For patients with relapsed or refractory multiple myeloma (RRMM) complicated by true extramedullary disease (EMD) – defined as non-contiguous soft-tissue plasmacytomas [ 1 ] – outcomes remain poor [ 2 , 3 ]. Conventional salvage regimens yield response rates below 25%, and even modern T-cell redirecting monotherapies have shown limited efficacy. In the MajesTEC-1 trial, teclistamab (BCMA-targeted) achieved an overall response rate (ORR) of 48% in EMD patients versus 66% in those without [ 4 ]. Similarly, talquetamab (GPRC5D-targeted) in MagnetisMM-3 gave an ORR of 56% in EMD [ 5 ]. BCMA CAR T-cell therapy (ide-cel) has also shown reduced activity in EMD [ 6 ]. The suboptimal performance of single-target immunotherapies likely reflects tumor heterogeneity, antigen escape, and an immunosuppressive niche.
Against this backdrop, the phase 2 RedirecTT-1 study by Kumar et al. (N Engl J Med, 2026) evaluating dual talquetamab plus teclistamab represents an important advance [ 7 ]. Rather than treating this as a simple potency enhancement, we argue that the success of dual targeting in EMD provides clues to overcoming resistance mechanisms – which we present below as testable hypotheses. To provide a biological foundation, it is useful to recall the mechanism of action of these agents. Talquetamab and teclistamab are bispecific T-cell-redirecting antibodies that simultaneously bind CD3 on T cells and tumor-associated antigens (GPRC5D or BCMA, respectively) on malignant plasma cells. This dual engagement promotes the formation of a cytolytic immune synapse, resulting in T-cell activation, cytokine release, and targeted killing of myeloma cells via perforin- and granzyme-mediated cytotoxicity [ 4 , 5 , 7 ]. Understanding this mechanism is essential for interpreting the potential advantages of dual targeting.
Key findings and translational implications for clinical practice
The RedirecTT-1 trial showed that concurrent GPRC5D and BCMA targeting induced deep and durable responses in true extramedullary myeloma [ 7 ]. In a single-arm design with centralized imaging, the combination yielded an ORR of 79%, with 54% achieving complete response or better. Median progression-free survival was 15.4 months, and 12-month PFS was 61%. While these results compare favorably with historical data from monotherapy trials in EMD, it is important to note that cross-trial comparisons are inherently unreliable due to differences in patient populations, entry criteria, and supportive care. The single-arm design does not permit definitive conclusions about superiority over sequential or single-agent approaches. Nonetheless, responses occurred even in patients previously treated with BCMA-directed CAR T or bispecific antibodies, suggesting non-overlapping resistance pathways. The trial also included non-secretory disease patients, broadening applicability.
From a translational and clinical standpoint, these findings compel a re-evaluation of how we sequence and combine immunotherapies for high-risk EMD. First, the depth of responses observed in patients with prior BCMA exposure challenges the notion of complete resistance to BCMA-directed therapy after failure of a BCMA-targeted agent, suggesting that GPRC5D engagement may restore or complement anti-tumor activity. Second, the high CR rate of 54% raises the possibility that dual targeting could deepen responses to the point where consolidative strategies, such as transplantation, may become reconsidered or even supplanted in this subset. Third, the impressive activity in non-secretory disease—a historically neglected population—provides a practical salvage option where traditional response monitoring is challenging. These observations suggest that EMD should no longer be viewed as uniformly terminal, but as a potential indication for combination immunotherapy. However, institutions must prepare for toxicities: cytokine release syndrome (all grades 76%, grade 3-4 6%), infections (grade 3-4 31%, with five infection-related deaths), and GPRC5D-related oral/cutaneous effects (mostly grade 1-2) [ [7] , [8] , [9] ]. The infection rate, in particular, signals that this regimen is not simply a more potent version of monotherapy but a qualitatively different immunosuppressive challenge, demanding enhanced supportive care protocols and perhaps prophylactic antimicrobial strategies beyond current standards.
Mechanistic hypotheses: how dual targeting might overcome resistance in EMD
The improved efficacy of GPRC5D+BCMA co-targeting in EMD observed in the RedirecTT-1 trial is likely multifactorial. Below we outline three mechanistic hypotheses. None of these are proven by the current trial, and the wording is deliberately framed as speculative rather than causal. Each can be tested in future correlative studies ( Fig. 1 ).
Raising the genetic barrier to antigen escape. EMD lesions harbor greater clonal diversity than bone marrow-confined disease. Single-antigen targeting exerts selective pressure leading to outgrowth of antigen-low or antigen-negative subclones – well documented with BCMA-directed therapies [ [4] , [5] , [6] ]. By engaging two independent, highly expressed antigens on overlapping tumor cell populations, dual targeting would require simultaneous loss or downregulation of both antigens for escape – a statistically rare event. This could explain the high CR rates even after prior BCMA exposure. Supporting this hypothesis, preclinical models of dual-targeted CAR T cells (e.g., against CD19 and CD22 in B-cell malignancies) have shown reduced antigen escape [Zhao et al., Nat Med 2021]. Although direct evidence in myeloma is lacking, similar principles likely apply. Testable prediction: In relapsed lesions after dual targeting, we would expect rare co-loss of BCMA and GPRC5D, whereas after monotherapy, single antigen loss should predominate. Single-cell RNA-seq of paired pre-treatment and relapse biopsies would be informative.
Enhancing immune synapse quality and overcoming T-cell fitness defects. Simultaneous engagement of two antigens on the same tumor cell might lead to more stable immunological synapse formation, stronger T-cell activation, and more potent degranulation. This could be especially relevant in the EMD microenvironment, which is often T-cell-poor or contains exhausted T cells. Preclinical evidence indicates that bispecific antibodies with higher avidity due to dual antigen binding can enhance synapse stability and reduce the activation threshold [Bacac et al., Clin Cancer Res 2016]. Testable prediction: Ex vivo co-culture assays with EMD-derived tumor cells and autologous T cells would show higher synapse stability (e.g., by imaging) and greater cytotoxic activity when both BCMA and GPRC5D are targeted versus either alone.
Mitigating T-cell exhaustion. Continuous exposure to a single T-cell engager can drive terminal exhaustion. By distributing signaling across two antigens, dual targeting might allow efficient tumor killing at lower per-antigen activation intensity. Moreover, activity against BCMA-negative cells via GPRC5D could preserve a pool of functional T cells not chronically stimulated by persistent BCMA-low disease. In support of this concept, studies of dual-targeting CAR T cells have demonstrated preserved TCF-1+ stem-like memory T cells and reduced expression of exhaustion markers compared to single targeting [Fry et al., Blood 2018]. Testable prediction: Longitudinal T-cell phenotyping (e.g., PD-1, TIM-3, TCF-1) in patients receiving dual vs. sequential monotherapy would show less accumulation of exhausted subsets and retention of stem-like memory T cells with dual targeting.
These hypotheses provide a framework for why this combination might outperform sequential monotherapy, but they require dedicated translational studies. Until such data emerge, the proposed mechanisms remain speculative.
Dosing, schedule, and infection risk: A practical dilemma
A critical barrier is the toxicity profile, particularly infections. In RedirecTT-1, grade 3–4 infections occurred in 31%, with five infection-related deaths. This reflects profound immunosuppression from T-cell redirection, prior lines of therapy, and disease-related immune dysfunction. Other notable toxicities included cytokine release syndrome (grade 3–4, 6%) and GPRC5D-related oral mucositis and nail disorders (mostly low-grade). Thus, when we refer to "toxicity", we specifically mean the high rate of serious infections as well as CRS and mucosal side effects. The trial allowed a switch to monthly dosing after response – an opportunity not fully discussed in the original commentary. We believe reduced-intensity maintenance (e.g., monthly talquetamab+teclistamab after ≥3 months of response) could potentially lower infection risk while preserving efficacy. This is a key practical question for future studies: prospective dose-de-escalation or interval prolongation trials should be designed, with close monitoring of minimal residual disease and infection rates. Until then, mandatory antimicrobial prophylaxis and routine IVIG replacement are essential [ 8 , 9 ].
Limitations and future directions
The single-arm design, exclusion of CNS disease/plasma cell leukemia, and short follow-up (median 12.6 months) limit generalizability [ 7 ]. Moreover, the comparison with historical monotherapy outcomes is not definitive; the apparent superiority of dual targeting could be influenced by patient selection, changes in supportive care, or publication bias. A randomized phase 3 trial (e.g., MonumenTAL-6) is awaited. High cost may restrict access. Moving forward, we need:
Predictive biomarkers: Patients with high-risk cytogenetics, bulky EMD, or prior BCMA failure may derive greatest benefit. Conversely, those with indolent disease or pre-existing immunocompromise might be better served by sequential therapy to preserve T-cell fitness.
Optimal sequencing relative to CAR T : Concurrent dual T-cell engagers might exhaust T cells and compromise subsequent CAR T efficacy – an open question.
Confirmatory phase 3 data .
Table 1 summarizes efficacy and safety across monotherapy and dual therapy. Note that cross-trial comparisons are shown for illustrative purposes only and should not be interpreted as evidence of superiority. ( Table 1 ).
Table 1
Comparison of single-agent vs. dual-targeting bispecific antibodies in extramedullary myeloma.
*Note: EMD-specific infection rates not uniformly reported; dual-therapy data from RedirecTT-1. Standard care (e.g., conventional chemotherapy) ORR <25% not shown due to lack of recent EMD-specific trial.*.
| Regimen | Target(s) | ORR (EMD) | CR rate (EMD) | Grade 3-4 infections | Key trial (EMD subset) |
| Teclistamab monotherapy | BCMA | 48% | ∼25% | Not reported separately | MajesTEC-1 (Moreau et al.) |
| Talquetamab monotherapy | GPRC5D | 56% | ∼30% | ∼20% (overall) | MagnetisMM-3 (Chari et al.) |
| Talquetamab + teclistamab | BCMA + GPRC5D | 79% | 54% | 31% | RedirecTT-1 (Kumar et al.) |
Conclusion
The RedirecTT-1 study opens a new avenue for treating extramedullary myeloma. Dual targeting of BCMA and GPRC5D produces response rates that compare favorably with historical monotherapy data, but the high infection risk demands careful patient selection and supportive care. The mechanistic hypotheses outlined here – antigen escape barrier, synapse enhancement, exhaustion mitigation – remain speculative and await formal testing. We urge the inclusion of correlative studies (serial T-cell phenotyping, single-cell genomics of relapsed lesions) in future trials. Only then can we move from empirical combination to precision immunotherapy for this high-risk population.
Ethical statement
As this article is a commentary on published clinical trial data and does not involve original research with human participants, patient data, or animal subjects, no ethical approval was required.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
CRediT authorship contribution statement
Shiqiong Zhou: Writing – review & editing, Writing – original draft, Conceptualization. Qinghua Ke: Writing – review & editing, Writing – original draft, Conceptualization.
Declaration of competing interest
We declare no competing interests. All authors had full access to the complete data of the study and took final responsibility for the decision to submit the manuscript for publication. Data and codes are available from the corresponding author upon reasonable request.
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