B cell maturation antigen (BCMA)

Overview

TNF receptor superfamily member 17 (TNFRSF17), known as B-cell maturation antigen (BCMA), is a transmembrane receptor of the tumor necrosis factor receptor superfamily. Its expression is acquired late in B-cell differentiation, appearing on plasmablasts and long-lived plasma cells while being largely absent from naive and memory B cells and from non-hematopoietic tissue. Its ligands APRIL and BAFF deliver survival signals through NF-κB, sustaining the long-lived plasma cell compartment of the bone marrow — the reservoir responsible for durable antibody production.

That restricted distribution is what makes BCMA an unusually clean target. It is upregulated on malignant plasma cells in multiple myeloma, so directing therapy at it spares nearly everything except the plasma cell compartment itself. Three modalities are now established in relapsed and refractory disease: antibody-drug conjugates, bispecific T-cell engagers that bridge BCMA to CD3, and chimeric antigen receptor (CAR) T cells, the last producing deep and sometimes prolonged responses in patients who have exhausted other options. The shared toxicity follows directly from the target — loss of normal plasma cells causes hypogammaglobulinemia and infection risk — while the T-cell-redirecting approaches add cytokine release syndrome and neurotoxicity.

Two features complicate the picture, both traceable to the receptor's biology. Gamma-secretase cleaves BCMA from the cell surface, lowering the density of target available to a CAR or bispecific while releasing a soluble form (sBCMA) that circulates and can absorb the drug as a decoy; the same soluble protein is a useful pharmacodynamic and disease-monitoring biomarker, and gamma-secretase inhibitors are being combined with BCMA-directed agents to raise surface expression. Relapse frequently occurs with antigen loss, including biallelic deletion of TNFRSF17, which has prompted dual-targeting constructs directed at BCMA together with a second plasma cell antigen.

Recent Publications Summary

Recent publications on BCMA focused largely on BCMA-directed therapies in relapsed/refractory multiple myeloma, including CAR T-cell products, bispecific T-cell engagers, and antibody-drug conjugates. A phase 1 study of durcabtagene autoleucel, a rapidly manufactured BCMA-directed CAR T-cell therapy, reported successful manufacturing in all 55 treated patients, a median vein-to-vein time of 24 days, an overall response rate of 98%, a stringent complete response rate of 55%, and minimal residual disease negativity in 80% of evaluable patients, with no unexpected safety findings 42202046May. In a separate phase 1/1b study, the BCMA-targeting bispecific T-cell engager pavurutamab showed an overall response rate of 46.5% across all treated patients and 65.8% at the recommended phase 2 dose, with cytokine release syndrome, cytopenias, and infections among the most common toxicities 41950113Apr. Belantamab mafodotin combined with carfilzomib, lenalidomide, and dexamethasone also showed promising activity in relapsed/refractory disease, with an overall response rate of 89.5% and manageable ocular toxicity in a small phase 1/2 study 41719502Feb.

Other studies examined BCMA-directed CAR T-cell therapy in different clinical settings. A phase 1 study of BCMA/CD19 dual-targeting CAR T-cell therapy (AZD0120) in older patients with newly diagnosed multiple myeloma reported that all eight treated patients achieved stringent complete response, with cytokine release syndrome occurring in half of patients and no immune effector cell-associated neurotoxicity syndrome observed 41925575Apr. Real-world and subgroup analyses also continued to evaluate approved BCMA-directed agents such as ciltacabtagene autoleucel and elranatamab, including earlier-line use of cilta-cel and outcomes in BCMA-naive patients treated with elranatamab 42163304May42159085May. Preclinical work further suggested that targeting CD74 may mitigate immune-escape features and enhance BCMA CAR-T activity in relapsed/refractory multiple myeloma models 42134899May, while endogenous CD28 signaling was shown to support persistent CAR T-cell activity in myeloma and lymphoma models, with effects on proliferation, mitochondrial metabolism, and inflammatory cytokine release in the tumor microenvironment 41627211Feb.

BCMA was also studied as a biomarker and imaging target. An LC-MS/MS assay was developed to quantify total soluble BCMA in human serum in the presence of natural and therapeutic ligands, with the goal of improving measurement of disease burden and monitoring during anti-BCMA therapy 41880915Mar. In a separate preclinical imaging study, the extracellular domain of BCMA was repurposed as a molecular recognizer to detect BCMA CAR-positive lymphoma using a novel PET/MR probe, [68Ga]Ga-BCMA-NOTA, which showed nanomolar affinity for the BCMA CAR scFv and specific uptake in BCMA CAR-positive tumors 42207978May. Outside oncology, teclistamab, a BCMA-directed bispecific T-cell engager, was reported to produce rapid clinical and electrophysiologic improvement in two patients with treatment-refractory autoimmune neuropathy, accompanied by reductions in serum neurofilament levels and disappearance of IgM kappa paraprotein or high-titer MAG antibodies during follow-up 42218153May.

What Changes, What Holds

1. BCMA-directed therapy is now supported by stronger efficacy signals but still carries class-limiting toxicities
REINFORCES Rapidly manufactured CAR T cells, a BCMA bispecific, and a combination with belantamab mafodotin all extend the already established therapeutic case for BCMA in relapsed/refractory multiple myeloma, rather than changing what BCMA is used for 42202046May41950113Apr. What these studies add is practical confidence that the target remains highly actionable across modalities, while also reminding readers that cytokine release syndrome, cytopenias, infections, and ocular toxicity remain part of the tradeoff.

2. BCMA targeting is moving earlier and broader, but the core therapeutic role remains unchanged
REINFORCES Dual-target CAR T-cell therapy in newly diagnosed disease and real-world analyses of approved agents in earlier-line or BCMA-naive settings broaden the clinical settings in which BCMA-directed treatment is being tested, yet they do not overturn the baseline account of BCMA as a plasma-cell target in myeloma 41925575Apr42163304May. The more interesting implication is that the field is now probing whether the same biology can be leveraged sooner, in different combinations, and against escape mechanisms, rather than redefining BCMA itself.

3. BCMA is becoming a measurement and imaging tool as well as a therapeutic target
METHOD The new assay and PET/MR probe do not alter the biological role of BCMA described in the Overview; they change how BCMA and BCMA-directed therapy can be tracked, quantified, and visualized 41880915Mar42207978May. That makes this paragraph a methodological expansion: soluble BCMA measurement may become more robust during anti-BCMA treatment, and BCMA-based imaging may help study CAR-positive disease, but these are tools layered onto the existing target biology. Outside oncology, the autoimmune neuropathy report is a separate use case that the baseline does not address.