Human anti-CD40 antagonist antibody triggers significant antitumor activity against human multiple myeloma

Development of therapeutic monoclonal antibodies against DKK1 peptide-HLA-A2 complex to treat human cancers

BACKGROUND

Targeted immunotherapy with monoclonal antibodies (mAbs) is an effective and safe method for the treatment of malignancies. Development of mAbs with improved cytotoxicity, targeting new and known tumor-associated antigens, therefore continues to be an active research area. We reported that Dickkopf-1 (DKK1) is a good target for immunotherapy of human cancers based on its wide expression in different cancers but not in normal tissues. As DKK1 is a secreted protein, mAbs binding directly to DKK1 have limited effects on cancer cells in vivo.

METHODS

The specificity and antibody-binding capacity of DKK1-A2 mAbs were determined using indirect ELISA, confocal imaging, QIFIKIT antibody-binding capacity and cell surface binding assays. The affinity of mAbs was determined using a surface plasmon resonance biosensor. A flow cytometry-based cell death was performed to detect tumor cell apoptosis. Antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays were used to evaluate the ability of DKK1-A2 mAbs to mediate ADCC and CDC activities against tumor cells in vitro. Flow cytometry data were collected with an FACSymphony A3 cell analyzer and analyzed with FlowJo V.10.1 software. Human cancer xenograft mouse models were used to determine the in vivo therapeutic efficacy and the potential safety and toxicity of DKK1-A2 mAbs. In situ TUNEL assay was performed to detect apoptosis in tumors and mouse organs.

RESULTS

We generated novel DKK1-A2 mAbs that recognize the DKK1 P20 peptide presented by human HLA-A*0201 (HLA-A2) molecules (DKK1-A2 complexes) that are naturally expressed by HLA-A2+DKK1+ cancer cells. These mAbs directly induced apoptosis in HLA-A2+DKK1+ hematologic and solid cancer cells by activating the caspase-9 cascade, effectively lysed the cancer cells in vitro by mediating CDC and ADCC and were therapeutic against established cancers in their xenograft mouse models. As DKK1 is not detected in most human tissues, DKK1-A2 mAbs neither bound to or killed HLA-A2+ blood cells in vitro nor caused tissue damage in tumor-free or tumor-bearing HLA-A2-transgenic mice.

CONCLUSION

Our study suggests that DKK1-A2 mAbs may be a promising therapeutic agent to treat human cancers.

FcγRs and Their Relevance for the Activity of Anti-CD40 Antibodies

Inhibitory targeting of the CD40L-CD40 system is a promising therapeutic option in the field of organ transplantation and is also attractive in the treatment of autoimmune diseases. After early complex results with neutralizing CD40L antibodies, it turned out that lack of Fcγ receptor (FcγR)-binding is the crucial factor for the development of safe inhibitory antibodies targeting CD40L or CD40. Indeed, in recent years, blocking CD40 antibodies not interacting with FcγRs, has proven to be well tolerated in clinical studies and has shown initial clinical efficacy. Stimulation of CD40 is also of considerable therapeutic interest, especially in cancer immunotherapy. CD40 can be robustly activated by genetically engineered variants of soluble CD40L but also by anti-CD40 antibodies. However, the development of CD40L-based agonists is biotechnologically and pharmacokinetically challenging, and anti-CD40 antibodies typically display only strong agonism in complex with FcγRs or upon secondary crosslinking. The latter, however, typically results in poorly developable mixtures of molecule species of varying stoichiometry and FcγR-binding by anti-CD40 antibodies can elicit unwanted side effects such as antibody-dependent cellular cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP) of CD40 expressing immune cells. Here, we summarize and compare strategies to overcome the unwanted target cell-destroying activity of anti-CD40-FcγR complexes, especially the use of FcγR type-specific mutants and the FcγR-independent cell surface anchoring of bispecific anti-CD40 fusion proteins. Especially, we discuss the therapeutic potential of these strategies in view of the emerging evidence for the dose-limiting activities of systemic CD40 engagement.

In ovo model in cancer research and tumor immunology

Considering cancer not only as malignant cells on their own but as a complex disease in which tumor cells interact and communicate with their microenvironment has motivated the establishment of clinically relevant 3D models in past years. Technological advances gave rise to novel bioengineered models, improved organoid systems, and microfabrication approaches, increasing scientific importance in preclinical research. Notwithstanding, mammalian in vivo models remain closest to mimic the patient’s situation but are limited by cost, time, and ethical constraints. Herein, the in ovo model bridges the gap as an advanced model for basic and translational cancer research without the need for ethical approval. With the avian embryo being a naturally immunodeficient host, tumor cells and primary tissues can be engrafted on the vascularized chorioallantoic membrane (CAM) with high efficiencies regardless of species-specific restrictions. The extraembryonic membranes are connected to the embryo through a continuous circulatory system, readily accessible for manipulation or longitudinal monitoring of tumor growth, metastasis, angiogenesis, and matrix remodeling. However, its applicability in immunoncological research is largely underexplored. Dual engrafting of malignant and immune cells could provide a platform to study tumor-immune cell interactions in a complex, heterogenic and dynamic microenvironment with high reproducibility. With some caveats to keep in mind, versatile methods for in and ex ovo monitoring of cellular and molecular dynamics already established in ovo are applicable alike. In this view, the present review aims to emphasize and discuss opportunities and limitations of the chicken embryo model for pre-clinical research in cancer and cancer immunology.

The Sec61 translocon is a therapeutic vulnerability in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy characterized by the uncontrolled expansion of plasma cells in the bone marrow. While proteasome inhibitors like bortezomib efficiently halt MM progression, drug resistance inevitably develop, and novel therapeutic approaches are needed. Here, we used a recently discovered Sec61 inhibitor, mycolactone, to assess the interest of disrupting MM proteostasis via protein translocation blockade. In human MM cell lines, mycolactone caused rapid defects in secretion of immunoglobulins and expression of pro‐survival interleukin (IL)‐6 receptor and CD40, whose activation stimulates IL‐6 production. Mycolactone also triggered pro‐apoptotic endoplasmic reticulum stress responses synergizing with bortezomib for induction of MM cell death and overriding acquired resistance to the proteasome inhibitor. Notably, the mycolactone–bortezomib combination rapidly killed patient‐derived MM cells ex vivo, but not normal mononuclear cells. In immunodeficient mice engrafted with MM cells, it demonstrated superior therapeutic efficacy over single drug treatments, without inducing toxic side effects. Collectively, these findings establish Sec61 blockers as novel anti‐MM agents and reveal the interest of targeting both the translocon and the proteasome in proteostasis‐addicted tumors.

Can Targeting Hypoxia-Mediated Acidification of the Bone Marrow Microenvironment Kill Myeloma Tumor Cells?

Multiple myeloma (MM) is an incurable cancer arising from malignant plasma cells that engraft in the bone marrow (BM). The physiology of these cancer cells within the BM microenvironment (TME) plays a critical role in MM development. These processes may be similar to what has been observed in the TME of other (non-hematological) solid tumors. It has been long reported that within the BM, vascular endothelial growth factor (VEGF), increased angiogenesis and microvessel density, and activation of hypoxia-induced transcription factors (HIF) are correlated with MM progression but despite a great deal of effort and some modest preclinical success the overall clinical efficacy of using anti-angiogenic and hypoxia-targeting strategies, has been limited. This review will explore the hypothesis that the TME of MM engrafted in the BM is distinctly different from non-hematological-derived solid tumors calling into question how effective these strategies may be against MM. We further identify other hypoxia-mediated effectors, such as hypoxia-mediated acidification of the TME, oxygen-dependent metabolic changes, and the generation of reactive oxygen species (ROS), that may prove to be more effective targets against MM.

CD40- and CD95-specific antibody single chain-Baff fusion proteins display BaffR-, TACI- and BCMA-restricted agonism

Antibodies that target a clinically relevant group of receptors within the tumor necrosis factor receptor superfamily (TNFRSF), including CD40 and CD95 (Fas/Apo-1), also require binding to Fc gamma receptors (FcγRs) to elicit a strong agonistic activity. This FcγR dependency largely relies on the mere cellular anchoring through the antibody’s Fc domain and does not involve the engagement of FcγR signaling. The aim of this study was to elicit agonistic activity from αCD40 and αCD95 antibodies in a myeloma cell anchoring-controlled FcγR-independent manner. For this purpose, various antibody variants (IgG1, IgG1_N297A, Fab₂) against the TNFRSF members CD40 and CD95 were genetically fused to a single-chain-encoded B-cell activating factor (scBaff) trimer as a C-terminal myeloma-specific anchoring domain substituting for Fc domain-mediated FcγR binding. The antibody-scBaff fusion proteins were evaluated in binding studies and functional assays using tumor cell lines expressing one or more of the three receptors of Baff: BaffR, transmembrane activator and CAML interactor (TACI) and B-cell maturation antigen (BCMA). Cellular binding studies showed that the binding properties of the different domains within the fusion proteins remained fully intact in the antibody-scBaff fusion proteins. In co-culture assays of CD40- and CD95-responsive cells with BaffR, BCMA or TACI expressing anchoring cells, the antibody fusion proteins displayed strong agonism while only minor receptor stimulation was observed in co-cultures with cells without expression of Baff-interacting receptors. Thus, our CD40 and CD95 antibody fusion proteins display myeloma cell-dependent activity and promise reduced systemic side effects compared to conventional CD40 and CD95 agonists.

A Review of Chimeric Antigen Receptor T-Cell Therapy for Myeloma and Lymphoma

Collectively, hematological malignancies account for the fourth most common malignancy. Myeloma and lymphoma are the most common types of hematological malignancies. Unfortunately, the management of refractory myeloma and lymphoma remains challenging. The discovery of new immunological therapies, namely chimeric antigen receptors T cells (CAR-T), outlined unprecedented B cell malignancies results. In this context, the CAR-T-based approach has led to the proliferation of many clinical studies. In this review, we will deal with the CAR-T structure, and we will summarize the primary clinical studies assessing the risks and benefits of CAR-T cell therapy. We will also deal with the adverse events and management of cytokine release syndromes/immune effector cell-associated neurotoxicity syndrome (ICANS). Subsequently, we will review potential future improvements to overcome refractoriness and improve expansion while decreasing CAR-T's off-target effects. The advances in the CAR-T platform represent a step forward with promising unlimited future possibilities that made it a paradigm-shifting for the management of B cell malignancies.

A Bispecific Antibody Antagonizes Prosurvival CD40 Signaling and Promotes Vγ9Vδ2 T cell-Mediated Antitumor Responses in Human B-cell Malignancies

Novel T cell-based therapies for the treatment of B-cell malignancies, such as chronic lymphocytic leukemia (CLL) and multiple myeloma (MM), are thought to have strong potential. Progress, however, has been hampered by low efficacy and high toxicity. Tumor targeting by Vγ9Vδ2 T cells, a conserved T-cell subset with potent intrinsic antitumor properties, mediated by a bispecific antibody represents a novel approach promising high efficacy with limited toxicity. Here, we describe the generation of a bispecific Vγ9Vδ2 T-cell engager directed against CD40, which, due to its overexpression and biological footprint in malignant B cells, represents an attractive target. The CD40-targeting moiety of the bispecific antibody was selected because it can prevent CD40L-induced prosurvival signaling and reduce CD40-mediated resistance of CLL cells to venetoclax. Selective activation of Vγ9Vδ2 T cells in the presence of CD40⁺ tumor cells induced potent Vγ9Vδ2 T-cell degranulation, cytotoxicity against CLL and MM cells in vitro, and in vivo control of MM in a xenograft model. The CD40-bispecific γδ T-cell engager demonstrated lysis of leukemic cells by autologous Vγ9Vδ2 T cells present in patient-derived samples. Taken together, our CD40 bispecific γδ T-cell engager increased the sensitivity of leukemic cells to apoptosis and induced a potent Vγ9Vδ2 T cell-dependent antileukemic response. It may, therefore, represent a potential candidate for the development of novel treatments for B-cell malignancies.

Chimeric Antigen Receptor T-cell Therapy for Multiple Myeloma

Relapsed/refractory multiple myeloma (MM) remains a significant clinical challenge, despite a wide array of approved therapeutic agents. Immunotherapy offers an advantage in this setting. Chimeric antigen receptor (CAR) modified T-cells have transformed care for patients with hematologic malignancies. CAR-T cells targeting CD-19 B-cell lymphoma cells have shown prominent activity in lymphoma and acute lymphoblastic leukemia. Recently, the CAR-T cell platform for MM demonstrated therapeutic benefit. Hence, it is rapidly progressing. The most commonly tested target for MM is the B-cell maturation antigen. Complexities involved in the generation and use of CAR-T cells for MM include the identification of appropriate target antigens that are specific, and tumor type restricted, in addition to the optimization of CAR constructs to mitigate toxicities including cytokine release syndrome. CAR-T cells hold immense promise as a therapeutic modality for the treatment of MM. In this article, we provide an updated review of clinical trials of MM-specific CAR-T cells.

The potentials of immune checkpoints for the treatment of blood malignancies

Immune checkpoints are the regulators of the immune system, which include stimulatory and inhibitory receptors. They play substantial roles in the maintenance of immune system homeostasis and the prevention of autoimmunity and cancer. In the current review, immune checkpoints roles are surveyed in the initiation, progression, and treatment of blood malignancies. The significant roles of immune checkpoints are discussed as clinical markers in the diagnosis and prognosis of a plethora of blood malignancies and also as potential targets for the treatment of these malignancies. It could be concluded that the regulation of immune checkpoints in various blood cancers can be employed as a novel strategy to obtain effective results in leukemia treatment and introduce immune checkpoint inhibitors as sufficient weapons against blood cancers in the future.

Mechanistic basis of co-stimulatory CD40-CD40L ligation mediated regulation of immune responses in cancer and autoimmune disorders

Generation of an accurate humoral and a cell mediated adaptive immune responsesare dictated by binding of an antigen to a T- and a B-cell receptor, respectively (first signal) followed by ligation of costimulatory molecules (second signal). CD40, a costimulatory receptor molecule, expressed mainly on antigen presenting cells, some non-immune cells and tumors, binds to CD40 ligand molecule expressed transiently on T-cells and non-immune cells under inflammatory conditions. In the past decade, the CD40-CD40L interaction has emerged as an immune-potentiating system that governs and regulates host immune response against various diseases and pathogens, failing of which results in detrimental patho-physiologies including cancer and autoimmune disorders. CD40-CD40L transduces immune signals intracellularly via TRAF-dependent and independent mechanisms and further downstream by different MAPK pathways and transcription factors such as NF-κB, p38 etc. While CD40 signaling pathway through its cognate interaction between B and T cells promotes activation and proliferation of B-cells, Ig class switching, and generation of B cell memory; however, CD40-CD40L interaction involving other APCs and non-immune cells relay distinct cell signaling resulting in production of a variety of cytokines/chemokines and cell adhesion molecules ultimately conferring host defense against pathogen. In cancer and autoimmune disorders, CD40-CD40L interaction is also responsible for aberrant expression of many disease specific markers, class I/II MHC molecules and other co-stimulatory molecules such as B7 and CD28 in cell- and disease-specific manner. In the present review, the current state of understanding about the CD40-CD40L mediated regulation of immune and non-immune cells is presented. The current paradigm is to target CD40 using agonist anti-CD40 mAbs alone or in synergistic combination with chemotherapy in order to harness or confer anti-tumor and anti-inflammatory immunity.

The Use of Anti-CD40 mAb in Cancer

Immunomodulatory monoclonal antibody (mAb) therapy is at the forefront of developing cancer therapeutics with numerous targeted agents proving highly effective in selective patients at stimulating protective host immunity, capable of eradicating established tumours and leading to long-term disease-free states. The cell surface marker CD40 is expressed on a range of immune cells and transformed cells in malignant states whose signalling plays a critical role in modulating adaptive immune responses. Anti-CD40 mAb therapy acts via multiple mechanisms to stimulate anti-tumour immunity across a broad range of lymphoid and solid malignancies. A wealth of preclinical research in this field has led to the successful development of multiple anti-CD40 mAb agents that have shown promise in early-phase clinical trials. Significant progress has been made to enhance the engagement of antibodies with immune effectors through their interactions with Fcγ receptors (FcγRs) by the process of Fc engineering. As more is understood about how to best optimise these agents, principally through the fine-tuning of mAb structure and choice of synergistic partnerships, our ability to generate robust, clinically beneficial anti-tumour activity will form the foundation for the next generation of cancer therapeutics.

Expression analysis of two SLAM family receptors, SLAMF2 and SLAMF7, in patients with multiple myeloma

Monoclonal antibodies against surface antigens on MM cells, such as anti-SLAMF7 and anti-CD38 antibodies, represent an attractive therapeutic modality for the eradication of multiple myeloma (MM) cells. However, further exploration of target molecules is urgently needed for the development of more effective therapies. In the present study, we studied the expression of CD48 in a total of 74 primary MM samples derived from patients to evaluate SLAMF2 (CD48) as a candidate in mAb therapy for MM. Of 74 samples, 39 were subjected to SLAMF7 analysis. Most of the MM cells, defined as CD38 and CD138 double-positive cells, showed strong expression of CD48 or SLAMF7 independent of disease stage or treatment history. In these 39 samples, most MM cells showed expression of both SLAMF7 and CD48; however, several samples showed expression of either only CD48 or only SLAMF7, including seven cases that were only highly positive for SLAMF7, and five that were only highly positive for CD48. Our study demonstrates that the immune receptor CD48 is overexpressed on MM cells together with SLAMF7, and that CD48 may be considered as an alternative target for treatment of MM in cases showing weak expression of SLAMF7.

CD40L inhibits cell growth of THP-1 cells by suppressing the PI3K/Akt pathway

Introduction

Acute myeloid leukemia (AML), the hematological malignant tumor with high mortality, is still difficult to treat. CD40L is a type II transmembrane protein, which has been reported to have the potential to inhibit growth of some cancer cells.

Materials and methods

In order to determine the role of CD40L on AML-M5 cell line THP-1, we overexpressed CD40L in the cells using a lentiviral vector system (pHBLV-CMVIE-Zs Green-T2A-puro vector); overexpression was confirmed by the detection of green fluorescent protein and CD40L protein expression.

Results

Cellular apoptosis, proliferation, and cycle assays showed that CD40L could promote the apoptosis of, suppress the proliferation of, and stimulate the arrest of the G1/S phase of THP-1 cells. Finally, the protein expression of P53, Bax/Bcl-2, cyclinD1, PCNA, PTEN, and p-Akt illustrated that CD40L may partly influence cell growth of THP-1 cells through those genes, which was confirmed by immunohistochemistry and a PI3K/Akt activator.

Conclusion

Taken together, CD40L could inhibit cell growth of THP-1 cells through the PI3K/Akt pathway, indicating that the overexpression of CD40L may be a potential target to treat the AML-M5 disease.

Monoclonal Antibodies for the Treatment of Multiple Myeloma: An Update

The past two decades have seen a revolution in multiple myeloma (MM) therapy with the introduction of several small molecules, mostly orally effective, whose mechanisms are based on proteasome inhibition, histone deacetylase (HDAC) blockade, and immunomodulation. Immunotherapeutic approaches to MM treatment using monoclonal antibodies (mAbs), while long in development, began to reap success with the identification of CD38 and SLAMF7 as suitable targets for development, culminating in the 2015 Food and Drug Administration (FDA) approval of daratumumab and elotuzumab, respectively. This review highlights additional mAbs now in the developmental pipeline. Isatuximab, another anti-CD38 mAb, currently is under study in four phase III trials and may offer certain advantages over daratumumab. Several antibody-drug conjugates (ADCs) in the early stages of development are described, including JNJ-63723283, which has attained FDA breakthrough status for MM. Other mAbs described in this review include denosumab, recently approved for myeloma-associated bone loss, and checkpoint inhibitors, although the future status of the latter combined with immunomodulators has been clouded by unacceptably high death rates that caused the FDA to issue clinical holds on several of these trials. Also highlighted are the therapies based on the B Cell Maturation Antigen (BCMA), another very promising target for anti-myeloma development.

The NF-κB Activating Pathways in Multiple Myeloma

Multiple myeloma(MM), an incurable plasma cell cancer, represents the second most prevalent hematological malignancy. Deregulated activity of the nuclear factor kappaB (NF-κB) family of transcription factors has been implicated in the pathogenesis of multiple myeloma. Tumor microenvironment-derived cytokines and cancer-associated genetic mutations signal through the canonical as well as the non-canonical arms to activate the NF-κB system in myeloma cells. In fact, frequent engagement of both the NF-κB pathways constitutes a distinguishing characteristic of myeloma. In turn, NF-κB signaling promotes proliferation, survival and drug-resistance of myeloma cells. In this review article, we catalog NF-κB activating genetic mutations and microenvironmental cues associated with multiple myeloma. We then describe how the individual canonical and non-canonical pathways transduce signals and contribute towards NF-κB -driven gene-expressions in healthy and malignant cells. Furthermore, we discuss signaling crosstalk between concomitantly triggered NF-κB pathways, and its plausible implication for anomalous NF-κB activation and NF-κB driven pro-survival gene-expressions in multiple myeloma. Finally, we propose that mechanistic understanding of NF-κB deregulations may provide for improved therapeutic and prognostic tools in multiple myeloma.

Monoclonal Antibody Therapies for Hematological Malignancies: Not Just Lineage-Specific Targets

Today, monoclonal antibodies (mAbs) are a widespread and necessary tool for biomedical science. In the hematological cancer field, since rituximab became the first mAb approved by the Food and Drug Administration for the treatment of B-cell malignancies, a number of effective mAbs targeting lineage-specific antigens (LSAs) have been successfully developed. Non-LSAs (NLSAs) are molecules that are not restricted to specific leukocyte subsets or tissues but play relevant pathogenic roles in blood cancers including the development, proliferation, survival, and refractoriness to therapy of tumor cells. In consequence, efforts to target NLSAs have resulted in a plethora of mAbs-marketed or in development-to achieve different goals like neutralizing oncogenic pathways, blocking tumor-related chemotactic pathways, mobilizing malignant cells from tumor microenvironment to peripheral blood, modulating immune-checkpoints, or delivering cytotoxic drugs into tumor cells. Here, we extensively review several novel mAbs directed against NLSAs undergoing clinical evaluation for treating hematological malignancies. The review focuses on the structure of these antibodies, proposed mechanisms of action, efficacy and safety profile in clinical studies, and their potential applications in the treatment of hematological malignancies.

NF-κB in Hematological Malignancies

NF-κB (Nuclear Factor Κ-light-chain-enhancer of activated B cells) transcription factors are critical regulators of immunity, stress response, apoptosis, and differentiation. Molecular defects promoting the constitutive activation of canonical and non-canonical NF-κB signaling pathways contribute to many diseases, including cancer, diabetes, chronic inflammation, and autoimmunity. In the present review, we focus our attention on the mechanisms of NF-κB deregulation in hematological malignancies. Key positive regulators of NF-κB signaling can act as oncogenes that are often prone to chromosomal translocation, amplifications, or activating mutations. Negative regulators of NF-κB have tumor suppressor functions, and are frequently inactivated either by genomic deletions or point mutations. NF-κB activation in tumoral cells is also driven by the microenvironment or chronic signaling that does not rely on genetic alterations.

Identification and expression of MMSA-8, and its clinical significance in multiple myeloma

In our previous studies, we identified 12 multiple myeloma (MM)-associated antigens by serological analysis of tumor-associated antigens with a recombinant cDNA expression library (SEREX) on MM. MM-associated antigen-8 (MMSA-8) was one of the new antigens identified. We determined the 3′- and 5′-ends of MMSA-8 using SMART-rapid amplification of cDNA ends (RACE) and then cloned its full-length cDNA in the U266 cell line. The full cDNA sequence revealed that MMSA-8 is RPS27A-related transcript variant 1 that is specifically associated with MM. We examined its prognostic significance for the first time, by investigating the correlations between MMSA-8 expression and definite clinicopathological features. We quantitatively assessed MMSA-8 expression using qRT-PCR and western blot analysis in healthy donors and MM patients. The expression levels of MMSA-8 were upregulated with statistical significance in MM patients in contrast to those in healthy donors. The expression of MMSA-8 was also upregulated in relapsed patients compared with that in the complete remission (CR) group. Contrasting MMSA-8 expression levels in different patients with definite clinicopathological features suggested an association between MMSA-8 with unfavorable clinicopathological characteristics, such as international staging system (ISS) stage III, higher lactate dehydrogenase (LDH) levels and higher C-reactive protein (CRP) levels. The expression of MMSA-8 was also increased in patients with unfavorable cytogenetic and genetic abnormalities, including the presence of t(11;14), t(4;14), t(14;16), del(17p), del(13q) and p53 deletion, which was statistically significant. The expression of MMSA-8 exhibited significant variance in the treatment responses of the CR, PR, progression and relapse groups. Univariate and multivariate analyses revealed that high MMSA-8 values were associated with poorer progression-free survival (PFS) and overall survival (OS) in MM patients independently. In conclusion, our data indicated that MMSA-8 is an independent and unfavorable prognostic risk factor in MM; MMSA-8 is also a promising diagnostic and therapeutic target in MM patients, but further validation is needed.

Autologous bone marrow Th cells can support multiple myeloma cell proliferation in vitro and in xenografted mice

Multiple myeloma (MM) is a plasma cell malignancy where MM cell growth is supported by the bone marrow (BM) microenvironment with poorly defined cellular and molecular mechanisms. MM cells express CD40, a receptor known to activate autocrine secretion of cytokines and elicit proliferation. Activated T helper (Th) cells express CD40 ligand (CD40L) and BM Th cells are significantly increased in MM patients. We hypothesized that activated BM Th cells could support MM cell growth. We here found that activated autologous BM Th cells supported MM cell growth in a contact- and CD40L-dependent manner in vitro. MM cells had retained the ability to activate Th cells that reciprocated and stimulated MM cell proliferation. Autologous BM Th cells supported MM cell growth in xenografted mice and were found in close contact with MM cells. MM cells secreted chemokines that attracted Th cells, secretion was augmented by CD40-stimulation. Within 14 days of culture of whole BM aspirates in autologous serum, MM cells and Th cells mutually stimulated each other, and MM cells required Th cells for further expansion in vitro and in mice. The results suggest that Th cells may support the expansion of MM cells in patients.

Development of Novel Immunotherapies for Multiple Myeloma

Multiple myeloma (MM) is a disorder of terminally differentiated plasma cells characterized by clonal expansion in the bone marrow (BM). It is the second-most common hematologic malignancy. Despite significant advances in therapeutic strategies, MM remains a predominantly incurable disease emphasizing the need for the development of new treatment regimens. Immunotherapy is a promising treatment modality to circumvent challenges in the management of MM. Many novel immunotherapy strategies, such as adoptive cell therapy and monoclonal antibodies, are currently under investigation in clinical trials, with some already demonstrating a positive impact on patient survival. In this review, we will summarize the current standards of care and discuss major new approaches in immunotherapy for MM.

NF-κB dysregulation in multiple myeloma

The nuclear factor-κB (NF-κB) transcription factor family plays critical roles in the pathophysiology of hematologic neoplasias, including multiple myeloma. The current review examines the roles that this transcription factor system plays in multiple myeloma cells and the nonmalignant accessory cells of the local microenvironment; as well as the evidence indicating that a large proportion of myeloma patients harbor genomic lesions which perturb diverse genes regulating the activity of NF-κB. This article also discusses the therapeutic targeting of the NF-κB pathway using proteasome inhibitors, a pharmacological class that has become a cornerstone in the therapeutic management of myeloma; and reviews some of the future challenges and opportunities for NF-κB-related research in myeloma.

Glucolipotoxicity initiates pancreatic β-cell death through TNFR5/CD40-mediated STAT1 and NF-κB activation

Type 2 diabetes is a chronic metabolic disorder, where failure to maintain normal glucose homoeostasis is associated with, and exacerbated by, obesity and the concomitant-elevated free fatty acid concentrations typically found in these patients. Hyperglycaemia and hyperlipidaemia together contribute to a decline in insulin-producing β-cell mass through activation of the transcription factors nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription (STAT)-1. There are however a large number of molecules potentially able to modulate NF-κB and STAT1 activity, and the mechanism(s) by which glucolipotoxicity initially induces NF-κB and STAT1 activation is currently poorly defined. Using high-density microarray analysis of the β-cell transcritptome, we have identified those genes and proteins most sensitive to glucose and fatty acid environment. Our data show that of those potentially able to activate STAT1 or NF-κB pathways, tumour necrosis factor receptor (TNFR)-5 is the most highly upregulated by glucolipotoxicity. Importantly, our data also show that the physiological ligand for TNFR5, CD40L, elicits NF-κB activity in β-cells, whereas selective knockdown of TNFR5 ameliorates glucolipotoxic induction of STAT1 expression and NF-κB activity. This data indicate for the first time that TNFR5 signalling has a major role in triggering glucolipotoxic islet cell death.

Expression, purification and biological characterization of the extracellular domain of CD40 from Pichia pastoris

BACKGROUND

CD40, also called Bp50, is a novel member of the TNF receptor superfamily. Based on its important role in multiple physiological and pathological processes, the CD40 signaling pathway has become a vital target for treating transplantation, autoimmune diseases and cancers. This study generated a protein fragment that disrupts this signaling pathway.

RESULTS

A DNA fragment encoding the extracellular domain of CD40 (CD40-N) has been codon-optimized and cloned into pPIC9K to create a Pichia pastoris expression and secretion strain. SDS-PAGE and Western blotting assays using the culture media from methanol-induced expression strains showed that recombinant CD40-N, a 27 kDa glycosylated protein, was secreted into the culture broth. The recombinant protein was purified to more than 90 % using Sephadex G-50 size-exclusion chromatography and Q Sepharose Fast Flow ion exchange. Finally, 120 mg of the protein was obtained at a relatively high purity from 3 l supernatant. Binding assay (ITC200 assay) shown the direct interaction of CD40-N and CD40 agonist antibody (G28-5). The bioactivity of recombinant CD40-N was confirmed by its ability to disrupt non-canonical NF-κB signaling activated by CD40 agonist antibody or CD40 ligand and to inhibit ant-CD40 agonist antibody-induced TNF-alpha expression in BJAB cells in vitro. In addition, our data indicate that the protein has curative potential in treating dextran sulfate sodium (DSS)-induced colitis in vivo.

CONCLUSIONS

The results show that the experimental procedure we have developed using P. pastoris can be used to produce large amounts of active CD40-N for research and industrial purposes. The protein fragment we have acquired has potential to be used in research or even treating inflammation diseases such as colitis.

Anti-β₂-microglobulin monoclonal antibodies overcome bortezomib resistance in multiple myeloma by inhibiting autophagy

Our previous studies showed that anti-β2M monoclonal antibodies (mAbs) have strong and direct apoptotic effects on multiple myeloma (MM) cells, suggesting that anti-β2M mAbs might be developed as a novel therapeutic agent. In this study, we investigated the anti-MM effects of combination treatment with anti-β2M mAbs and bortezomib (BTZ). Our results showed that anti-β2M mAbs enhanced BTZ-induced apoptosis of MM cell lines and primary MM cells. Combination treatment could also induce apoptosis of BTZ-resistant MM cells, and the enhanced effect depended on the surface expression of β2M on MM cells. BTZ up-regulated the expression of autophagy proteins, whereas combination with anti-β2M mAbs inhibited autophagy. Sequence analysis of the promoter region of beclin 1 identified 3 putative NF-κB-binding sites from -615 to -789 bp. BTZ treatment increased, whereas combination with anti-β2M mAbs reduced, NF-κB transcription activities in MM cells, and combination treatment inhibited NF-κB p65 binding to the beclin 1 promoter. Furthermore, anti-β2M mAbs and BTZ combination treatment had anti-MM activities in an established MM mouse model. Thus, our studies provide new insight and support for the clinical development of an anti-β2M mAb and BTZ combination treatment to overcome BTZ drug resistance and improve MM patient survival.

Recent advances in antimultiple myeloma drug development

Multiple myeloma (MM) is the second most common hematological malignancy and is characterized by the aberrant proliferation of terminally differentiated plasma B cells with impairment in apoptosis capacity. Particularly, osteolytic bone diseases and renal failure resulting from hyperparaproteinemia and hypercalcemia have been the major serious sequelae that are inextricably linked with MM tumor progression. Despite the introduction of new treatment regimens, problematic neuropathy, thrombocytopenia, drug resistance and high MM relapse rates continue to plague the current therapies. New chemical agents are in development on the basis of understanding several signaling pathways and molecular mechanisms like tumor necrosis factor-α, proteasome, PI3K and MARKs. This review focuses on the most recent patents and clinical trials in the development of new medicine for the treatment of multiple myeloma. Furthermore, the important signaling pathways involved in the proliferation, survival and apoptosis of myeloma cells will be discussed.

The human agonistic CD40 antibody ADC-1013 eradicates bladder tumors and generates T-cell-dependent tumor immunity

PURPOSE

Local administration of immune-activating antibodies may increase the efficacy and reduce the immune-related adverse events associated with systemic immunotherapy of cancer. Here, we report the development and affinity maturation of a fully human agonistic CD40 antibody (IgG1), ADC-1013.

EXPERIMENTAL DESIGN

We have used molecular engineering to generate an agonistic antibody with high affinity for CD40. The functional activity of ADC-1013 was investigated in human and murine in vitro models. The in vivo effect was investigated in two separate bladder cancer models, both using human xenograft tumors in immune deficient NSG mice and using a syngeneic bladder cancer model in a novel human CD40 transgenic mouse.

RESULTS

Activation of dendritic cells (DC) by ADC-1013 results in upregulation of the costimulatory molecules CD80 and CD86, and secretion of IL12. ADC-1013 also activates DCs from human CD40 transgenic mice, and peptide-pulsed and ADC-1013-stimulated DCs induce antigen-specific T-cell proliferation in vitro. In vivo, treatment with ADC-1013 in a syngeneic bladder cancer model, negative for hCD40, induces significant antitumor effects and long-term tumor-specific immunity. Furthermore, ADC-1013 demonstrates significant antitumor effects in a human bladder cancer transplanted into immunodeficient NSG mice.

CONCLUSIONS

Our data demonstrate that ADC-1013 induces long-lasting antitumor responses and immunologic memory mediated by CD40 stimulation. To the best of our knowledge, ADC-1013 represents the first immunomodulatory antibody developed for local immunotherapy of cancer.

Multifunctional CD40L: pro- and anti-neoplastic activity

The CD40 ligand is a type I transmembrane protein that belongs to a tumor necrosis factor (TNF) superfamily. It is present not only on the surface of activated CD4+ T cells, B cells, blood platelets, monocytes, and natural killer (NK) cells but also on cancer cells. The receptor for ligand is constitutively expressed on cells, TNF family protein: CD40. The role of the CD40/CD40L pathway in the induction of body immunity, in inflammation, or in hemostasis has been well documented, whereas its involvement in neoplastic disease is still under investigation. CD40L ligand may potentiate apoptosis of tumor cells by activation of nuclear factor-κB (NF-κB), AP-1, CD95, or caspase-depended pathways and stimulate host immunity to defend against cancer. Although CD40L has a major contribution to anti-cancer activity, many reports point at its ambivalent nature. CD40L enhance release of strongly pro-angiogenic factor, vascular endothelial growth factor (VEGF), and activator of coagulation, TF, the level of which is correlated with tumor metastasis. CD40L involvement in the inhibition of tumor progression has led to the emergence of not only therapy using recombinant forms of the ligand and vaccines in the treatment of cancer but also therapy consisting of inhibiting platelets-main source of CD40L. This article is a review of studies on the ambivalent role of CD40L in neoplastic diseases.

CD28/CTLA-4/B7 and CD40/CD40L costimulation and activation of regulatory T cells

Costimulatory signals are crucial for T cell activation. Attempts to block costimulatory pathways have been effective in preventing unwanted immune reactions. In particular, blocking the CD28/cytotoxic T lymphocyte antigen (CTLA)-4/B7 interaction (using CTLA-4Ig) and the CD40/CD40L interaction (using anti-CD40L antibodies) prevents T cell mediated autoimmune diseases, transplant rejection and graft vs host disease in experimental models. Moreover, CTLA-4Ig is in clinical use to treat rheumatoid arthritis (abatacept) and to prevent rejection of renal transplants (belatacept). Under certain experimental conditions, this treatment can even result in tolerance. Surprisingly, the underlying mechanisms of immune modulation are still not completely understood. We here discuss the evidence that costimulation blockade differentially affects effector T cells (Teff) and regulatory T cells (Treg). The latter are required to control inappropriate and unwanted immune responses, and their activity often contributes to tolerance induction and maintenance. Unfortunately, our knowledge on the costimulatory requirements of Treg cells is very limited. We therefore summarize the current understanding of the costimulatory requirements of Treg cells, and elaborate on the effect of anti-CD40L antibody and CTLA-4Ig treatment on Treg cell activity. In this context, we point out that the outcome of a treatment aiming at blocking the CD28/CTLA-4/B7 costimulatory interaction can vary with dosing, timing and underlying immunopathology.

Targeted therapy for HM1.24 (CD317) on multiple myeloma cells

Multiple myeloma (MM) still remains an incurable disease, at least because of the existence of cell-adhesion mediated drug-resistant MM cells and/or continuous recruitment of presumed MM cancer stem cell-like cells (CSCs). As a new alternative treatment modality, immunological approaches using monoclonal antibodies (mAbs) and/or cytotoxic T lymphocytes (CTLs) are now attracting much attention as a novel strategy attacking MM cells. We have identified that HM1.24 [also known as bone marrow stromal cell antigen 2 (BST2) or CD317] is overexpressed on not only mature MM cells but also MM CSCs. We then have developed a humanized mAb to HM1.24 and defucosylated version of the mAb to adapt to clinical practice. Moreover, we have successfully induced HM1.24-specific CTLs against MM cells. The combination of these innovative therapeutic modalities may likely exert an anti-MM activity by evading the drug resistance mechanism and eliminating presumed CSCs in MM.

Anti-CD40-mediated cancer immunotherapy: an update of recent and ongoing clinical trials

The costimulatory molecule CD40 is a member of the tumor necrosis factor (TNF) receptor superfamily and is expressed on various antigen presenting cells (APCs) as well as some tumor cells. The binding to the natural ligand CD40L, which is expressed on T helper cells, leads to APC activation and thus enhancement of immune responses. Treatment with anti-CD40 monoclonal antibodies has been exploited in several cancer immunotherapy studies in mice and led to the development of anti-CD40 antibodies for clinical use. Here, Dacetuzumab and Lucatumumab are in the most advanced stage and are being tested as treatment for malignancies such as chronic lymphatic leukemia (CLL), Multiple Myeloma (MM), and non-Hodgkin's lymphoma (NHL). The promising results from these early clinical trials have encouraged clinical drug development in order to investigate the effect of CD40 mAbs in combination with other cancer immunotherapies, in particular interleukin (IL)-2. An in-depth analysis of this immunotherapy is provided elsewhere. In the present review, we provide an update of the most recent clinical trials with anti-CD40 antibodies. We present and discuss recent and ongoing clinical trials in this field, including clinical studies which combine anti-CD40 treatment with other cancer-treatments, such as Rituximab and Tremelimumab.

Anti-β₂M monoclonal antibodies kill myeloma cells via cell- and complement-mediated cytotoxicity

Our previous studies showed that anti-β2M monoclonal antibodies (mAbs) at high doses have direct apoptotic effects on myeloma cells, suggesting that anti-β2M mAbs might be developed as a novel therapeutic agent. In this study, we investigated the ability of the mAbs at much lower concentrations to indirectly kill myeloma cells by utilizing immune effector cells or molecules. Our results showed that anti-β2M mAbs effectively lysed MM cells via antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), which were correlated with and dependent on the surface expression of β2M on MM cells. The presence of MM bone marrow stromal cells or addition of IL-6 did not attenuate anti-β2M mAb-induced ADCC and CDC activities against MM cells. Furthermore, anti-β2M mAbs only showed limited cytotoxicity toward normal B cells and nontumorous mesenchymal stem cells, indicating that the ADCC and CDC activities of the anti-β2M mAbs were more prone to the tumor cells. Lenalidomide potentiated in vitro ADCC activity against MM cells and in vivo tumor inhibition capacity induced by the anti-β2M mAbs by enhancing the activity of NK cells. These results support clinical development of anti-β2M mAbs, both as a monotherapy and in combination with lenalidomide, to improve MM patient outcome.

Monoclonal antibody-based immunotherapy for multiple myeloma

Multiple myeloma (MM) is a life-threatening hematological malignancy. High-dose chemotherapy followed by autologous stem cell transplantation is a relatively effective treatment, but disease recurrence remains a major obstacle. Allogeneic transplantation may result in durable responses and cure due to antitumor immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. This review will focus on MM antigens and their specific antibodies. These monoclonal antibodies are an attractive therapeutic tool for MM humoral immunotherapy, with most promising preclinical results.

Clinical targeting of the TNF and TNFR superfamilies

Inhibitors of tumour necrosis factor (TNF) are among the most successful protein-based drugs (biologics) and have proven to be clinically efficacious at reducing inflammation associated with several autoimmune diseases. As a result, attention is focusing on the therapeutic potential of additional members of the TNF superfamily of structurally related cytokines. Many of these TNF-related cytokines or their cognate receptors are now in preclinical or clinical development as possible targets for modulating inflammatory diseases and cancer as well as other indications. This Review focuses on the biologics that are currently in clinical trials for immune-related diseases and other syndromes, discusses the successes and failures to date as well as the expanding therapeutic potential of modulating the activity of this superfamily of molecules.

Integrin alpha4 blockade sensitizes drug resistant pre-B acute lymphoblastic leukemia to chemotherapy

Bone marrow (BM) provides chemoprotection for acute lymphoblastic leukemia (ALL) cells, contributing to lack of efficacy of current therapies. Integrin alpha4 (alpha4) mediates stromal adhesion of normal and malignant B-cell precursors, and according to gene expression analyses from 207 children with minimal residual disease, is highly associated with poorest outcome. We tested whether interference with alpha4-mediated stromal adhesion might be a new ALL treatment. Two models of leukemia were used, one genetic (conditional alpha4 ablation of BCR-ABL1 [p210(+)] leukemia) and one pharmacological (anti-functional alpha4 antibody treatment of primary ALL). Conditional deletion of alpha4 sensitized leukemia cell to nilotinib. Adhesion of primary pre-B ALL cells was alpha4-dependent; alpha4 blockade sensitized primary ALL cells toward chemotherapy. Chemotherapy combined with Natalizumab prolonged survival of NOD/SCID recipients of primary ALL, suggesting adjuvant alpha4 inhibition as a novel strategy for pre-B ALL.

T-cell-independent antitumor effects of CD40 ligation

CD40 ligation has been shown to induce antitumor effects in mice and cancer patients. Most of the studies have focused on the ability of an agonistic anti-CD40 mAb to either directly kill CD40-positive tumor cells or activate T-cell immune responses. In this review the authors focus on the ability of CD40 ligation to activate antitumor effector mechanisms of the cells of innate immunity such as macrophages and NK cells.

A phase 1 study of lucatumumab, a fully human anti-CD40 antagonist monoclonal antibody administered intravenously to patients with relapsed or refractory multiple myeloma

In this open-label, multicentre, phase 1 study a fully human anti-CD40 antagonist monoclonal antibody, lucatumumab, was evaluated in patients with relapsed/refractory multiple myeloma (MM). The primary objective was to determine the maximum tolerated dose (MTD) based on dose-limiting toxicities (DLTs). Secondary objectives included safety, pharmacokinetics, pharmacodynamics and antimyeloma activity. Twenty-eight patients, enrolled using a standard '3 + 3' dose escalation, received one or two (n = 3) cycles of lucatumumab 1·0, 3·0, 4·5 or 6·0 mg/kg once weekly for 4 weeks. Common lucatumumab-related adverse events were reversible, mild-to-moderate infusion reactions. Severe adverse events were anaemia, chills, hypercalcaemia and pyrexia (7% each). DLTs included grade 4 thrombocytopenia, grade 3 increased alanine aminotransferase and grade 4 increased lipase (n = 1 each). The MTD was 4·5 mg/kg. At doses ≥3·0 mg/kg, sustained receptor occupancy (≥87%), observed throughout weekly infusions up to 5 weeks after the last infusion, correlated with an estimated half-life of 4-19 d. Twelve patients (43%) had stable disease, and one patient (4%) maintained a partial response for ≥8 months. These findings indicate that single-agent lucatumumab was well tolerated up to 4·5 mg/kg with modest clinical activity in relapsed/refractory MM, warranting further study as a combination therapy.

A phase 1, multicenter, open-label, dose escalation study of elotuzumab in patients with advanced multiple myeloma

This multicenter, first-in-human study evaluated the safety, tolerability, and pharmacokinetic and pharmacodynamic properties of the anti-CS1 monoclonal antibody elotuzumab. A standard 3 + 3 design was used to determine maximum tolerated dose; dose-limiting toxicities were assessed during cycle 1. Thirty-five patients with relapsed/refractory multiple myeloma were treated with intravenous elotuzumab at doses ranging from 0.5 to 20 mg/kg every 2 weeks. Patients who achieved at least stable disease after 4 treatments could receive another 4 treatments. No maximum tolerated dose was identified up to the maximum planned dose of 20 mg/kg. The most common adverse events, regardless of attribution, were cough, headache, back pain, fever, and chills. Adverse events were generally mild to moderate in severity, and adverse events attributed to study medication were primarily infusion-related. Plasma elotuzumab levels and terminal half-life increased with dose whereas clearance decreased, suggesting target-mediated clearance. CS1 on bone marrow-derived plasma cells was reliably saturated (≥ 95%) at the 10-mg/kg and 20-mg/kg dose levels. Using the European Group for Bone and Marrow Transplantation myeloma response criteria, 9 patients (26.5%) had stable disease. In summary, elotuzumab was generally well tolerated in this population, justifying further exploration of this agent in combination regimens.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

Intrinsic modulation of lymphocyte function by stromal cell network: advance in therapeutic targeting of cancer

Advances in tumor biology have demonstrated a point of critical importance: tumor are established as an intersection of malignant clone cells and surrounding stromal cells. The stroma is composed of nonhematopoietic cells, including connective tissue cells, blood vessels, nerves, fat and smooth muscle cells, in the extracellular matrix niche. Recent studies have demonstrated that stromal cells regulate immune responses by: coordinating lymphocyte homing, differentiation, activation and antigen responses; inducing tolerance; and maintaining immunologic memory. Hence, elucidation of the interaction between stromal cells and lymphocytes is essential for generating effective immunotherapies. In this article, we summarize what is currently known about the interactions between stromal cells and lymphocytes in the tumor microenvironment, as well as potential immunotherapeutic approaches targeting stroma-lymphocyte interactions; both in the context of our work on multiple myeloma, and of recent literature in both solid tumors and hematologic malignancies.

Potent in vitro and in vivo activity of an Fc-engineered humanized anti-HM1.24 antibody against multiple myeloma via augmented effector function

HM1.24, an immunologic target for multiple myeloma (MM) cells, has not been effectively targeted with therapeutic monoclonal antibodies (mAbs). In this study, we investigated in vitro and in vivo anti-MM activities of XmAb5592, a humanized anti-HM1.24 mAb with Fc-domain engineered to significantly enhance FcγR binding and associated immune effector functions. XmAb5592 increased antibody-dependent cellular cytotoxicity (ADCC) several fold relative to the anti-HM1.24 IgG1 analog against both MM cell lines and primary patient myeloma cells. XmAb5592 also augmented antibody dependent cellular phagocytosis (ADCP) by macrophages. Natural killer (NK) cells became more activated by XmAb5592 than the IgG1 analog, evidenced by increased cell surface expression of granzyme B-dependent CD107a and MM cell lysis, even in the presence of bone marrow stromal cells. XmAb5592 potently inhibited tumor growth in mice bearing human MM xenografts via FcγR-dependent mechanisms, and was significantly more effective than the IgG1 analog. Lenalidomide synergistically enhanced in vitro ADCC against MM cells and in vivo tumor inhibition induced by XmAb5592. A single dose of 20 mg/kg XmAb5592 effectively depleted both blood and bone marrow plasma cells in cynomolgus monkeys. These results support clinical development of XmAb5592, both as a monotherapy and in combination with lenalidomide, to improve patient outcome of MM.