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

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.

Treating Multiple Myeloma in the Context of the Bone Marrow Microenvironment

The treatment landscape of multiple myeloma (MM) has evolved considerably with the FDA-approval of at least 15 drugs over the past two decades. Together with the use of autologous stem cell transplantation, these novel therapies have resulted in significant survival benefit for patients with MM. In particular, our improved understanding of the BM and immune microenvironment has led to the development of highly effective immunotherapies that have demonstrated unprecedented response rates even in the multiple refractory disease setting. However, MM remains challenging to treat especially in a high-risk setting. A key mediator of therapeutic resistance in MM is the bone marrow (BM) microenvironment; a deeper understanding is necessary to facilitate the development of therapies that target MM in the context of the BM milieu to elicit deeper and more durable responses with the ultimate goal of long-term control or a cure of MM. In this review, we discuss our current understanding of the role the BM microenvironment plays in MM pathogenesis, with a focus on its immunosuppressive nature. We also review FDA-approved immunotherapies currently in clinical use and highlight promising immunotherapeutic approaches on the horizon.

Factors Affecting the Cancer Immunotherapeutic Efficacy of T Cell Bispecific Antibodies and Strategies for Improvement

T-cell bispecific antibodies (T-BsAbs) are a new class of cancer immunotherapy drugs that can simultaneously bind to tumor-associated antigens on target cells and to the CD3 subunit of the T-cell receptor (TCR) on T cells. In the last decade, numerous T-BsAbs have been developed for the treatment of both hematological malignancies and solid tumors. Among them, blinatumomab has been successfully used to treat CD19 positive malignancies and has been approved by the FDA as standard care for acute lymphoblastic leukemia (ALL). However, in many clinical scenarios, the efficacy of T-BsAbs remains unsatisfactory. To further improve T-BsAb therapy, it will be crucial to better understand the factors affecting treatment efficacy and the nature of the T-BsAb-induced immune response. Herein, we first review the studies on the potential mechanisms by which T-BsAbs activate T-cells and how they elicit efficient target killing despite suboptimal costimulatory support. We focus on analyzing reports from clinical trials and preclinical studies, and summarize the factors that have been identified to impact the efficacy of T-BsAbs. Lastly, we review current and propose new approaches to improve the clinical efficacy of T-BsAbs.

Bispecific antibodies in multiple myeloma treatment: A journey in progress

The incorporation of novel agents and monoclonal antibody-based therapies into the treatment of multiple myeloma (MM) has significantly improved long-term patient survival. However, the disease is still largely incurable, with high-risk patients suffering shorter survival times, partly due to weakened immune systems. Bispecific molecules, including bispecific antibodies (BisAbs) and bispecific T-cell engagers (BiTEs), encourage immune cells to lyse MM cells by simultaneously binding antigens on MM cells and immune effector cells, bringing those cells into close proximity. BisAbs that target B-cell maturation antigen (BCMA) and GPRC5D have shown impressive clinical activity, and the results of early-phase clinical trials targeting FcRH5 in patients with relapsed/refractory MM (RRMM) are also promising. Furthermore, the safety profile of these agents is favorable, including mainly low-grade cytokine release syndrome (CRS). These off-the-shelf bispecific molecules will likely become an essential part of the MM treatment paradigm. Here, we summarize and highlight various bispecific immunotherapies under development in MM treatment, as well as the utility of combining them with current standard-of-care treatments and new strategies. With the advancement of novel combination treatment approaches, these bispecific molecules may lead the way to a cure for MM.

Preclinical InVivo Data Integrated in a Modeling Network Informs a Refined Clinical Strategy for a CD3 T-Cell Bispecific in Combination with Anti-PD-L1

TYRP1-TCB is a CD3 T-cell bispecific (CD3-TCB) antibody for the treatment of advanced melanoma. A tumor growth inhibition (TGI) model was developed using mouse xenograft data with TYRP1-TCB monotherapy or TYRP1-TCB plus anti-PD-L1 combination. The model was translated to humans to inform a refined clinical strategy. From xenograft mouse data, we estimated an EC₅₀ of 0.345 mg/L for TYRP1-TCB, close to what was observed in vitro using the same tumor cell line. The model showed that, though increasing the dose of TYRP1-TCB in monotherapy delays the time to tumor regrowth and promotes higher tumor cell killing, it also induces a faster rate of tumor regrowth. Combination with anti-PD-L1 extended the time to tumor regrowth by 25% while also decreasing the tumor regrowth rate by 69% compared to the same dose of TYRP1-TCB alone. The model translation to humans predicts that if patients' tumors were scanned every 6 weeks, only 46% of the monotherapy responders would be detected even at a TYRP1-TCB dose resulting in exposures above the EC₉₀. However, combination of TYRP1-TCB and anti-PD-L1 in the clinic is predicted to more than double the overall response rate (ORR), duration of response (DoR) and progression-free survival (PFS) compared to TYRP1-TCB monotherapy. As a result, it is highly recommended to consider development of CD3-TCBs as part of a combination therapy from the outset, without the need to escalate the CD3-TCB up to the Maximum Tolerated Dose (MTD) in monotherapy and without gating the combination only on RECIST-derived efficacy metrics.

Proceedings from the Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Immune and Cellular Therapy in Multiple Myeloma

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) Myeloma Intergroup conducted a workshop on Immune and Cellular Therapy in Multiple Myeloma on January 7, 2022. This workshop included presentations by basic, translational, and clinical researchers with expertise in plasma cell dyscrasias. Four main topics were discussed: platforms for myeloma disease evaluation, insights into pathophysiology, therapeutic target and resistance mechanisms, and cellular therapy for multiple myeloma. Here we provide a comprehensive summary of these workshop presentations.

Invariant NKT cells dictate antitumor immunity elicited by a bispecific antibody cotargeting CD3 and BCMA

CD3-engaging bispecific antibodies (BsAbs) have emerged as powerful therapeutic approaches by their ability to redirect T cells to eliminate tumor cells in an MHC-independent manner. However, it remains largely unknown how we can potentiate the efficacy of BsAbs. To address this, we investigated immunological mechanisms of action of a BsAb co-targeting CD3 and B-cell maturation antigen (BCMA) in syngeneic preclinical myeloma models. Treatment with the CD3/BCMA BsAb stimulated multiple CD3-expressing T cell subsets, as well as natural killer (NK) cells in the myeloma bone marrow (BM), highlighting its broad immunostimulatory effect. Notably, the BsAb-mediated immunostimulatory and anti-tumor effects were abrogated in mice lacking invariant NKT (iNKT) cells. Mechanistically, activation of iNKT cells and IL-12 production from dendritic cells (DCs) were crucial upstream events for triggering effective anti-tumor immunity by the BsAb. Myeloma progression was associated with reduced numbers of BM iNKT cells. Importantly, the therapeutic efficacy of a single dose of the CD3/BCMA BsAb was remarkably augmented by restoring iNKT cell activity using adoptive transfer of α-galactosylceramide-loaded DCs. Together, these results reveal iNKT cells as a critical player for the anti-tumor activity of CD3-engaging BsAbs, providing important translational implications.

Bispecific Antibodies in Cancer Immunotherapy: A Novel Response to an Old Question

Immunotherapy has redefined the treatment of cancer patients and it is constantly generating new advances and approaches. Among the multiple options of immunotherapy, bispecific antibodies (bsAbs) represent a novel thoughtful approach. These drugs integrate the action of the immune system in a strategy to redirect the activation of innate and adaptive immunity toward specific antigens and specific tumor locations. Here we discussed some basic aspects of the design and function of bsAbs, their main challenges and the state-of-the-art of these molecules in the treatment of hematological and solid malignancies and future perspectives.

Transplantation of autologous bone marrow pre-loaded ex vivo with oncolytic myxoma virus is efficacious against drug-resistant Vk*MYC mouse myeloma

Multiple myeloma (MM) is a hematological malignancy of plasma cells that remains incurable despite significant progress with myeloablative regimens and autologous stem cell transplantation for eligible patients and, more recently with T cell redirected immunotherapy. Recently, we reported that ex vivo virotherapy with oncolytic myxoma virus (MYXV) improved MM-free survival in an autologous-transplant Balb/c mouse model. Here, we tested the Vk*MYC transplantable C57BL/6 mouse MM model that more closely recapitulates human disease. In vitro, the murine bortezomib-resistant Vk12598 cell line is fully susceptible to MYXV infection. In vivo results demonstrate: (i) autologous bone marrow (BM) leukocytes armed ex vivo with MYXV exhibit moderate therapeutic effects against MM cells pre-seeded into recipient mice; (ii) Cyclophosphamide in combination with BM/MYXV delays the onset of myeloma in mice seeded with Vk12598 cells; (iii) BM/MYXV synergizes with the Smac-mimetics LCL161 and with immune checkpoint inhibitor α-PD-1 to control the progression of established MM in vivo, resulting in significant improvement of survival rates and decreased of tumor burden; (iv) Survivor mice from (ii) and (iii), when re-challenged with fresh Vk12598 cells, developed acquired anti-MM immunity. These results highlight the utility of autologous BM grafts armed ex vivo with oncolytic MYXV alone or in combination with chemotherapy/immunotherapy to treat drug-resistant MM in vivo.

T Cell Bispecific Antibodies: An Antibody-Based Delivery System for Inducing Antitumor Immunity

As a breakthrough immunotherapy, T cell bispecific antibodies (T-BsAbs) are a promising antibody therapy for various kinds of cancer. In general, T-BsAbs have dual-binding specificity to a tumor-associated antigen and a CD3 subunit forming a complex with the TCR. This enables T-BsAbs to crosslink tumor cells and T cells, inducing T cell activation and subsequent tumor cell death. Unlike immune checkpoint inhibitors, which release the brake of the immune system, T-BsAbs serve as an accelerator of T cells by stimulating their immune response via CD3 engagement. Therefore, they can actively redirect host immunity toward tumors, including T cell recruitment from the periphery to the tumor site and immunological synapse formation between tumor cells and T cells. Although the low immunogenicity of solid tumors increases the challenge of cancer immunotherapy, T-BsAbs capable of immune redirection can greatly benefit patients with such tumors. To investigate the detailed relationship between T-BsAbs delivery and their T cell redirection activity, it is necessary to determine how T-BsAbs deliver antitumor immunity to the tumor site and bring about tumor cell death. This review article discusses T-BsAb properties, specifically their pharmacokinetics, redirection of anticancer immunity, and local mechanism of action within tumor tissues, and discuss further challenges to expediting T-BsAb development.