AMG 701 induces cytotoxicity of multiple myeloma cells and depletes plasma cells in cynomolgus monkeys

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 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.

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.

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.

Targeted immunotherapy: harnessing the immune system to battle multiple myeloma

Multiple myeloma (MM) remains an incurable hematological malignancy disease characterized by the progressive dysfunction of the patient's immune system. In this context, immunotherapy for MM has emerged as a prominent area of research in recent years. Various targeted immunotherapy strategies, such as monoclonal antibodies, antibody-drug conjugates, bispecific antibodies, chimeric antigen receptor T cells/natural killer (NK) cells, and checkpoint inhibitors have been developed for MM. This review aims to discuss promising experimental and clinical evidence as well as the mechanisms of action underlying these immunotherapies. Specifically, we will explore the design of exosome-based bispecific monoclonal antibodies that offer cell-free immunotherapy options. The treatment landscape for myeloma continues to evolve with the development of numerous emerging immunotherapies. Given their significant advantages in modulating the MM immune environment through immune-targeted therapy, these approaches provide novel perspectives in selecting cutting-edge treatments for MM.

T-cell redirecting bispecific and trispecific antibodies in multiple myeloma beyond BCMA

PURPOSE OF REVIEW

B-cell maturation antigen (BCMA)-directed T-cell immunotherapies, such as chimeric antigen receptor T-cells (CAR T-cells) and bispecific antibodies (BsAbs) have markedly improved the survival of triple-class refractory multiple myeloma (MM). However, the majority of patients still develops disease progression, underlining the need for new agents for these patients.

RECENT FINDINGS

Novel T-cell redirecting BsAbs targeting alternative tumor-associated antigens have shown great promise in heavily pretreated MM, including patients previously exposed to BCMA-directed therapies. This includes the G-protein-coupled receptor class 5 member D (GPRC5D)-targeting BsAbs talquetamab and forimtamig, as well as the Fc receptor-homolog 5 (FcRH5)-targeting BsAb cevostamab. Toxicity associated with these BsAbs includes cytokine-release syndrome, cytopenias, and infections. In addition, GPRC5D-targeting BsAbs are associated with specific 'on target/off tumor' toxicities including rash, nail disorders, and dysgeusia. Trispecifc antibodies targeting two different MM-associated antigens to prevent antigen escape are in early clinical development, as well as trispecific antibodies (TsAbs) that provide an additional co-stimulatory signal to T-cells to prevent their exhaustion.

SUMMARY

Various T-cell redirecting BsAbs are in advanced stages of clinical development with promising activity and a manageable toxicity profile. Ongoing studies are evaluating combination strategies, fixed-duration treatment, and use of BsAbs in earlier lines of therapy. TsAbs hold great promise for the future.

Multi-targeted immunotherapeutics to treat B cell malignancies

The concept of multi-targeted immunotherapeutic systems has propelled the field of cancer immunotherapy into an exciting new era. Multi-effector molecules can be designed to engage with, and alter, the patient's immune system in a plethora of ways. The outcomes can vary from effector cell recruitment and activation upon recognition of a cancer cell, to a multipronged immune checkpoint blockade strategy disallowing evasion of the cancer cells by immune cells, or to direct cancer cell death upon engaging multiple cell surface receptors simultaneously. Here, we review the field of multi-specific immunotherapeutics implemented to treat B cell malignancies. The mechanistically diverse strategies are outlined and discussed; common B cell receptor antigen targeting strategies are outlined and summarized; and the challenges of the field are presented along with optimistic insights for the future.

Preclinical discovery and initial clinical data of WVT078, a BCMA × CD3 bispecific antibody

B-cell maturation antigen (BCMA) is an ideal target in multiple myeloma (MM) due to highly specific expression in malignant plasma cells. BCMA-directed therapies including antibody drug conjugates, chimeric antigen receptor-T cells and bispecific antibodies (BsAbs) have shown high response rates in MM. WVT078 is an anti-BCMA× anti-CD3 BsAb that binds to BCMA with subnanomolar-affinity. It was selected based on potent T cell activation and anti-MM activity in preclinical models with favorable tolerability in cynomolgus monkey. In the ongoing first-in-human phase I dose-escalation study (NCT04123418), 33 patients received intravenous WVT078 once weekly at escalated dosing. At the active doses of 48-250 µg/kg tested to date (n = 26), the overall response rate (ORR) was 38.5% (90% CI: 22.6-56.4%) and the complete response rate (CRR, stringent complete response + complete response) was 11.5%, (90% CI: 3.2-27.2%). At the highest dose level tested, the ORR was 75% (3 of 4 patients). 26 (78.8%) patients reported at least one Grade ≥3 AE and 16 of these AEs were suspected to be drug related. 20 patients (60.6%) experienced cytokine release syndrome. WVT078 has an acceptable safety profile and shows preliminary evidence of clinical activity at doses tested to date.

Bispecific T-cell engagers for treatment of multiple myeloma

Bispecific T cell engagers (TCE) derive from monoclonal antibodies and concomitantly engage a target on the surface of cancer cell and CD3 on the surface of T-cells. TCEs promote T cell activation and lysis of tumor cells. Most TCEs in development for multiple myeloma (MM) target the B cell maturation antigen (BCMA) and differ among themselves in structure, pharmacokinetics, route and schedule of administration. CD3/BCMA TCEs produce response in ~60% of patients treated in phase 1 trials. TCEs are also in development targeting the G protein-coupled receptor, class C group 5 member D (GPRC5D) and the Fc receptor homologue 5 (FcRH5). Main toxicities are cytokine release syndrome and cytopenias. Here we review the current development and future directions of TCEs in MM.

Considerations for design, manufacture, and delivery for effective and safe T-cell engager therapies

T-cell engager (TCE) molecules provide a targeted immunotherapy approach to treat hematologic malignancies and solid tumors. Since the approval of the CD19-targeted BiTE® (bispecific T-cell engager) molecule blinatumomab, multiple TCE molecules against different targets have been developed in several tumor types, with the approval of three additional TCE molecules in 2022. Some of the initial challenges, such as the need for continuous intravenous administration and low productivity, have been addressed in subsequent iterations of the platform by advancing half-life extended, Fc-based molecules. As clinical data from these molecules emerge, additional optimization of formats and manufacturability will be necessary. Ongoing efforts are focused on further improving TCE efficacy, safety, and convenience of administration.

Targeting SARS-CoV-2 infection through CAR-T-like bispecific T cell engagers incorporating ACE2

Objectives

Despite advances in antibody treatments and vaccines, COVID-19 caused by SARS-CoV-2 infection remains a major health problem resulting in excessive morbidity and mortality and the emergence of new variants has reduced the effectiveness of current vaccines.

Methods

Here, as a proof-of-concept, we engineered primary CD8 T cells to express SARS-CoV-2 Spike protein-specific CARs, using the extracellular region of ACE2 and demonstrated their highly specific and potent cytotoxicity towards Spike-expressing target cells. To improve on this concept as a potential therapeutic, we developed a bispecific T cell engager combining ACE2 with an anti-CD3 scFv (ACE2-Bite) to target infected cells and the virus.

Results

As in CAR-T cell approach, ACE2-Bite endowed cytotoxic cells to selectively kill Spike-expressing targets. Furthermore, ACE2-Bite neutralized the pseudoviruses of SARS-CoV, SARS-CoV-2 wild-type, and variants including Delta and Omicron, as a decoy protein. Remarkably, ACE2-Bite molecule showed a higher binding and neutralization affinity to Delta and Omicron variants compared to SARS-CoV-2 wild-type Spike proteins.

Conclusion

In conclusion, these results suggest the potential of this approach as a variant-proof, therapeutic strategy for future SARS-CoV-2 variants, employing both humoral and cellular arms of the adaptive immune response.

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.

Nonclinical Pharmacokinetics, Pharmacodynamics, and Translational Model of RO7297089, A Novel Anti-BCMA/CD16A Bispecific Tetravalent Antibody for the Treatment of Multiple Myeloma

RO7297089, an anti-B-cell maturation antigen (BCMA)/CD16A bispecific tetravalent antibody, is being developed as a multiple myeloma (MM) therapeutic. This study characterized nonclinical pharmacokinetics (PK), pharmacodynamics (PD), soluble BCMA (sBCMA), and soluble CD16 (sCD16) changes following administration of RO7297089 to support clinical trials. Unbound and total RO7297089 concentrations were measured in cynomolgus monkeys. RO7297089 exhibited a bi-phasic systemic concentration-time profile, similar to a typical human immunoglobulin 1 antibody. Target engagement by RO7297089 led to a robust increase (~100-fold) in total systemic sBCMA levels and relatively mild increase (~2-fold) in total sCD16 levels. To describe the relationship of nonclinical PK/PD data, we developed a target-mediated drug disposition (TMDD) model that includes the systemic target engagement of membrane BCMA (mBCMA), sBCMA, membrane CD16 (mCD16), and sCD16. We then used this model to simulate the PK/PD relationship of RO7297089 in MM patients by translating relevant PK parameters and target levels, based on the literature and newly generated data such as baseline sCD16A levels. Our model suggested that the impact of TMDD on RO7297089 exposure may be more significant in MM patients due to significantly higher expression levels of both mBCMA and sBCMA compared to healthy cynomolgus monkeys. Based on model simulations, we propose more frequent dosing of RO7297089 compared to regular monthly frequency in the clinic at the beginning of treatment to ensure sustained target engagement. This study demonstrates a translational research strategy for collecting relevant nonclinical data, establishing a TMDD model, and using simulations from this model to inform clinical dose regimens.

Race for the Cure: From the Oldest to the Newest Monoclonal Antibodies for Multiple Myeloma Treatment

Multiple myeloma is characterized by a wide clinical heterogeneity due to an intricate network of interactions between bone marrow-resident clonal plasma cells and the microenvironment. Over the last years, dramatic improvement in the understanding of these pathways led to the introduction of novel drugs with immune-mediated mechanisms of action. Some of these compounds, such as the anti-cd38 daratumumab and isatuximab, the anti-slamf-7 elotuzumab, and the antibody-drug conjugate belantamab-mafodotin, have been tested in large clinical trials and have now fully entered the real-life management. The bispecific T-cell engagers are under investigation with promising results, and other satisfactory data is expected from the application of nanotechnologies. The perfect timing to introduce these drugs in the sequence of treatment and their adverse events represent new challenges to be addressed, and further experience is required to improve their use.

Promising Antigens for the New Frontier of Targeted Immunotherapy in Multiple Myeloma

Simple Summary

Defining the specificity and biological sequalae induced by receptors differentiated expressed in multiple myeloma cells are critical for the development of effective immunotherapies based on monoclonal antibodies. Ongoing studies continue to discover new antigens with superior tumor selectivity and defined function in regulating the pathophysiology of myeloma cells directly or indirectly in the immunosuppressive bone marrow microenvironment. Meanwhile, it is urgent to identify mechanisms of immune resistance and design more potent immunotherapies, alone and/or with best combination partners to further prolong anti-MM immunity.

Abstract

The incorporation of novel agents in recent treatments in multiple myeloma (MM) has improved the clinical outcome of patients. Specifically, the approval of monoclonal antibody (MoAb) against CD38 (daratumumab) and SLAMF7 (elotuzumab) in relapsed and refractory MM (RRMM) represents an important milestone in the development of targeted immunotherapy in MM. These MoAb-based agents significantly induce cytotoxicity of MM cells via multiple effector-dependent mechanisms and can further induce immunomodulation to repair a dysfunctional tumor immune microenvironment. Recently, targeting B cell maturation antigen (BCMA), an even MM-specific antigen, has shown high therapeutic activities by chimeric antigen receptor T cells (CAR T), antibody-drug conjugate (ADC), bispecific T-cell engager (BiTE), as well as bispecific antibody (BiAb), with some already approved for heavily pretreated RRMM patients. New antigens, such as orphan G protein-coupled receptor class C group 5 member D (GPRC5D) and FcRH5, were identified and rapidly moved to ongoing clinical studies. We here summarized the pathobiological function of key MM antigens and the status of the corresponding immunotherapies. The potential challenges and emerging treatment strategies are also discussed.

Dual Targeting of Multiple Myeloma Stem Cells and Myeloid-Derived Suppressor Cells for Treatment of Chemotherapy-Resistant Multiple Myeloma

Here we review the insights and lessons learned from early clinical trials of T-cell engaging bispecific antibodies (BsABs) as a new class of biotherapeutic drug candidates with clinical impact potential for the treatment of multiple myeloma (MM). BsABs are capable of redirecting host T-cell cytotoxicity in an MHC-independent manner to malignant MM clones as well as immunosuppressive myeloid-derived suppressor cells (MDSC). T-cell engaging BsAB targeting the BCMA antigen may help delay disease progression in MM by destroying the MM cells. T-cell engaging BsAB targeting the CD38 antigen may help delay disease progression in MM by depleting both the malignant MM clones and the MDSC in the bone marrow microenvironment (BMME). BsABs may facilitate the development of a new therapeutic paradigm for achieving improved survival in MM by altering the immunosuppressive BMME. T-cell engaging BsiABs targeting the CD123 antigen may help delay disease progression in MM by depleting the MDSC in the BMME and destroying the MM stem cells that also carry the CD123 antigen on their surface.

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

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

Bispecific antibodies for non-Hodgkin's lymphomas and multiple myeloma

Immunotherapy has revolutionized the treatment of cancers. There are several approaches, including naked monoclonal antibodies, antibody–drug conjugates, immune-checkpoint inhibitors and chimeric antigen receptor T cell therapies with important success. Bispecific antibodies represent a novel immunotherapeutic approach for the treatment of several malignancies, in particular non-Hodgkin’s lymphoma (NHL) and multiple myeloma (MM). Early-phase studies have shown encouraging clinical activity in poor-risk B cell NHL and MM. Several constructs are currently available and in clinical development for the treatment of these malignancies. Here, we present a narrative review of the most current data on bispecific antibodies in B cell NHL and MM.

The Role of Monoclonal Antibodies in the Era of Bi-Specifics Antibodies and CAR T Cell Therapy in Multiple Myeloma

Multiple myeloma (MM) remains largely incurable despite enormous improvement in the outcome of patients. Over the past decade, we have witnessed the "era of monoclonal antibody (moAb)", setting new benchmarks in clinical outcomes for relapsed and newly diagnosed MM. Due to their excellent efficacy and relative safe toxicity profile, moAbs in combination with immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs) have become the new backbone of upfront anti-MM therapy. Yet, most patients will eventually relapse and patients who become refractory to IMiDs, PIs and moAbs have a dismal outcome. Emerging T-cell directing therapies, such as bispecific antibody (bsAb) and chimeric antigen receptor T cells (CAR T) have shown unprecedented responses and outcomes in these heavily pretreated and treatment-refractory patients. Their clinical efficacy combined with high tolerability will likely lead to the use of these agents earlier in the treatment course and there is great enthusiasm that a combination of T cell directed therapy with moAbs can lead to long duration remission in the near future, possibly even without the need of high dose chemotherapy and stem cell transplantation. Herein, we summarize the role of naked moAbs in MM in the context of newer immunotherapeutic agents like bsAb and CAR T therapy.

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

Simple Summary

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

Abstract

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

BCMA in Multiple Myeloma-A Promising Key to Therapy

Despite the discoveries of numerous agents including next generation proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies, multiple myeloma (MM) remains an incurable disease. The field of myeloma treatment in refractory or relapsed patients after standard therapy entered a new era due to the B-cell maturation antigen (BMCA) targeted approach. BCMA is a member of the tumor necrosis factor receptor family with high expression in mature B-lymphocytes and plasma cells. Given the understanding of BCMA mechanism of action in MM, BCMA plays a promising role as a therapeutic target. Several clinical trials are underway to evolve the current BCMA targeted treatment concept such as antibody-drug conjugates (ADCs), bispecific T cell engagers (BITEs) and chimeric antigen receptor (CAR) T cell therapy. Current results of representative BCMA trials may close the gap of the unmet clinical need to further improve the outcome of heavily pretreated MM patients with the potency to change the paradigm in newly diagnosed and refractory MM. This comprehensive review will give an update on various BMCA targeted treatment modalities (ADCs, BITEs, CAR T cell therapy) and its existing results on efficacy and safety from preclinical and clinical trials.

Preclinical Assessment of a MUC12-Targeted BiTE® (Bispecific T Cell Engager) Molecule

MUC12 is a transmembrane mucin that is highly expressed in >50% of primary and metastatic colorectal tumors. MUC12 is also expressed by normal epithelial cells of the colon and small intestine. While MUC12 localization in normal epithelial cells is restricted to the apical membrane, expression in tumors is depolarized and shows broad membrane localization. The differential localization of MUC12 in tumor cells as compared to normal cells makes it a potential therapeutic target. Here, we evaluated targeting of MUC12 with a BiTE® (bispecific T cell engager) molecule. We generated a panel of proof-of-concept half-life extended (HLE) BiTE molecules that bind MUC12 on tumor cells and CD3 on T cells. We prioritized one molecule based on in vitro activity for further characterization in vivo. In vitro, the MUC12 HLE BiTE molecule mediated T cell redirected lysis of MUC12-expressing cells with half-maximal lysis of 4.4 {plus minus} 0.9 pM to 117 {plus minus} 78 pM. In an exploratory cynomolgus monkey toxicology study, the MUC12 HLE BiTE molecule administered at 200 µg/kg with a step dose to 1000 µg/kg was tolerated with minimal clinical observations. However, higher doses were not tolerated, and there was evidence of damage in the gastrointestinal tract, suggesting dose levels projected to be required for antitumor activity may be associated with on-target toxicity. Together, these data demonstrate that the apically restricted expression of MUC12 in normal tissues is accessible to BiTE molecule target engagement and highlight the difficult challenge of identifying tumor-selective antigens for solid tumor T cell engagers.

Mechanisms of Action of the New Antibodies in Use in Multiple Myeloma

Monoclonal antibodies (mAbs) directed against antigen-specific of multiple myeloma (MM) cells have Fc-dependent immune effector mechanisms, such as complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP), but the choice of the antigen is crucial for the development of effective immuno-therapy in MM. Recently new immunotherapeutic options in MM patients have been developed against different myeloma-related antigens as drug conjugate-antibody, bispecific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR)-T cells. In this review, we will highlight the mechanism of action of immuno-therapy currently available in clinical practice to target CD38, SLAMF7, and BCMA, focusing on the biological role of the targets and on mechanisms of actions of the different immunotherapeutic approaches underlying their advantages and disadvantages with critical review of the literature data.

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

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

Laboratory Mice - A Driving Force in Immunopathology and Immunotherapy Studies of Human Multiple Myeloma

Mouse models of human cancer provide an important research tool for elucidating the natural history of neoplastic growth and developing new treatment and prevention approaches. This is particularly true for multiple myeloma (MM), a common and largely incurable neoplasm of post-germinal center, immunoglobulin-producing B lymphocytes, called plasma cells, that reside in the hematopoietic bone marrow (BM) and cause osteolytic lesions and kidney failure among other forms of end-organ damage. The most widely used mouse models used to aid drug and immunotherapy development rely on in vivo propagation of human myeloma cells in immunodeficient hosts (xenografting) or myeloma-like mouse plasma cells in immunocompetent hosts (autografting). Both strategies have made and continue to make valuable contributions to preclinical myeloma, including immune research, yet are ill-suited for studies on tumor development (oncogenesis). Genetically engineered mouse models (GEMMs), such as the widely known Vκ*MYC, may overcome this shortcoming because plasma cell tumors (PCTs) develop de novo (spontaneously) in a highly predictable fashion and accurately recapitulate many hallmarks of human myeloma. Moreover, PCTs arise in an intact organism able to mount a complete innate and adaptive immune response and tumor development reproduces the natural course of human myelomagenesis, beginning with monoclonal gammopathy of undetermined significance (MGUS), progressing to smoldering myeloma (SMM), and eventually transitioning to frank neoplasia. Here we review the utility of transplantation-based and transgenic mouse models of human MM for research on immunopathology and -therapy of plasma cell malignancies, discuss strengths and weaknesses of different experimental approaches, and outline opportunities for closing knowledge gaps, improving the outcome of patients with myeloma, and working towards a cure.

The immunomodulatory drugs lenalidomide and pomalidomide enhance the potency of AMG 701 in multiple myeloma preclinical models

We investigated here the novel immunomodulation and anti-multiple myeloma (MM) function of T cells engaged by the bispecific T-cell engager molecule AMG 701, and further examined the impact of AMG 701 in combination with immunomodulatory drugs (IMiDs; lenalidomide and pomalidomide). AMG 701 potently induced T-cell-dependent cellular cytotoxicity (TDCC) against MM cells expressing B-cell maturation antigen, including autologous cells from patients with relapsed and refractory MM (RRMM) (half maximal effective concentration, <46.6 pM). Besides inducing T-cell proliferation and cytolytic activity, AMG 701 also promoted differentiation of patient T cells to central memory, effector memory, and stem cell-like memory (scm) phenotypes, more so in CD8 vs CD4 T subsets, resulting in increased CD8/CD4 ratios in 7-day ex vivo cocultures. IMiDs and AMG 701 synergistically induced TDCC against MM cell lines and autologous RRMM patient cells, even in the presence of immunosuppressive bone marrow stromal cells or osteoclasts. IMiDs further upregulated AMG 701-induced patient T-cell differentiation toward memory phenotypes, associated with increased CD8/CD4 ratios, increased Tscm, and decreased interleukin 10-positive T and T regulatory cells (CD25highFOXP3high), which may downregulate T effector cells. Importantly, the combination of AMG 701 with lenalidomide induced sustained inhibition of MM cell growth in SCID mice reconstituted with human T cells; tumor regrowth was eventually observed in cohorts treated with either agent alone (P < .001). These results strongly support AMG 701 clinical studies as monotherapy in patients with RRMM (NCT03287908) and the combination with IMiDs to improve patient outcomes in MM.

Bispecific T cell engagers: an emerging therapy for management of hematologic malignancies

Harnessing the power of immune cells, especially T cells, to enhance anti-tumor activities has become a promising strategy in clinical management of hematologic malignancies. The emerging bispecific antibodies (BsAbs), which recruit T cells to tumor cells, exemplified by bispecific T cell engagers (BiTEs), have facilitated the development of tumor immunotherapy. Here we discussed the advances and challenges in BiTE therapy developed for the treatment of hematologic malignancies. Blinatumomab, the first BiTE approved for the treatment of acute lymphocytic leukemia (ALL), is appreciated for its high efficacy and safety. Recent studies have focused on improving the efficacy of BiTEs by optimizing treatment regimens and refining the molecular structures of BiTEs. A considerable number of bispecific T cell-recruiting antibodies which are potentially effective in hematologic malignancies have been derived from BiTEs. The elucidation of mechanisms of BiTE action and neonatal techniques used for the construction of BsAbs can improve the treatment of hematological malignancies. This review summarized the features of bispecific T cell-recruiting antibodies for the treatment of hematologic malignancies with special focus on preclinical experiments and clinical studies.

An update on B-cell maturation antigen-targeted therapies in Multiple Myeloma

Introduction: B-cell maturation antigen (BCMA) targeted therapy (BCMA-TT) has emerged as a promising treatment for Multiple Myeloma (MM). the three most common treatment modalities for targeting BCMA are antibody-drug conjugates (ADCs), bispecific antibody constructs, including BiTE (bispecific T-cell engager) immuno-oncology therapies, and chimeric antigen receptor (CAR)-modified T-cell therapy.Areas covered: The review provides an overview of the main published studies on clinical and pre-clinical data from trials using BCMA-TT.Expert opinion: Despite progresses in survival outcomes and the availability of new drugs, MM remains an incurable disease. ADC is a promising antibody-based treatment and Belantamab mafodotin showed an anti-myeloma effect alone or in combination with other drugs. The major issue of ADC is the occurrence of events interfering with the efficacy and the off-target cytotoxicity. Bispecific antibody constructs are off-the-shelf therapies characterized by a potential rapid availability. The most critical limitation of bispecific antibody constructs is their short half-life necessitating prolonged intravenous infusion. CAR-T cells produced unprecedented results in heavily pretreated RRMM. The most common toxicities include neurologic toxicity and cytokine release syndrome, B-cell aplasia, cytopenias, and hypogammaglobulinemia. Further studies are needed to detect which are the eligible patients who could benefit from one treatment more than another.