Tumor burden limits bispecific antibody efficacy through T cell exhaustion averted by concurrent cytotoxic therapy

High baseline levels of PD-L1 reduce the heterogeneity of immune checkpoint signature and sensitize anti-PD1 therapy in lung and colorectal cancers

Immune checkpoint blockade (ICB) therapy only induces durable responses in a subset of cancer patients. The underlying mechanisms of such selective efficacy remain largely unknown. By analyzing the expression profiles of immune checkpoint molecules in different statuses of murine tumors, we found that tumor progression generally randomly upregulated multiple immune checkpoints, thus increased the Heterogeneity of Immune checkpoint Signature (HIS) and resulted in immunotherapeutic resistance. Interestingly, overexpressing one pivotal immune checkpoint in a tumor hindered the upregulation of a majority of other immune checkpoint genes during tumor progression via suppressing interferon γ, resulting in HIS-low. Indeed, PD-L1 high-expression sensitized baseline large tumors to anti-PD1 therapy without altering the sensitivity of baseline small tumors. In line with these preclinical results, a retrospective analysis of a phase III study involving patients with non-small cell lung cancer (NSCLC) revealed that PD-L1 tumor proportion score (TPS) ≥ 50% more reliably predicted therapeutic response in NSCLC patients with baseline tumor volume (BTV)-large compared to patients with BTV-small. Notably, TPS combined with BTV significantly improved the predictive accuracy. Collectively, the data suggest that HIS reflects the dynamic features of tumor immune evasion and dictates the selective efficacy of ICB in a tumor size-dependent manner, providing a potential novel strategy to improve precision ICB. These findings highlight the application of ICB to earlier stages of cancer patients. The integration of PD-L1 with BTV may immediately improve patient stratification and prediction performance in the clinic.

Current treatment approach and future perspectives in B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL) represent the two major subtypes of mature B cell lymphoma. A deeper understanding of tumor biology, as well as molecular classification characterized by targetable gene alterations, and the introduction of novel treatment options, including targeted drugs (e.g., antibody-drug conjugates and small molecules [e.g., Bruton tyrosine kinase inhibitor]) and immune therapies (e.g., chimeric antigen receptor [CAR] T cell therapy and bispecific antibody [BsAb]), has changed the treatment paradigms for DLBCL and FL. In clinical practice, however, treatment regimens are determined mainly based on prior treatment history, duration of response after previous treatment, patient age, and patient frailty because there have been few randomized trials to inform treatment selection for patients with relapsed or refractory disease and because there is no single prognostic index that guides suitable treatment for each patient. In this review, we summarize the treatment options for DLBCL and FL and discuss the treatment strategies for these two subtypes. We also discuss future perspectives for the treatment of these subtypes.

Mechanisms for resistance to BCMA-targeted immunotherapies in multiple myeloma

Multiple myeloma (MM) remains incurable and patients eventually face the relapse/refractory dilemma. B cell maturation antigen (BCMA)-targeted immunotherapeutic approaches have shown great effectiveness in patients with relapsed/refractory MM, mainly including chimeric antigen receptor T cells (CAR-T), bispecific T cell engagers (TCEs), and antibody-drug conjugates (ADCs). However, their impact on long-term survival remains to be determined. Nonetheless, resistance to these novel therapies is still inevitable, raising a challenge that we have never met in both laboratory research and clinical practice. In this scenario, the investigation aiming to enhance and prolong the anti-MM activity of BCMA-targeted therapies has been expanding rapidly. Despite considerable uncertainty in our understanding of the mechanisms for their resistance, they have mainly been attributed to antigen-dependency, T cell-driven factors, and (immune) tumor microenvironment. In this review, we summarize the current understanding of the mechanisms for resistance to BCMA-targeted immunotherapies and discuss potential strategies for overcoming it.

International myeloma working group immunotherapy committee recommendation on sequencing immunotherapy for treatment of multiple myeloma

T-cell redirecting therapy (TCRT), specifically chimeric antigen receptor T-cell therapy (CAR T-cells) and bispecific T-cell engagers (TCEs) represent a remarkable advance in the treatment of multiple myeloma (MM). There are several products available around the world and several more in development targeting primarily B-cell maturation antigen (BCMA) and G protein-coupled receptor class C group 5 member D (GRPC5D). The relatively rapid availability of multiple immunotherapies brings the necessity to understand how a certain agent may affect the safety and efficacy of a subsequent immunotherapy so MM physicians and patients can aim at optimal sequential use of these therapies. The International Myeloma Working Group conveyed panel of experts to review patient and disease-related factors affecting efficacy and safety of immunotherapy, summarize existing information on sequencing therapy and provide a series of core recommendations.

Targets Selection for Precision Therapy of Relapsed/Refractory Multiple Myeloma: the Latest Advancements

OPINION STATEMENT

According to the guidelines, the primary treatment for multiple myeloma is still based on drugs such as carfilzomib, lenalidomide, or daratumumab. However, patients with relapsed/refractory multiple myeloma (RRMM) may be insensitive or develop resistance to the above therapeutic medications. Thus, formulating standardized and rational treatment regimens for such patients remains an area for consideration. Multidrug combinations are available for the therapy of patients with relapsed/refractory multiple myeloma to improve their clinical outcome and prevent the occurrence of multidrug resistance. For instance, combination therapy with immunomodulators, proteasome inhibitors, and CD38 monoclonal antibodies. With the development of genomics and molecular diagnostic technologies, RRMM has entered the era of precision therapy. Targeted immunotherapeutic drugs such as monoclonal antibodies, bispecific antibodies, antibody-drug conjugates (ADCs), and chimeric antigen receptor-T (CAR-T) cells have shown promising clinical response rates and favorable safety profiles in several clinical and experimental studies. These cutting-edge medicinal treatments may provide new hope for a cure for RRMM. However, the choice of treatment regimen still needs to adhere to the principle of individualization. Generally, we recommend treatment with drugs of a new generation or novel mechanism of action for patients with RRMM who are first relapsed, such as next-generation proteasome inhibitors, next-generation immunomodulators, and CD38-based monoclonal antibody regimens. For multiple relapsed RRMM, we recommend choosing a combination regimen or participating in relevant clinical trials. Additionally, monoclonal antibodies have become the standard of care for patients with RRMM. With the introduction of CAR-T therapy, ADCs, and bispecific antibodies, RRMM patients are expected to achieve deep remissions and long-term survival again.

Cancer vaccines compensate for the insufficient induction of protective tumor-specific immunity of CD3 bispecific antibody therapy

BACKGROUND

CD3 bispecific antibody (CD3 bsAb) therapy has become an established treatment modality for some cancer types and exploits endogenous T cells irrespective of their specificity. However, durable clinical responses are hampered by immune escape through loss of tumor target antigen expression. Induction of long-lasting tumor-specific immunity might therefore improve therapeutic efficacy, but has not been studied in detail yet for CD3 bsAbs. Here, we examined multiple combination strategies aiming to improve survival rates in solid tumors and, simultaneously, install endogenous immunity capable of protection to tumor rechallenge.

METHODS

Two syngeneic mouse tumor models were employed: The immunologically "cold" B16F10 melanoma and the immunologically "hot" MC38.TRP1 colon carcinoma model. Mice were treated with CD3xTRP1 bsAb (murine Fc-inert immunoglobulin G2a) as monotherapy, or in combination with agonistic costimulatory antibodies, Fc-active tumor-opsonizing antibodies, or tumor-(non)specific vaccines. Treatment efficacy of primary tumors and protection from rechallenge was monitored, as well as induction of tumor-specific T-cell responses.

RESULTS

In the immunologically "cold" B16F10 model, all combination therapies improved antitumor activity compared with CD3 bsAb monotherapy and induced systemic tumor-specific T-cell responses. However, this endogenous T-cell immunity swiftly waned and failed to protect mice from subsequent tumor rechallenge, except for combination therapy with tumor-specific vaccination. These vaccines strongly improved the therapeutic efficacy of CD3 bsAb against primary tumors and led to long-term immunological protection. In the immunologically "hot" MC38.TRP1 model, CD3 bsAb combined with only the vaccine adjuvant was sufficient to generate protective T-cell immunity and, moreover, prevented tumor escape via antigen loss.

CONCLUSIONS

These results demonstrate the impact of tumor antigenicity on the induction of protective endogenous antitumor immunity during CD3 bsAb treatment and, importantly, show that the combination with tumor-specific vaccines improves therapeutic efficacy and installs long-term immunological memory in both "hot" and "cold" tumors.

Advancements in bispecific antibodies for multiple myeloma: What's new and what lies ahead

Recent advancements in multiple myeloma (MM) treatment-including immunomodulatory drugs, proteasome inhibitors, monoclonal antibodies, and T cell-redirecting therapies like chimeric antigen receptor (CAR) T cells and bispecific antibodies (BsAbs)-have significantly improved patient outcomes. However, MM remains incurable, highlighting the need for novel therapeutic strategies. BsAbs, which simultaneously target a tumor-specific antigen and CD3 on T cells, have shown promising efficacy. Three BsAbs - teclistamab, elranatamab, and talquetamab - have been approved for relapsed or refractory MM, demonstrating response rates of 60 %-74 % and median progression-free survival of approximately 1 year. This review provides a comprehensive overview of the latest advancements in BsAb therapy for MM, focusing on new therapeutic targets such as BCMA, GPRC5D, and FcRH5, recent clinical trial data, safety considerations, and future directions. We discuss tumor-intrinsic mechanisms of resistance, including antigen expression variability and antigen escape, as well as immune-related factors like T-cell exhaustion and an immunosuppressive microenvironment. Future strategies involve integrating BsAbs earlier in treatment, combining them with other agents to enhance efficacy and overcome resistance, and optimizing administration protocols to mitigate adverse effects. By examining these developments, we highlight how BsAbs are reshaping the treatment landscape of MM and underscore the importance of ongoing research to improve survival and quality of life for patients.

Impact of immunological aging on T cell-mediated therapies in older adults with multiple myeloma and lymphoma

The treatment landscape for lymphoma and multiple myeloma, which disproportionally affect older adults, has been transformed by the advent of T cell-mediated immunotherapies, including immune checkpoint inhibition, T cell-engaging bispecific antibodies, and chimeric antigen receptor (CAR) T cell therapy, during the last decade. These treatment modalities re-enable the patient's own immune system to combat malignant cells and offer the potential for sustained remissions and cure for various diseases.Age profoundly affects the physiological function of the immune system. The process of biological aging is largely driven by inflammatory signaling, which is reciprocally fueled by aging-related alterations of physiology and metabolism. In the T cell compartment, aging contributes to T cell senescence and exhaustion, increased abundance of terminally differentiated cells, a corresponding attrition in naïve T cell numbers, and a decrease in the breadth of the receptor repertoire. Furthermore, inflammatory signaling drives aging-related pathologies and contributes to frailty in older individuals. Thus, there is growing evidence of biological aging modulating the efficacy and toxicity of T cell-mediated immunotherapies.Here, we review the available evidence from biological and clinical studies focusing on the relationship between T cell-mediated treatment of hematologic malignancies and age. We discuss biological features potentially impacting clinical outcomes in various scenarios, and potential strategies to improve the safety and efficacy of immune checkpoint inhibitors, T cell-engaging bispecific antibodies, and CAR-T cell therapy in older patients.

CAR-T cell therapy in Multiple Myeloma: current status and future challenges

The treatment of multiple myeloma has changed dramatically in recent years, with huge strides forward made in the field. Chimeric antigen receptor T-cell therapy targeting the B cell maturation antigen (BCMA) is now widely approved in relapsed refractory patients and is moving into earlier treatment lines. In this review, we discuss the evidence underpinning current regulatory approvals and consider mechanisms through which CAR-T cell efficacy could be improved. These include tackling BCMA-loss, harnessing the immunosuppressive tumour microenvironment, manufacturing concerns including the potential role of other cellular sources, safety issues such as cytokine release syndrome and neurotoxicity, and optimal patient selection.

Immunocompetent mouse models of multiple myeloma

Immunocompetent murine models of multiple myeloma are critical for understanding the pathogenesis of multiple myeloma and for the development of novel immunotherapeutics. Different models are available in Balb/c and C57Bl strains, each with different advantages and disadvantages. The availability of many transplantable cell lines allows for the conduct of experiments with large cohorts of mice bearing identical tumors, while cell lines that grow in vitro can be used for genetic manipulations. The introduction of human CRBN into these models allows for the study of IMiDs and cereblon based PROTACs in mice. New genetically engineered models based on germinal center cell activation of Nsd2 or Ccnd1 together with constitutive NFkB are being developed to model some of the important genetic subtypes of human multiple myeloma.

T Cell-Redirecting Bispecific Antibodies in Multiple Myeloma: Optimal Dosing Schedule and Duration of Treatment

T cell-redirecting bispecific antibodies (BsAb) induce significant responses in heavily pretreated multiple myeloma. BsAbs are currently administered in a dose-dense manner until disease progression. However, continuous therapy is associated with safety concerns, including a high risk of infections and high costs. In addition, chronic exposure to BsAbs, and thus long-term T-cell stimulation, induces T-cell exhaustion, which may contribute to relapse. There is increasing evidence that the strategy of induction treatment followed by maintenance with longer intervals between BsAb doses, or limited treatment duration with cessation of therapy in patients who achieve deep remission, improves the balance between toxicity and efficacy. Significance: There is increasing evidence that after initial debulking, less-frequent BsAb administration mitigates T-cell exhaustion and minimizes the potential for chronic or cumulative toxicity while maintaining durable clinical responses. In addition, specific patient subsets may experience an extended treatment-free period following fixed-duration treatment. Fixed-duration treatment may, therefore, decrease cumulative toxicities and the burden on patients and healthcare systems.

Bispecific antibody (ABL602 2 + 1) induced bistable acute myeloid leukemia kinetics

ABL602 2 + 1, a bispecific antibody with two distinct domains binding to CLL-1 on leukemias and CD3 on T cells, exhibits superior T cell activation and tumour lysing activity. Treatment outcomes of bispecific antibody rely on acute myeloid leukemia cell replication and antibody induced tumour lysing, but their quantitative relationship was unknown. Mathematical models are employed to quantitatively investigate HL-60 cell kinetics determined by bispecific antibody and tumour burden. First, we analysed cytotoxicity assay data testing HL-60 cell against bispecific antibody and T cells, and found efficiency of bispecific antibody induced tumour lysing increases but saturates with increase of HL-60 cell, T cell and bispecific antibody concentration. As a result, their interaction leads to bistable HL-60 cell kinetics; namely, at a given bispecific antibody and T cell concentration interval, HL-60 cell kinetics with small tumour burdens are inhibited but refractory to large tumour burdens. T cell concentration is strong negatively correlated with HL-60 cell concentration. With bispecific antibody clearance, observed bistable HL-60 cell kinetics still exists. Our finding explains observed phenomenon that bispecific antibody was less efficacious at high tumour burden even with enough activated cytotoxic CD8 + T cells. Maintaining high antibody concentration and preventing T-cell exhaustion are equivalently important to sustain long-term control.

Bispecific antibody targets and therapies in multiple myeloma

Recently, several bispecific antibodies (BsAbs) have been approved for the treatment of relapsed multiple myeloma (MM) after early phase trials in heavily pre-treated patients demonstrated high response rates and impressive progression-free survival with monotherapy. These BsAbs provide crucial treatment options for relapsed patients and challenging decisions for clinicians. Evidence on the optimal patient population, treatment sequence, and duration of these therapeutics is unknown and subject to active investigation. While rates of cytokine release syndrome and neurotoxicity appear to be lower with BsAbs than with CAR T-cells, morbidity from infection is high and novel pathways of treatment resistance arise from the longitudinal selection pressure of chronic BsAb therapy. Lastly, a wealth of novel T-cell engagers with unique antibody-structures and antigenic targets are under active investigation with promising early outcome data. In this review, we examine the mechanism of action, therapeutic targets, combinational approaches, sequencing and mechanisms of disease relapse for BsAbs in MM.

Bispecific antibodies in the treatment of multiple myeloma

The treatment paradigm in myeloma is constantly changing. Upfront use of monoclonal antibodies like daratumumab along with proteasome inhibitors (PI)s, and immune modulators (IMiD)s have significantly improved survival and outcomes, but also cause unique challenges at the time of relapse. Engaging immune T cells for tumour cell kill with chimeric antigenic T-cell (CAR T-cell) therapy and bispecific antibodies have become important therapeutic options in relapsed multiple myeloma. Bispecific antibodies are dual antigen targeting constructs that engage the T cells to plasma cells through various target antigens like B-cell membrane antigen (BCMA), G-protein-coupled receptor family C group 5 member D (GPRC5D), and Fc receptor-homolog 5 (FcRH5). These agents have proven to induce deep and durable responses in heavily pre-treated myeloma patients with a predictable safety profile and the ease of off-the-shelf availability. Significant research is ongoing to overcome resistance mechanisms like T cell exhaustion, target antigen mutation or loss and high disease burden. Various trials are also studying these agents as first line options in the newly diagnosed setting. These agents play an important role in the relapsed setting, and efforts are underway to optimize their sequencing in the myeloma treatment algorithm.

Mechanisms of resistance against T-cell engaging bispecific antibodies in multiple myeloma: implications for novel treatment strategies

Off-the-shelf T-cell-redirecting bispecific antibodies targeting BCMA, GPRC5D, and FcRH5 have high activity in multiple myeloma with a manageable toxicity profile. However, not all patients respond to bispecific antibodies and patients can develop bispecific antibody resistance after an initial response. Mechanisms that contribute to bispecific antibody resistance are multifactorial and include tumour-related factors, such as high tumour burden, expression of T-cell inhibitory ligands, and antigen loss. Resistance due to antigen escape can be prevented by simultaneously targeting two tumour-associated antigens with a trispecific antibody or a combination of two bispecific antibodies. There is also increasing evidence that primary resistance to bispecific antibodies is associated with impaired baseline T-cell function. Long-term exposure to bispecific antibodies with chronic T-cell stimulation further aggravates T-cell dysfunction, which could contribute to failure of disease control. Therapeutic interference with T-cell exhaustion by targeting inhibitory or costimulatory pathways could improve bispecific antibody-mediated antitumour activity. The immunosuppressive microenvironment also contributes to bispecific antibody resistance. CD38-targeting antibodies hold promise as combination partners for bispecific antibodies because of their potential to eliminate CD38+ immune suppressor cells. In conclusion, a better understanding of the mechanisms underlying the absence of disease response has provided novel insights to optimise T-cell activity and bispecific antibody efficacy in multiple myeloma.

T-cell redirecting bispecific antibody treatment in multiple myeloma: current knowledge and future strategies for sustained T-cell engagement

INTRODUCTION

T-cell redirecting bispecific antibodies (BsAbs), targeting B-cell maturation antigen (BCMA) or G-protein - coupled receptor class C group 5 member D (GPRC5D), are efficacious new agents for the treatment of patients with relapsed or refractory MM.

AREAS COVERED

This review discusses the pharmacokinetic properties, efficacy, and safety profile of T-cell redirecting BsAbs in MM, with a special focus on their optimal dosing schedule, resistance mechanisms and future strategies to enhance efficacy, reduce toxicity, and maximize duration of response.

EXPERT OPINION

To further improve the efficacy of BsAbs, ongoing studies are investigating whether combination therapy can enhance depth and duration of response. An important open question is also to what extent response to BsAbs can be improved when these agents are used in earlier lines of therapy. In addition, more evidence is needed on rational de-intensification strategies of BsAb dosing upon achieving a sufficient response, and if (temporary) treatment cessation is possible in patients who have achieved a deep remission (e.g. complete response or minimal residual disease-negative status).

Targeted protein degradation in hematologic malignancies: clinical progression towards novel therapeutics

Targeted therapies, such as small molecule kinase inhibitors, have made significant progress in the treatment of hematologic malignancies by directly modulating protein activity. However, issues such as drug toxicity, drug resistance due to target mutations, and the absence of key active sites limit the therapeutic efficacy of these drugs. Targeted protein degradation (TPD) presents an emergent and rapidly evolving therapeutic approach that selectively targets proteins of interest (POI) based on endogenous degradation processes. With an event-driven pharmacology of action, TPD achieves efficacy with catalytic amounts, avoiding drug-related toxicity. Furthermore, TPD has the unique mode of degrading the entire POI, such that resistance derived from mutations in the targeted protein has less impact on its degradation function. Proteolysis-targeting chimeras (PROTACs) and molecular glue degraders (MGDs) are the most maturely developed TPD techniques. In this review, we focus on both preclinical experiments and clinical trials to provide a comprehensive summary of the safety and clinical effectiveness of PROTACs and MGDs in hematologic malignancies over the past two decades. In addition, we also delineate the challenges and opportunities associated with these burgeoning degradation techniques. TPD, as an approach to the precise degradation of specific proteins, provides an important impetus for its future application in the treatment of patients with hematologic malignancies.

Targeting the tumor microenvironment for treating double-refractory chronic lymphocytic leukemia

ABSTRACT

The introduction of BTK inhibitors and BCL2 antagonists to the treatment of chronic lymphocytic leukemia (CLL) has revolutionized therapy and improved patient outcomes. These agents have replaced chemoimmunotherapy as standard of care. Despite this progress, a new group of patients is currently emerging, which has become refractory or intolerant to both classes of agents, creating an unmet medical need. Here, we propose that the targeted modulation of the tumor microenvironment provides new therapeutic options for this group of double-refractory patients. Furthermore, we outline a sequential strategy for tumor microenvironment-directed combination therapies in CLL that can be tested in clinical protocols.

T-Cell Characteristics Impact Response and Resistance to T-Cell-Redirecting Bispecific Antibodies in Multiple Myeloma

PURPOSE

Bispecific antibodies (BsAb) directed against B-cell maturation antigen (teclistamab) or the orphan G protein-coupled receptor GPRC5D (talquetamab) induce deep and durable responses in heavily pretreated patients with multiple myeloma. However, mechanisms underlying primary and acquired resistance remain poorly understood.

EXPERIMENTAL DESIGN

The anti-multiple myeloma activity of teclistamab and talquetamab was evaluated in bone marrow (BM) samples from patients with multiple myeloma. T-cell phenotype and function were assessed in BM/peripheral blood samples obtained from patients with multiple myeloma who were treated with these BsAb.

RESULTS

In ex vivo killing assays with 41 BM samples from BsAb-naive patients with multiple myeloma, teclistamab- and talquetamab-mediated multiple myeloma lysis was strongly correlated (r = 0.73, P < 0.0001). Both BsAb exhibited poor activity in samples with high regulatory T-cell (Treg) numbers and a low T-cell/multiple myeloma cell ratio. Furthermore, comprehensive phenotyping of BM samples derived from patients treated with teclistamab or talquetamab revealed that high frequencies of PD-1+ CD4+ T cells, CTLA4+ CD4+ T cells, and CD38+ CD4+ T cells were associated with primary resistance. Although this lack of response was linked to a modest increase in the expression of inhibitory receptors, increasing T-cell/multiple myeloma cell ratios by adding extra T cells enhanced sensitivity to BsAb. Further, treatment with BsAb resulted in an increased proportion of T cells expressing exhaustion markers (PD-1, TIGIT, and TIM-3), which was accompanied by reduced T-cell proliferative potential and cytokine secretion, as well as impaired antitumor efficacy in ex vivo experiments.

CONCLUSIONS

Primary resistance is characterized by a low T-cell/multiple myeloma cell ratio and Treg-driven immunosuppression, whereas reduced T-cell fitness due to continuous BsAb-mediated T-cell activation may contribute to the development of acquired resistance.

Harnessing the cytotoxic granule exocytosis to augment the efficacy of T-cell-engaging bispecific antibody therapy

T-cell-engaging bispecific antibody (T-BsAb, also known as BiTE) therapy has emerged as a powerful therapeutic modality against multiple myeloma. Given that T-BsAb therapy redirects endogenous T cells to eliminate tumor cells, reinvigorating dysfunctional T cells may be a potential approach to improve the efficacy of T-BsAb. While various immunostimulatory cytokines can potentiate effector T-cell functions, the optimal cytokine treatment for T-BsAb therapy is yet to be established, partly due to a concern of cytokine release syndrome driven by aberrant interferon (IFN)-γ production. Here, we functionally screen immunostimulatory cytokines to determine an ideal combination partner for T-BsAb therapy. This approach reveals interleukin (IL)-21 as a potential immunostimulatory cytokine with the ability to augment T-BsAb-mediated release of granzyme B and perforin, without increasing IFN-γ release. Transcriptome profiling and functional characterization strongly support that IL-21 selectively targets the cytotoxic granule exocytosis pathway, but not pro-inflammatory responses. Notably, IL-21 modulates multiple steps of cytotoxic effector functions including upregulation of co-activating CD226 receptor, increasing cytotoxic granules, and promoting cytotoxic granule delivery at the immunological synapse. Indeed, T-BsAb-mediated myeloma killing is cytotoxic granule-dependent, and IL-21 priming significantly augments cytotoxic activities. Furthermore, in vivo IL-21 treatment induces cytotoxic effector reprogramming in bone marrow T cells, showing synergistic anti-myeloma effects in combination with T-BsAb therapy. Together, harnessing the cytotoxic granule exocytosis pathway by IL-21 may be a potential approach to achieve better responses by T-BsAb therapy.

T-cell exhaustion in multiple myeloma

INTRODUCTION

Chimeric Antigen Receptor (CAR) T-cells and Bispecific Antibodies (BsAb) are the leading platforms for redirecting the immune system against cells expressing the specific antigen, revolutionizing the treatment of hematological malignancies, including multiple myeloma (MM). In MM, drug-resistant relapses are the main therapy-limiting factor and the leading cause of why the disease is still considered incurable. T-cell-engaging therapies hold promise in improving the treatment of MM. However, the effectiveness of these treatments may be hindered by T-cell fitness. T-cell exhaustion is a condition of a gradual decline in effector function, reduced cytokine secretion, and increased expression of inhibitory receptors due to chronic antigen stimulation.

AREAS COVERED

This review examines findings about T-cell exhaustion in MM in the context of T-cell redirecting BsAbs and CAR-T treatment.

EXPERT OPINION

The fitness of T-cells has become an important factor in the development of T-cell redirecting therapies. The way T-cell exhaustion relates to these therapies could affect the further development of CAR and BsAbs technologies, as well as the strategies used for clinical use. Therefore, this review aims to explore the current understanding of T-cell exhaustion in MM and its relationship to these therapies.

Bispecific antibodies for multiple myeloma: past, present and future

Despite the development of various therapeutic agents, multiple myeloma remains incurable. Recently, T-cell redirected immunotherapy has become a promising strategy for the treatment of refractory myeloma. Clinical trials using chimeric antigen receptor (CAR)-T cells and bispecific antibodies have demonstrated successful anti-myeloma responses in triple-class-refractory patients. However, unique and unwanted immune effects associated with on-target/off-target reactivity of activated immune cells need to be considered and properly managed. This review summarizes recent advances in bispecific antibodies for the treatment of refractory myeloma. It outlines the history of their development, along with a discussion of their mechanisms of action and their current and potential future role in myeloma therapy. As more evidence emerges to inform the timing of CAR-T-cell therapy, the results of clinical trials and off-the-shelf nature of bispecifics also suggest the timing of their treatment. These findings will promote further development and application of bispecifics for refractory myeloma in combination with other appropriate agents.

Unraveling the complexity of drug resistance mechanisms to SINE, T cell-engaging therapies and CELMoDs in multiple myeloma: a comprehensive review

Despite significant advances in the understanding of multiple myeloma (MM) biology and the development of novel treatment strategies in the last two decades, MM is still an incurable disease. Novel drugs with alternative mechanisms of action, such as selective inhibitors of nuclear export (SINE), modulators of the ubiquitin pathway [cereblon E3 ligase modulatory drugs (CELMoDs)], and T cell redirecting (TCR) therapy, have led to significant improvement in patient outcomes. However, resistance still emerges, posing a major problem for the treatment of myeloma patients. This review summarizes current data on treatment with SINE, TCR therapy, and CELMoDs and explores their mechanism of resistance. Understanding these resistance mechanisms is critical for developing strategies to overcome treatment failure and improve therapeutic outcomes.

Mechanisms of resistance to bispecific T-cell engagers in multiple myeloma and their clinical implications

ABSTRACT

Bispecific T-cell engagers (TCEs) are revolutionizing patient care in multiple myeloma (MM). These monoclonal antibodies, that redirect T cells against cancer cells, are now approved for the treatment of triple-class exposed relapsed/refractory MM (RRMM). They are currently tested in earlier lines of the disease, including in first line. Yet, primary resistance occurs in about one-third of patients with RRMM, and most responders eventually develop acquired resistance. Understanding the mechanisms of resistance to bispecific TCE is thus essential to improve immunotherapies in MM. Here, we review recent studies investigating the clinical and molecular determinants of resistance to bispecific TCE. Resistance can arise from tumor-intrinsic or tumor-extrinsic mechanisms. Tumor-intrinsic resistance involves various alterations leading to the loss of the target antigen, such as chromosome deletions, point mutations, or epigenetic silencing. Loss of major histocompatibility complex (MHC) class I, preventing MHC class I: T-cell receptor (TCR) costimulatory signaling, was also reported. Tumor-extrinsic resistance involves abundant exhausted T-cell clones and several factors generating an immunosuppressive microenvironment. Importantly, some resistance mechanisms impair response to 1 TCE while preserving the efficacy of others. We next discuss the clinical implications of these findings. Monitoring the status of target antigens in tumor cells and their immune environment will be key to select the most appropriate TCE for each patient and to design combination and sequencing strategies for immunotherapy in MM.

Stepping forward: T-cell redirecting bispecific antibodies in cancer therapy

T cell-redirecting bispecific antibodies are specifically designed to bind to tumor-associated antigens, thereby engaging with CD3 on the T cell receptor. This linkage between tumor cells and T cells actively triggers T cell activation and initiates targeted killing of the identified tumor cells. These antibodies have emerged as one of the most promising avenues within tumor immunotherapy. However, despite success in treating hematological malignancies, significant advancements in solid tumors have yet to be explored. In this review, we aim to address the critical challenges associated with T cell-redirecting bispecific antibodies and explore novel strategies to overcome these obstacles, with the ultimate goal of expanding the application of this therapy to include solid tumors.

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.

Next-Generation Therapies for Multiple Myeloma

Recent therapeutic advances have significantly improved the outcome for patients with multiple myeloma (MM). The backbone of successful standard therapy is the combination of Ikaros degraders, glucocorticoids, and proteasome inhibitors that interfere with the integrity of myeloma-specific superenhancers by directly or indirectly targeting enhancer-bound transcription factors and coactivators that control expression of MM dependency genes. T cell engagers and chimeric antigen receptor T cells redirect patients' own T cells onto defined tumor antigens to kill MM cells. They have induced complete remissions even in end-stage patients. Unfortunately, responses to both conventional therapy and immunotherapy are not durable, and tumor heterogeneity, antigen loss, and lack of T cell fitness lead to therapy resistance and relapse. Novel approaches are under development to target myeloma-specific vulnerabilities, as is the design of multimodality immunological approaches, including and beyond T cells, that simultaneously recognize multiple epitopes to prevent antigen escape and tumor relapse.

Immune status and selection of patients for immunotherapy in myeloma: a proposal

ABSTRACT

Newer immune-based approaches based on recruitment and redirection of endogenous and/or synthetic immunity such as chimeric antigen receptor T cells or bispecific antibodies are transforming the clinical management of multiple myeloma (MM). Contributions of the immune system to the antitumor effects of myeloma therapies are also increasingly appreciated. Clinical malignancy in MM originates in the setting of systemic immune alterations that begin early in myelomagenesis and regional changes in immunity affected by spatial contexture. Preexisting and therapy-induced changes in immune cells correlate with outcomes in patients with MM including after immune therapies. Here, we discuss insights from and limitations of available data about immune status and outcomes after immune therapies in patients with MM. Preexisting variation in systemic and/or regional immunity is emerging as a major determinant of the efficacy of current immune therapies as well as vaccines. However, MM is a multifocal malignancy. As with solid tumors, integrating spatial aspects of the tumor and consideration of immune targets with the biology of immune cells may be critical to optimizing the application of immune therapy, including T-cell redirection, in MM. We propose 5 distinct spatial immune types of MM that may provide an initial framework for the optimal application of specific immune therapies in MM: immune depleted, immune permissive, immune excluded, immune suppressed, and immune resistant. Such considerations may also help optimize rational patient selection for emerging immune therapies to improve outcomes.

The genomic landscape of Vk*MYC myeloma highlights shared pathways of transformation between mice and humans

Multiple myeloma (MM) is a heterogeneous disease characterized by frequent MYC translocations. Sporadic MYC activation in the germinal center of genetically engineered Vk*MYC mice is sufficient to induce plasma cell tumors in which a variety of secondary mutations are spontaneously acquired and selected over time. Analysis of 119 Vk*MYC myeloma reveals recurrent copy number alterations, structural variations, chromothripsis, driver mutations, apolipoprotein B mRNA-editing enzyme, catalytic polypeptide (APOBEC) mutational activity, and a progressive decrease in immunoglobulin transcription that inversely correlates with proliferation. Moreover, we identify frequent insertional mutagenesis by endogenous retro-elements as a murine specific mechanism to activate NF-kB and IL6 signaling pathways shared with human MM. Despite the increased genomic complexity associated with progression, advanced tumors remain dependent on MYC. In summary, here we credential the Vk*MYC mouse as a unique resource to explore MM genomic evolution and describe a fully annotated collection of diverse and immortalized murine MM tumors.

Bispecific antibodies for the treatment of relapsed/refractory multiple myeloma: updates and future perspectives

Patients with relapsed/refractory multiple myeloma (RRMM) that are refractory to the five most active anti-MM drugs, so-called penta-refractory MM, have historically had dismal outcomes with subsequent therapies. Progressive immune dysfunction, particularly of the T-cell repertoire, is implicated in the development of disease progression and refractory disease. However, the advent of novel immunotherapies such as bispecific antibodies are rapidly changing the treatment landscape and improving the survival outcomes of patients with RRMM. Bispecific antibodies are antibodies that are engineered to simultaneously engage cytotoxic immune effector cells (T cells or NK cells) and malignant plasma cells via binding to immune effector cell antigens and extracellular plasma cell antigens leading to immune effector cell activation and malignant plasma cell destruction. Currently, bispecific antibodies that bind CD3 on T cells and plasma cell epitopes such as B-cell maturation antigen (BCMA), G-protein coupled receptor family C group 5 member D (GPRC5d), and Fc receptor homologue 5 (FcRH5) are the most advanced in clinical development and are showing unprecedented response rates in patients with RRMM, including patients with penta-refractory disease. In this review article, we explore the available clinical data of bispecific antibodies in RRMM and summarize the efficacy, safety, toxicity, clinical outcomes, mechanisms of resistance, and future directions of these therapies in patients with RRMM.

Immunocompetent Mouse Models of Multiple Myeloma: Therapeutic Implications

Immunocompetent mouse models of multiple myeloma (MM) are particularly needed in the era of T cell redirected therapy to understand drivers of sensitivity and resistance, optimize responses, and prevent toxicities. Three mouse models have been extensively characterized: the Balb/c plasmacytomas, the 5TMM, and the Vk*MYC. In the last year, additional models have been generated, which, for the first time, capture primary MM initiating events, like MMSET/NSD2 or cyclin D1 dysregulation. However, the long latency needed for tumor development and the lack of transplantable lines limit their utilization. Future studies should focus on modeling hyperdiploid MM.

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.

BCMA- or GPRC5D-targeting bispecific antibodies in multiple myeloma: efficacy, safety, and resistance mechanisms

ABSTRACT

Bispecific antibodies that engage T cells to target B-cell maturation antigen or G-protein-coupled receptor class C group 5 member D have demonstrated remarkable efficacy in heavily pretreated relapsed or refractory multiple myeloma (MM), leading to the recent accelerated approval of teclistamab, elranatamab, and talquetamab by health agencies. Future challenges, however, remain to define their optimal dosing schedule and duration, sequencing, and integration with established anti-MM therapeutics as well as delineating the biological and clinical mediators of immune escape.

Regulatory T cells hamper the efficacy of T-cell-engaging bispecific antibody therapy

T-cell-engaging bispecific antibodies (T-BsAb) have produced impressive clinical responses in patients with relapsed/refractory B-cell malignancies, although treatment failure remains a major clinical challenge. Growing evidence suggests that a complex interplay between immune cells and tumor cells is implicated in the mechanism of action and therefore, understanding immune regulatory mechanisms might provide a clue for how to improve the efficacy of T-BsAb therapy. Here, we investigated the functional impact of regulatory T (Treg) cells on anti-tumor immunity elicited by T-BsAb therapy. In a preclinical model of myeloma, the activation and expansion of Treg cells in the bone marrow were observed in response to anti-B-cell maturation antigen (BCMA) T-BsAb therapy. T-BsAb triggered the generation of induced Treg cells from human conventional CD4 cells after co-culture with tumor cells. Moreover, T-BsAb directly activated freshly isolated circulating Treg cells, leading to the production of interleukin-10 and inhibition of T-BsAb-mediated CD8 T-cell responses. The activation of Treg cells was also seen in bone marrow samples from myeloma patients after ex vivo treatment with T-BsAb, further supporting that T-BsAb have an impact on Treg homeostasis. Importantly, transient ablation of Treg cells in combination with T-BsAb therapy dramatically improved effector lymphocyte activities and disease control in the preclinical myeloma model, leading to prolonged survival. Together, this information suggests that therapy-induced activation of Treg cells critically regulates anti-tumor immunity elicited by T-BsAb therapy, with important implications for improving the efficacy of such treatment.

Real-world analysis of teclistamab in 123 RRMM patients from Germany

Teclistamab, a B-cell maturation antigen (BCMA) × CD3 directed bispecific antibody, has shown high response rates and durable remissions in the MAJESTEC-1 trial in patients with relapsed and refractory multiple myeloma (RRMM). We retrospectively assessed efficacy and tolerability in 123 patients treated at 18 different German centers to determine whether outcome is comparable in the real-world setting. Most patients had triple-class (93%) or penta-drug (60%) refractory disease, 37% of patients had received BCMA-directed pretreatment including idecabtagene vicleucel (ide-cel) CAR-T cell therapy (21/123, 17.1%). With a follow-up of 5.5 months, we observed an overall response rate (ORR) of 59.3% and a median progression-free survival (PFS) of 8.7 months. In subgroup analyses, we found significantly lower ORR and median PFS in patients with extramedullary disease (37%/2.1 months), and/or an ISS of 3 (37%/1.3 months), and ide-cel pretreated patients (33%/1.8 months). Nonetheless, the duration of response in ide-cel pretreated patients was comparable to that of anti-BCMA naive patients. Infections and grade ≥3 cytopenias were the most frequent adverse events. In summary, we found that teclistamab exhibited a comparable efficacy and safety profile in the real-world setting as in the pivotal trial.

Transcriptional Heterogeneity Overcomes Super-Enhancer Disrupting Drug Combinations in Multiple Myeloma

Multiple myeloma (MM) is a malignancy that is often driven by MYC and that is sustained by IRF4, which are upregulated by super-enhancers. IKZF1 and IKZF3 bind to super-enhancers and can be degraded using immunomodulatory imide drugs (IMiD). Successful IMiD responses downregulate MYC and IRF4; however, this fails in IMiD-resistant cells. MYC and IRF4 downregulation can also be achieved in IMiD-resistant tumors using inhibitors of BET and EP300 transcriptional coactivator proteins; however, in vivo these drugs have a narrow therapeutic window. By combining IMiDs with EP300 inhibition, we demonstrate greater downregulation of MYC and IRF4, synergistic killing of myeloma in vitro and in vivo, and an increased therapeutic window. Interestingly, this potent combination failed where MYC and IRF4 expression was maintained by high levels of the AP-1 factor BATF. Our results identify an effective drug combination and a previously unrecognized mechanism of IMiD resistance.

SIGNIFICANCE

These results highlight the dependence of MM on IKZF1-bound super-enhancers, which can be effectively targeted by a potent therapeutic combination pairing IMiD-mediated degradation of IKZF1 and IKZF3 with EP300 inhibition. They also identify AP-1 factors as an unrecognized mechanism of IMiD resistance in MM. See related article by Neri, Barwick, et al., p. 56. See related commentary by Yun and Cleveland, p. 5. This article is featured in Selected Articles from This Issue, p. 4.

Current use of bispecific antibodies to treat multiple myeloma

Targeted immunotherapy has significantly improved the outcome of patients with hematological malignancies by leveraging the power of the immune system to eliminate tumor cells. In multiple myeloma (MM), bispecific T-cell engagers (BsAb) targeting B-cell maturation antigen (BCMA), G protein-coupled receptor, class C, group 5, member D (GPRC5D), and Fc receptor-like 5 (FcRL5) have already demonstrated remarkable clinical activity in triple-class refractory patients. However, responses to BsAb are not universal, and resistance often emerges while on therapy. Mechanisms mediating resistance are tumor intrinsic or immune dependent. Reported tumor intrinsic factors include antigenic loss (biallelic or functional) through deletions or mutations of target genes, increased soluble BCMA (for BCMA targeting BsAb), high tumor burden, and extramedullary disease. Immune-mediated resistance are largely dependent on T-cell fitness and tolerant immune environment. Understanding these mechanisms will allow the design of optimized BsAb therapy and an informed approach to sequencing and combining these molecules with other anti-MM agents and immune therapies.

Cancer therapeutic trispecific antibodies recruiting both T and natural killer cells to cancer cells

T cells and natural killer (NK) cells are major effector cells recruited by cancer therapeutic bispecific antibodies; however, differences in the populations of these cells in individual tumors limit the general use of these antibodies. In the present study, trispecific antibodies were created, namely T cell and NK cell engagers (TaKEs), that recruit both T cells and NK cells. Notably, three Fc‑fused TaKEs were designed, TaKE1‑Fc, TaKE2‑Fc and TaKE3‑Fc, using variable fragments targeting the epidermal growth factor receptor on tumor cells, CD3 on T cells, and CD16 on NK cells. Among them, TaKE1‑Fc was predicted to form a circular tetrabody‑like configuration and exhibited the highest production and greatest cancer growth inhibitory effects. TaKE1 was prepared from TaKE1‑Fc by digesting the Fc region for further functional evaluation. The resulting TaKE1 exhibited trispecificity via its ability to bind cancer cells, T cells and NK cells, as well as comparable or greater cancer growth inhibitory effects to those of two bispecific antibodies that recruit T cells and NK cells, respectively. A functional trispecific antibody with the potential to exert strong therapeutic effects independent of T cell and NK cell populations was developed.

Revolutionizing cancer immunotherapy: unleashing the potential of bispecific antibodies for targeted treatment

Recent progressions in immunotherapy have transformed cancer treatment, providing a promising strategy that activates the immune system of the patient to find and eliminate cancerous cells. Bispecific antibodies, which engage two separate antigens or one antigen with two distinct epitopes, are of tremendous concern in immunotherapy. The bi-targeting idea enabled by bispecific antibodies (BsAbs) is especially attractive from a medical standpoint since most diseases are complex, involving several receptors, ligands, and signaling pathways. Several research look into the processes in which BsAbs identify different cancer targets such angiogenesis, reproduction, metastasis, and immune regulation. By rerouting cells or altering other pathways, the bispecific proteins perform effector activities in addition to those of natural antibodies. This opens up a wide range of clinical applications and helps patients with resistant tumors respond better to medication. Yet, further study is necessary to identify the best conditions where to use these medications for treating tumor, their appropriate combination partners, and methods to reduce toxicity. In this review, we provide insights into the BsAb format classification based on their composition and symmetry, as well as the delivery mode, focus on the action mechanism of the molecule, and discuss the challenges and future perspectives in BsAb development.

Reinforced antimyeloma therapy via dual-lymphoid activation mediated by a panel of antibodies armed with bridging-BiTE

Immunotherapy using bispecific antibodies including bispecific T-cell engager (BiTE) has the potential to enhance the efficacy of treatment for relapsed/refractory multiple myeloma. However, myeloma may still recur after treatment because of downregulation of a target antigen and/or myeloma cell heterogeneity. To strengthen immunotherapy for myeloma while overcoming its characteristics, we have newly developed a BiTE-based modality, referred to as bridging-BiTE (B-BiTE). B-BiTE was able to bind to both a human immunoglobulin G-Fc domain and the CD3 molecule. Clinically available monoclonal antibodies (mAbs) were bound with B-BiTE before administration, and the mAb/B-BiTE complex induced antitumor T-cell responses successfully while preserving and supporting natural killer cell reactivity, resulting in enhanced antimyeloma effects via dual-lymphoid activation. In contrast, any unwanted off-target immune-cell reactivity mediated by mAb/B-BiTE complexes or B-BiTE itself appeared not to be observed in vitro and in vivo. Importantly, sequential immunotherapy using 2 different mAb/B-BiTE complexes appeared to circumvent myeloma cell antigen escape, and further augmented immune responses to myeloma relative to those induced by mAb/B-BiTE monotherapy or sequential therapy with 2 mAbs in the absence of B-BiTE. Therefore, this modality facilitates easy and prompt generation of a broad panel of bispecific antibodies that can induce deep and durable antitumor responses in the presence of clinically available mAbs, supporting further advancement of reinforced immunotherapy for multiple myeloma and other refractory hematologic malignancies.

Bispecific Antibodies in Hematological Malignancies: A Scoping Review

Bispecific T-cell engagers (BiTEs) and bispecific antibodies (BiAbs) have revolutionized the treatment landscape of hematological malignancies. By directing T cells towards specific tumor antigens, BiTEs and BiAbs facilitate the T-cell-mediated lysis of neoplastic cells. The success of blinatumomab, a CD19xCD3 BiTE, in acute lymphoblastic leukemia spearheaded the expansive development of BiTEs/BiAbs in the context of hematological neoplasms. Nearly a decade later, numerous BiTEs/BiAbs targeting a range of tumor-associated antigens have transpired in the treatment of multiple myeloma, non-Hodgkin's lymphoma, acute myelogenous leukemia, and acute lymphoblastic leukemia. However, despite their generally favorable safety profiles, particular toxicities such as infections, cytokine release syndrome, myelosuppression, and neurotoxicity after BiAb/BiTE therapy raise valid concerns. Moreover, target antigen loss and the immunosuppressive microenvironment of hematological neoplasms facilitate resistance towards BiTEs/BiAbs. This review aims to highlight the most recent evidence from clinical trials evaluating the safety and efficacy of BiAbs/BiTEs. Additionally, the review will provide mechanistic insights into the limitations of BiAbs whilst outlining practical applications and strategies to overcome these limitations.

Teclistamab for Multiple Myeloma: Clinical Insights and Practical Considerations for a First-in-Class Bispecific Antibody

Teclistamab is a BCMAxCD3 bispecific antibody, the first approved for the treatment of relapsed or refractory multiple myeloma. Given its impressive efficacy in heavily pretreated patients and better accessibility compared to BCMA-directed CAR T cells, teclistamab is sure to become a staple of relapsed/refractory multiple myeloma therapy. Teclistamab carries a set of notable adverse effects including cytokine release syndrome (CRS), infections, and neurotoxicity for which providers must take unique precautions and prophylactic measures. Here, we review the preclinical and clinical data, which led to teclistamab's approval, important patient selection considerations, strategies for managing CRS and other side effects, and finally the future of bispecific antibody therapy in multiple myeloma.

T-cell-engaging bispecific antibodies in cancer

T-cell-engaging bispecific antibodies (BsAbs) simultaneously bind to antigens on tumour cells and CD3 subunits on T cells. This simultaneous binding results in the recruitment of T cells to the tumour, followed by T-cell activation and degranulation, and tumour cell elimination. T-cell-engaging BsAbs have shown substantial activity in several haematological malignancies by targeting CD19 in acute lymphoblastic leukaemia, CD20 in B-cell non-Hodgkin lymphoma, and BCMA and GPRC5D in multiple myeloma. Progress with solid tumours has been slower, in part due to the paucity of therapeutic targets with a tumour-specific expression profile, which is needed to limit on-target off-tumour side-effects. Nevertheless, BsAb-mediated recognition of a peptide fragment of gp100 presented by HLA-A2:01 molecules has shown marked activity in patients with unresectable or metastatic uveal melanoma. Cytokine release syndrome is the most frequent toxicity associated with BsAb treatment and is caused by activated T cells secreting proinflammatory cytokines. Understanding of resistance mechanisms has resulted in the development of new T cell-redirecting formats and novel combination strategies, which are expected to further improve depth and duration of response.

Revisiting the Role of Alkylating Agents in Multiple Myeloma: Up-to-Date Evidence and Future Perspectives

From the 1960s to the early 2000s, alkylating agents (e.g., melphalan, cyclophosphamide, and bendamustine) remained a key component of standard therapy for newly-diagnosed or relapsed/refractory multiple myeloma (MM). Later on, their associated toxicities (including second primary malignancies) and the unprecedented efficacy of novel therapies have led clinicians to increasingly consider alkylator-free approaches. Meanwhile, new alkylating agents (e.g., melflufen) and new applications of old alkylators (e.g., lymphodepletion before chimeric antigen receptor T-cell [CAR-T] therapy) have emerged in recent years. Given the expanding use of antigen-directed modalities (e.g., monoclonal antibodies, bispecific antibodies, and CAR-T therapy), this review explores the current and future role of alkylating agents in different treatment settings (e.g., induction, consolidation, stem cell mobilization, pre-transplant conditioning, salvage, bridging, and lymphodepleting chemotherapy) to ellucidate the role of alkylator-based regimens in modern-day MM management.

Bispecific Antibodies in Multiple Myeloma: Opportunities to Enhance Efficacy and Improve Safety

Multiple myeloma (MM) is the second most common haematological neoplasm of adults in the Western world. Overall survival has doubled since the advent of proteosome inhibitors (PIs), immunomodulatory agents (IMiDs), and monoclonal antibodies. However, patients with adverse cytogenetics or high-risk disease as determined by the Revised International Staging System (R-ISS) continue to have poorer outcomes, and triple-refractory patients have a median survival of less than 1 year. Bispecific antibodies (BsAbs) commonly bind to a tumour epitope along with CD3 on T-cells, leading to T-cell activation and tumour cell killing. These treatments show great promise in MM patients, with the first agent, teclistamab, receiving regulatory approval in 2022. Their potential utility is hampered by the immunosuppressive tumour microenvironment (TME), a hallmark of MM, which may limit efficacy, and by undesirable adverse events, including cytokine release syndrome (CRS) and infections, some of which may be fatal. In this review, we first consider the means of enhancing the efficacy of BsAbs in MM. These include combining BsAbs with other drugs that ameliorate the effect of the immunosuppressive TME, improving target availability, the use of BsAbs directed against multiple target antigens, and the optimal time in the treatment pathway to employ BsAbs. We then discuss methods to improve safety, focusing on reducing infection rates associated with treatment-induced hypogammaglobulinaemia, and decreasing the frequency and severity of CRS. BsAbs offer a highly-active therapeutic option in MM. Improving the efficacy and safety profiles of these agents may enable more patients to benefit from these novel therapies and improve outcomes for patients with high-risk disease.

The pre-existing T cell landscape determines the response to bispecific T cell engagers in multiple myeloma patients

Bispecific T cell engagers (TCEs) have shown promise in the treatment of various cancers, but the immunological mechanism and molecular determinants of primary and acquired resistance to TCEs remain poorly understood. Here, we identify conserved behaviors of bone marrow-residing T cells in multiple myeloma patients undergoing BCMAxCD3 TCE therapy. We show that the immune repertoire reacts to TCE therapy with cell state-dependent clonal expansion and find evidence supporting the coupling of tumor recognition via major histocompatibility complex class I (MHC class I), exhaustion, and clinical response. We find the abundance of exhausted-like CD8⁺ T cell clones to be associated with clinical response failure, and we describe loss of target epitope and MHC class I as tumor-intrinsic adaptations to TCEs. These findings advance our understanding of the in vivo mechanism of TCE treatment in humans and provide the rationale for predictive immune-monitoring and conditioning of the immune repertoire to guide future immunotherapy in hematological malignancies.

Trial designs and endpoints for immune therapies in multiple myeloma

Immune therapies, including CAR-T cells, bispecific antibodies, and antibody-drug conjugates, are revolutionizing the treatment of multiple myeloma. In this review, we discuss clinical trial design considerations relevant to immune therapies. We first examine issues pertinent to specific populations, including elderly, patients with renal impairment, high-risk/extramedullary disease, and prior immune therapies. We then highlight trial designs to optimize the selection of dose and schedule, explore rational combination therapies based on preclinical data, and evaluate the nuances of commonly used endpoints. By exploiting their pharmacokinetic/pharmacodynamic profiles and utilizing novel translational insights, we can optimize the use of immune therapies in multiple myeloma.

Preclinical models for prediction of immunotherapy outcomes and immune evasion mechanisms in genetically heterogeneous multiple myeloma

The historical lack of preclinical models reflecting the genetic heterogeneity of multiple myeloma (MM) hampers the advance of therapeutic discoveries. To circumvent this limitation, we screened mice engineered to carry eight MM lesions (NF-κB, KRAS, MYC, TP53, BCL2, cyclin D1, MMSET/NSD2 and c-MAF) combinatorially activated in B lymphocytes following T cell-driven immunization. Fifteen genetically diverse models developed bone marrow (BM) tumors fulfilling MM pathogenesis. Integrative analyses of ∼500 mice and ∼1,000 patients revealed a common MAPK-MYC genetic pathway that accelerated time to progression from precursor states across genetically heterogeneous MM. MYC-dependent time to progression conditioned immune evasion mechanisms that remodeled the BM microenvironment differently. Rapid MYC-driven progressors exhibited a high number of activated/exhausted CD8⁺ T cells with reduced immunosuppressive regulatory T (T_reg) cells, while late MYC acquisition in slow progressors was associated with lower CD8⁺ T cell infiltration and more abundant T_reg cells. Single-cell transcriptomics and functional assays defined a high ratio of CD8⁺ T cells versus T_reg cells as a predictor of response to immune checkpoint blockade (ICB). In clinical series, high CD8⁺ T/T_reg cell ratios underlie early progression in untreated smoldering MM, and correlated with early relapse in newly diagnosed patients with MM under Len/Dex therapy. In ICB-refractory MM models, increasing CD8⁺ T cell cytotoxicity or depleting T_reg cells reversed immunotherapy resistance and yielded prolonged MM control. Our experimental models enable the correlation of MM genetic and immunological traits with preclinical therapy responses, which may inform the next-generation immunotherapy trials.

The role of soluble B cell maturation antigen as a biomarker in multiple myeloma

Currently used stratification models in myeloma precursor disease as well as staging systems and response criteria in myeloma have limitations including failure to identify functionally high-risk myeloma patients. B-cell maturation antigen, a transmembrane glycoprotein required for long-lived plasma cells, is specific and expressed by myeloma cells. When it sheds from the surface of myeloma cells it can be measured in the blood as serum (sBCMA) and correlated with clinical outcomes in myeloma precursor disease as well as in active myeloma. We performed a literature review using PubMed and found 825 articles since 1992 of which any articles related to sBCMA were reviewed. These studies show the potential of sBCMA to become an important biomarker in myeloma. Here, we describe the potential advantages of sBCMA in the biology, diagnosis, prognosis, and surveillance of myeloma, while also reviewing the challenges that lie ahead before it can be implemented as a clinical tool.

Normalization of the Immunological Microenvironment and Sustained Minimal Residual Disease Negativity: Do We Need Both for Long-Term Control of Multiple Myeloma?

Over the past two decades, the treatment landscape for multiple myeloma (MM) has progressed significantly, with the introduction of several new drug classes that have greatly improved patient outcomes. At present, it is well known how the bone marrow (BM) microenvironment (ME) exerts an immunosuppressive action leading to an exhaustion of the immune system cells and promoting the proliferation and sustenance of tumor plasma cells. Therefore, having drugs that can reconstitute a healthy BM ME can improve results in MM patients. Recent findings clearly demonstrated that achieving minimal residual disease (MRD) negativity and sustaining MRD negativity over time play a pivotal prognostic role. However, despite the achievement of MRD negativity, patients may still relapse. The understanding of immunologic changes in the BM ME during treatment, complemented by a deeper knowledge of plasma cell genomics and biology, will be critical to develop future therapies to sustain MRD negativity over time and possibly achieve an operational cure. In this review, we focus on the components of the BM ME and their role in MM, on the prognostic significance of MRD negativity and, finally, on the relative contribution of tumor plasma cell biology and BM ME to long-term disease control.