe BM pathogenesis and current treatment options in different clinical settings, as well as to explore the mechanism of action of novel potential therapeutic agents for which further investigation is needed.

Overexpression of miR‑146a blocks the effect of LPS on RANKL‑induced osteoclast differentiation

The concept that inflammation serves a leading role in osteoclast-induced bone loss under pathological circumstances is now widely accepted. In the present study, it was observed that lipopolysaccharides (LPSs) demonstrated a synergic effect on receptor activator of nuclear factor κ-B ligand (RANKL)-induced osteoclast differentiation in Raw264.7 cells, with increasing levels of multiple pro-inflammatory cytokines including interleukin (IL)-6, tumor necrosis factor-α and IL-1β. Furthermore, microRNA (miR)-146a was highly induced by LPS and RANKL co-stimulation during the process of osteoclast differentiation. Overexpression of miR-146a inhibited osteoclast transformation by targeting the key regulators of nuclear factor (NF)-κβ signaling, TNF receptor-associated factor 6 and interleukin-1 receptor-associated kinase 1. The downstream activation of NF-κβ signaling was also inhibited by transfection with a miR-146a mimic. Altogether, the results of the present study demonstrated that miR-146a prevents osteoclast differentiation induced by LPS and RANKL co-stimulation, suggesting that miR-146a may be a promising therapeutic target for treatment of inflammation mediated bone loss.

Dendritic cells in inflammatory angiogenesis and lymphangiogenesis

Lymph node (LN) expansion during inflammation is essential to establish immune responses and relies on the development of blood and lymph vessels. Human dendritic cells (DCs), subdivided into two main subsets, namely conventional DCs (cDCs) and plasmacytoid DCs (pDCs), are professional antigen presenting cells endowed with the capability to produce soluble mediators regulating inflammation and tissue repair. cDCs support angiogenesis in secondary LNs both directly and indirectly through the secretion of vascular endothelial growth factor-A (VEGF)-A and VEGF-C and the production of several other mediators endowed with angiogenic properties. Finally, cDCs can affect neovascular formation via a transdifferentiation process. At variance with cDCs, the angiogenic properties of pDCs still remain poorly explored.

Vitamin D in melanoma: Controversies and potential role in combination with immune check-point inhibitors

The role of vitamin D in melanoma is still controversial. Although several Authors described a correlation between vitamin D deficiency and poor survival in metastatic melanoma patients, clinical trials exploring the effects of vitamin D supplementation in this clinical setting were mostly inconclusive. However, recent evidence suggests that vitamin D exerts both anti-proliferative effects on tumor cells and immune-modulating activities, that have been widely explored in auto-immune disorders. On the one hand, vitamin D has been shown to inhibit T-helper17 lymphocytes, notoriously involved in the pathogenesis of immune-related adverse events (iAEs) which complicate immune-checkpoint inhibitor (ICI) treatment. On the other hand, vitamin D up-regulates PDL-1 expression on both epithelial and immune cells, suggesting a synergic effect in combination with ICIs, for which further investigation is needed.

Exosomes in melanoma: a role in tumor progression, metastasis and impaired immune system activity

Exosomes (Exo) are small vesicles produced by melanoma cells and the accessory cells of the tumor microenvironment. They emerge via both classical and direct pathways and actively participate in tumor colonisation of distant tissues. The proteins, nucleic acids, cytokines and growth factors engulfed by Exo are transferred to recipient cells, where they drive numerous functions required for the tumor escape from immune system control and tumor progression. By positively or negatively modulating immune cell properties, Exo provoke immune suppression and, in turn, defective dendritic cell (DC) functions. Together, these effects limit the cytotoxicity of T-cells and expand both T-regulatory and myeloid-derived suppressor populations. They also hinder perforin and granzyme production by natural killer cells. Finally, Exo also control the organotropism of melanoma cells. The distinct phenotypic properties of Exo can be exploited both for diagnostic purposes and in the early identification of melanoma patients likely to respond to immunotherapy. The potential therapeutic application of Exo derived from DCs has been demonstrated in vaccination trials, which showed an increase in anti-melanoma activity with respect to circulating tumor cells. However, additional studies are required before Exo can be effectively used in diagnostic and therapeutic applications in melanoma.

Identification and characterization of HLA-A24-specific XBP1, CD138 (Syndecan-1) and CS1 (SLAMF7) peptides inducing antigens-specific memory cytotoxic T lymphocytes targeting multiple myeloma

X-box binding protein 1 (XBP1), CD138 (Syndecan-1) and CS1 (SLAMF7) are highly expressed antigens in cancers including multiple myeloma (MM). Here, we identify and characterize immunogenic HLA-A24 peptides derived from these antigens for potential vaccination therapy of HLA-A24+ patients with MM. The identified immunogenic HLA-A24-specific XBP1 unspliced (UN)185-193 (I S P W I L A V L), XBP1 spliced (SP)223-231 (V Y P E G P S S L), CD138265-273 (I F A V C L V G F) and CS1240-248 (L F V L G L F L W) peptides induced antigen-specific CTL with anti-MM activity in an HLA-A24 restricted manner. Furthermore, a cocktail containing the four HLA-A24 peptides evoked MM-specific CTL with distinct phenotypic profiles (CD28, CD40L, 41BB, CD38, CD69) and anti-tumor activities, evidenced by perforin upregulation, CD107a degranulation (cytotoxicity) and Th1-type cytokines (IFN-γ/IL-2/TNF-α) production in response to HLA-A24+ MM cells. The multipeptide-specific CTL included antigen-specific memory CD8+ T cells expressing both T-cell activation (CD38, CD69) and immune checkpoints antigens (CTLA, PD-1, LAG-3, TIM-3). These results provide the framework for a multipeptide vaccination therapy to induce tumor-specific CTL in HLA-A24-positive patients with myeloma and other cancers expressing these antigens.

MiR-29b antagonizes the pro-inflammatory tumor-promoting activity of multiple myeloma-educated dendritic cells

Dendritic cells (DCs) have a key role in regulating tumor immunity, tumor cell growth and drug resistance. We hypothesized that multiple myeloma (MM) cells might recruit and reprogram DCs to a tumor-permissive phenotype by changes within their microRNA (miRNA) network. By analyzing six different miRNA-profiling data sets, miR-29b was identified as the only miRNA upregulated in normal mature DCs and significantly downregulated in tumor-associated DCs. This finding was validated in primary DCs co-cultured in vitro with MM cell lines and in primary bone marrow DCs from MM patients. In DCs co-cultured with MM cells, enforced expression of miR-29b counteracted pro-inflammatory pathways, including signal transducer and activator of transcription 3 and nuclear factor-κB, and cytokine/chemokine signaling networks, which correlated with patients' adverse prognosis and development of bone disease. Moreover, miR-29b downregulated interleukin-23 in vitro and in the SCID-synth-hu in vivo model, and antagonized a Th17 inflammatory response. All together, these effects translated into strong anti-proliferative activity and reduction of genomic instability of MM cells. Our study demonstrates that MM reprograms the DCs functional phenotype by downregulating miR-29b whose reconstitution impairs DCs ability to sustain MM cell growth and survival. These results underscore miR-29b as an innovative and attractive candidate for miRNA-based immune therapy of MM.

Serum exosomes as predictors of clinical response to ipilimumab in metastatic melanoma

Immunotherapy is effective in metastatic melanoma (MM) but most studies failed in discovering a biomarker predictive of clinical response. Exosomes (Exo) from melanoma cells are detectable in sera of MM patients similarly to those produced by immune cells that control the tumor progression. Here, we investigated by flow-cytometry the levels of Exo from both T-cells and dendritic cells (DCs) in 59 patients with MM treated with IPI and the relative expression of PD-1, CD28 and ICOS as well as CD80 and CD86. We found a significant increment of PD-1 and CD28 expression in patients achieving a clinical response reflected by improvement of both PFS and OS. Furthermore, MM patients receiving IPI who showed extended PFS underwent increased expression of CD80 and CD86 on DC-derived Exo at the end of treatment. These results suggest a possible association of both PD-1 and CD28 up-regulation on immune cell-derived Exo in patients with better clinical response to IPI.

Emerging Roles of Osteoclasts in the Modulation of Bone Microenvironment and Immune Suppression in Multiple Myeloma

Multiple myeloma (MM) is one of the most common forms of hematologic malignancy resulting from cancerous proliferation of mature malignant plasma cells (MPCs). But despite the real improvement in therapeutics in the past years, it remains largely incurable. MM is the most frequent cancer to involve bone due to the stimulation of osteoclast (OCL) differentiation and activity. OCLs have a unique capacity to resorb bone. However, recent studies reveal that they are not restrained to this sole function. They participate in the control of angiogenesis, medullary niches, and immune responses, including in MM. Therefore, therapeutic approaches targeting OCLs probably affect not only bone resorption but also many other functions, and OCLs should not be considered anymore only as targets to improve the bone phenotype but also to modulate bone microenvironment. In this review, we explore these novel contributions of OCLs to MM which reveal their strong implication in the MM physiopathology. We also underline the therapeutic interest of targeting OCLs not only to overcome bone lesions, but also to improve bone microenvironment and anti-tumoral immune responses.

TRAF6 regulates the effects of polarized maturation of tolerability: Marrow-derived dendritic cells on collagen-induced arthritis in mice

The study aimed to investigate the relationship between tumor necrosis factor receptor-associated factor 6 (TRAF6) and a differentially mature dendritic cell (mDC) in collagen-induced arthritis (CIA) mice and to determine whether or not TRAF6 regulates the activation of an immature dendritic cell (iDC) and inhibits iDC maturation to induce immune tolerance. The mouse bone marrow stem cells were induced with recombinant granulocyte-macrophage colony-stimulating factor (rmGM-CSF) and recombinant interleukin-4 (rmIL-4) to differentiate immature dendritic cells (DCs), which were divided into four groups with different maturation states: rmGM-CSF, rmIL-4; TNF-α; LPS; and FK506 group. The levels of the cell surfaces of CD80, CD86, and MHI-II were analyzed by flow cytometry to prove DCs at different levels of maturity. The expression of IL-12 in DCs at different maturation states was detected by enzyme-linked immunosorbent assay (ELISA). The expression of TRAF6 mRNA and protein in each group of DCs was detected by a reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. The results revealed that the differentiation of bone marrow cells into iDCs was significantly induced by cytokines (rmGM-CSF, IL-4). CD80, CD86, MHC-II were expressed in the four groups, and the difference between them was statistically significant (P<0.05). A higher degree of DC differentiation led to a gradual increase of IL-12 secretion in the four groups. The difference was statistically significant (P<0.05) for this secretion (group D, 10,620.73±276.73 pg/ml). The expression levels of TRAF6 mRNA were significantly higher in group D than those in the other three groups (P<0.01). Although there was no significant difference in the expression levels of TRAF6 mRNA between groups B and C, the expression levels of TRAF6 mRNA between groups B and C were higher than those of the control group. The TRAF6 protein expression was higher in group D than that in the other three groups (P<0.01), and the difference was statistically significant. There was a statistically significant difference in the TRAF6 protein expression between group A and groups B and C, but the expression in group C was higher than that in group B (P<0.01). In conclusion, the expression of co-stimulatory molecules gradually increased in the DCs of different maturation states, and the expression of IL-12, TRAF6 mRNA, and TRAF6 protein positively correlated with the degree of DC maturation. TRAF6 is important in iDC polarity and maturation.

IL21R expressing CD14+CD16+ monocytes expand in multiple myeloma patients leading to increased osteoclasts

Bone marrow monocytes are primarily committed to osteoclast formation. It is, however, unknown whether potential primary alterations are specifically present in bone marrow monocytes from patients with multiple myeloma, smoldering myeloma or monoclonal gammopathy of undetermined significance. We analyzed the immunophenotypic and transcriptional profiles of bone marrow CD14⁺ monocytes in a cohort of patients with different types of monoclonal gammopathies to identify alterations involved in myeloma-enhanced osteoclastogenesis. The number of bone marrow CD14⁺CD16⁺ cells was higher in patients with active myeloma than in those with smoldering myeloma or monoclonal gammopathy of undetermined significance. Interestingly, sorted bone marrow CD14⁺CD16⁺ cells from myeloma patients were more pro-osteoclastogenic than CD14⁺CD16-cells in cultures ex vivo. Moreover, transcriptional analysis demonstrated that bone marrow CD14⁺ cells from patients with multiple myeloma (but neither monoclonal gammopathy of undetermined significance nor smoldering myeloma) significantly upregulated genes involved in osteoclast formation, including IL21R. IL21R mRNA over-expression by bone marrow CD14⁺ cells was independent of the presence of interleukin-21. Consistently, interleukin-21 production by T cells as well as levels of interleukin-21 in the bone marrow were not significantly different among monoclonal gammopathies. Thereafter, we showed that IL21R over-expression in CD14⁺ cells increased osteoclast formation. Consistently, interleukin-21 receptor signaling inhibition by Janex 1 suppressed osteoclast differentiation from bone marrow CD14⁺ cells of myeloma patients. Our results indicate that bone marrow monocytes from multiple myeloma patients show distinct features compared to those from patients with indolent monoclonal gammopathies, supporting the role of IL21R over-expression by bone marrow CD14⁺ cells in enhanced osteoclast formation.

Everolimus restrains the IL-17A-dependent osteoclast-like transdifferentiation of dendritic cells in multiple myeloma

Interleukin-17A (IL-17A) promotes the osteoclast (OC)-like differentiation of dendritic cells (DCs) in multiple myeloma (MM) and contributes to the pathogenesis of myeloma bone disease (MBD). In our study, everolimus (EVR) abrogated the in vitro OC-like activity of DCs from 12 MM patients significantly. Exploring the EVR effects, we found that the inhibition of the osteoerosive activity of OC-DCs was mostly due to the blockade of signals driven by the IL-17A receptor toward the CCAAT/enhancer-binding protein beta/musculoaponeurotic fibrosarcoma oncogene homolog B axis Therefore, MM patients with MBD would probably benefit from mammalian target of rapamycin inhibition.

Dendritic-cell-derived osteoclasts: a new game changer in bone-resorption-associated diseases

Bone-resorbing cells, osteoclasts (OCs), and antigen-presenting cells, dendritic cells (DCs), share several features. They are derived from a common hematopoietic precursor, exhibit phagocytic activities and their functions are dependent upon receptor activator of nuclear factor κB ligand (RANKL). Upon inflammatory conditions, DCs can transdifferentiate toward functional OCs in the presence of RANKL. It has then been assumed that the increase in proinflammatory cytokines could provide a supportive environment for this transdifferentiation. In this review, we emphasize the molecular mechanisms underlying the potential for DCs to give rise to resorbing OCs in the context of bone-destruction-associated diseases upon inflammatory conditions. Whether these mechanisms reveal new strategies for the discovery of therapeutic targets and drugs is discussed extensively.

Non-redundant roles for Th17 and Th22 cells in multiple myeloma clinical correlates

We recently reported that in multiple myeloma increased Th22 cell frequencies correlate with poor prognosis. Here we show that within the same patients' cohort Th17 cells associate with bone disease and not with prognosis. Thus, we propose that Th22 and Th17 cells play non-redundant roles in multiple myeloma and constitute independent therapeutic targets.

Dissecting the multiple myeloma-bone microenvironment reveals new therapeutic opportunities

Multiple myeloma is a plasma cell skeletal malignancy. While therapeutic agents such as bortezomib and lenalidomide have significantly improved overall survival, the disease is currently incurable with the emergence of drug resistance limiting the efficacy of chemotherapeutic strategies. Failure to cure the disease is in part due to the underlying genetic heterogeneity of the cancer. Myeloma progression is critically dependent on the surrounding microenvironment. Defining the interactions between myeloma cells and the more genetically stable hematopoietic and mesenchymal components of the bone microenvironment is critical for the development of new therapeutic targets. In this review, we discuss recent advances in our understanding of how microenvironmental elements contribute to myeloma progression and, therapeutically, how those elements can or are currently being targeted in a bid to eradicate the disease.

Regulatory T cell-mediated anti-inflammatory effects promote successful tissue repair in both indirect and direct manners

Regulatory T cells (Tregs) offer new immunotherapeutic options to control undesired immune reactions, such as those in transplant rejection and autoimmunity. In addition, tissue repair and regeneration depend on a multitude of tightly regulated immune and non-immune cells and signaling molecules. There is mounting evidence that adequate innate responses, and even more importantly balanced adaptive immune responses, are key players in the tissue repair and regeneration processes, even in absence of any immune-related disease or infection. Thus, the anti-inflammatory and anti-apoptotic capacities of Treg can affect not only the effector immune response, creating the appropriate immune environment for successful tissue repair and regeneration, but growing evidence shows that they also have direct effects on tissue cell functions. Here we summarize the present views on how Treg might support tissue regeneration by direct control of undesired immune reactivity and also by direct interaction with non-immune tissue cells. We describe tissue-resident Treg and their specific phenotypes in skin, visceral adipose tissue, and skeletal muscle. In addition, we touch on the topic of osteoimmunology, discussing the direct interactions of Treg with bone-forming cells, such as osteoblasts and their mesenchymal stromal cell (MSC) progenitors-a field which is under-investigated. We hypothesize a cross-talk between Treg and bone-forming cells through the CD39-CD73-(adenosine)-adenosine receptor pathway, which might also potentiate the differentiation of MSCs, thus facilitating bone regeneration. This hypothesis may provide a road map for further investigations on the cross-talk between the immune and the skeletal system, and also enable the development of better strategies to promote bone repair and regeneration.

Targeting IL-17A in multiple myeloma: a potential novel therapeutic approach in myeloma

We have previously demonstrated that interleukin-17A (IL-17) producing Th17 cells are significantly elevated in blood and bone marrow (BM) in multiple myeloma (MM) and IL-17A promotes MM cell growth via the expression of IL-17 receptor. In this study, we evaluated anti-human IL-17A human monoclonal antibody (mAb), AIN457 in MM. We observe significant inhibition of MM cell growth by AIN457 both in the presence and absence of BM stromal cells (BMSC). While IL-17A induces IL-6 production, AIN457 significantly down-regulated IL-6 production and MM cell-adhesion in MM-BMSC co-culture. AIN-457 also significantly inhibited osteoclast cell–differentiation. More importantly, in the SCIDhu model of human myeloma administration of AIN-457 weekly for 4 weeks after the first detection of tumor in mice led to a significant inhibition of tumor growth and reduced bone damage compared to isotype control mice. To understand the mechanism of action of anti-IL-17A mAb, we report here, that MM cells express IL-17A. We also observed that IL-17A knock-down inhibited MM cell growth and their ability to induce IL-6 production in co-cultures with BMSC. These pre-clinical observations suggest efficacy of AIN 457 in myeloma and provide the rationale for its clinical evaluation for anti-myeloma effects and for improvement of bone disease.

Avβ3 integrin: Pathogenetic role in osteotropic tumors

The interplay of cancer cells and accessory cells within the microenvironment drives signals regulating the proliferation, migration and skeleton colonization. Osteotropism of tumor cells depends on chemokine activation, production of soluble factors and defective gene expression that cooperate within the metastatic niche to the bone resorbing functions of osteoclasts. Adhesion of cancer cells to the extracellular matrix is regulated by integrins as αvβ3 that enhances their invasiveness, pro-tumor angiogenesis and skeleton invasion. Therefore, αvβ3 signaling is implicated in enhancing osteotropism of breast and prostate cancers as well as of multiple myeloma. Targeting of αvβ3 has been adopted to restrain the tumor progression in several cancer models leading to improvement of overall survival as effect of the reduction of both tumor burden and osteotropism by malignant cells. Here, we review both the role of αvβ3 in malignant osteoclastogenesis and its potential targeting to restrain the bone colonization by skeleton invading cancers.

The proportion of CD16(+)CD14(dim) monocytes increases with tumor cell load in bone marrow of patients with multiple myeloma

Multiple myeloma is an incurable cancer with expansion of malignant plasma cells in the bone marrow. Previous studies have shown that monocytes and macrophages in the bone marrow milieu are important for tumor growth and may play a role in the drug response. We therefore characterized monocytes in bone marrow aspirates by flow cytometry. We found that there was significant correlation between the proportion of CX₃CR₁⁺, CD16⁺CD14^dim non classical monocytes, and percent plasma cells (PC) in the bone marrow of myeloma patients. The bone marrow monocytes could be stimulated by TLR ligands to produce cytokines which promote myeloma cell growth. The proportion of the non-classical monocytes increased with the tumor load, particularly in patients with tumor loads in the range of 10–30% bone marrow PC.

Alternative pathways of osteoclastogenesis in inflammatory arthritis

Osteoclasts are cells of haematopoietic origin that are uniquely specialized to degrade bone. Under physiological conditions, the osteoclastogenesis pathway depends on macrophage colony-stimulating factor 1 (CSF-1, also known as M-CSF) and receptor activator of nuclear factor κB ligand (RANKL). However, an emerging hypothesis is that alternative pathways of osteoclast generation might be active during inflammatory arthritis. In this Perspectives article, we summarize the physiological pathway of osteoclastogenesis and then focus on experimental findings that support the hypothesis that infiltrating inflammatory cells and the cytokine milieu provide multiple routes to bone destruction. The precise identity of osteoclast precursor(s) is not yet known. We propose that myeloid cell differentiation during inflammation could be an important contributor to the differentiation of osteoclast populations and their associated pathologies. Understanding the dynamics of osteoclast differentiation in inflammatory arthritis is crucial for the development of therapeutic strategies for inflammatory joint disease in children and adults.

Bone and the innate immune system

The immune system and bone are intimately linked with significant physical and functionally related interactions. The innate immune system functions as an immediate response system to initiate protections against local challenges such as pathogens and cellular damage. Bone is a very specific microenvironment, in which infectious attack is less common but repair and regeneration are ongoing and important functions. Thus, in the bone the primary goal of innate immune and bone interactions is to maintain tissue integrity. Innate immune signals are critical for removal of damaged and apoptotic cells and to stimulate normal tissue repair and regeneration. In this review we focus on the innate immune mechanisms that function to regulate bone homeostasis.

New insights into the molecular pathogenesis of langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a rare proliferative disorder characterized by an accumulation of cells sharing the major phenotypic features of cutaneous Langerhans cells. Given its variable clinical evolution, ranging from self-limiting lesions to multisystemic forms with a poor prognosis, in the last decades it has been debated whether LCH might not have a neoplastic rather than an inflammatory nature. However, although the fundamental events underlying the pathogenesis of LCH are still elusive, recent advances have strikingly improved our understanding of the disease. In particular, the identification of multiple interplays between LCH cells and their tumor microenvironment, along with the recognition of the lesional cytokine storm as a key determinant of LCH progression, has substantiated new opportunities for devising targeted therapeutic approaches. Strikingly, the detection of the rapidly accelerated fibrosarcoma isoform B(V600E) gain-of-function mutation as a genetic alteration recurring in more than 50% of patients has fueled the paradoxical picture of LCH as a tumor of the antigen-presenting cells that can evade rejection by the immune system. Thus, new evidence regarding the ontogeny of LCH cells, as well as a better understanding of the putative immune system frustrating strategy in LCH, may help to define the precise pathogenesis.