The Role of B-Cell Maturation Antigen in the Biology and Management of, and as a Potential Therapeutic Target in, Multiple Myeloma

Bispecific antibody and chimeric antigen receptor (CAR) modified T-cell in the treatment of multiple myeloma: Where do we stand today?

Although the prognosis of patients with multiple myeloma (MM) has been significantly improved by the introduction of proteasome inhibitors, immunomodulatory drugs and monoclonal antibodies, MM is still considered an incurable disease in the vast majority of the patients. In recent years, T-cell based immunotherapy represents a novel treatment strategy for relapsed/refractory (RR) MM. So far, chimeric antigen receptor (CAR) modified T-cells and bispecific T-cell engaging antibodies (bsAb) have shown promising anti-MM efficacy and manageable safety profile within clinical trials, and B-cell maturation antigen (BCMA) is the most commonly used immune target for T-cell based immunotherapies in MM. To date, several CAR T-cell and bsAb products have already been approved for the treatment of RRMM, leading to a paradigm shift in the MM therapy and providing a potential curative option. In this review, we provide a summary of mechanisms of action, immune targets, selected clinical data, resistance mechanisms and therapy sequencing of CAR T-cell and bsAb in MM.

Tumor-infiltrating B cells: Their dual mechanistic roles in the tumor microenvironment

The occurrence and development of tumors are closely associated with abnormalities in the immune system's structure and function, with tumor immunotherapy being intricately linked to the tumor microenvironment (TME). Early studies on lymphocytes within the TME primarily concentrated on T cells. However, as research has advanced, the multifaceted roles of tumor-infiltrating B cells (TIL-Bs) in tumor immunity, encompassing both anti-tumor and pro-tumor effects, have garnered increasing attention. This paper explored the composition of the TME and the biological characteristics of TIL-Bs, investigating the dual roles within the TME to offer new insights and strategies for tumor immunotherapy.

Telitacicept: A novel horizon in targeting autoimmunity and rheumatic diseases

BLyS and APRIL have the capability to bind to B cells within the body, allowing these cells to evade elimination when they should naturally be removed. While BLyS primarily plays a role in B cell development and maturation, APRIL is linked to B cell activation and the secretion of antibodies. Thus, in theory, inhibiting BLyS or APRIL could diminish the population of aberrant B cells that contribute to SLE and reduce disease activity in patients. Telitacicept functions by binding to and neutralizing the activities of both BLyS and APRIL, thus hindering the maturation and survival of plasma cells and fully developed B cells. The design of telitacicept is distinctive; it is not a monoclonal antibody but a TACI-Fc fusion protein generated through recombinant DNA technology. This fusion involves merging gene segments of the TACI protein, which can target BLyS/APRIL simultaneously, with the Fc gene segment of the human IgG protein. The TACI-Fc fusion protein exhibits the combined characteristics of both proteins. Currently utilized for autoimmune disease treatment, telitacicept is undergoing clinical investigations globally to assess its efficacy in managing various autoimmune conditions. This review consolidates information on the mechanistic actions, dosing regimens, pharmacokinetics, efficacy, and safety profile of telitacicept-a dual-targeted biological agent. It integrates findings from prior experiments and pharmacokinetic analyses in the treatment of RA and SLE, striving to offer a comprehensive overview of telitacicept's research advancements.

B-cell intrinsic RANK signaling cooperates with TCL1 to induce lineage-dependent B-cell transformation

B-cell malignancies, such as chronic lymphocytic leukemia (CLL) and multiple myeloma (MM), remain incurable, with MM particularly prone to relapse. Our study introduces a novel mouse model with active RANK signaling and the TCL1 oncogene, displaying both CLL and MM phenotypes. In younger mice, TCL1 and RANK expression expands CLL-like B1-lymphocytes, while MM originates from B2-cells, becoming predominant in later stages and leading to severe disease progression and mortality. The induced MM mimics human disease, exhibiting features like clonal plasma cell expansion, paraproteinemia, anemia, and kidney and bone failure, as well as critical immunosurveillance strategies that promote a tumor-supportive microenvironment. This research elucidates the differential impacts of RANK activation in B1- and B2-cells and underscores the distinct roles of single versus combined oncogenes in B-cell malignancies. We also demonstrate that human MM cells express RANK and that inhibiting RANK signaling can reduce MM progression in a xenotransplantation model. Our study provides a rationale for further investigating the effects of RANK signaling in B-cell transformation and the shaping of a tumor-promoting microenvironment.

Delivery of CD47-SIRPα checkpoint blocker by BCMA-directed UCAR-T cells enhances antitumor efficacy in multiple myeloma

In the treatment of relapsed or refractory multiple myeloma patients, BCMA-directed autologous CAR-T cells have showed excellent anti-tumor activity. However, their widespread application is limited due to the arguably cost and time-consuming. Multiple myeloma cells highly expressed CD47 molecule and interact with the SIRPα ligand on the surface of macrophages, in which evade the clearance of macrophages through the activation of "don't eat me" signal. In this study, a BCMA-directed universal CAR-T cells, BC404-UCART, secreting a CD47-SIRPα blocker was developed using CRISPR/Cas9 gene-editing system. BC404-UCART cells significantly inhibited tumor growth and prolonged the survival of mice in the xenograft model. The anti-tumor activity of BC404-UCART cells was achieved via two mechanisms, on the one hand, the UCAR-T cells directly killed tumor cells, on the other hand, the BC404-UCART cells enhanced the phagocytosis of macrophages by secreting anti-CD47 nanobody hu404-hfc fusion that blocked the "don't eat me" signal between macrophages and tumor cells, which provides a potential strategy for the development of novel "off-the-shelf" cellular immunotherapies for the treatment of multiple myeloma.

Differentiation of BCMA-specific induced pluripotent stem cells into rejuvenated CD8αβ+ T cells targeting multiple myeloma

ABSTRACT

A major hurdle in adoptive T-cell therapy is cell exhaustion and failure to maintain antitumor responses. Here, we introduce an induced pluripotent stem cell (iPSC) strategy for reprogramming and revitalizing precursor exhausted B-cell maturation antigen (BCMA)-specific T cells to effectively target multiple myeloma (MM). Heteroclitic BCMA72-80 (YLMFLLRKI)-specific CD8+ memory cytotoxic T lymphocytes (CTL) were epigenetically reprogrammed to a pluripotent state, developed into hematopoietic progenitor cells (CD34+ CD43+/CD14- CD235a-), differentiated into the T-cell lineage and evaluated for their polyfunctional activities against MM. The final T-cell products demonstrated (1) mature CD8αβ+ memory phenotype, (2) high expression of activation or costimulatory molecules (CD38, CD28, and 41BB), (3) no expression of immune checkpoint and senescence markers (CTLA4, PD1, LAG3, and TIM3; CD57), and (4) robust proliferation and polyfunctional immune responses to MM. The BCMA-specific iPSC-T cells possessed a single T-cell receptor clonotype with cognate BCMA peptide recognition and specificity for targeting MM. RNA sequencing analyses revealed distinct genome-wide shifts and a distinctive transcriptional profile in selected iPSC clones, which can develop CD8αβ+ memory T cells. This includes a repertoire of gene regulators promoting T-cell lineage development, memory CTL activation, and immune response regulation (LCK, IL7R, 4-1BB, TRAIL, GZMB, FOXF1, and ITGA1). This study highlights the potential application of iPSC technology to an adaptive T-cell therapy protocol and identifies specific transcriptional patterns that could serve as a biomarker for selection of suitable iPSC clones for the successful development of antigen-specific CD8αβ+ memory T cells to improve the outcome in patients with MM.

Genetic defects of gamma-secretase genes in a multiple myeloma patient with high and dysregulated BCMA surface density: A case report

Multiple myeloma (MM) cells from 1 out of 20 patient expressed high basal levels of membrane B-cell maturation antigen (BCMA, TNFRSF17, CD269), which was not upregulated by gamma-secretase inhibitor, suggesting a defective BCMA shedding by gamma-secretase. Genetic analyses of the patient's bone marrow DNA showed no mutations within the BCMA coding region, but rather partial deletion of PSEN1 and amplification of PSEN2, which encode alternative catalytic units of gamma-secretase. Altogether the data suggest that pt#12 MM cells express high and dysregulated BCMA with no shedding, due to genetic alterations of one or more gamma-secretase subunits.

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.

Identification and Targeting of Mutant Neoantigens in Multiple Myeloma Treatment

Multiple myeloma (MM) is malignant disease characterized by the clonal proliferation of plasma cells in the bone marrow, leading to anemia, immunosuppression, and other symptoms, that is generally hard to treat. In MM, the immune system is likely exposed to neoplasia-associated neoantigens for several years before the tumor onset. Different types of neoantigens have been identified. Public or shared neoantigens derive from tumor-specific modifications often reported in several patients or across diverse tumors. They are intriguing therapeutic targets because they are frequently observed, and they have an oncogenic effect. Only a small number of public neoantigens have been recognized. Most of the neoantigens that have been identified are patient-specific or "private", necessitating a personalized approach for adaptive cell treatment. It was demonstrated that the targeting of a single greatly immunogenic neoantigen may be appropriate for tumor control. The purpose of this review was to analyze the neoantigens present in patients with MM, and to evaluate the possibility of using their presence as a prognostic factor or as a therapeutic target. We reviewed the most recent literature on neoantigen treatment strategies and on the use of bispecific, trispecific, and conjugated antibodies for the treatment of MM. Finally, a section was dedicated to the use of CAR-T in relapsed and refractory patients.

Serum levels and significance of soluble B-cell maturation antigen in childhood-onset systemic lupus erythematosus with renal involvement

OBJECTIVE

The aim of this study was to investigate serum levels of soluble B-cell maturation antigen (sBCMA) in childhood-onset systemic lupus erythematous (cSLE) patients with renal involvement, and to elucidate their association with clinical characteristics.

METHODS

116 cases of cSLE patients with renal involvement (84 females and 32 males; median age 11.6 (10.1, 12.9) years) hospitalized in Department of Pediatric Nephrology and Rheumatology, the First Affiliated Hospital, Sun Yat-sen University and 31 healthy controls (HCs) were enrolled. Serum concentrations of sBCMA were determined using enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory information of cSLE patients were retrospectively analyzed.

RESULTS

Serum sBCMA levels were significantly increased in primary cSLE when compared with treated cSLE patients and HCs, whereas there was no significant difference between treated cSLE patients and HCs. Patients with high disease activity displayed higher serum sBCMA levels compared with those with no or mild to moderate disease activity. Positive correlation was observed between serum sBCMA levels and systemic lupus erythematosus disease activity index-2K (SLEDAI-2K), antinuclear antibody titers, anti-double-stranded DNA titers, erythrocyte sedimentation rate, and immunoglobulin G levels, while sBCMA levels were negatively correlated with blood white blood cell count, hemoglobin, platelet count, complement C3 and C4 levels. Serum sBCMA levels decreased as disease ameliorated after treatments among 11 cases with follow-up examinations.

CONCLUSIONS

In cSLE patients with renal involvement, serum sBCMA levels correlated significantly with disease activity, immunological, and hematological parameters, but not with renal parameters. Our results suggest the potential and significance of serum sBCMA as a biomarker in cSLE patients.

Establishment of a prediction model for disease progression within one year in newly diagnosed multiple myeloma patients

Multiple myeloma is still an incurable disease In the past decade, with the continuous progress of treatment methods, the progression-free survival of patients has been prolonged, but some patients still progress in the early stage of the disease. Our research analyses the clinical laboratory indicators of newly diagnosed multiple myeloma (NDMM) patients, to obtain the relevant factors of disease progression within one year in MM patients and to establish a prediction model.

108 MM patients treated in our hospital from January 2015 to January 2020 were retrospectively analyzed. After univariate and multivariate logistic regression analyses, the related factors of disease progression within one year in NDMM patients were obtained, and a prediction model was established.

Treatment regimen containing at least two targeted drugs (OR = 0.226, 95% CI 0.068-0.753), increased lactate dehydrogenase(LDH, OR = 3.452, 95% CI 1.101-10.826) and increased serum corrected calcium(OR =  4.466, 95% CI 1.346-14.811) were identified as potential predictors by statistical analysis. The prediction model was obtained: x = -2.042-1.489 × treatment regimen (including at least two targeted drug assignment as 1, otherwise 0) + 1.239 ×LDH (U/L, lactate dehydrogenase elevation assignment as 1, normal as 0) +1.496 × serum corrected calcium (mmol/L, serum corrected calcium elevation assignment as 1, normal as 0). Receiver operating characteristic curve analysis showed that the model has good predictive performance.

The possibility of disease progression within one year can be predicted by the prediction model. The model can be used as a reference for clinicians to make individualized treatment plans for patients so that patients can obtain better treatment effects.

B-cell maturation antigen targeting strategies in multiple myeloma treatment, advantages and disadvantages

B cell maturation antigen (BCMA), a transmembrane glycoprotein member of the tumor necrosis factor receptor superfamily 17 (TNFRSF17), highly expressed on the plasma cells of Multiple myeloma (MM) patients, as well as the normal population. BCMA is used as a biomarker for MM. Two members of the TNF superfamily proteins, including B-cell activating factor (BAFF) and A proliferation-inducing ligand (APRIL), are closely related to BCMA and play an important role in plasma cell survival and progression of MM. Despite the maximum specificity of the monoclonal antibody technologies, introducing the tumor-specific antigen(s) is not applicable for all malignancies, such as MM that there plenty of relatively specific antigens such as GPCR5D, MUC1, SLAMF7 and etc., but higher expression of BCMA on these cells in comparison with normal ones can be regarded as a relatively exclusive marker. Currently, different monoclonal antibody (mAb) technologies applied in anti-MM therapies such as daratuzumab, SAR650984, GSK2857916, and CAR-T cell therapies are some of these tools that are reviewed in the present manuscript. By the way, the structure, function, and signaling of the BCMA and related molecule(s) role in normal plasma cells and MM development, evaluated as well as the potential side effects of its targeting by different CAR-T cells generations. In conclusion, BCMA can be regarded as an ideal molecule to be targeted in immunotherapeutic methods, regarding lower potential systemic and local side effects.

Practical guidance for new multiple myeloma treatment regimens: A nursing perspective

As is the case for solid tumors, treatment paradigms have shifted from non-specific chemotherapeutic agents towards novel targeted drugs in the treatment of patients with multiple myeloma (MM). Currently, multiple targeted therapies are available to treat patients augmenting the arsenal of modalities which also includes chemotherapy, immunotherapy, radiation therapy, hematopoietic stem cell transplantation (HSCST) and chimeric antigen T-cell therapy (CAR-T). These novel, targeted agents have dramatically increased optimism for patients, who may now be treated over many years with successive regimens. As fortunate as we are to have these new therapies available for our patients, this advantage is juxtaposed with the challenges involved with delivering them safely. While each class of agents has demonstrated efficacy, in terms of response rates and survival, they also exert class effects which pose risks for toxicity. In addition, newer generation agents within the classes often have slightly different toxicity profiles than did their predecessors. These factors must be addressed, and their risks mitigated by the multidisciplinary team. This review presents a summary of the evolution of drug development for MM. For each targeted agent, the efficacy data from pivotal trials and highlights of the risks that were demonstrated in trials, as well as during post-marketing surveillance, are presented. Specific risks associated with agents within the classes, that are not shared with all new class members, are described. A table presenting these potential risks, with recommended nursing actions to mitigate toxicity, is provided as a quick reference that nurses may use during the planning, and provision, of patient care.

Idecabtagene vicleucel (ide-cel) CAR T-cell therapy for relapsed and refractory multiple myeloma

Idecabtagene vicleucel (ide-cel), a novel chimeric antigen receptor (CAR) T-cell therapy targeting B-cell maturation antigen (BCMA), has recently gained approval by the US FDA for relapsed and refractory multiple myeloma (RRMM) after multicenter trials have demonstrated unprecedented results in this difficult-to-treat subgroup of patients. As the first CAR T-cell product approved for myeloma, ide-cel is poised to become a practice-changing treatment option. This first-in-class therapeutic offers hope for more durable remissions, as well as better quality of life, following a single infusion in a group of patients that previously had little hope. This paper reviews the ide-cel product in terms of design, pharmacology, efficacy and toxicity as described in studies reported to date.

Rethinking mechanisms of neurotoxicity with BCMA directed therapy

B-cell maturation antigen (BCMA) has become a key target for antibody-drug conjugates, bispecific antibodies, chimeric antigen receptor T-cell therapies, and other immunotherapies in multiple myeloma. Some of these agents such as belantamab mafodotin and idecabtagene vicleucel have already received regulatory approval in the United States. Although BCMA has generally been considered to be expressed almost exclusively in plasma cells with a low likelihood of on-target off-tumor toxicity, there has been a range of unusual neurotoxicity observed across the spectrum of BCMA immunotherapies. In certain cases, these unusual neurotoxicity presentations have led to patient death or withdrawal of agents from further development. Our review summarizes the literature in this field and highlights the possibility of on-target toxicities due to neural expression of BCMA. We draw attention to the need for further investigation of these toxicities. This risk becomes increasingly important as BCMA targeted therapies are brought to earlier lines of treatment.

Serum BCMA levels predict outcomes in MGUS and smoldering myeloma patients

Soluble BCMA (sBCMA) levels are elevated in monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). However, the association between sBCMA levels and prognosis in MGUS and SMM has not been studied. We retrospectively analyzed sBCMA levels in stored samples from 99 MGUS and 184 SMM patients. Baseline sBCMA levels were significantly higher in MGUS and SMM patients progressing to MM during clinical follow up. When stratified according to the median baseline sBCMA level for each cohort, higher levels were associated with a shorter PFS for MGUS (HR 3.44 comparing sBCMA ≥77 vs <77 ng/mL [95% CI 2.07-5.73, p < 0.001] and SMM (HR 2.0 comparing sBCMA ≥128 vs <128 ng/mL, 95% 1.45-2.76, p < 0.001) patients. The effect of sBCMA on PFS was similar even after adjusting for the baseline MGUS or SMM risk stratification. We evaluated paired serum samples and found that sBCMA increased significantly in MGUS and SMM patients who eventually progressed to MM, whereas among MGUS non-progressors the sBCMA level remained stable. While our results require independent validation, they suggest that sBCMA may be a useful biomarker to identify MGUS and SMM patients at increased risk of progression to MM independent of the established risk models.

Highly Sensitive Detection of miRNA-155 Using Molecular Beacon-Functionalized Monolayer MoS₂ Nanosheet Probes with Duplex-Specific Nuclease-Mediated Signal Amplification

MicroRNA-155 (miRNA-155) as a characteristic myeloma-associated biomarker exhibits significant potential application in the diagnosis of multiple myeloma (MM). In this paper, a novel type of molecular beacon (MB)-functionalized monolayer MoS₂ nanosheet probe was proposed as fluorescent probe for high-sensitive assays of miRNA-155that uses a duplexspecificnuclease (DSN) enzyme to amplify the fluorescence signal. The preparation and detection conditions of the fluorescent probes were optimized in some aspects, such as the concentration of MoS₂ (0.80 μM) and DSN (0.2 U), and the incubation time of DSN (30 min). The probesexhibited a sensitive fluorescence response to miRNA-155 and the fluorescence signal of the assay was significantly amplified by the cleavage of DSN. The relationship between F/F₀ and logC miRNA follows a linear calibration curve, and the limit of detection (LOD) of miRNA-155 in 10% human serum is calculated to be 10.96 fM based on this relationship. The good performance and fluorescence amplification effect of the fluorescent probe were confirmed by studying the recovery of miRNA-155 in 10% human serum, which was ranged from 98.32% to 106.3% with a relative standard deviation of less than 4.14%. Besides, the high expression of miRNA-155 in clinic blood of MM patients was sensitively distinguished from healthy peoples by using the proposed probes. The proposed novel fluorescent probe based on the DSN can be used to detect miRNA-155 in human serum and provide a potential, convenient and reliable tool for diagnosis of MM.

Belantamab mafodotin in the treatment of relapsed or refractory multiple myeloma

Multiple myeloma remains an incurable disease, with a large proportion of patients in the relapsed/refractory setting often unable to achieve durable responses. Novel, well-tolerated and highly effective therapies in this patient population represent an unmet need. Preclinical studies have shown that B-cell maturation antigen is nearly exclusively expressed on normal and malignant plasma cells, thereby identifying it as a highly selective target for immunotherapeutic approaches. Belantamab mafodotin (GSK2857916, belamaf) is a first-in-class antibody-drug conjugate directed at B-cell maturation antigen and has shown promising activity in clinical trials. In this review, we provide an overview of belantamab mafodotin as a compound and present the available clinical efficacy and safety data in the treatment of relapsed/refractory multiple myeloma.

Therapeutic effect of dual CAR-T targeting PDL1 and MUC16 antigens on ovarian cancer cells in mice

BACKGROUND

More favorable treatment against epithelial ovarian cancer (EOC) is urgently needed because of its insidious nature at an early stage and a low rate of five-year survival. The current primary treatment, extensive surgery combined with chemotherapy, exhibits limited benefits for improving prognosis. Chimeric antigen receptor T (CAR-T) cell technology as novel immunotherapy has made breakthrough progress in the treatment of hematologic malignancies, and there were also benefits shown in a partial solid tumor in previous research. Therefore, CAR-T cell technology may be a promising candidate as an immunotherapeutic tool against EOC. However, there are some weaknesses in targeting one antigen from the previous preclinical assay, such as on-target off-tumor cytotoxicity. The dual-target CAR-T cell may be a better choice.

METHODS

We constructed tandem PD1-antiMUC16 dual-CAR, PD1 single-CAR, and anti-MUC16 single-CAR fragments by PCR and genetic engineering, followed by preparing CAR-T cells via lentiviral infection. The expression of CAR molecules on single and dual CAR-T cells was detected by flow cytometry. The killing capacity and activation of CAR-T cells were measured by cytotoxic assays and cytokines release assays in vitro. The therapeutic capacity of CAR-T cells was assessed by tumor-bearing mice model assay in vivo.

RESULTS

We successfully constructed CARs lentiviral expression vectors and obtained single and dual CAR-T cells. CAR-T cells demonstrated robust killing capacity against OVCAR-3 cells in vitro. Meanwhile, CAR-T cells released plenty of cytokines such as interleukin-2(IL-2), interferon-γ (IFN-γ) and tumor necrosis factor-α(TNF-α). CAR-T cells showed a therapeutic benefit against OVCAR-3 tumor-bearing mice and significantly prolonged the survival time. Dual CAR-T cells were shown to be two to four times more efficacious than single CAR-T cells in terms of survival time.

CONCLUSION

Although exhibiting a similar ability as single CAR-T cells against OVCAR-3 cells in vitro, dual CAR-T cells demonstrated enhanced killing capacity against OVCAR-3 cells as compared to single CAR-T cells in vivo and significantly prolonged the survival time of tumor-bearing mice. PD1-antiMUC16 CAR-T cells showed more potent antitumor activity than single CAR-T cells in vivo. The present experimental data may support further research work that will have the potential to lead to clinical studies.

Normalization of serum B-cell maturation antigen levels predicts overall survival among multiple myeloma patients starting treatment

Serum B-cell maturation antigen (sBCMA) is a novel biomarker for B-cell malignancies. A normal reference range (<82·59 ng/ml) has been recently established but the impact of achieving normal levels to outcomes for patients receiving treatment for B-cell malignancies has not been studied. We first found that among multiple myeloma (MM) patients starting a new treatment, those who begin treatment within normal sBCMA limits (<82·59 ng/ml) have improved progression-free survival (PFS; P = 0·0398) and overall survival (OS; P = 0·0217) than those who do not. Furthermore, among patients who begin treatment with elevated (≥82·59 ng/ml) sBCMA levels, we assessed the relationship of a decrease in sBCMA to the normal range to OS and found that those who normalize sBCMA demonstrated improved OS (P = 0·0078). Normalizing patients also experienced a markedly improved overall response rate (P < 0·0001). Moreover, all patients who achieved complete remission (CR) showed normalization of sBCMA, and time to normalization (median 0·9 months) was faster than time to CR (5·0 months; P = 0·0036) for these patients. These results suggest that normalization of sBCMA may be an accurate predictor of OS for MM patients during treatment and predict for a higher likelihood of response.

Transmembrane Activator and CAML Interactor (TACI): Another Potential Target for Immunotherapy of Multiple Myeloma?

Multiple myeloma (MM) has emerged as the next most likely oncological or hematological disease indication amenable for cellular immunotherapy. Much of the attention has been focused on B cell maturation antigen (BCMA) as a unique cell surface protein on myeloma cells that is available for monoclonal antibodies, antibody drug conjugates (ADCs), T-cell redirecting bispecific molecules, and chimeric antigen receptor (CAR) T cell targeting. BCMA is a member of the tumor necrosis factor receptor (TNFR) superfamily that binds two ligands B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) and mediates the growth and survival of plasma and MM cells. Interestingly, transmembrane activator and CAML interactor (TACI), another TNFR superfamily member, also binds the same ligands and plays largely overlapping roles as BCMA in normal plasma and malignant MM cells. In this article, we review the biology of TACI, focusing on its role in normal B and plasma cells and malignant MM cells, and also discuss various ways to incorporate TACI as a potential target for immunotherapies against MM.

Estimating a normal reference range for serum B-cell maturation antigen levels for multiple myeloma patients

The serum B-cell maturation antigen (sBCMA) has been identified as a novel serum biomarker for patients with multiple myeloma. However, no study has yet established a reference range for sBCMA levels. Its levels were determined in 196 healthy subjects and showed a right-tailed distribution with a median value of 37·51 ng/ml with a standard deviation of 22·54 ng/ml (range 18·78-180·39 ng/ml). Partitioning of subgroup reference ranges was considered but determined to be irrelevant. A non-parametric method using the median ± 2 standard deviations suggests using a universal reference interval of <82·59 ng/ml.

Analysis of the receptor BCMA as a biomarker in systemic lupus erythematosus patients

B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) play central roles in B cell development and maturation. Soluble forms of their receptors can be generated by proteolytic cleavage; however, their physiological and clinical roles are unknown. This study aimed to assess the relationships between the receptor soluble B cell maturation antigen (sBCMA) and clinical variables in systemic lupus erythematosus (SLE) patients. Serum cytokine concentrations were measured by ELISA for 129 SLE patients and 34 healthy controls (HCs), and the expression of the receptor BCMA was evaluated on B and plasma cells from 40 subjects. SLE patients showed aberrant expression of the receptor BCMA on B and plasma cells. Soluble levels of the receptor sBCMA and its ligands sAPRIL and sBAFF were increased in SLE patients compared with HCs. Additionally, sBCMA (rs = 0.6177) and sAPRIL (rs = 0.4952) correlated strongly with disease activity. Active SLE patients who achieved low disease activity showed decreased sBCMA (53.30 vs 35.30 ng/mL; p < 0.05) and sBAFF (4.48 vs 2.27 ng/mL; p < 0.05) serum levels after treatment, while sAPRIL expression remained unchanged. At a cutoff value of 22.40 ng/mL, sAPRIL showed high sensitivity (96.12%) and specificity (94.12%) for discrimination between HCs and SLE patients, while sBAFF showed lower sensitivity (82.2%) but higher specificity (94.1%) at a cutoff of 1.195 ng/mL. Relatively high levels of sAPRIL and sBCMA clustered active SLE patients. The receptor sBCMA could be a potential biomarker of disease activity in SLE.

Unraveling the mysteries of plasma cells

Antibody-secreting plasma cells are the central pillars of humoral immunity. They are generated in a fundamental cellular restructuring process from naive B cells upon contact with antigen. This outstanding process is guided and controlled by a complex transcriptional network accompanied by a fascinating morphological metamorphosis, governed by the combined action of Blimp-1, Xbp-1 and IRF-4. The survival of plasma cells requires the intimate interaction with a specific microenvironment, consisting of stromal cells and cells of hematopoietic origin. Cell-cell contacts, cytokines and availability of metabolites such as glucose and amino acids modulate the survival abilities of plasma cells in their niches. Moreover, plasma cells have been shown to regulate immune responses by releasing cytokines. Furthermore, plasma cells are central players in autoimmune diseases and malignant transformation of plasma cells can result in the generation of multiple myeloma. Hence, the development of sophisticated strategies to deplete autoreactive plasma cells and myeloma cells represents a challenge for current and future research.

B-cell maturation antigen (BCMA) in multiple myeloma: rationale for targeting and current therapeutic approaches

Despite considerable advances in the treatment of multiple myeloma (MM) in the last decade, a substantial proportion of patients do not respond to current therapies or have a short duration of response. Furthermore, these treatments can have notable morbidity and are not uniformly tolerated in all patients. As there is no cure for MM, patients eventually become resistant to therapies, leading to development of relapsed/refractory MM. Therefore, an unmet need exists for MM treatments with novel mechanisms of action that can provide durable responses, evade resistance to prior therapies, and/or are better tolerated. B-cell maturation antigen (BCMA) is preferentially expressed by mature B lymphocytes, and its overexpression and activation are associated with MM in preclinical models and humans, supporting its potential utility as a therapeutic target for MM. Moreover, the use of BCMA as a biomarker for MM is supported by its prognostic value, correlation with clinical status, and its ability to be used in traditionally difficult-to-monitor patient populations. Here, we review three common treatment modalities used to target BCMA in the treatment of MM: bispecific antibody constructs, antibody–drug conjugates, and chimeric antigen receptor (CAR)-modified T-cell therapy. We provide an overview of preliminary clinical data from trials using these therapies, including the BiTE® (bispecific T-cell engager) immuno-oncology therapy AMG 420, the antibody–drug conjugate GSK2857916, and several CAR T-cell therapeutic agents including bb2121, NIH CAR-BCMA, and LCAR-B38M. Notable antimyeloma activity and high minimal residual disease negativity rates have been observed with several of these treatments. These clinical data outline the potential for BCMA-targeted therapies to improve the treatment landscape for MM. Importantly, clinical results to date suggest that these therapies may hold promise for deep and durable responses and support further investigation in earlier lines of treatment, including newly diagnosed MM.

An Anti-BCMA RNA Aptamer for miRNA Intracellular Delivery

B cell maturation antigen is highly expressed on malignant plasma cells in human multiple myeloma and has recently emerged as a very promising target for therapeutic interventions. Nucleic-acid-based aptamers are small oligonucleotides with high selective targeting properties and functional advantages over monoclonal antibodies, as both diagnostic and therapeutic tools. Here, we describe the generation of the first-ever-described nuclease resistant RNA aptamer selectively binding to B cell maturation antigen. We adopted a modified cell-based systematic evolution of ligands by exponential enrichment approach allowing the enrichment for internalizing aptamers. The selected 2′Fluoro-Pyrimidine modified aptamer, named apt69.T, effectively and selectively bound B cell maturation antigen-expressing myeloma cells with rapid and efficient internalization. Interestingly, apt69.T inhibited APRIL-dependent nuclear factor κB (NF-κB) pathway in vitro. Moreover, the aptamer was conjugated to microRNA-137 (miR-137) and anti-miR-222, demonstrating high potential against tumor cells. In conclusion, apt69.T is a novel tool suitable for direct targeting and delivery of therapeutics to B cell maturation antigen-expressing myeloma cells.

Selective targeting of multiple myeloma by B cell maturation antigen (BCMA)-specific central memory CD8+ cytotoxic T lymphocytes: immunotherapeutic application in vaccination and adoptive immunotherapy

To expand the breadth and extent of current multiple myeloma (MM)-specific immunotherapy, we have identified various antigens on CD138⁺ tumor cells from newly diagnosed MM patients (n = 616) and confirmed B-cell maturation antigen (BCMA) as a key myeloma-associated antigen. The aim of this study is to target the BCMA, which promotes MM cell growth and survival, by generating BCMA-specific memory CD8⁺ CTL that mediate effective and long-lasting immunity against MM. Here we report the identification of novel engineered peptides specific to BCMA, BCMA_72-80 (YLMFLLRKI), and BCMA_54-62 (YILWTCLGL), which display improved affinity/stability to HLA-A2 compared to their native peptides and induce highly functional BCMA-specific CTL with increased activation (CD38, CD69) and co-stimulatory (CD40L, OX40, GITR) molecule expression. Importantly, the heteroclitic BCMA_72-80 specific CTL demonstrated poly-functional Th1-specific immune activities [IFN-γ/IL-2/TNF-α production, proliferation, cytotoxicity] against MM, which were correlated with expansion of Tetramer⁺ and memory CD8⁺ CTL. Additionally, heteroclitic BCMA_72-80 specific CTL treated with anti-OX40 (immune agonist) or anti-LAG-3 (checkpoint inhibitor) display increased immune function, mainly by central memory CTL. These results provide the framework for clinical application of heteroclitic BCMA_72-80 peptide, alone and in combination with anti-LAG3 and/or anti-OX40 therapy, in vaccination and/or adoptive immunotherapeutic strategies to generate long-lasting anti-tumor immunity in patients with MM or other BCMA expressing tumors.

BAFF-driven B cell hyperplasia underlies lung disease in common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency and is frequently complicated by interstitial lung disease (ILD) for which etiology is unknown and therapy inadequate.

METHODS

Medical record review implicated B cell dysregulation in CVID ILD progression. This was further studied in blood and lung samples using culture, cytometry, ELISA, and histology. Eleven CVID ILD patients were treated with rituximab and followed for 18 months.

RESULTS

Serum IgM increased in conjunction with ILD progression, a finding that reflected the extent of IgM production within B cell follicles in lung parenchyma. Targeting these pulmonary B cell follicles with rituximab ameliorated CVID ILD, but disease recurred in association with IgM elevation. Searching for a stimulus of this pulmonary B cell hyperplasia, we found B cell-activating factor (BAFF) increased in blood and lungs of progressive and post-rituximab CVID ILD patients and detected elevation of BAFF-producing monocytes in progressive ILD. This elevated BAFF interacts with naive B cells, as they are the predominant subset in progressive CVID ILD, expressing BAFF receptor (BAFF-R) within pulmonary B cell follicles and blood to promote Bcl-2 expression. Antiapoptotic Bcl-2 was linked with exclusion of apoptosis from B cell follicles in CVID ILD and increased survival of naive CVID B cells cultured with BAFF.

CONCLUSION

CVID ILD is driven by pulmonary B cell hyperplasia that is reflected by serum IgM elevation, ameliorated by rituximab, and bolstered by elevated BAFF-mediated apoptosis resistance via BAFF-R.

FUNDING

NIH, Primary Immune Deficiency Treatment Consortium, and Rare Disease Foundation.

Targeting B Cell Maturation Antigen (BCMA) in Multiple Myeloma: Potential Uses of BCMA-Based Immunotherapy

The approval of the first two monoclonal antibodies targeting CD38 (daratumumab) and SLAMF7 (elotuzumab) in late 2015 for treating relapsed and refractory multiple myeloma (RRMM) was a critical advance for immunotherapies for multiple myeloma (MM). Importantly, the outcome of patients continues to improve with the incorporation of this new class of agents with current MM therapies. However, both antigens are also expressed on other normal tissues including hematopoietic lineages and immune effector cells, which may limit their long-term clinical use. B cell maturation antigen (BCMA), a transmembrane glycoprotein in the tumor necrosis factor receptor superfamily 17 (TNFRSF17), is expressed at significantly higher levels in all patient MM cells but not on other normal tissues except normal plasma cells. Importantly, it is an antigen targeted by chimeric antigen receptor (CAR) T-cells, which have already shown significant clinical activities in patients with RRMM who have undergone at least three prior treatments, including a proteasome inhibitor and an immunomodulatory agent. Moreover, the first anti-BCMA antibody–drug conjugate also has achieved significant clinical responses in patients who failed at least three prior lines of therapy, including an anti-CD38 antibody, a proteasome inhibitor, and an immunomodulatory agent. Both BCMA targeting immunotherapies were granted breakthrough status for patients with RRMM by FDA in Nov 2017. Other promising BCMA-based immunotherapeutic macromolecules including bispecific T-cell engagers, bispecific molecules, bispecific or trispecific antibodies, as well as improved forms of next generation CAR T cells, also demonstrate high anti-MM activity in preclinical and even early clinical studies. Here, we focus on the biology of this promising MM target antigen and then highlight preclinical and clinical data of current BCMA-targeted immunotherapies with various mechanisms of action. These crucial studies will enhance selective anti-MM response, transform the treatment paradigm, and extend disease-free survival in MM.

T Cells Genetically Modified to Express an Anti-B-Cell Maturation Antigen Chimeric Antigen Receptor Cause Remissions of Poor-Prognosis Relapsed Multiple Myeloma

Purpose Therapies with novel mechanisms of action are needed for multiple myeloma (MM). T cells can be genetically modified to express chimeric antigen receptors (CARs), which are artificial proteins that target T cells to antigens. B-cell maturation antigen (BCMA) is expressed by normal and malignant plasma cells but not normal essential cells. We conducted the first-in-humans clinical trial, to our knowledge, of T cells expressing a CAR targeting BCMA (CAR-BCMA). Patients and Methods Sixteen patients received 9 × 106 CAR-BCMA T cells/kg at the highest dose level of the trial; we are reporting results of these 16 patients. The patients had a median of 9.5 prior lines of MM therapy. Sixty-three percent of patients had MM refractory to the last treatment regimen before protocol enrollment. T cells were transduced with a γ-retroviral vector encoding CAR-BCMA. Patients received CAR-BCMA T cells after a conditioning chemotherapy regimen of cyclophosphamide and fludarabine. Results The overall response rate was 81%, with 63% very good partial response or complete response. Median event-free survival was 31 weeks. Responses included eradication of extensive bone marrow myeloma and resolution of soft-tissue plasmacytomas. All 11 patients who obtained an anti-MM response of partial response or better and had MM evaluable for minimal residual disease obtained bone marrow minimal residual disease-negative status. High peak blood CAR+ cell levels were associated with anti-MM responses. Cytokine-release syndrome toxicities were severe in some cases but were reversible. Blood CAR-BCMA T cells were predominantly highly differentiated CD8+ T cells 6 to 9 days after infusion. BCMA antigen loss from MM was observed. Conclusion CAR-BCMA T cells had substantial activity against heavily treated relapsed/refractory MM. Our results should encourage additional development of CAR T-cell therapies for MM.