FcRL5 as a Target of Antibody–Drug Conjugates for the Treatment of Multiple Myeloma

Antibody-drug conjugates, bispecific antibodies and CAR-T cells therapy in multiple myeloma

INTRODUCTION

Modern immunotherapy approaches are revolutionizing the treatment scenario of relapsed/refractory (RR) multiple myeloma (MM) patients, providing an opportunity to reach deep level of responses and extend survival outcomes.

AREAS COVERED

Antibody-drug conjugates (ADCs) and T-cell redirecting treatments, including bispecific antibodies (BsAbs) and chimeric antigen receptor (CAR) T cells therapy, have been recently introduced in the treatment of RRMM. Some agents have already received regulatory approval, while newer constructs, novel combinations, and applications in earlier lines of therapy are currently being explored. This review discusses the current landscape and possible development of ADCs, BsAbs and CAR-T cells immunotherapies.

EXPERT OPINION

ADCs, BsAbs, and CAR-T therapy have demonstrated substantial activity in heavily pretreated, triple-class exposed (TCE) MM patients, and T-cell redirecting treatments represent new standards of care after third (European Medicines Agency, EMA), or fourth (Food and Drug Administration, FDA), line of therapy. All these three immunotherapies carry advantages and disadvantages, with different accessibility and new toxicities that require appropriate management and guidelines. Multiple on-going programs include combinations therapies and applications in earlier lines of treatment, as well as the development of novel agents or construct to enhance potency, reduce toxicity and facilitate administration. Sequencing is a challenge, with few data available and mechanisms of resistance still to be unraveled.

Bispecific Antibodies in the Treatment of Multiple Myeloma

The treatment of multiple myeloma (MM) is evolving rapidly. In recent years, T-cell-based novel immunotherapies emerged as new treatment strategies for patients with relapsed/refractory MM, including highly effective new options like chimeric antigen receptor (CAR)-modified T cells and bispecific antibodies (bsAbs). Currently, B-cell maturation antigen is the most commonly used target antigen for CAR T-cell and bsAb therapies in MM. Results from different clinical trials have demonstrated promising efficacy and acceptable safety profile of bsAb in RRMM.

Fc receptor-like 5 (FCRL5)-directed CAR-T cells exhibit antitumor activity against multiple myeloma

Multiple myeloma (MM) remains a challenging hematologic malignancy despite advancements in chimeric antigen receptor T-cell (CAR-T) therapy. Current targets of CAR-T cells used in MM immunotherapy have limitations, with a subset of patients experiencing antigen loss resulting in relapse. Therefore, novel targets for enhancing CAR-T cell therapy in MM remain needed. Fc receptor-like 5 (FCRL5) is a protein marker with considerably upregulated expression in MM and has emerged as a promising target for CAR-T cell therapeutic interventions, offering an alternative treatment for MM. To further explore this option, we designed FCRL5-directed CAR-T cells and assessed their cytotoxicity in vitro using a co-culture system and in vivo using MM cell-derived xenograft models, specifically focusing on MM with gain of chromosome 1q21. Given the challenges in CAR-T therapies arising from limited T cell persistence, our approach incorporates interleukin-15 (IL-15), which enhances the functionality of central memory T (TCM) cells, into the design of FCRL5-directed CAR-T cells, to improve cytotoxicity and reduce T-cell dysfunction, thereby promoting greater CAR-T cell survival and efficacy. Both in vitro and xenograft models displayed that FCRL5 CAR-T cells incorporating IL-15 exhibited potent antitumor efficacy, effectively inhibiting the proliferation of MM cells and leading to remarkable tumor suppression. Our results highlight the capacity of FCRL5-specific CAR-T cells with the integration of IL-15 to improve the therapeutic potency, suggesting a potential novel immunotherapeutic strategy for MM treatment.

Chimeric Antigen Receptor T Cell Therapy for Myeloma: Where Are We Now and What Is Needed to Move Chimeric Antigen Receptor T Cells Forward to Earlier Lines of Therapy? Expert Panel Opinion from the American Society for Transplantation and Cellular Therapy

Since 2021, 2 B cell maturation antigen (BCMA)-directed chimeric antigen receptor T cell (CAR-T) therapies-idecabtagene vicleucel (ide-cel), and ciltacabtagene autoleucel (cilta-cel)-have been approved by the US Food and Drug Administration (FDA) for treating relapsed or refractory multiple myeloma (RRMM) after 4 or more prior lines of therapy, including an immunomodulatory drug, a proteasome inhibitor, and an anti-CD38 antibody. The 2 products have shown unprecedented activity in RRMM, but relapses remain common, and access to and safety of CAR-T therapy in patients with rapidly progressing advanced disease are not ideal. Sequencing CAR-T therapy with other options, including the 2 recently approved BCMA-directed T cell-engaging bispecific antibodies teclistamab and elranatamab, has become increasingly challenging owing to data showing inferior outcomes from CAR-T therapy after prior BCMA-directed therapy. This has led to the consideration of CAR-T therapy earlier in the course of disease for myeloma, when T cells are potentially healthier and the myeloma is less aggressive. To address the question of earlier use of CAR-T therapy, several trials are either ongoing or planned, and results have recently been reported for 2 randomized trials of CAR-T therapy showing improved progression-free survival compared to standard of care therapy in second-line (CARTITUDE-4) or third-line therapy (KarMMA-3). With the anticipation of the FDA possibly expanding approval of CAR-T to earlier lines of myeloma therapy, the American Society for Transplantation and Cellular Therapy convened a group of experts to provide a comprehensive review of the studies that led to the approval of CAR-T therapy in late-line therapy for myeloma, discuss the recently reported and ongoing studies designed to move CAR-T therapy to earlier lines of therapy, and share insights and considerations for sequencing therapy and optimization of patient selection for BCMA-directed therapies in current practice.

Chimeric Antigen Receptor T-Cell and Bispecific Antibody Therapy in Multiple Myeloma: Moving Into the Future

Historically, the outcomes for individuals with triple-class refractory and penta-drug refractory multiple myeloma (MM) have been poor because of a dearth of effective treatment options. However, the advent of chimeric antigen receptor (CAR) T-cell and T-cell redirecting bispecific antibody (BsAb) therapies has led to unprecedented response rates and durations of response in heavily relapsed/refractory (R/R) populations. Currently, two B-cell maturation antigen (BCMA)-directed CAR T-cell therapies (idecabtagene vicleucel and ciltacabtagene autoleucel) as well as one BCMA/CD3 BsAb (teclistamab) have been approved for late-line (greater than four previous lines) R/R MM in the United States. The purpose of this review is to analyze the recent data for these approved therapies as well as provide an overview of other related CAR T-cell and BsAb therapies under development, including non-BCMA-targeting agents. We review efficacy and safety considerations, with particular focus on cytokine release syndrome, neurotoxicity, and infection risk. The relative merits and limitations of each class of therapy are discussed, as well as the areas of unmet need with respect to optimal sequencing and supportive care measures. We examine the factors that challenge equitable access to these novel therapies across minoritized racial, ethnic, and socioeconomic populations. Although it is evident that CAR T-cell and BsAb therapies will transform treatment paradigms in MM for years to come, significant work remains to identify the optimal utilization of these novel therapies and ensure equitable access.

T-cell redirecting bispecific antibodies in multiple myeloma: Current landscape and future directions

T-cell engaging bispecific antibodies (BsAbs) have substantial activity in heavily pretreated patients with multiple myeloma (MM). The overall response rate obtained with B-cell maturation antigen (BCMA)-targeting BsAbs is approximately 60%-70%, including a high proportion of patients achieving very good partial response or complete response. Comparable efficacy is seen with BsAbs targeting GPRC5D or FcRH5. Cytokine release syndrome is frequently observed with BsAb treatment, but mostly during the step-up doses and the first full dose. Early intervention with IL-6 receptor blocking antibodies (e.g., tocilizumab) prevents escalation to severe manifestations. Infections are also common during treatment and related to the extent of exposure to immune suppressive anti-MM agents, as well as development of hypogammaglobulinemia due to elimination of normal plasma cells, and probably because of T-cell exhaustion resulting from continuous BsAb-mediated T-cell activation. Adequate monitoring for infections and institution of infectious prophylaxis are essential. Patients treated with GPRC5D-targteing BsAbs often develop skin and nail disorders and loss of taste, which is likely related to GPRC5D expression in cells that produce hard keratin. Currently ongoing studies are aiming at further improving these results by evaluating BsAbs in combination with other drugs, such as immunomodulatory agents and anti-CD38 antibodies, as well as the application of BsAbs in earlier lines of therapy, including patients with newly diagnosed disease. We expect that the outcomes of patients with MM will further improve by the introduction of this novel type of T-cell immunotherapy.

Risk of infections associated with the use of bispecific antibodies in multiple myeloma: a pooled analysis

The use of bispecific antibodies (BsAbs) in the treatment of relapsed/refractory multiple myeloma (MM) is showing early promising overall response rates in heavily pretreated patients. Infectious complications related to the use of BsAbs are not well described. We conducted a pooled analysis that included all single-agent BsAbs used in MM with no prior use of different BsAbs. A total of 1185 patients with MM were treated with a BsAb in the studied period (71.6% of the patients treated with an agent targeting B-cell maturation antigen (BCMA). Pooled median follow-up was short at 6.1 months (7.5 vs 5.2 months for BCMA vs non-BCMA BsAbs, respectively). Adverse events of interest included all grade neutropenia in 38.6%, all grade infections in 50% (n = 542/1083), all grade cytokine release syndrome in 59.6% (n = 706/1185), grade III/IV neutropenia in 34.8% (n = 372/1068), grade III/IV infections in 24.5% (n = 272/1110), grade III/IV pneumonia in 10% (n = 52.4/506), and grade III/IV coronavirus disease 2019 in 11.4% (n = 45.4/395) of the patients. Non-BCMA-targeted BsAbs were associated with lower grade III/IV neutropenia (25.3% vs 39.2%) and lower grade III/IV infections (11.9% vs 30%) when compared with BCMA-targeted BsAbs. Hypogammaglobulinemia was reported in 4 studies, with a prevalence of 75.3% (n = 256/340) of the patients, with IV immunoglobulin used in 48% (n = 123/256) of them. Death was reported in 110 patients, of which 28 (25.5%) were reported to be secondary to infections. Certain precautions should be used when using BsAbs to mitigate the risk and/or identify and treat infections promptly.

Chimeric antigen receptor T cells targeting FcRH5 provide robust tumour-specific responses in murine xenograft models of multiple myeloma

BCMA-targeting chimeric antigen receptor (CAR) T cell therapy demonstrates impressive clinical response in multiple myeloma (MM). However, some patients with BCMA-deficient tumours cannot benefit from this therapy, and others can experience BCMA antigen loss leading to relapse, thus necessitating the identification of additional CAR-T targets. Here, we show that FcRH5 is expressed on multiple myeloma cells and can be targeted with CAR-T cells. FcRH5 CAR-T cells elicited antigen-specific activation, cytokine secretion and cytotoxicity against MM cells. Moreover, FcRH5 CAR-T cells exhibited robust tumoricidal efficacy in murine xenograft models, including one deficient in BCMA expression. We also show that different forms of soluble FcRH5 can interfere with the efficacy of FcRH5 CAR-T cells. Lastly, FcRH5/BCMA-bispecific CAR-T cells efficiently recognized MM cells expressing FcRH5 and/or BCMA and displayed improved efficacy, compared with mono-specific CAR-T cells in vivo. These findings suggest that targeting FcRH5 with CAR-T cells may represent a promising therapeutic avenue for MM.

Targeting B Cell Maturation Antigen in Patients with Multiple Myeloma: Current Perspectives

Relapsed/refractory multiple myeloma remains a challenging disease necessitating the development of more effective treatment options. In the past decade, myeloma therapies have made significant advancements with the introduction of new treatment modalities. One of the new major targets for these novel therapeutics has been B-cell maturation antigen (BCMA), which is expressed on mature B-lymphocytes and plasma cells. There are three main categories of BCMA-targeted therapies currently available, including bispecific antibodies (BsAbs), antibody drug conjugates (ADCs), and chimeric antigen receptor (CAR) T-cell therapies. In this review, we discuss the existing BCMA-targeted therapies and provide insights into currently available treatment and future developments, with a particular focus on clinical efficacy and common drug-related adverse events.

Single cell clonotypic and transcriptional evolution of multiple myeloma precursor disease

Multiple myeloma remains an incurable disease, and the cellular and molecular evolution from precursor conditions, including monoclonal gammopathy of undetermined significance and smoldering multiple myeloma, is incompletely understood. Here, we combine single-cell RNA and B cell receptor sequencing from fifty-two patients with myeloma precursors in comparison with myeloma and normal donors. Our comprehensive analysis reveals early genomic drivers of malignant transformation, distinct transcriptional features, and divergent clonal expansion in hyperdiploid versus non-hyperdiploid samples. Additionally, we observe intra-patient heterogeneity with potential therapeutic implications and identify distinct patterns of evolution from myeloma precursor disease to myeloma. We also demonstrate distinctive characteristics of the microenvironment associated with specific genomic changes in myeloma cells. These findings add to our knowledge about myeloma precursor disease progression, providing valuable insights into patient risk stratification, biomarker discovery, and possible clinical applications.

Bispecific Antibody Format and the Organization of Immunological Synapses in T Cell-Redirecting Strategies for Cancer Immunotherapy

T cell-redirecting strategies have emerged as effective cancer immunotherapy approaches. Bispecific antibodies (bsAbs) are designed to specifically recruit T cells to the tumor microenvironment and induce the assembly of the immunological synapse (IS) between T cells and cancer cells or antigen-presenting cells. The way that the quality of the IS might predict the effectiveness of T cell-redirecting strategies, including those mediated by bsAbs or by chimeric antigen receptors (CAR)-T cells, is currently under discussion. Here we review the organization of the canonical IS assembled during natural antigenic stimulation through the T cell receptor (TCR) and to what extent different bsAbs induce T cell activation, canonical IS organization, and effector function. Then, we discuss how the biochemical parameters of different formats of bsAbs affect the effectivity of generating an antigen-induced canonical IS. Finally, the quality of the IS assembled by bsAbs and monoclonal antibodies or CAR-T cells are compared, and strategies to improve bsAb-mediated T cell-redirecting strategies are discussed.

Characterization of BCMA Expression in Circulating Rare Single Cells of Patients with Plasma Cell Neoplasms

B-cell maturation antigen (BCMA), a key regulator of B-cell proliferation and survival, is highly expressed in almost all cases of plasma cell neoplasms and B-lymphoproliferative malignancies. BCMA is a robust biomarker of plasma cells and a therapeutic target with substantial clinical significance. However, the expression of BCMA in circulating tumor cells of patients with hematological malignancies has not been validated for the detection of circulating plasma and B cells. The application of BCMA as a biomarker in single-cell detection and profiling of circulating tumor cells in patients' blood could enable early disease profiling and therapy response monitoring. Here, we report the development and validation of a slide-based immunofluorescence assay (i.e., CD138, BCMA, CD45, DAPI) for enrichment-free detection, quantification, and morphogenomic characterization of BCMA-expressing cells in patients (N = 9) with plasma cell neoplasms. Varying morphological subtypes of circulating BCMA-expressing cells were detected across the CD138(+/-) and CD45(+/-) compartments, representing candidate clonotypic post-germinal center B cells, plasmablasts, and both normal and malignant plasma cells. Genomic analysis by single-cell sequencing and correlation to clinical FISH cytogenetics provides validation, with data showing that patients across the different neoplastic states carry both normal and altered BCMA-expressing cells. Furthermore, altered cells harbor cytogenetic events detected by clinical FISH. The reported enrichment-free liquid biopsy approach has potential applications as a single-cell methodology for the early detection of BCMA+ B-lymphoid malignancies and in monitoring therapy response for patients undergoing anti-BCMA treatments.

Multiple Myeloma Therapy: Emerging Trends and Challenges

Multiple myeloma (MM) is a complex hematologic malignancy characterized by the uncontrolled proliferation of clonal plasma cells in the bone marrow that secrete large amounts of immunoglobulins and other non-functional proteins. Despite decades of progress and several landmark therapeutic advancements, MM remains incurable in most cases. Standard of care frontline therapies have limited durable efficacy, with the majority of patients eventually relapsing, either early or later. Induced drug resistance via up-modulations of signaling cascades that circumvent the effect of drugs and the emergence of genetically heterogeneous sub-clones are the major causes of the relapsed-refractory state of MM. Cytopenias from cumulative treatment toxicity and disease refractoriness limit therapeutic options, hence creating an urgent need for innovative approaches effective against highly heterogeneous myeloma cell populations. Here, we present a comprehensive overview of the current and future treatment paradigm of MM, and highlight the gaps in therapeutic translations of recent advances in targeted therapy and immunotherapy. We also discuss the therapeutic potential of emerging preclinical research in multiple myeloma.

Comprehensive Characterizations of Immune Receptor Repertoire in Tumors and Cancer Immunotherapy Studies

We applied our computational algorithm TRUST4 to assemble immune receptor (T-cell receptor/B-cell receptor) repertoires from approximately 12,000 RNA sequencing samples from The Cancer Genome Atlas and seven immunotherapy studies. From over 35 million assembled complete complementary-determining region 3 sequences, we observed that the expression of CCL5 and MZB1 is the most positively correlated genes with T-cell clonal expansion and B-cell clonal expansion, respectively. We analyzed amino acid evolution during B-cell receptor somatic hypermutation and identified tyrosine as the preferred residue. We found that IgG1+IgG3 antibodies together with FcRn were associated with complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity or phagocytosis. In addition to B-cell infiltration, we discovered that B-cell clonal expansion and IgG1+IgG3 antibodies are also correlated with better patient outcomes. Finally, we created a website, VisualizIRR, for users to interactively explore and visualize the immune repertoires in this study. See related Spotlight by Liu and Han, p. 786.

Harnessing the T Cell to Treat Multiple Myeloma: Dawn of a New Therapeutic Paradigm

Multiple myeloma is an incurable hematologic malignancy. The typical disease course for myeloma patients is characterized by initial response to treatment followed by eventual development of resistance. Subsequent cycles of remission and relapse proceed as long as patients have new lines of therapy available to them. This reality has prompted development of many novel immunotherapeutics. Many of these drugs exploit the cytotoxic capabilities of the patients' own T cells, effectively redirecting them to myeloma cells that are otherwise evading immune attack. Approaches including CAR T cell therapy and bispecific antibodies have displayed impressive efficacy in clinical trials for myeloma patients. This review examines the different approaches that utilize T cells in multiple myeloma therapy and investigates the benefits and risks of these exciting new strategies.

Clinical Management of Triple-Class Refractory Multiple Myeloma: A Review of Current Strategies and Emerging Therapies

Major progress has been made in the upfront treatment of multiple myeloma, but the disease ultimately relapses and leads to death in the vast majority of those afflicted. New treatment strategies and modalities are necessary to treat myeloma in relapse, particularly in cases of triple-refractory status defined by disease progression during or shortly after treatment with immunomodulatory agents, proteasome inhibitors, and anti-CD38 monoclonal antibody therapy. In this manuscript, we review recent promising developments in the treatment of triple-class refractory myeloma including bispecific antibodies and T cell engagers, chimeric antigen receptor cellular therapies, as well as chemotherapeutics with novel mechanisms of action.

Patient selection for CAR T or BiTE therapy in multiple myeloma: Which treatment for each patient?

Multiple myeloma (MM) is a plasma cell malignancy that affects an increasing number of patients worldwide. Despite all the efforts to understand its pathogenesis and develop new treatment modalities, MM remains an incurable disease. Novel immunotherapies, such as CAR T cell therapy (CAR) and bispecific T cell engagers (BiTE), are intensively targeting different surface antigens, such as BMCA, SLAMF7 (CS1), GPRC5D, FCRH5 or CD38. However, stem cell transplantation is still indispensable in transplant-eligible patients. Studies suggest that the early use of immunotherapy may improve outcomes significantly. In this review, we summarize the currently available clinical literature on CAR and BiTE in MM. Furthermore, we will compare these two T cell-based immunotherapies and discuss potential therapeutic approaches to promote development of new clinical trials, using T cell-based immunotherapies, even as bridging therapies to a transplant.

T-cell redirecting bispecific antibodies in multiple myeloma: a revolution?

Bispecific antibodies are designed to link a surface target molecule on the malignant plasma cells to CD3 on T-cells and thereby redirect activated T-cells to induce tumor cell death. Early-phase clinical trials targeting B-cell maturation antigen, GPRC5D or FcRH5, have demonstrated a favorable safety profile and promising efficacy data in triple-class refractory multiple myeloma. This novel immunotherapeutic modality will likely change the treatment paradigm in the coming years.

Emerging Role of Antibody-Drug Conjugates and Bispecific Antibodies for the Treatment of Multiple Myeloma

Multiple myeloma (MM) is characterized by malignant proliferation of malignant plasma cells; it is the second most common hematological malignancy associated with significant morbidity. Genetic intricacy, instability, and diverse clinical presentations remain a barrier to cure. The treatment of MM is modernized with the introduction of newer therapeutics agents, i.e., target-specific monoclonal antibodies. The currently available literature lacks the benefits of newer targeted therapy being developed with an aim to reduce side effects and increase effectiveness, compared to conventional chemotherapy regimens. This article aims to review literature about the current available monoclonal antibodies, antibody-drug conjugates, and bispecific antibodies for the treatment of MM.

Chimeric antigen receptor T-cells, bispecific antibodies, and antibody-drug conjugates for multiple myeloma: An update

Patients with multiple myeloma who are refractory to currently available effective therapies have short expected survival. Modalities harvesting the knowledge of the immune characteristics and microenvironment of myeloma such as chimeric antigen receptor (CAR) T-lymphocytes, bispecific antibodies (bsAbs), and antibody-drug conjugates (ADCs) have shown potential in early phase trials. Based on data from phase 2 studies, idecabtagene vicleucel (ide cel), an anti-B-cell maturation antigen CAR T-product and belantamab mafodotin (belamaf), an ADC are currently approved in the relapsed/refractory setting. bsAbs have shown promise with quick and deep responses. In this review, we summarize the available evidence on these treatments from clinical trials.

[Bispecific antibodies in multiple myeloma]

Immunotherapies have recently emerged as potential game changers in the treatment of multiple myeloma (MM). Those include monoclonal antibodies (targeting CD38 or CS1), bispecific antibodies (BsAb, mainly targeting BCMA, GPRC5D or FcRH5), antibody-drug conjugate (mainly targeting BCMA) and CAR-T cells (mainly targeting BCMA). BsAb have the capacity to bind two different antigens, one at the tumor cell surface and one on T cells (CD3), recreating the immune synapse. In this article, we discuss the main clinical data on BsAb in MM, as well as their different constructs and the potential mechanism of resistance.

Current State of the Art and Prospects of T Cell-Redirecting Bispecific Antibodies in Multiple Myeloma

Multiple myeloma (MM) patients eventually develop multi-drug-resistant disease with poor survival. Hence, the development of novel treatment strategies is of great importance. Recently, different classes of immunotherapeutic agents have shown great promise in heavily pre-treated MM, including T cell-redirecting bispecific antibodies (BsAbs). These BsAbs simultaneously interact with CD3 on effector T cells and a tumor-associated antigen on MM cells, resulting in redirection of T cells to MM cells. This leads to the formation of an immunologic synapse, the release of granzymes/perforins, and subsequent tumor cell lysis. Several ongoing phase 1 studies show substantial activity and a favorable toxicity profile with BCMA-, GPRC5D-, or FcRH5-targeting BsAbs in heavily pre-treated MM patients. Resistance mechanisms against BsAbs include tumor-related features, T cell characteristics, and impact of components of the immunosuppressive tumor microenvironment. Various clinical trials are currently evaluating combination therapy with a BsAb and another agent, such as a CD38-targeting antibody or an immunomodulatory drug (e.g., pomalidomide), to further improve response depth and duration. Additionally, the combination of two BsAbs, simultaneously targeting two different antigens to prevent antigen escape, is being explored in clinical studies. The evaluation of BsAbs in earlier lines of therapy, including newly diagnosed MM, is warranted, based on the efficacy of BsAbs in advanced MM.

The Agony of Choice-Where to Place the Wave of BCMA-Targeted Therapies in the Multiple Myeloma Treatment Puzzle in 2022 and Beyond

Simple Summary

There is no doubt that immunotherapeutic approaches will change the current treatment landscape of multiple myeloma in the near future; in particular, a wave of BCMA-targeted therapies is currently entering clinical routine. Although the increasing availability of different therapeutic approaches is highly welcome, it also increases the daily challenges in clinical decision making if they all use the same target. Here, we provide a comprehensive summary of BCMA-targeted approaches in myeloma and aim to share some basic concepts in clinical decision making.

Abstract

Since the introduction of first-generation proteasome inhibitors and immunomodulatory agents, the multiple myeloma (MM) treatment landscape has undergone a remarkable development. Most recently, immunotherapeutic strategies targeting the B cell maturation antigen (BCMA) entered the clinical stage providing access to highly anticipated novel treatment strategies. At present, numerous different approaches investigate BCMA as an effective multi-modal target. Currently, BCMA-directed antibody–drug conjugates, bispecific and trispecific antibodies, autologous and allogeneic CAR-T cell as well as CAR-NK cell constructs are either approved or in different stages of clinical and preclinical development for the treatment of MM. This armamentarium of treatment choices raises several challenges for clinical decision making, particularly in the absence of head-to-head comparisons. In this review, we provide a comprehensive overview of BCMA-targeting therapeutics, deliver latest updates on clinical trial data, and focus on potential patient selection criteria for different BCMA-targeting immunotherapeutic strategies.

Bispecific Antibodies in Multiple Myeloma: Present and Future

Despite many recent advances in therapy, there is still no plateau in overall survival curves in multiple myeloma. Bispecific antibodies are a novel immunotherapeutic approach designed to bind antigens on malignant plasma cells and cytotoxic immune effector cells. Early-phase clinical trials targeting B-cell maturation antigen (BCMA), GPRC5D, and FcRH5 have demonstrated a favorable safety profile, with mainly low-grade cytokine release syndrome, cytopenias, and infections. Although dose escalation is ongoing in several studies, early efficacy data show response rates in the most active dose cohorts between 61% and 83% with many deep responses; however, durability remains to be established. Further clinical trial data are eagerly anticipated.

SIGNIFICANCE

Overall survival of triple-class refractory multiple myeloma remains poor. Bispecific antibodies are a novel immunotherapeutic modality with a favorable safety profile and impressive preliminary efficacy in heavily treated patients. Although more data are needed, bispecifics will likely become an integral part of the multiple myeloma treatment paradigm in the near future. Studies in earlier lines of therapy and in combination with other active anti-multiple myeloma agents will help further define the role of bispecifics in multiple myeloma.

The evolving status of immunotherapies in multiple myeloma: the future role of bispecific antibodies

Treatment outcomes in multiple myeloma (MM) have improved dramatically over the past 10 years. However, patients with high-risk disease such as those with Stage III disease by the Revised International Staging System, the presence of adverse cytogenetics, or who are refractory to proteosome inhibitors, immunomodulatory drugs and monoclonal antibodies may have dismal outcomes. These patients represent an urgent ongoing need in MM. One of the hallmarks of MM is immune dysfunction and a tumour-permissive immune microenvironment. Ameliorating the immune-paresis could lead to improved outcomes. The role of immunotherapies has been growing at an exponential pace with numerous agents under development in clinical trials. In the present review, we provide an overview of immunotherapies in MM, focussing on bispecific antibodies (BsAbs). We review efficacy outcomes from the published clinical trials and consider the important safety aspects of these therapies, in particular the risk of cytokine-release syndrome and immune effector cell-associated neurotoxicity syndrome, and how these compare with patients receiving chimeric antigen receptor T cells. We discuss the MM epitopes being targeted by BsAbs, either in clinical or preclinical stages, and we consider where these therapies might best fit within the future ever-changing paradigm of MM treatment.

Bispecific T Cell Engagers for the Treatment of Multiple Myeloma: Achievements and Challenges

MM is the second most common hematological malignancy and represents approximately 20% of deaths from hematopoietic cancers. The advent of novel agents has changed the therapeutic landscape of MM treatment; however, MM remains incurable. T cell-based immunotherapy such as BTCEs is a promising modality for the treatment of MM. This review article discusses the advancements and future directions of BTCE treatments for MM.

Targeted Therapies for Multiple Myeloma

Multiple myeloma continues to be a challenging disorder to treat despite improved therapies and the widespread use of proteasome inhibitors and immunomodulatory drugs. Although patient outcomes have improved, the disease continues to invariably relapse, and in the majority of cases, a cure remains elusive. In the last decade, there has been an explosion of novel drugs targeting cellular proteins essential for malignant plasma cell proliferation and survival. In this review, we focus on novel druggable targets leading to the development of monoclonal antibodies and cellular therapies against surface antigens (CD38, CD47, CD138, BCMA, SLAMF7, GPRC5D, FcRH5), inhibitors of epigenetic regulators such as histone deacetylase (HDAC), and agents targeting anti-apoptotic (BCL-2), ribosomal (eEF1A2) and nuclear export (XPO1) proteins.

Expression profile of Fc receptor-like molecules in patients with IgA nephropathy

BACKGROUND

Fc receptor-like (FCRL) molecules were considered to play a role in the pathogenesis of certain autoimmune diseases. Nonetheless, the clinical significance of FCRLs in IgA nephropathy (IgAN) remains unclear.

OBJECTIVE

This study is aimed at investigating the expression levels of FCRLs molecules in IgAN patients and determining its relevance to disease activity.

METHODS

The mRNA expression levels of FCRLs were determined in peripheral blood mononuclear cells (PBMCs) of 42 IgAN patients and 48 healthy controls by quantitative real-time PCR (qRT-PCR). FCRLs proteins expression in B cells of 25 IgAN patients, 14 patients with non-IgAN glomerulonephritis, and 29 healthy controls were detected by Flow cytometry. The Spearman correlation test was used to assess the correlation of FCRLs expression with clinical parameters of IgAN patients.

RESULTS

Our results indicated significant down-regulation of FCRL2 and FCRL3 mRNA levels in IgAN patients compared to healthy subjects. Surface protein expression of FCRLs molecules confirmed the qRT-PCR results. But FCRL2 and FCRL3 protein levels did not correlate with clinicopathologic phenotypes of IgAN patients. However, we found a significant positively correlation of FCRL2 and FCRL3 mRNA expression with the core 1 β1,3-galactosyltransferase (C1GALT1) and its molecular chaperone (Cosmc) mRNA levels in IgAN patients.

CONCLUSIONS

FCRL2 and FCRL3 expression levels in IgAN patients are significantly decreased and correlated with CIGALT1 and Cosmc mRNA expression.

Roles for the FCRL6 Immunoreceptor in Tumor Immunology

Members of the Fc receptor-like (FCRL1-6) gene family encode transmembrane glycoproteins that are preferentially expressed by B cells and generally repress responses via cytoplasmic tyrosine-based regulation. Given their distribution and function, there is a growing appreciation for their roles in lymphoproliferative disorders and as immunotherapeutic targets. In contrast to FCRL1-5, FCRL6 is distinctly expressed outside the B lineage by cytotoxic T and NK lymphocytes. Its restricted expression by these orchestrators of cell-mediated immunity, along with its inhibitory properties and extracellular interactions with MHCII/HLA-DR, represent a newly appreciated axis with relevance in tolerance and cancer defense. The significance of FCRL6 in this arena has been recently demonstrated by its upregulation in HLA-DR⁺ tumor samples from melanoma, breast, and lung cancer patients who relapsed following PD-1 blockade. These findings imply a potential mechanistic role for FCRL6 in adaptive evasion to immune checkpoint therapy. Here we review these new developments in the FCRL field and identify new evidence for the prognostic significance of FCRL6 in malignancies that collectively indicate its potential as a biomarker and therapeutic target.

New drugs in early development for treating multiple myeloma: all that glitters is not gold

INTRODUCTION

The last twenty years have introduced new therapeutic agents for multiple myeloma (MM); these include proteasome inhibitors (PIs), immunomodulatory drugs (IMDs) and monoclonal antibodies (mAbs). However, MM remains incurable, hence there is an unmet need for new agents for the treatment of advanced refractory disease. New agents could also be used in early lines to achieve improved, more sustained remission.

AREAS COVERED

We review the most promising agents investigated in early-phase trials for the treatment of MM and provide an emphasis on new agents directed against well-known targets (new PIs, IMDs and anti-CD38 mAbs). Drugs that work through distinct and numerous mechanisms of action (e.g. pro-apoptotic agents and tyrosine kinase inhibitors) and innovative immunotherapeutic approaches are also described. The paper culminates with our perspective on therapeutic approaches on the horizon for this disease.

EXPERT OPINION

IMD iberdomide and the export protein inhibitor selinexor demonstrated efficacy in heavily pretreated patients who had no other therapeutic options. We expect that immunotherapy with anti-BCMA BTEs and ADCs will revolutionize the approach to treating the early stages of the disease. Data on venetoclax in t(11;14)-positive patients may pave the way for personalized therapy. Not all new agents under early clinical evaluation will be investigated in regulatory phase III trials; one of the most important challenges is to identify those that could make a difference.

Emerging immunotherapies in multiple myeloma

Despite considerable advances in treatment approaches in the past two decades, multiple myeloma remains an incurable disease. Treatments for myeloma continue to evolve with many emerging immunotherapies. The first immunotherapy used to treat hematologic cancers, including multiple myeloma, was an allogeneic stem cell transplant. In the mid-2000s, immunomodulatory drugs thalidomide, lenalidomide, and subsequently pomalidomide were proven to be effective in multiple myeloma and substantially improved survival. The next wave of immunotherapies for multiple myeloma included the monoclonal antibodies daratumumab and elotuzumab, which were approved by the Food and Drug Administration in 2015. Subsequently, a variety of immunotherapies have been developed for multiple myeloma, including chimeric antigen receptor T cells, bispecific antibodies, antibody drug conjugates, and checkpoint inhibitors. Many of these emerging treatments target the B cell maturation antigen, which is expressed on plasma cells, although several other novel receptors are also being studied. This review summarizes the evidence of these various immunotherapies, their mechanism of action, and data from clinical trials regarding the treatments' safety and efficacy.

Bispecific Antibodies: A New Era of Treatment for Multiple Myeloma

Despite the introduction of novel agents such as proteasome inhibitors, immunomodulatory drugs, and autologous stem cell transplant, multiple myeloma (MM) largely remains an incurable disease. In recent years, monoclonal antibody-based treatment strategies have been developed to target specific surface antigens on MM cells. Treatment with bispecific antibodies (bsAbs) is an immunotherapeutic strategy that leads to an enhanced interaction between MM cells and immune effector cells, e.g., T-cells and natural killer cells. With the immune synapse built by bsAbs, the elimination of MM cells can be facilitated. To date, bsAbs have demonstrated encouraging results in preclinical studies, and clinical trials evaluating bsAbs in patients with MM are ongoing. Early clinical data show the promising efficacy of bsAbs in relapsed/refractory MM. Together with chimeric antigen receptor-modified (CAR)-T-cells, bsAbs represent a new dimension of precision medicine. In this review, we provide an overview of rationale, current clinical development, resistance mechanisms, and future directions of bsAbs in MM.

Targeted Therapy With Immunoconjugates for Multiple Myeloma

The introduction of proteasome inhibitors (PI) and immunomodulatory drugs (IMiD) has markedly increased the survival of multiple myeloma (MM) patients. Also, the unconjugated monoclonal antibodies (mAb) daratumumab (anti-CD38) and elotuzumab (anti-SLAMF7) have revolutionized MM treatment given their clinical efficacy and safety, illustrating the potential of targeted immunotherapy as a powerful treatment strategy for MM. Nonetheless, most patients eventually develop PI-, IMiD-, and mAb-refractory disease because of the selection of resistant MM clones, which associates with a poor prognosis. Accordingly, these patients remain in urgent need of new therapies with novel mechanisms of action. In this respect, mAbs or mAb fragments can also be utilized as carriers of potent effector moieties to specifically target surface antigens on cells of interest. Such immunoconjugates have the potential to exert anti-MM activity in heavily pretreated patients due to their distinct and pleiotropic mechanisms of action. In addition, the fusion of highly cytotoxic compounds to mAbs decreases the off-target toxicity, thereby improving the therapeutic window. According to the effector moiety, immunoconjugates are classified into antibody-drug conjugates, immunotoxins, immunocytokines, or radioimmunoconjugates. This review will focus on the mechanisms of action, safety and efficacy of several promising immunoconjugates that are under investigation in preclinical and/or clinical MM studies. We will also include a discussion on combination therapy with immunoconjugates, resistance mechanisms, and future developments.

Bispecific Antibodies for Multiple Myeloma: A Review of Targets, Drugs, Clinical Trials, and Future Directions

Multiple myeloma (MM) is a plasma cell malignancy and the second most common hematological neoplasm in adults, comprising 1.8% of all cancers. With an annual incidence of ~30,770 cases in the United States, MM has a high mortality rate, leading to 12,770 deaths per year. MM is a genetically complex, highly heterogeneous malignancy, with significant inter- and intra-patient clonal variability. Recent years have witnessed dramatic improvements in the diagnostics, classification, and treatment of MM. However, patients with high-risk disease have not yet benefited from therapeutic advances. High-risk patients are often primary refractory to treatment or relapse early, ultimately resulting in progression toward aggressive end-stage MM, with associated extramedullary disease or plasma cell leukemia. Therefore, novel treatment modalities are needed to improve the outcomes of these patients. Bispecific antibodies (BsAbs) are immunotherapeutics that simultaneously target and thereby redirect effector immune cells to tumor cells. BsAbs have shown high efficacy in B cell malignancies, including refractory/relapsed acute lymphoblastic leukemia. Various BsAbs targeting MM-specific antigens such as B cell maturation antigen (BCMA), CD38, and CD138 are currently in pre-clinical and clinical development, with promising results. In this review, we outline these advances, focusing on BsAb drugs, their targets, and their potential to improve survival, especially for high-risk MM patients. In combination with current treatment strategies, BsAbs may pave the way toward a cure for MM.

Measurable disease evaluation in patients with myeloma

Recent years saw significant breakthroughs in treatment of multiple myeloma. Durable remissions are now seen in a significant proportion of patients with the previously uniformly incurable and progressive disease. Yet because of deep suppression of the neoplastic myeloma clones by the newer therapies, older disease monitoring techniques are insufficient to distinguish between the patients at high risk of imminent relapse and those in whom durable remission is expected. This review briefly describes prognostic and therapeutic implications of measurable disease (MRD) evaluation, explains why deep MRD evaluation is needed for patients without morphologic evidence of disease, and reviews the state of the art of evaluation of myeloma MRD by flow cytometry.

First-in-Human Phase I Study of ABBV-838, an Antibody-Drug Conjugate Targeting SLAMF7/CS1 in Patients with Relapsed and Refractory Multiple Myeloma

PURPOSE

ABBV-838 is an antibody-drug conjugate targeting a unique epitope of CD2 subset 1, a cell-surface glycoprotein expressed on multiple myeloma cells. This phase I/Ib first-in-human, dose-escalation study (trial registration ID: NCT02462525) evaluated the safety, pharmacokinetics, and preliminary activity of ABBV-838 in patients with relapsed and refractory multiple myeloma (RRMM).

PATIENTS AND METHODS

Eligible patients (≥18 years) received ABBV-838 (3+3 design) intravenously starting from 0.6 mg/kg up to 6.0 mg/kg for 3-week dosing intervals (Q3W). Patients could continue ABBV-838 for up to 24 months. Assessment of alternate dosing intervals (Q1W and Q2W) was conducted in parallel.

RESULTS

As of March 2017, 75 patients received at least one dose of ABBV-838. The most common any-grade treatment-emergent adverse events (TEAE) were neutropenia and anemia (28.0% each), fatigue (26.7%), and nausea (25.3%). Grade 3/4/5 TEAEs were reported in 73.3% of patients across all treatment groups; most common were neutropenia (20.0%), anemia (18.7%), and leukopenia (13.3%). Grade 3/4/5 ABBV-838-related TEAEs were reported by 40.0% of patients across all treatment groups. Overall, 4.0% of patients experienced TEAEs leading to death, none ABBV-838 related. The MTD was not reached; the selected recommended dose for the expansion cohort was 5.0 mg/kg Q3W. Pharmacokinetic analysis showed that exposure was approximately dose proportional. The overall response rate was 10.7%; very good partial responses and partial responses were achieved by 2 (2.7%) and 6 (8.0%) patients, respectively.

CONCLUSIONS

These results demonstrate that ABBV-838 is safe and well-tolerated in patients with RRMM with a very limited efficacy.

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

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

Phase I study of the anti-FcRH5 antibody-drug conjugate DFRF4539A in relapsed or refractory multiple myeloma

FcRH5 is a cell surface marker enriched on malignant plasma cells when compared to other hematologic malignancies and normal tissues. DFRF4539A is an anti-FcRH5 antibody-drug conjugated to monomethyl auristatin E (MMAE), a potent anti-mitotic agent. This phase I study assessed safety, tolerability, maximum tolerated dose (MTD), anti-tumor activity, and pharmacokinetics of DFRF4539A in patients with relapsed/refractory multiple myeloma. DFRF4539A was administered at 0.3-2.4 mg/kg every 3 weeks or 0.8-1.1 mg/kg weekly as a single-agent by intravenous infusion to 39 patients. Exposure of total antibody and antibody-conjugate-MMAE analytes was linear across the doses tested. There were 37 (95%) adverse events (AEs), 8 (21%) serious AEs, and 15 (39%) AEs ≥ grade 3. Anemia (n = 10, 26%) was the most common AE considered related to DFRF4539A. Two cases of grade 3 acute renal failure were attributed to DFRF4539A. There were no deaths; the MTD was not reached. DFRF4539A demonstrated limited activity in patients at the doses tested with 2 (5%) partial response, 1 (3%) minimal response, 18 (46%) stable disease, and 16 (41%) progressive disease. FcRH5 was confirmed to be expressed and occupied by antibody post-treatment and thus remains a valid myeloma target. Nevertheless, this MMAE-based antibody-drug-conjugate targeting FcRH5 was unsuccessful for myeloma.

Multiple Myeloma: Personalised Medicine Based on Pathogenesis

Multiple myeloma is increasingly being recognised as more than one disease, characterised by marked cytogenetic, molecular, and proliferative heterogeneity. The prognosis is widely varied, ranging from low to very high-risk, based on cytogenetic and molecular studies. Although novel agents, such as proteasome inhibitors and immunomodulators, have been developed, which have improved treatment responses and disease prognosis, multiple myeloma remains an incurable disease. Based on highly sensitive detection tools, such as gene expression profiling and next generation sequence analysis, and the understanding of the pathogenesis of multiple myeloma, many potential agents, including monoclonal antibodies, drug-conjugated antibodies, drugs targeted to molecular abnormalities, microRNA inhibitors or mimics, and immune therapies, such as chimeric antigen receptors T cells and anti-PD1 agents, can be considered personalised therapies. In this paper, multiple myeloma pathogenesis and potential molecular and immunotherapies are reviewed.

Update on Fc receptor-like (FCRL) family: new immunoregulatory players in health and diseases

INTRODUCTION

Fc receptor-like (FCRL) molecules, as recently identified members of the immunoglobulin superfamily (IgSF), are preferentially expressed by B-cells. They have variable number of extracellular immunoglobulin-like domains and cytoplasmic activating ITAMs and/or inhibitory ITIMs. FCRL1-5 are dominantly expressed in different stages of B-cells development. But, FCRL6 is preferentially expressed in different subsets of T-cells and NK cells. FCRL1-5 could regulate different features of B-cell evolution such as development, differentiation, activation, antibody secretion and isotype switching. Areas covered: Improved understanding of FCRL expression may grant B-cells and finally its signaling pathways, alone or in cooperation with other signaling molecules, as interesting new targets for diagnostic, monitoring and immunotherapeutic modalities; although further investigations remain to be defined. Recent investigations on different family members of FCRL proteins have substantiated their differential expression on different tissues, malignancies, immune related disease and infectious diseases. Expert opinion: FCRLs restricted expressions in normal B-cells and T-cell subsets accompanied with their overexpression in B-cell malignancies introduce them as logical candidates for the development of antibody- and cell-based immunotherapy approaches in B-cell malignancies, immune-mediated and infectious diseases. FCRLs would be applied as attractive and specific targets for immunodiagnostic approaches, clinical prognosis as well as disease monitoring of relevant patients.

Minimal Residual Disease Detection by Flow Cytometry in Multiple Myeloma: Why and How?

The outlook for myeloma patients has steadily improved with the introduction of newer drug combinations in recent years. Unlike older therapies that largely achieved only modest levels of neoplastic clone reduction, the newer drug combinations have led to deeper suppression of myeloma clones in most patients. Frequently the neoplastic clones become undetectable with traditional disease evaluation approaches. Recent studies using ultrasensitive disease monitoring have demonstrated that patients with disease undetectable by traditional techniques show wide heterogeneity in disease levels varying by several orders of magnitude. Moreover, measurement of the depth of disease suppression even at very low level has emerged as the most powerful prognostication tool in myeloma. Minimal (or measurable) residual disease (MRD) evaluation has also been proposed as a relevant tool in assessment of drug efficacy and in selection of further therapeutic options. In the face of the robust MRD measurement utility data, it has become critical to develop widely applicable disease monitoring techniques that can be applied to more patients in a variety of clinical setting. Both DNA-based and flow cytometry-based approaches have been successfully developed for this purpose achieving sensitivity approaching 1 neoplastic cell in a million. This review article focuses on the theoretical and practical aspects and challenges of deep MRD monitoring in myeloma by flow cytometry. Challenges of flow cytometric disease monitoring in the era of antigen-directed therapy are also discussed.

A rational approach for cancer stem-like cell isolation and characterization using CD44 and prominin-1(CD133) as selection markers

The availability of adequate cancer stem cells or cancer stem-like cell (CSC) is important in cancer study. From ovarian cancer cell lines, SKOV3 and OVCAR3, we induced peritoneal ascites tumors in immunodeficient mice. Among the cells (SKOV3.PX1 and OVCAR3.PX1) from those tumors, we sorted both CD44 and CD133 positive cells (SKOV3.PX1_133+44+, OVCAR3.PX1_133+44+), which manifest the characteristics of self-renewal, multi-lineage differentiation, chemoresistance and tumorigenicity, those of cancer stem-like cells (CSLC). Intraperitoneal transplantation of these CD44 and CD133 positive cells resulted in poorer survival in the engrafted animals. Clinically, increased CD133 expression was found in moderately and poorly differentiated (grade II and III) ovarian serous cystadenocarcinomas. The ascites tumor cells from human ovarian cancers demonstrated more CD133 and CD44 expressions than those from primary ovarian or metastatic tumors and confer tumorigenicity in immunodeficient mice. Compared to their parental cells, the SKOV3.PX1_133+44+ and OVCAR3.PX1_133+44+ cells uniquely expressed 5 CD markers (CD97, CD104, CD107a, CD121a, and CD125). Among these markers, CD97, CD104, CD107a, and CD121a are significantly more expressed in the CD133+ and CD44+ double positive cells of human ovarian ascites tumor cells (Ascites_133+44+) than those from primary ovarian or metastatic tumors. The cancer stem-like cells were enriched from 3% to more than 70% after this manipulation. This intraperitoneal enrichment of cancer stem-like cells, from ovarian cancer cell lines or primary ovarian tumor, potentially provides an adequate amount of ovarian cancer stem-like cells for the ovarian cancer study and possibly benefits cancer therapy.

Emerging antibody-drug conjugates for treating lymphoid malignancies

INTRODUCTION

Antibody-drug conjugates (ADC) are monoclonal antibodies (Mabs) attached to biologically active drugs through specialized chemical linkers. They deliver and release cytotoxic agents at the tumor site, reducing the likelihood of systemic exposure and therefore toxicity. These agents should improve the potency of chemotherapy by increasing the accumulation of cytotoxic the drug within or near the neoplastic cells with reduced systemic effects. Areas covered: A literature review was conducted of the MEDLINE database PubMed for articles in English examining Mabs, B-cell receptor pathway inhibitors and immunomodulating drugs. Publications from 2000 through April 2017 were scrutinized. Conference proceedings from the previous five years of the American Society of Hematology, European Hematology Association, American Society of Clinical Oncology, and ACR/ARHP Annual Scientific Meetings were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles. Expert opinion: Newer ADCs show promise as treatment for several hematologic malignancies, especially lymphoma, multiple myeloma, and leukemia. However, definitive data from ongoing and future clinical trials will aid in better defining the status of these agents in the treatment of these diseases.

Standardisation of minimal residual disease in multiple myeloma

The assessment of the effectiveness of chemotherapy in oncology cannot disregard the concept of minimal residual disease (MRD). In fact, the efforts of numerous scientific groups all over the world are currently focusing on this issue, with the sole purpose of defining sensitive, effective assessment criteria that are, above all, able to give acceptable, easily repeatable results worldwide. Regarding this issue, especially with the advent of new drugs, multiple myeloma is one of the haematologic malignancies for which a consensus has not yet been reached. In this review, we analyse various techniques that have been used to improve the sensitivity of response, aimed at reducing the cut-off values previously allowed, as well as serological values like serum-free light chain, or immunophenotypic tools on bone marrow or peripheral blood, like multi-parameter flow cytometry, or molecular ones such as allele-specific oligonucleotide (ASO)-qPCR and next-generation/high-throughput sequencing technologies (NGS). Moreover, our discussion makes a brief reference to promising techniques, such as mass spectrometry for identifying Ig light chain (LC) in peripheral blood, and the assessment of gene expression profile not only in defining prognostic risk at the diagnosis but also as a tool for evaluation of response.

Monoclonal Antibodies in Multiple Myeloma: A New Wave of the Future

In 2015, 2 monoclonal antibodies were approved for the treatment of relapsed or refractory multiple myeloma (RRMM), elotuzumab and daratumumab. Elotuzumab is a monoclonal IgG-κ antibody directed against SLAMF7 (signaling lymphocytic activation molecule F7), a cell surface receptor involved in natural killer cell activation. Daratumumab is a monoclonal IgG-κ antibody that binds to CD38, a transmembrane protein found on the surface of myeloma cells and responsible for cellular adhesion and ectoenzymatic activity. Both elotuzumab and daratumumab act through recruitment of the immune system to enhance cellular cytotoxicity directed against myeloma cells. Elotuzumab requires lenalidomide and dexamethasone combined to enhance progression-free survival in patients with RRMM, and daratumumab has both single-agent and combination activity with either lenalidomide or the proteasome inhibitor bortezomib in RRMM. The adverse effect profile of both agents mainly consists of allergic-type infusion reactions. Other considerations for monoclonal antibody use in the treatment of MM include the potential for interference in serum protein electrophoresis testing and cross-reactivity of daratumumab with CD38 present on red blood cells. In the present report, we discussed the clinical development of daratumumab and elotuzumab and newer immunologic approaches to the treatment of MM.

Membrane-Proximal Epitope Facilitates Efficient T Cell Synapse Formation by Anti-FcRH5/CD3 and Is a Requirement for Myeloma Cell Killing

The anti-FcRH5/CD3 T cell-dependent bispecific antibody (TDB) targets the B cell lineage marker FcRH5 expressed in multiple myeloma (MM) tumor cells. We demonstrate that TDBs trigger T cell receptor activation by inducing target clustering and exclusion of CD45 phosphatase from the synapse. The dimensions of the target molecule play a key role in the efficiency of the synapse formation. The anti-FcRH5/CD3 TDB kills human plasma cells and patient-derived myeloma cells at picomolar concentrations and results in complete depletion of B cells and bone marrow plasma cells in cynomolgus monkeys. These data demonstrate the potential for the anti-FcRH5/CD3 TDB, alone or in combination with inhibition of PD-1/PD-L1 signaling, in the treatment of MM and other B cell malignancies.

Immune recruitment or suppression by glycan engineering of endogenous and therapeutic antibodies

Human serum IgG contains multiple glycoforms which exhibit a range of binding properties to effector molecules such as cellular Fc receptors. Emerging knowledge of how the Fc glycans contribute to the antibody structure and effector functions has opened new avenues for the exploitation of defined antibody glycoforms in the treatment of diseases. Here, we review the structure and activity of antibody glycoforms and highlight developments in antibody glycoengineering by both the manipulation of the cellular glycosylation machinery and by chemoenzymatic synthesis. We discuss wide ranging applications of antibody glycoengineering in the treatment of cancer, autoimmunity and inflammation. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Fc Receptor-Like Proteins in Pathophysiology of B-cell Disorder

Members of the family of Fc receptor-like (FcRL) proteins, homologous to FcγRI, have been identified by multiple research groups. Consequently, they have been described using multiple nomenclatures including Fc receptor homologs (FcRH), immunoglobulin superfamily receptor translocation-associated genes (IRTA), immunoglobulin-Fc-gp42-related genes (IFGP), Src homology 2 domain-containing phosphatase anchor proteins (SPAP), and B cell cross-linked by anti-immunoglobulin M-activating sequences (BXMAS). They are now referred to under a unified nomenclature as FCRL. Eight different human FCRL genes have been identified, all of which appear to be related to the genes of the immunoglobulin superfamily (IgSF) of cellular adhesion molecules. These type 1 transmembrane glycoproteins are composed of different combinations of 5 types of immunoglobulin-like domains, with each protein consisting of 3 to 9 domains, and no individual domain type conserved throughout all of the FCRL proteins. Ligands for the majority of the FCRLs remain unknown. In general, FCRL expression is restricted to lymphocytes and is primarily expressed in B-lymphocytes, supporting FCRL’s involvement in a variety of immune disorders. Most FCRLs functionally repress B-cell activation; however, they might have dual roles in lymphocyte functions as these proteins often possess immunoreceptor tyrosine activation (ITAM) and inhibitory (ITIM) motif elements. The biological functions of these newly recognized FCRL proteins are just beginning to emerge, and might provide the insight necessary for understanding pathophysiology of lymphocyte disorders and treating different immune diseases.

B cell receptor induced Fc receptor-like 5 expression is mediated by multiple signaling pathways converging on NF-κB and NFAT

Fc receptor-like (FCRL) proteins are novel regulators of the B cell response to antigen. Human FCRL5 binds intact IgG and modifies the strength of antigen receptor (BCR) signaling. Altering FCRL5 expression could therefore regulate the B cell response to antigen. In this study, we found that FCRL5 expression is induced specifically upon BCR stimulation and dissected the molecular mechanism. FCRL5 mRNA and cell surface protein expression required prolonged BCR stimulation and de novo protein synthesis. Using chemical inhibitors and activators, we identified roles for several signaling pathways, indicating a complex mechanism. Specifically, the PI3K/AKT, JNK, PKC and IKK2-dependent classical NF-κB pathways were involved in induced FCRL5 expression. Furthermore, induced FCRL5 expression required elevation of intracellular Ca(++) and was partially blocked by cyclosporine A, a calcineurin inhibitor. The importance of the transcription factors NF-κB, NFAT and CREB-binding protein was revealed based on sensitivity to inhibitors. Using reporter gene assays, we showed that the core FCRL5 promoter was sufficient to drive induced gene expression. Mutations of two predicted NF-κB sites or an NFAT site in the core promoter abrogated induced gene expression, suggesting direct regulation of the FCRL5 gene by NF-κB and NFAT. In support, we detected binding of NF-κB and NFAT family proteins to oligonucleotides corresponding to the predicted sites. We propose that the identified intricate mechanism serves to ensure that FCRL5 is expressed on B cells at a precise time following antigen encounter, with potential implications regarding regulation of the B cell response.

A New Triglycyl Peptide Linker for Antibody-Drug Conjugates (ADCs) with Improved Targeted Killing of Cancer Cells

A triglycyl peptide linker (CX) was designed for use in antibody -: drug conjugates (ADC), aiming to provide efficient release and lysosomal efflux of cytotoxic catabolites within targeted cancer cells. ADCs comprising anti-epithelial cell adhesion molecule (anti-EpCAM) and anti-EGFR antibodies with maytansinoid payloads were prepared using CX or a noncleavable SMCC linker (CX and SMCC ADCs). The in vitro cytotoxic activities of CX and SMCC ADCs were similar for several cancer cell lines; however, the CX ADC was more active (5-100-fold lower IC50) than the SMCC ADC in other cell lines, including a multidrug-resistant line. Both CX and SMCC ADCs showed comparable MTDs and pharmacokinetics in CD-1 mice. In Calu-3 tumor xenografts, antitumor efficacy was observed with the anti-EpCAM CX ADC at a 5-fold lower dose than the corresponding SMCC ADC in vivo Similarly, the anti-EGFR CX ADC showed improved antitumor activity over the respective SMCC conjugate in HSC-2 and H1975 tumor models; however, both exhibited similar activity against FaDu xenografts. Mechanistically, in contrast with the charged lysine-linked catabolite of SMCC ADC, a significant fraction of the carboxylic acid catabolite of CX ADC could be uncharged in the acidic lysosomes, and thus diffuse out readily into the cytosol. Upon release from tumor cells, CX catabolites are charged at extracellular pH and do not penetrate and kill neighboring cells, similar to the SMCC catabolite. Overall, these data suggest that CX represents a promising linker option for the development of ADCs with improved therapeutic properties. Mol Cancer Ther; 15(6); 1311-20. ©2016 AACR.