Macrophages in multiple myeloma: emerging concepts and therapeutic implications

Increased PVR Expression on Bone Marrow Macrophages May Promote Resistance to TIGIT Blockade in Multiple Myeloma

PURPOSE

TIGIT blockade in our ex vivo model of bone marrow (BM) reduced the number of malignant plasma cells (PC) in only half of patients with multiple myeloma. Here, we wanted to investigate whether increased expression of TIGIT ligands may inhibit T-cell immune response promoting resistance to TIGIT blockade.

EXPERIMENTAL DESIGN

We first characterized the number and phenotype of BM macrophages in different stages of the disease by multiparameter flow cytometry. We assessed the effect of TIGIT ligands on PC survival by performing experiments in the ex vivo BM model and analyzed changes in gene expression by using NanoString technology and real-time PCR.

RESULTS

The frequency of BM macrophages was significantly decreased in multiple myeloma, which was accompanied by changes in their immunophenotype. Moreover, we found a higher number of malignant PC in ex vivo BM cells cultured onto the poliovirus receptor (PVR) and nectin-2 compared with control, suggesting that both ligands may support PC survival. In addition, the presence of PVR, but not nectin-2, overcame the therapeutic effect of TIGIT blockade or exogenous IL2. Furthermore, exogenous IL2 increased TIGIT expression on both CD4+ and CD8+ T cells and, indirectly, PVR on BM macrophages. Consistently, PVR reduced the number of cytotoxic T cells and promoted a gene signature with reduced effector molecules.

CONCLUSIONS

IL2 induced TIGIT on T cells in the BM, in which increased PVR expression resulted in cytotoxic T-cell inhibition, promoting PC survival and resistance to TIGIT blockade.

miR-34a promotes the immunosuppressive function of multiple myeloma-associated macrophages by dampening the TLR-9 signaling

BACKGROUND

Promising outcomes have been observed in multiple myeloma (MM) with the use of immunotherapies, specifically chimeric antigen receptor T (CAR-T) cell therapy. However, a portion of MM patients do not respond to CAR-T therapy, and the reasons for this lack of response remain unclear. The objective of this study was to investigate the impact of miR-34a on the immunosuppressive polarization of macrophages obtained from MM patients.

METHODS

The levels of miR-34a and TLR9 (Toll-like receptor 9) were examined in macrophages obtained from both healthy individuals and patients with MM. ELISA was employed to investigate the cytokine profiles of the macrophage samples. Co-culture experiments were conducted to evaluate the immunomodulatory impact of MM-associated macrophages on CAR-T cells.

RESULTS

There was an observed suppressed activation of macrophages and CD4+ T lymphocytes in the blood samples of MM patients. Overexpression of miR-34a in MM-associated macrophages dampened the TLR9 expression and impaired the inflammatory polarization. In both the co-culture system and an animal model, MM-associated macrophages suppressed the activity and tumoricidal effect of CAR-T cells in a miR-34a-dependent manner.

CONCLUSION

The findings imply that targeting the macrophage miR-34a/TLR9 axis could potentially alleviate the immunosuppression associated with CAR-T therapy in MM patients.

Preclinical and clinical evaluation of the Janus Kinase inhibitor ruxolitinib in multiple myeloma

Multiple myeloma (MM) is the most common primary malignancy of the bone marrow. No established curative treatment is currently available for patients diagnosed with MM. In recent years, new and more effective drugs have become available for the treatment of this B-cell malignancy. These new drugs have often been evaluated together and in combination with older agents. However, even these novel combinations eventually become ineffective; and, thus, novel therapeutic approaches are necessary to help overcome resistance to these treatments. Recently, the Janus Kinase (JAK) family of tyrosine kinases, specifically JAK1 and JAK2, has been shown to have a role in the pathogenesis of MM. Preclinical studies have demonstrated a role for JAK signaling in direct and indirect growth of MM and downregulation of anti-tumor immune responses in these patients. Also, inhibition of JAK proteins enhances the anti-MM effects of other drugs used to treat MM. These findings have been confirmed in clinical studies which have further demonstrated the safety and efficacy of JAK inhibition as a means to overcome resistance to currently available anti-MM therapies. Additional studies will provide further support for this promising new therapeutic approach for treating patients with MM.

Bispecific BCMA/CD24 CAR-T cells control multiple myeloma growth

Anti-multiple myeloma B cell maturation antigen (BCMA)-specific chimeric antigen receptor (CAR) T-cell therapies represent a promising treatment strategy with high response rates in myeloma. However, durable cures following anti-BCMA CAR-T cell treatment of myeloma are rare. One potential reason is that a small subset of minimal residual myeloma cells seeds relapse. Residual myeloma cells following BCMA-CAR-T-mediated treatment show less-differentiated features and express stem-like genes, including CD24. CD24-positive myeloma cells represent a large fraction of residual myeloma cells after BCMA-CAR-T therapy. In this work, we develop CD24-CAR-T cells and test their ability to eliminate myeloma cells. We find that CD24-CAR-T cells block the CD24-Siglec-10 pathway, thereby enhancing macrophage phagocytic clearance of myeloma cells. Additionally, CD24-CAR-T cells polarize macrophages to a M1-like phenotype. A dual-targeted BCMA-CD24-CAR-T exhibits improved efficacy compared to monospecific BCMA-CAR-T-cell therapy. This work presents an immunotherapeutic approach that targets myeloma cells and promotes tumor cell clearance by macrophages.

Immunomodulatory properties of CD38 antibodies and their effect on anticancer efficacy in multiple myeloma

BACKGROUND

CD38 has been established as an important therapeutic target for multiple myeloma (MM), for which two CD38 antibodies are currently approved-daratumumab and isatuximab. CD38 is an ectoenzyme that degrades NAD and its precursors and is involved in the production of adenosine and other metabolites.

AIM

Among the various mechanisms by which CD38 antibodies can induce MM cell death is immunomodulation, including multiple pathways for CD38-mediated T-cell activation. Patients who respond to anti-CD38 targeting treatment experience more marked changes in T-cell expansion, activity, and clonality than nonresponders.

IMPLICATIONS

Resistance mechanisms that undermine the immunomodulatory effects of CD38-targeting therapies can be tumor intrinsic, such as the downregulation of CD38 surface expression and expression of complement inhibitor proteins, and immune microenvironment-related, such as changes to the natural killer (NK) cell numbers and function in the bone marrow niche. There are numerous strategies to overcome this resistance, which include identifying and targeting other therapeutic targets involved in, for example, adenosine production, the activation of NK cells or monocytes through immunomodulatory drugs and their combination with elotuzumab, or with bispecific T-cell engagers.

Macrophages and Urokinase Plasminogen Activator Receptor System in Multiple Myeloma: Case Series and Literature Review

The microenvironment plays an essential role in multiple myeloma (MM) development, progression, cell proliferation, survival, immunological escape, and drug resistance. Mesenchymal stromal cells and macrophages release tolerogenic cytokines and favor anti-apoptotic signaling pathway activation, while the urokinase plasminogen activator receptor (uPAR) system contributes to migration through an extracellular matrix. Here, we first summarized the role of macrophages and the uPAR system in MM pathogenesis, and then we reported the potential therapeutic effects of uPAR inhibitors in a case series of primary MM-derived adherent cells. Our preliminary results showed that after uPAR inhibitor treatments, interleukein-6 (mean ± SD, 8734.95 ± 4169.2 pg/mL vs. 359.26 ± 393.8 pg/mL, pre- vs. post-treatment; p = 0.0012) and DKK-1 levels (mean ± SD, 7005.41 ± 6393.4 pg/mL vs. 61.74 ± 55.2 pg/mL, pre- vs. post-treatment; p = 0.0043) in culture medium were almost completely abolished, supporting further investigation of uPAR blockade as a therapeutic strategy for MM treatment. Therefore, uPAR inhibitors could exert both anti-inflammatory and pro-immunosurveillance activity. However, our preliminary results need further validation in additional in vitro and in vivo studies.

Extracellular vesicle proteomic analysis leads to the discovery of HDGF as a new factor in multiple myeloma biology

HDGF is secreted by and found in multiple myeloma cell extracellular vesicles; it activates AKT and sustains multiple myeloma cell growth.

HDGF polarizes naïve macrophages to an M1 phenotype and generates immunosuppressive M-MDSC.

Identifying factors secreted by multiple myeloma (MM) cells that may contribute to MM tumor biology and progression is of the utmost importance. In this study, hepatoma-derived growth factor (HDGF) was identified as a protein present in extracellular vesicles (EVs) released from human MM cell lines (HMCLs). Investigation of the role of HDGF in MM cell biology revealed lower proliferation of HMCLs following HDGF knockdown and AKT phosphorylation following the addition of exogenous HDGF. Metabolic analysis demonstrated that HDGF enhances the already high glycolytic levels of HMCLs and significantly lowers mitochondrial respiration, indicating that HDGF may play a role in myeloma cell survival and/or act in a paracrine manner on cells in the bone marrow (BM) tumor microenvironment (ME). Indeed, HDGF polarizes macrophages to an M1-like phenotype and phenotypically alters naïve CD14⁺ monocytes to resemble myeloid-derived suppressor cells which are functionally suppressive. In summary, HDGF is a novel factor in MM biology and may function to both maintain MM cell viability as well as modify the tumor ME.

Langerhans dendritic cell vaccines bearing mRNA-encoded tumor antigens induce anti-myeloma immunity after autotransplant

Triple antigen–bearing mRNA-electroporated autologous LC vaccines after ASCT for MM are safe and immunogenic.

Posttransplant vaccination targeting residual disease is an immunotherapeutic strategy to improve antigen-specific immune responses and prolong disease-free survival after autologous stem cell transplantation (ASCT) for multiple myeloma (MM). We conducted a phase 1 vaccine trial to determine the safety, toxicity, and immunogenicity of autologous Langerhans-type dendritic cells (LCs) electroporated with CT7, MAGE-A3, and Wilms tumor 1 (WT1) messenger RNA (mRNA), after ASCT for MM. Ten patients received a priming immunization plus 2 boosters at 12, 30, and 90 days, respectively, after ASCT. Vaccines contained 9 × 10⁶ mRNA-electroporated LCs. Ten additional patients did not receive LC vaccines but otherwise underwent identical ASCT and supportive care. At 3 months after ASCT, all patients started lenalidomide maintenance therapy. Vaccinated patients developed mild local delayed-type hypersensitivity reactions after booster vaccines, but no toxicities exceeded grade 1. At 1 and 3 months after vaccines, antigen-specific CD4 and CD8 T cells increased secretion of proinflammatory cytokines (interferon-γ, interleukin-2, and tumor necrosis factor-α) above prevaccine levels, and also upregulated the cytotoxicity marker CD107a. CD4 and CD8 T-cell repertoire analysis showed a trend for increased clonal expansion in the vaccine cohort, which was more pronounced in the CD4 compartment. Although not powered to assess clinical efficacy, treatment responses favored the vaccine arm. Triple antigen–bearing mRNA-electroporated autologous LC vaccination initiated at engraftment after ASCT, in conjunction with standard lenalidomide maintenance therapy for MM, is safe and induces antigen-specific immune reactivity. This trial was registered at www.clinicaltrials.gov as #NCT01995708.

Current Progress in Delineating the Roles of Pseudokinase TRIB1 in Controlling Human Diseases

Tribbles homolog 1 (TRIB1) is a member of the tribbles family of pseudoprotein kinases and is widely expressed in numerous tissues, such as bone marrow, skeletal muscle, liver, heart, and adipose tissue. It is closely associated with acute myeloid leukemia, prostate cancer, and tumor drug resistance, and can interfere with the hematopoietic stem cell cycle, promote tumor cell proliferation, and inhibit apoptosis. Recent studies have shown that TRIB1 can regulate acute and chronic inflammation by affecting the secretion of inflammatory factors, which is closely related to the occurrence of hyperlipidemia and cardiovascular diseases. Given the important biological functions of TRIB1, the reviews published till now are not sufficiently comprehensive. Therefore, this paper reviews the progress in TRIB1 research aimed at exploring its roles in cancer, hyperlipidemia, and cardiovascular disease, and providing a theoretical basis for further studies on the biological roles of TRIB1.

Harnessing the Immune System to Fight Multiple Myeloma

Multiple myeloma (MM) is a heterogeneous plasma cell malignancy differing substantially in clinical behavior, prognosis, and response to treatment. With the advent of novel therapies, many patients achieve long-lasting remissions, but some experience aggressive and treatment refractory relapses. So far, MM is considered incurable. Myeloma pathogenesis can broadly be explained by two interacting mechanisms, intraclonal evolution of cancer cells and development of an immunosuppressive tumor microenvironment. Failures in isotype class switching and somatic hypermutations result in the neoplastic transformation typical of MM and other B cell malignancies. Interestingly, although genetic alterations occur and evolve over time, they are also present in premalignant stages, which never progress to MM, suggesting that genetic mutations are necessary but not sufficient for myeloma transformation. Changes in composition and function of the immune cells are associated with loss of effective immune surveillance, which might represent another mechanism driving malignant transformation. During the last decade, the traditional view on myeloma treatment has changed dramatically. It is increasingly evident that treatment strategies solely based on targeting intrinsic properties of myeloma cells are insufficient. Lately, approaches that redirect the cells of the otherwise suppressed immune system to take control over myeloma have emerged. Evidence of utility of this principle was initially established by the observation of the graft-versus-myeloma effect in allogeneic stem cell-transplanted patients. A variety of new strategies to harness both innate and antigen-specific immunity against MM have recently been developed and intensively tested in clinical trials. This review aims to give readers a basic understanding of how the immune system can be engaged to treat MM, to summarize the main immunotherapeutic modalities, their current role in clinical care, and future prospects.

The Role of Marrow Microenvironment in the Growth and Development of Malignant Plasma Cells in Multiple Myeloma

The development and effectiveness of novel therapies in multiple myeloma have been established in large clinical trials. However, multiple myeloma remains an incurable malignancy despite significant therapeutic advances. Accumulating data have elucidated our understanding of the genetic background of the malignant plasma cells along with the role of the bone marrow microenvironment. Currently, the interaction among myeloma cells and the components of the microenvironment are considered crucial in multiple myeloma pathogenesis. Adhesion molecules, cytokines and the extracellular matrix play a critical role in the interplay among genetically transformed clonal plasma cells and stromal cells, leading to the proliferation, progression and survival of myeloma cells. In this review, we provide an overview of the multifaceted role of the bone marrow microenvironment in the growth and development of malignant plasma cells in multiple myeloma.

Overcoming the Immunosuppressive Tumor Microenvironment in Multiple Myeloma

Simple Summary

This article provides a comprehensive review of new and emerging treatment strategies against multiple myeloma that employ precision medicines and/or drugs capable of improving the ability of the immune system to prevent or slow down the progression of multiple myeloma. These rationally designed new treatment methods have the potential to change the therapeutic landscape in multiple myeloma and improve the long-term survival outcome.

Abstract

SeverFigurel cellular elements of the bone marrow (BM) microenvironment in multiple myeloma (MM) patients contribute to the immune evasion, proliferation, and drug resistance of MM cells, including myeloid-derived suppressor cells (MDSCs), tumor-associated M2-like, “alternatively activated” macrophages, CD38+ regulatory B-cells (Bregs), and regulatory T-cells (Tregs). These immunosuppressive elements in bidirectional and multi-directional crosstalk with each other inhibit both memory and cytotoxic effector T-cell populations as well as natural killer (NK) cells. Immunomodulatory imide drugs (IMiDs), protease inhibitors (PI), monoclonal antibodies (MoAb), adoptive T-cell/NK cell therapy, and inhibitors of anti-apoptotic signaling pathways have emerged as promising therapeutic platforms that can be employed in various combinations as part of a rationally designed immunomodulatory strategy against an immunosuppressive tumor microenvironment (TME) in MM. These platforms provide the foundation for a new therapeutic paradigm for achieving improved survival of high-risk newly diagnosed as well as relapsed/refractory MM patients. Here we review the scientific rationale and clinical proof of concept for each of these platforms.

Tumor cells educate mesenchymal stromal cells to release chemoprotective and immunomodulatory factors

Factors released by surrounding cells such as cancer-associated mesenchymal stromal cells (CA-MSCs) are involved in tumor progression and chemoresistance. In this study, we characterize the mechanisms by which naïve mesenchymal stromal cells (MSCs) can acquire a CA-MSCs phenotype. Ovarian tumor cells trigger the transformation of MSCs to CA-MSCs by expressing pro-tumoral genes implicated in the chemoresistance of cancer cells, resulting in the secretion of high levels of CXC chemokine receptors 1 and 2 (CXCR1/2) ligands such as chemokine (C-X-C motif) ligand 1 (CXCL1), CXCL2, and interleukin 8 (IL-8). CXCR1/2 ligands can also inhibit the immune response against ovarian tumor cells. Indeed, through their released factors, CA-MSCs promote the differentiation of monocytes towards M2 macrophages, which favors tumor progression. When CXCR1/2 receptors are inhibited, these CA-MSC-activated macrophages lose their M2 properties and acquire an anti-tumoral phenotype. Both ex vivo and in vivo, we used a CXCR1/2 inhibitor to sensitize ovarian tumor cells to carboplatin and circumvent the pro-tumoral effects of CA-MSCs. Since high concentrations of CXCR1/2 ligands in patients’ blood are associated with chemoresistance, CXCR1/2 inhibition could be a potential therapeutic strategy to revert carboplatin resistance.

Tumor-Associated Macrophages in Osteosarcoma: From Mechanisms to Therapy

Osteosarcomas (OSs) are bone tumors most commonly found in pediatric and adolescent patients characterized by high risk of metastatic progression and recurrence after therapy. Effective therapeutic management of this disease still remains elusive as evidenced by poor patient survival rates. To achieve a more effective therapeutic management regimen, and hence patient survival, there is a need to identify more focused targeted therapies for OSs treatment in the clinical setting. The role of the OS tumor stroma microenvironment plays a significant part in the development and dissemination of this disease. Important components, and hence potential targets for treatment, are the tumor-infiltrating macrophages that are known to orchestrate many aspects of OS stromal signaling and disease progression. In particular, increased infiltration of M2-like tumor-associated macrophages (TAMs) has been associated with OS metastasis and poor patient prognosis despite currently used aggressive therapies regimens. This review aims to provide a summary update of current macrophage-centered knowledge and to discuss the possible roles that macrophages play in the process of OS metastasis development focusing on the potential influence of stromal cross-talk signaling between TAMs, cancer-stem cells and additional OSs tumoral microenvironment factors.

The pro-tumorigenic host response to cancer therapies

Resistance to cancer therapy remains a major challenge in clinical oncology. Although the initial treatment phase is often successful, eventual resistance, characterized by tumour relapse or spread, is discouraging. The majority of studies devoted to investigating the basis of resistance have focused on tumour-related changes that contribute to therapy resistance and tumour aggressiveness. However, over the last decade, the diverse roles of various host cells in promoting therapy resistance have become more appreciated. A growing body of evidence demonstrates that cancer therapy can induce host-mediated local and systemic responses, many of which shift the delicate balance within the tumour microenvironment, ultimately facilitating or supporting tumour progression. In this Review, recent advances in understanding how the host response to different cancer therapies may promote therapy resistance are discussed, with a focus on therapy-induced immunological, angiogenic and metastatic effects. Also summarized is the potential of evaluating the host response to cancer therapy in an era of precision medicine in oncology.

Tumor-Associated Macrophages in Hematologic Malignancies: New Insights and Targeted Therapies

The growth of hematologic malignant cells can be facilitated by other non-tumor cells within the same microenvironment, including stromal, vascular, immune and mesenchymal stem cells. Macrophages are an integral part of the human innate immune system and the tumor microenvironment. Complex interplays between the malignant hematologic cells and the infiltrating macrophages promote the formation of leukemia, lymphoma or myeloma-associated macrophages. These pro-tumorigenic macrophages in turn play an important part in facilitating tumor growth, metastasis and chemotherapeutic resistance. Previous reports have highlighted the association between tumor-associated macrophages (TAMs) and disease progression in hematologic malignancies. This review summarizes the role of TAMs in different subtypes of leukemia, lymphoma and myeloma, focusing on new insights and targeted therapies.

Combined immune score of lymphocyte to monocyte ratio and immunoglobulin levels predicts treatment-free survival of multiple myeloma patients after autologous stem cell transplant

Outcomes after ASCT are highly variable making it difficult to predict risk of disease progression. We analyzed the impact of clinically available immune-related biomarkers on treatment-free survival (TFS) in 130 patients receiving Mel200 and ASCT. Absolute lymphocyte count (ALC), monocyte count (AMC), neutrophil count (ANC), and immunoglobulin (Ig) levels were collected on day -2 and 90 of ASCT. The lymphocyte-monocyte (LMR) and neutrophil-lymphocyte ratios (NLR) were then derived. At Day +90, we found that low ALC (18 versus 23 months, p = 0.04) or AMC (13 versus 25 months, p = 0.02) predicted for worse TFS. A low LMR predicted for worse TFS (16 versus 52 months, p = 0.004). Patients with two or three suppressed Ig levels had worse TFS (17 versus 51 months, p = 0.04). Median TFS for poor (low LMR and 2-3 suppressed Ig), intermediate, and good (high LMR and 0-1 suppressed Ig) risk groups was 7.5 versus 27 versus 79 months, respectively (p = 0.0004). In a multivariate analysis, a low LMR and suppressed Ig levels were strong independent predictors of poor TFS. We propose an immune score combining these available tests to stratify patients at risk for early progression and identify those who may benefit from intensified post-ASCT consolidation or immunotherapy based approaches.

JAK1/2 pathway inhibition suppresses M2 polarization and overcomes resistance of myeloma to lenalidomide by reducing TRIB1, MUC1, CD44, CXCL12, and CXCR4 expression

Monocytes polarize into pro-inflammatory macrophage-1 (M1) or alternative macrophage-2 (M2) states with distinct phenotypes and physiological functions. M2 cells promote tumour growth and metastasis whereas M1 macrophages show anti-tumour effects. We found that M2 cells were increased whereas M1 cells were decreased in bone marrow (BM) from multiple myeloma (MM) patients with progressive disease (PD) compared to those in complete remission (CR). Gene expression of Tribbles homolog 1 (TRIB1) protein kinase, an inducer of M2 polarization, was increased in BM from MM patients with PD compared to those in CR. Ruxolitinib (RUX) is an inhibitor of the Janus kinase family of protein tyrosine kinases (JAKs) and is effective for treating patients with myeloproliferative disorders. RUX markedly reduces both M2 polarization and TRIB1 gene expression in MM both in vitro and in vivo in human MM xenografts in severe combined immunodeficient mice. RUX also downregulates the expression of CXCL12, CXCR4, MUC1, and CD44 in MM cells and monocytes co-cultured with MM tumour cells; overexpression of these genes is associated with resistance of MM cells to the immunomodulatory agent lenalidomide. These results provide the rationale for evaluation of JAK inhibitors, including MM BM in combination with lenalidomide, for the treatment of MM patients.

Prevention Is the Best Treatment: The Case for Understanding the Transition from Monoclonal Gammopathy of Undetermined Significance to Myeloma

Multiple myeloma is an invariably fatal cancer of plasma cells. Despite tremendous advances in treatment, this malignancy remains incurable in most individuals. We postulate that strategies aimed at prevention have the potential to be more effective in preventing myeloma-related death than additional pharmaceutical strategies aimed at treating advanced disease. Here, we present a rationale for the development of prevention therapy and highlight potential target areas of study.

Hierarchical Involvement of Myeloid-Derived Suppressor Cells and Monocytes Expressing Latency-Associated Peptide in Plasma Cell Dyscrasias

Objective:

Plasma cell dyscrasias (PCDs) are disorders of plasma cells having in common the production of a monoclonal M-protein. They include a spectrum of conditions that may represent a natural progression of the same disease from monoclonal gammopathy of unknown significance to asymptomatic and symptomatic multiple myeloma, plasma cell leukemia, and Waldenström’s macroglobulinemia. In PCDs, the immune system is actively suppressed through the secretion of suppressive factors and the recruitment of immune suppressive subpopulations. In this study, we examined the expression of two subpopulations of cells with immunosuppressive activity, monocytic myeloid-derived suppressor cells (MDSCs) and monocytes expressing latency-associated peptide (LAP), in patients with different PCDs and in healthy volunteers.

Materials and Methods:

A total of 27 consecutive patients with PCDs were included in this study. Nineteen healthy volunteers served as controls.

Results:

We observed a hierarchical correlation between disease activity and the presence of monocytes with immunosuppressive activity.

Conclusion:

These results suggest that MDSCs and monocytes expressing LAP have diverging roles in PCDs and may perhaps serve as biomarkers of tumor activity and bulk.

Antibody-Dependent Cellular Phagocytosis by Macrophages is a Novel Mechanism of Action of Elotuzumab

Elotuzumab, a recently approved antibody for the treatment of multiple myeloma, has been shown to stimulate Fcγ receptor (FcγR)-mediated antibody-dependent cellular cytotoxicity by natural killer (NK) cells toward myeloma cells. The modulatory effects of elotuzumab on other effector cells in the tumor microenvironment, however, has not been fully explored. Antibody-dependent cellular phagocytosis (ADCP) is a mechanism by which macrophages contribute to antitumor potency of monoclonal antibodies. Herein, we studied the NK cell independent effect of elotuzumab on tumor-associated macrophages using a xenograft tumor model deficient in NK and adaptive immune cells. We demonstrate significant antitumor efficacy of single-agent elotuzumab in immunocompromised xenograft models of multiple myeloma, which is in part mediated by Fc-FcγR interaction of elotuzumab with macrophages. Elotuzumab is shown in this study to induce phenotypic activation of macrophages in vivo and mediates ADCP of myeloma cells though a FcγR-dependent manner in vitro Together, these findings propose a novel immune-mediated mechanism by which elotuzumab exerts anti-myeloma activity and helps to provide rationale for combination therapies that can enhance macrophage activity. Mol Cancer Ther; 17(7); 1454-63. ©2018 AACR.

Mechanisms of Resistance in Multiple Myeloma

Multiple myeloma (MM) is an incurable hematopoietic cancer that is characterized by malignant plasma cell infiltration of the bone marrow and/or extramedullary sites. Multi-modality approaches including "novel agents," traditional chemotherapy, and/or stem cell transplantation are used in MM therapy. Drug resistance, however, ultimately develops and the disease remains incurable for the vast majority of patients. In this chapter, we review both tumor cell-autonomous and non-autonomous (microenvironment-dependent) mechanisms of drug resistance. MM provides an attractive paradigm highlighting a number of current concepts and challenges in oncology. Firstly, identification of MM cancer stem cells and their unique drug resistance attributes may provide rational avenues towards MM eradication and cure. Secondly, the oligoclonal evolution of MM and alternation of "clonal tides" upon therapy challenge our current understanding of treatment responses. Thirdly, the success of MM "novel agents" provides exemplary evidence for the impact of therapies that target the immune and non-immune microenvironment. Fourthly, the rapid pace of drug approvals for MM creates an impetus for development of precision medicine strategies and biomarkers that promote efficacy and mitigate toxicity and cost. While routine cure of the disease remains the ultimate and yet unattainable prize, MM advances in the last 10-15 years have provided an astounding paradigm for the treatment of blood cancers in the modern era and have radically transformed patient outcomes.

Activation of NK cells and disruption of PD-L1/PD-1 axis: two different ways for lenalidomide to block myeloma progression

Natural Killer (NK) cells play a critical role against tumor cells in hematological malignancies. Their activating receptors are essential in tumor cell killing. In Multiple Myeloma (MM) patients, NK cell differentiation, activation and cytotoxic potential are strongly impaired leading to MM escape from immune surveillance in tissues and bone marrow. Mechanisms used by MM to affect NK cell functions are mediated by the release of soluble factors, the expression of activating and inhibitory NK cell ligands, and the expression of immune check-point inhibitors. Lenalidomide represents an efficient clinical approach in MM treatment to improve patients' survival. Lenalidomide does not only promotes tumor apoptosis, but also stimulates T and NK cells, thereby facilitating NK-mediated tumor recognition and killing. This occurs since Lenalidomide acts on several critical points: stimulates T cell proliferation and cytokine secretion; decreases the expression of the immune check-point inhibitor Programmed Death-1 (PD-1) on both T and NK cells in MM patients; decreases the expression of both PD-1 and PD-L1 on MM cells; promotes MM cell death and abrogates MM/stromal microenvironment cross-talk, a process known to promote the MM cell survival and proliferation. This leads to the inhibition of the negative signal induced by PD-1/PD-L1 axis on NK cells, restoring NK cell cytotoxic functions. Given the importance of an effective immune response to counteract the MM progression and the promising approaches using anti-PD-1/PD-L1 strategies, we will discuss in this review how Lenalidomide could represent an adequate approach to re-establish the recognition against MM by exhausted NK cell.

Prognostic role of TPL2 in early‑stage non‑small cell lung cancer

Non-small cell lung cancer (NSCLC) accounts for ~70% of all lung cancer-associated mortalities worldwide. The serine/threonine protein kinase tumor progression locus 2 [TPL2/MAP3 kinase 8 (MAP3K8)] may impact oncogenic events; however the role of TPL2 in lung carcinogenesis remains unclear. The present study was focused on the potential prognostic role of TPL2 in 101 patients with early-stage NSCLC. Since TPL2 is a potential target of miR-21, the association between TPL2 and miR-21 expression was also examined. TPL2 and miR-21 mRNA expression was quantified using reverse transcription quantitative polymerase chain reaction (RT-qPCR). TPL2 protein levels were evaluated by immunohistochemistry (IHC). The present study identified that the mRNA expression of TPL2 was low in 52/101 (51%) cases and high in 49/101 (49%) cases. IHC analysis of TPL2 protein expression often demonstrated identical mRNA results. No statistically significant associations were observed between the mRNA expression of TPL2 and the predominant clinicopathological characteristics of the patients with NSCLC, as well as identifying no association between TPL2 and miR-21. TPL2 mRNA expression was significantly higher in patients with NSCLC with good prognosis (disease-free interval P=0.009; overall survival P=0.024), when compared with those of poor prognosis. Focusing on the difference in mRNA expression of TPL2 among the adenocarcinomas in affected patients, TPL2 was more highly expressed in lepidic adenocarcinomas compared with in the other subtypes (P=0.012). The present study is the first examination, to the best of our knowledge, of TPL2 in early-stage NSCLC in relation to miR-21, and in different adenocarcinoma subtypes. Future studies must clarify the mechanism by which TPL2 is involved in lung carcinogenesis due to its important translational implications.

Extracellular matrix and the myeloid-in-myeloma compartment: balancing tolerogenic and immunogenic inflammation in the myeloma niche

The last 10-15 years have witnessed a revolution in treating multiple myeloma, an incurable cancer of Ab-producing plasma cells. Advances in myeloma therapy were ushered in by novel agents that remodel the myeloma immune microenvironment. The first generation of novel agents included immunomodulatory drugs (thalidomide analogs) and proteasome inhibitors that target crucial pathways that regulate immunity and inflammation, such as NF-κB. This paradigm continued with the recent regulatory approval of mAbs (elotuzumab, daratumumab) that impact both tumor cells and associated immune cells. Moreover, recent clinical data support checkpoint inhibition immunotherapy in myeloma. With the success of these agents has come the growing realization that the myeloid infiltrate in myeloma lesions-what we collectively call the myeloid-in-myeloma compartment-variably sustains or deters tumor cells by shaping the inflammatory milieu of the myeloma niche and by promoting or antagonizing immune-modulating therapies. The myeloid-in-myeloma compartment includes myeloma-associated macrophages and granulocytes, dendritic cells, and myeloid-derived-suppressor cells. These cell types reflect variable states of differentiation and activation of tumor-infiltrating cells derived from resident myeloid progenitors in the bone marrow-the canonical myeloma niche-or myeloid cells that seed both canonical and extramedullary, noncanonical niches. Myeloma-infiltrating myeloid cells engage in crosstalk with extracellular matrix components, stromal cells, and tumor cells. This complex regulation determines the composition, activation state, and maturation of the myeloid-in-myeloma compartment as well as the balance between immunogenic and tolerogenic inflammation in the niche. Redressing this balance may be a crucial determinant for the success of antimyeloma immunotherapies.

Evaluation of the potential therapeutic benefits of macrophage reprogramming in multiple myeloma

Tumor-associated macrophages (TAM) are important components of the multiple myeloma (MM) microenvironment that support malignant plasma cell survival and resistance to therapy. It has been proposed that macrophages (MØ) retain the capacity to change in response to stimuli that can restore their antitumor functions. Here, we investigated several approaches to reprogram MØ as a novel therapeutic strategy in MM. First, we found tumor-limiting and tumor-supporting capabilities for monocyte-derived M1-like MØ and M2-like MØ, respectively, when mixed with MM cells, both in vitro and in vivo. Multicolor confocal microscopy revealed that MM-associated MØ displayed a predominant M2-like phenotype in the bone marrow of MM patient samples, and a high expression of the pro-M2 cytokine macrophage migration inhibitory factor (MIF). To reprogram the protumoral M2-like MØ present in MM toward antitumoral M1-like MØ, we tested the pro-M1 cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) plus blockade of the M2 cytokines macrophage colony-stimulating factor or MIF. The combination of GM-CSF plus the MIF inhibitor 4-iodo-6-phenyl-pyrimidine achieved the best reprogramming responses toward an M1 profile, at both gene and protein expression levels, as well as remarkable tumoricidal effects. Furthermore, this combined treatment elicited MØ-dependent therapeutic responses in MM xenograft mouse models, which were linked to upregulation of M1 and reciprocal downregulation of M2 MØ markers. Our results reveal the therapeutic potential of reprogramming MØ in the context of MM.

Immunoregulatory roles of versican proteolysis in the myeloma microenvironment

Myeloma immunosurveillance remains incompletely understood. We have demonstrated proteolytic processing of the matrix proteoglycan, versican (VCAN), in myeloma tumors. Whereas intact VCAN exerts tolerogenic activities through Toll-like receptor 2 (TLR2) binding, the immunoregulatory consequences of VCAN proteolysis remain unknown. Here we show that human myeloma tumors displaying CD8(+) infiltration/aggregates underwent VCAN proteolysis at a site predicted to generate a glycosaminoglycan-bereft N-terminal fragment, versikine Myeloma-associated macrophages (MAMs), rather than tumor cells, chiefly produced V1-VCAN, the precursor to versikine, whereas stromal cell-derived ADAMTS1 was the most robustly expressed VCAN-degrading protease. Purified versikine induced early expression of inflammatory cytokines interleukin 1β (IL-1β) and IL-6 by human myeloma marrow-derived MAMs. We show that versikine signals through pathways both dependent and independent of Tpl2 kinase, a key regulator of nuclear factor κB1-mediated MAPK activation in macrophages. Unlike intact VCAN, versikine-induced Il-6 production was partially independent of Tlr2. In a model of macrophage-myeloma cell crosstalk, versikine induced components of "T-cell inflammation," including IRF8-dependent type I interferon transcriptional signatures and T-cell chemoattractant CCL2. Thus the interplay between stromal cells and myeloid cells in the myeloma microenvironment generates versikine, a novel bioactive damage-associated molecular pattern that may facilitate immune sensing of myeloma tumors and modulate the tolerogenic consequences of intact VCAN accumulation. Therapeutic versikine administration may potentiate T-cell-activating immunotherapies.

Multiple myeloma in the marrow: pathogenesis and treatments

Multiple myeloma (MM) is a B cell malignancy resulting in osteolytic lesions and fractures. In the disease state, bone healing is limited owing to increased osteoclastic and decreased osteoblastic activity, as well as an MM-induced forward-feedback cycle where bone-embedded growth factors further enhance tumor progression as bone is resorbed. Recent work on somatic mutation in MM tumors has provided insight into cytogenetic changes associated with this disease; the initiating driver mutations causing MM are diverse because of the complexity and multitude of mutations inherent in MM tumor cells. This manuscript provides an overview of MM pathogenesis by summarizing cytogenic changes related to oncogenes and tumor suppressors associated with MM, reviewing risk factors, and describing the disease progression from monoclonal gammopathy of undetermined significance to overt MM. It also highlights the importance of the bone marrow microenvironment (BMM) in the establishment and progression of MM, as well as associated MM-induced bone disease, and the relationship of the bone marrow to current and future therapeutics. This review highlights why understanding the basic biology of the healthy and diseased BMM is crucial in the quest for better treatments and work toward a cure for genetically diverse diseases such as MM.

Autopsy Analysis may Contribute to Establish Actual Incidence of Second Primary Malignancies in Myeloma

Second primary malignancies (SPMs) are issues for patients with multiple myeloma (MM). There may have been some limitations in prior studies, such as difficulties in a longer follow-up and absence of established screening methods. Therefore, we studied autopsied cases to overcome these limitations. This study aimed to examine SPMs using autopsy reports. Ninety-one cases of MM autopsied at our institution from 1979 to 2013 were analyzed. Median age of autopsied patients was 64.1 years, and proportion of male/female was 59/32. Autopsy was performed in 35.3% of patients died of MM. There were five cases of SPMs with a median confirmation time of 38 (12-132) months from the diagnosis of MM. In three of the five patients, the diagnosis of SPMs was established at autopsy. One case was of myelodysplastic syndrome, and the others were of non-hematological malignancies. The annual risk of SPM estimated using the Kaplan-Meier method was approximately 1%. Three of five SPM cases were detected at autopsy. Analysis of autopsy may contribute to estimate the actual risk of SPMs in MM.

Navigating the bone marrow niche: translational insights and cancer-driven dysfunction

The bone marrow niche consists of stem and progenitor cells destined to become mature cells such as haematopoietic elements, osteoblasts or adipocytes. Marrow cells, influenced by endocrine, paracrine and autocrine factors, ultimately function as a unit to regulate bone remodelling and haematopoiesis. Current evidence highlights that the bone marrow niche is not merely an anatomic compartment; rather, it integrates the physiology of two distinct organ systems, the skeleton and the marrow. The niche has a hypoxic microenvironment that maintains quiescent haematopoietic stem cells (HSCs) and supports glycolytic metabolism. In response to biochemical cues and under the influence of neural, hormonal, and biochemical factors, marrow stromal elements, such as mesenchymal stromal cells (MSCs), differentiate into mature, functioning cells. However, disruption of the niche can affect cellular differentiation, resulting in disorders ranging from osteoporosis to malignancy. In this Review, we propose that the niche reflects the vitality of two tissues - bone and blood - by providing a unique environment for stem and stromal cells to flourish while simultaneously preventing disproportionate proliferation, malignant transformation or loss of the multipotent progenitors required for healing, functional immunity and growth throughout an organism's lifetime. Through a fuller understanding of the complexity of the niche in physiologic and pathologic states, the successful development of more-effective therapeutic approaches to target the niche and its cellular components for the treatment of rheumatic, endocrine, neoplastic and metabolic diseases becomes achievable.

MicroC(3): an ex vivo microfluidic cis-coculture assay to test chemosensitivity and resistance of patient multiple myeloma cells

Chemosensitivity and resistance assays (CSRAs) aim to direct therapies based upon ex vivo responses of patient tumor cells to chemotherapeutic drugs. However, successful CSRAs are yet to be developed. Here, we exposed primary CD138(+) multiple myeloma (MM) cells to bortezomib, a clinical proteasome inhibitor, in microfluidic-cis-coculture (MicroC(3)) incorporating the patient's own CD138(-) tumor-companion mononuclear cells to integrate some of the patients' own tumor microenvironment components in the CSRA design. Statistical clustering techniques segregated MicroC(3) responses into two groups which correctly identified all seventeen patients as either clinically responsive or non-responsive to bortezomib-containing therapies. In contrast, when the same patient MM samples were analyzed in the absence of the CD138(-) cells (monoculture), the tumor cell responses did not segregate into clinical response clusters. Thus, MicroC(3) identified bortezomib-therapy MM patient responses making it a viable CSRA candidate toward enabling personalized therapy.

Cancer stem cells and tumor-associated macrophages: a roadmap for multitargeting strategies

The idea that tumor initiation and progression are driven by a subset of cells endowed with stem-like properties was first described by Rudolf Virchow in 1855. 'Cancer stem cells', as they were termed more than a century later, represent a subset of tumor cells that are able to generate all tumorigenic and nontumorigenic cell types within the malignancy. Although their existence was hypothesized >150 years ago, it was only recently that stem-like cells started to be isolated from different neoplastic malignancies. Interestingly, Virchow, in suggesting a correlation between cancer and the inflammatory microenvironment, also paved the way for the 'Seed and Soil' theory proposed by Paget a few years later. Despite the time that has passed since these two important concepts were suggested, the relationships between Virchow's 'stem-like cells' and Paget's 'soil' are far from being fully understood. One emerging topic is the importance of a stem-like niche in modulating the biological properties of stem-like cancer cells and thus in affecting the response of the tumor to drugs. This review aims to summarize the recent molecular data concerning the multilayered relationship between cancer stem cells and tumor-associated macrophages that form a key component of the tumor microenvironment. We also discuss the therapeutic implications of targeting this synergistic interplay.

Tumoricidal Effects of Macrophage-Activating Immunotherapy in a Murine Model of Relapsed/Refractory Multiple Myeloma

Myeloma remains a virtually incurable malignancy. The inevitable evolution of multidrug-resistant clones and widespread clonal heterogeneity limit the potential of traditional and novel therapies to eliminate minimal residual disease (MRD), a reliable harbinger of relapse. Here, we show potent anti-myeloma activity of macrophage-activating immunotherapy (αCD40+CpG) that resulted in prolongation of progression-free survival (PFS) and overall survival (OS) in an immunocompetent, preclinically validated, transplant-based model of multidrug-resistant, relapsed/refractory myeloma (t-Vκ*MYC). αCD40+CpG was effective in vivo in the absence of cytolytic natural killer, T, or B cells and resulted in expansion of M1-polarized (cytolytic/tumoricidal) macrophages in the bone marrow. Moreover, we show that concurrent loss/inhibition of Tpl2 kinase (Cot, Map3k8), a MAP3K that is recruited to activated CD40 complex and regulates macrophage activation/cytokine production, potentiated direct, ex vivo anti-myeloma tumoricidal activity of αCD40+CpG-activated macrophages, promoted production of antitumor cytokine IL12 in vitro and in vivo, and synergized with αCD40+CpG to further prolong PFS and OS in vivo. Our results support the combination of αCD40-based macrophage activation and TPL2 inhibition for myeloma immunotherapy. We propose that αCD40-mediated activation of innate antitumor immunity may be a promising approach to control/eradicate MRD following cytoreduction with traditional or novel anti-myeloma therapies.

TPL2 kinase regulates the inflammatory milieu of the myeloma niche

Targeted modulation of microenvironmental regulatory pathways may be essential to control myeloma and other genetically/clonally heterogeneous cancers. Here we report that human myeloma-associated monocytes/macrophages (MAM), but not myeloma plasma cells, constitute the predominant source of interleukin-1β (IL-1β), IL-10, and tumor necrosis factor-α at diagnosis, whereas IL-6 originates from stromal cells and macrophages. To dissect MAM activation/cytokine pathways, we analyzed Toll-like receptor (TLR) expression in human myeloma CD14(+) cells. We observed coregulation of TLR2 and TLR6 expression correlating with local processing of versican, a proteoglycan TLR2/6 agonist linked to carcinoma progression. Versican has not been mechanistically implicated in myeloma pathogenesis. We hypothesized that the most readily accessible target in the versican-TLR2/6 pathway would be the mitogen-activated protein 3 (MAP3) kinase, TPL2 (Cot/MAP3K8). Ablation of Tpl2 in the genetically engineered in vivo myeloma model, Vκ*MYC, led to prolonged disease latency associated with plasma cell growth defect. Tpl2 loss abrogated the "inflammatory switch" in MAM within nascent myeloma lesions and licensed macrophage repolarization in established tumors. MYC activation/expression in plasma cells was independent of Tpl2 activity. Pharmacologic TPL2 inhibition in human monocytes led to dose-dependent attenuation of IL-1β induction/secretion in response to TLR2 stimulation. Our results highlight a TLR2/6-dependent TPL2 pathway as novel therapeutic target acting nonautonomously through macrophages to control myeloma progression.

Preserved levels of uninvolved immunoglobulins are independently associated with favorable outcome in patients with symptomatic multiple myeloma

Suppression of uninvolved immunoglobulins is common in multiple myeloma (MM) but the prognostic significance of this phenomenon has not been assessed. We evaluated the prognostic significance of the preservation of uninvolved immunoglobulins in 1755 consecutive, unselected, patients with newly diagnosed, symptomatic MM with pre-therapy immunoglobulin levels measured by nephelometry. Suppression of at least one uninvolved immunoglobulin was observed in 87% of patients and was more common in patients with immunoglobulin A myeloma, those aged over 65 years, in patients with advanced-International Staging System (ISS) stage, extensive-bone marrow infiltration, anemia, low platelet counts, high levels of serum M-monoclonal protein or renal dysfunction. Patients with preserved immunoglobulins had a better survival than patients with suppressed immunoglobulins (median survival 55 vs 41.5 months, P<0.001). In multivariate analysis, preservation of uninvolved immunoglobulins was independently associated with better survival (hazard ratio: 0.781, 95% confidence interval: 0.618-0.987, P=0.039); irrespective of the treatment. In a subset of 500 patients, which were strictly followed for disease progression, preservation of uninvolved immunoglobulins was associated with a significantly longer progression-free survival (60 vs 25 months, P<0.001), independently of other common prognostic factors. In conclusion, preservation of uninvolved immunoglobulins in newly diagnosed patients with symptomatic MM was independently associated with long term disease control and improved survival.

Monocyte subpopulations in angiogenesis

Growing understanding of the role of the tumor microenvironment in angiogenesis has brought monocyte-derived cells into focus. Monocyte subpopulations are an increasingly attractive therapeutic target in many pathologic states, including cancer. Before monocyte-directed therapies can be fully harnessed for clinical use, understanding of monocyte-driven angiogenesis in tissue development and homeostasis, as well as malignancy, is required. Here, we provide an overview of the mechanisms by which monocytic subpopulations contribute to angiogenesis in tissue and tumor development, highlight gaps in our existing knowledge, and discuss opportunities to exploit these cells for clinical benefit.