Next-generation T cell engagers in oncology: Pharmacologic evolution from bispecific to trispecific antibodies

Abstract

Recent advances in immuno-oncology have led to the development of innovative T cell–engaging therapies, transforming the treatment landscape for hematologic and solid malignancies. Bispecific T cell engagers (BiTEs) have demonstrated clinical efficacy by redirecting T cell cytotoxicity toward tumor cells, yet challenges such as antigen escape, safety concerns, and limited durability remain. Building on the foundation established by BiTEs, the emergence of trispecific T cell engagers promises enhanced tumor selectivity, improved pharmacodynamic profiles, and potentially superior clinical outcomes. This minireview summarizes the pharmacology of T cell engagers, with a focus on the mechanistic evolution from BiTEs to next-generation trispecific antibodies. We highlight recent advances in molecular design, summarize current clinical evidence, and address ongoing challenges in drug development and safety. By critically synthesizing the latest preclinical and clinical findings, this review aims to inform future research directions and optimize the clinical translation of next-generation T cell–engaging therapeutics.

Significance Statement

This minireview synthesizes current knowledge on the pharmacology of T cell engagers, spotlighting the shift from bispecifics to trispecifics, and provides insights essential for advancing safer and more effective immunotherapies in oncology.

1. Introduction

Over the past decade, cancer treatment has undergone a transformative shift, driven by advances in immunotherapy that uses the body’s immune system to recognize and eradicate malignant cells. Despite this progress, cancer remains a leading cause of morbidity and mortality worldwide, with 611,720 cancer-related deaths in the United States alone in 2024.¹ Traditional cytotoxic chemotherapy and radiation therapies, while effective for some, are often limited by toxicity and the development of resistance, highlighting the urgent need for novel, targeted approaches to improve outcomes for patients with both hematologic and solid tumors.²

The introduction of immune checkpoint inhibitors (ICIs) and chimeric antigen receptor (CAR) T cell therapies has marked a new era in oncology, enabling durable responses in previously refractory cancers.^3,4 Checkpoint blockade has revolutionized the management of melanoma, lung cancer, and other malignancies, with over 50 US Food and Drug Administration approvals since 2011, with the first T cell–redirecting antibody being catumaxomab, a trifunctional antibody (EpCAM × CD3), being approved in 2009 in the European Union.^5,6 Similarly, CAR-T cell therapies have achieved impressive remission rates in relapsed/refractory (R/R) hematologic malignancies yet are associated with manufacturing challenges, high costs, and unique toxicities.⁷ Building on these advances, T cell engagers have emerged as a promising class of “off-the-shelf” immunotherapies that redirect endogenous T cells toward tumor cells.

Bispecific T cell engagers (BiTEs) have demonstrated clinical efficacy by redirecting T cells to target and eliminate malignant cells, establishing a new standard for immunotherapeutic interventions. However, their broader impact has been constrained by challenges including antigen escape, cytokine-release syndrome, neurotoxicity, and limited durability of response. In response to these limitations, next-generation trispecific antibodies are being developed to further refining immune activation, enhancing tumor selectivity, and improving pharmacodynamic profiles through simultaneous engagement of multiple antigens. This review explores the historic approvals of BiTE therapy and indications, its pharmacokinetic and pharmacodynamic characteristics, and the pharmacologic evolution from BiTEs to trispecific T cell engagers (TriTEs), with recent advances in molecular design and clinical evidence and future directions for advancing the safety and efficacy of T cell engager therapies in oncology.

2. Approvals and history

BiTE therapy has revolutionized cancer immunotherapy by redirecting T cells to eliminate malignant cells through dual-targeting antibodies. Once candidates are optimized, early-phase trials evaluate safety, dosing, and efficacy. The first and most established BiTE was blinatumomab (Blincyto; Amgen Inc), targeting CD19 on B-cell malignancies and CD3 on T cells. Blinatumomab’s approval was supported by the TOWER trial (NCT02013167), which demonstrated superior overall survival than standard chemotherapy in patients with R/R B-ALL.^8,9 In 2022, tebentafusp (Kimmtrak; Immunocore Limited), which targets HLA-A2 and CD3, became the first approved treatment for unresectable or metastatic uveal melanoma¹⁰ and teclistamab (Tecvayli; Janssen Biotech, Inc), a B-cell maturation antigen (BCMA) × CD3 bispecific antibody, for R/R multiple myeloma (MM),¹¹ and it is an National Comprehensive Cancer Network guidelines included option¹² for the management of patients with MM and exposed to at least 3 drug classes, having achieved a 63% overall response rate and a median duration of response of 18 months in the phase-II MajesTEC-1 trial. Following these approvals, in 2023, mosunetuzumab (Lunsumio; Genentech, Inc) was approved for R/R follicular lymphoma showing durable remissions at the 3-year follow-up,¹³ in addition to approvals for heavily pretreated diffuse large B-cell lymphoma such as epcoritamab (Epkinly; Genmab US, Inc, Abbvie Inc), which produced a 63% response rate and a 40% complete-response rate in the EPCORE NHL-1 study,¹⁴ and glofitamab (Columvi; Genentech Inc), with complete response in one-third of patients in the NP30137 trial. Despite a heavily pretreated cohort, all 3 drugs target CD20 × CD3.14, 15, 16 Elranatamab (Elrexfio; Pfizer Inc), a bispecific BCMA-directed CD3 T cell engager developed for R/R MM, was granted approval in August 2023 after showing promising response rates, with further global regulatory reviews and clinical trials ongoing.¹⁷ Additionally, in 2023, talquetamab (Talvey; Janssen Biotech, Inc), targeting GPRC5D and CD3, was approved for heavily pretreated R/R MM,¹⁸ and most recently, in 2024, tarlatamab (Imdelltra; Amgen Inc), a DLL3 × CD3 bispecific antibody, received approval for adults with extensive-stage small-cell lung cancer, who have progressed after platinum-based chemotherapy.¹⁹ Beyond hematologic cancers, next-generation BiTEs are under investigation in solid tumors. For instance, AMG 160, a half-life–extended (HLE) BiTE targeting prostate-specific membrane antigen (PSMA) in metastatic castration-resistant prostate cancer, has shown prostate-specific antigen reductions and disease stabilization in early trials.²⁰ Similarly, REGN4018, which targets MUC16 in ovarian cancer, and AMG 757, targeting DLL3 in small-cell lung cancer, are in development, highlighting the broadening scope of BiTE applications.^21,22 However, even with the immense progress and impact that the development of these drugs are seeing, patients receiving them are still facing multiple challenges in terms of toxicity, infusion, and resistance, which eventually lead to the quest for developing next-generation BiTE formats, including HLE constructs and trispecific, tetraspecific, and checkpoint-fused engagers, which aim to improve efficacy, safety, and durability. Collectively, BiTE therapy represents a rapidly evolving therapeutic class, with multiple approvals transforming hematologic cancer treatment and ongoing research with efforts striving to expand its impact to solid tumors. A summary of current approved BiTEs and their indications are presented in Table 1.

Table 1.

Bispecific T cell engagers and their targets, indications, approval year, and key trials

Drug Name	Targets (Tumor × CD3)	Indication	Approval Year	Key Trial and Outcome
Blinatumomab (Blincyto; Amgen Inc)	CD19 × CD3	R/R B-cell ALL	2014	TOWER trial: improved OS vs chemotherapy; CR rates, 34%–44%8
Tebentafusp (Kimmtrak; Immunocore Limited)	gp100 × CD3 (HLA-A2)	Metastatic uveal melanoma	2022	Phase 3: improved OS vs investigator’s choice10
Teclistamab (Tecvayli; Janssen Biotech, Inc)	BCMA × CD3	R/R multiple myeloma	2022	MajesTEC-1: 63% ORR; median DOR, 18 mo11
Mosunetuzumab (Lunsumio; Genentech, Inc)	CD20 × CD3	R/R follicular lymphoma	2023	3-y remission durability15
Epcoritamab (Epkinly; Genmab US, Inc, Abbvie Inc)	CD20 × CD3	R/R DLBCL	2023	EPCORE NHL-1: 63% ORR; 40% CR rate14
Glofitamab (Columvi; Genentech Inc)	CD20 × CD3	R/R DLBCL	2023	NP30137: ∼33% CR rate in heavily pretreated patients16
Elranatamab (Elrexfio; Pfizer Inc)	BCMA × CD3	R/R multiple myeloma	2023	Phase 2: promising response rates17
Talquetamab (Talvey; Janssen Biotech, Inc)	GPRC5D × CD3	R/R multiple myeloma	2023	Phase 2: activity in triple-class exposed MM18
Tarlatamab (Imdelltra; Amgen Inc)	DLL3 × CD3	Extensive-stage small-cell lung cancer	2024	Phase 2: activity after platinum chemotherapy19

CR, complete remission; DLBCL, diffuse large B-cell lymphoma; DOR, duration of response; ORR, overall response rate; OS, overall survival.

3. Bispecific T cell engager therapy in cancer

3.1. Mechanism of action and design

BiTEs are a class of immunotherapeutic agents designed to harness the cytotoxic potential of T cells by physically linking T cells to tumor cells, triggering T cell activation, immune synapse formation, and tumor cell lysis without the need for antigen presentation or costimulation.²³ By physically bridging T cells and tumor cells, a BiTE forces formation of an artificial immune synapse that closely mimics physiologic T cell–antigen-presenting cell interactions. CD3 clustering launches a sequential signaling cascade through Lck, ZAP-70, and LAT/SLP-76, which drives calcium influx and cytoskeletal polarization and ultimately directs the exocytosis of perforin and granzymes into the tumor membrane.²⁴ Because this process is independent of major histocompatibility complex and costimulation, BiTEs can redirect any resting T cell, whether naïve, memory, or exhausted, against tumor targets regardless of their antigen-presentation status or PD-L1 expression.²⁵ In the case of blinatumomab, the small (≈55 kDa) Fc-less scaffold diffuses readily through solid-tumor stroma and enables serial killing, allowing a single cytotoxic T cell to lyse multiple tumor cells in succession before undergoing activation-induced cell death or exhaustion.²⁶ Collectively, these properties confer potent, rapid antitumor activity that is orthogonal to both conventional monoclonal antibodies (which rely on Fc-mediated effector functions) and CAR-T cells (which require genetic manipulation, manufacturing time, and in vivo expansion).

BiTEs are typically composed of 2 single-chain variable fragments connected via a flexible linker: one targeting a T cell–specific antigen (most commonly CD3) and the other targeting a tumor-specific antigen such as CD19, BCMA, or PSMA. This format enables proximity-driven T cell activation and cytotoxicity.²⁷ The development of BiTEs typically began with preclinical studies using humanized mouse models or in vitro coculture systems. These studies assessed cytotoxicity, cytokine production, and T cell activation.^23,28

One important concept in the design of BiTEs is affinity balancing, where the 2 arms are constructed with different binding affinities: the tumor-targeting arm is engineered to have high affinity, often in the nanomolar or subnanomolar range to ensure sustained and selective binding to malignant cells, and in contrast, the CD3-binding arm is intentionally designed with lower affinity, usually in the micromolar range, to reduce nonspecific activation of T cells in the absence of tumor cells.²⁹ This differential affinity is crucial because overly strong CD3 binding can cause excessive or premature T cell activation, leading to increased cytokine release, off-tumor toxicity, and reduced therapeutic window.³⁰

Although BiTEs do not replace CAR-T cell therapy, they offer notable practical advantages, particularly in terms of cost and safety. BiTE therapies represent off-the-shelf biologics produced through standardized antibody-manufacturing processes, thus avoiding the patient-specific cell engineering and lengthy production timelines that substantially increase costs associated with CAR-T therapies.³¹ Additionally, CAR-T cell therapies have raised concerns related to insertional mutagenesis and the rare but serious risk of secondary T cell malignancies, such as T cell lymphomas, driven by genetic modifications or unintended genomic integrations.³² In contrast, BiTE therapies uses endogenous T cells without genetic manipulation, thereby eliminating risks associated with insertional oncogenesis and significantly reducing complexity and cost. This distinction positions BiTEs as economically viable and potentially safer immunotherapeutic alternatives to CAR-T cell therapies, particularly in resource-constrained or broader clinical settings. However, differences are still remarkable in terms of efficacy; although CAR-T therapy showed an 81% complete remission rate in the ELIANA trial, which focused on pediatric and young adult population, most of which were negative for minimal residual disease and durable beyond a year,³³ the TOWER study of blinatumomab, which was conducted exclusively in adults over 18 years, reported only 34%–44% complete remissions after a 28-day continuous infusion, with median remissions lasting 7 months.⁸ This shows that although BiTE may be better from a safety standpoint, efficacy remains a potential concern when compared with CAR-T therapy and should be a motive to develop more efficient agents.

3.2. Pharmacokinetics

Pharmacokinetically, BiTEs differ sharply from full-length IgG antibodies. Agents such as blinatumomab are given by continuous intravenous infusion and thus reach 100% systemic availability, whereas Fc-extended, subcutaneous formats (eg, teclistamab) attain peak serum levels 12–24 hours postdose, with approximately 72% bioavailability.³⁴ Because their molecular sizes cluster near plasma proteins (≈55 kDa for Fc-less BiTEs; ≈150 kDa after Fc fusion) and they bind avidly to circulating targets, volumes of distribution (Vd) remain close to blood volume (blinatumomab Vd ≈ 4.5 L).³⁵ Similar to other therapeutic proteins, BiTEs undergo intracellular lysosomal degradation rather than cytochrome P450–mediated metabolism Fc-less molecules that fall below the renal cutoff and are freely filtered, and clear rapidly, blinatumomab’s terminal t_½ is approximately 2 hours.³¹ In contrast, albumin hitchhiking trispecific constructs such as HPN328 (DLL3 × albumin × CD3) achieve linear kinetics with serum half-lives of 78–187 hours, enabling weekly or less-frequent outpatient dosing.³⁶ Given the nature of T cell engagers that bind to target cells, which include immune cells, and in the case of BiTEs that engage with high affinity to 2 targets, Schropp et al³⁷ developed a comprehensive model for bispecific antibodies that accounts for multiple binding events, complex internalization, and target turnover.³⁷ This leads to a phenomenon, known as target-mediated drug disposition, which is a phenomenon that occurs when a drug binds with high affinity to a specific biological target, and this binding significantly influences how the drug is distributed and cleared from the body. At low doses, clearance is often rapid because target-mediated drug disposition dominates; as target sites saturate at higher doses, clearance slows and pharmacokinetics can appear more linear.³⁷ A summary of pharmacokinetic characteristics of approved BiTEs is presented in Table 2.38, 39, 40, 41, 42, 43, 44, 45, 46

Table 2.

Pharmacokinetics of approved bispecific T cell engagers

Drug (Brand)	Route of Administration	Vd (L)	Clearance (CL)	Half-life
Blinatumomab (Blincyto; Amgen Inc)38	Continuous IV infusion	∼4.5	22.3 ± 5 L/day per square meter	∼2.1 h
Tebentafusp (Kimmtrak; Immunocore Limited)39	IV bolus	∼7.56	∼16.4 L/day	∼7.5 h
Teclistamab (Tecvayli; Janssen Biotech, Inc)40	SC	∼5.63	∼0.47 L/day	∼3.8 days (first IV dose)
Mosunetuzumab (Lunsumio; Genentech, Inc)41	IV	∼5.49	∼1.08 L/day (steady state); 0.584 L/day (baseline)	∼16.1 days (steady state)
Epcoritamab (Epkinly; Genmab US, Inc, Abbvie Inc)42	SC	∼25.6	∼0.53 L/day	∼22 days
Glofitamab (Columvi; Genentech Inc)43	IV	∼3.33 (central); ∼2.18 (peripheral)	∼0.396 L/day	4–8 days
Elranatamab (Elrexfio; Pfizer Inc)44	SC	∼7.76	∼0.324 L/day	∼22 days
Talquetamab (Talvey; Janssen Biotech, Inc)45	SC	∼10.1	∼0.9 L/day	∼8.4 days (first dose); ∼12.2 days (steady state)
Tarlatamab (Imdelltra; Amgen Inc)46	IV	∼8.6	∼0.65 L/day	∼11.2 days

IV, intravenous; SC, subcutaneous.

3.3. Toxicities and side effects of BiTEs

Despite their therapeutic promise, BiTEs exhibit a characteristic toxicity profile dominated by fever, neutropenia and thrombocytopenia. However, 2 main syndromes could potentially result from T cell engagers and constitute a real threat for patient safety: cytokine-release syndrome (CRS) and neurotoxicity. CRS typically emerges during the first step-up or full-dose infusion, when rapid, systemic T cell activation triggers high circulating interleukin 6, interferon gamma, and tumor necrosis factor α. In the registrational blinatumomab studies, any-grade CRS occurred in ≈25%–30% of adults and up to 80% of pediatric patients, with grade ≥3 events in 3%–5% and rare fatal cardiac or respiratory collapse.^47,48 Second-generation bispecifics show similarly high incidence but generally lower severity: in the pivotal MajesTEC-1 trial of teclistamab, 72% of patients experienced CRS, almost all grades 1 and 2 and only 1 grade 3, with more than 90% of episodes restricted to the first cycle after step-up dosing.⁴⁹ Premedication with prednisone or dexamethasone before the first dose and step-up dosing is recommended to reduce inflammatory reactions and the risk of CRS.²³

Immune effector cell–associated neurotoxicity syndrome is another potential side effect, with symptoms including confusion and encephalopathy. Immune effector cell–associated neurotoxicity syndrome is less common but clinically significant; recent real-world analyses report neurologic symptoms (eg, headache, aphasia, encephalopathy, and tremor) in 30%–60% of blinatumomab-treated patients, although grade ≥3 events remain below 5%.⁵⁰ To reduce off-tumor toxicity, newer BiTE formats use protease-activated or tumor-selective designs that become functional only within the tumor microenvironment.⁵¹

3.4. Current challenges of BiTE therapies and innovations

Initial BiTEs, such as blinatumomab, consist of 2 single-chain variable fragments linked in tandem without an Fc region; the resulting is a small 55-kDa molecule, which places these molecules under the filtration threshold and thus results in a clearance within 2 hours. Second, the absence of an Fc domain prevents interaction with neonatal Fc receptor, a receptor that rescues IgG antibodies from lysosomal degradation and recycles them back into circulation.³¹ This rapid clearance poses a challenge for patients receiving these treatments and imposes a 28-day continuous intravenous infusion to maintain cytolytic activity.^8,23 To overcome this constraint, HLE BiTEs incorporate either an Fc domain that engages neonatal Fc receptor recycling, lengthening serum t_½ to several days and enabling once-weekly or twice-monthly dosing. The PSMA-directed HLE BiTE acapatamab (AMG 160) uses an engineered IgG1 Fc and achieves sustained exposure with weekly administration in metastatic castration-resistant prostate cancer, where it has produced prostate-specific antigen declines and radiologic responses in early-phase trials.²¹ Collectively, these iterations demonstrate that BiTE architecture is no longer monolithic; instead, it is an adaptable scaffold whose pharmacology can be tuned by Fc engineering or subcutaneous formulation to better align efficacy with safety and patient convenience.

One additional obstacle that patients might face is the development of resistance to treatment, which extends beyond simple downregulation, involving complex intrinsic mechanisms within tumor cells that compromise their susceptibility to T cell–mediated killing. For example, in the study by Shen et al in 2022,⁵² genome-wide CRISPR screening in mice showed that the loss of critical costimulatory ligands, such as CD58, significantly diminishes BiTE efficacy by disrupting essential T cell–activation signals via the CD2–CD58 axis. This poses a real challenge for patients with advanced cancers to whom BiTE therapy was offered after R/R disease, decreasing the available courses of treatment of these patients. Strategies to counter resistance are being studied, and most involve combination of BiTE with additional therapies. One major combination is with ICIs, targeting pathways that mediate T cell exhaustion, and thus avoiding the linkage of tumoral cells with exhausted T cells, thus preventing dampened responses.⁵³ Additionally, other mechanisms contribute to treatment resistance, such as tumor antigen heterogeneity, especially seen in solid tumors and arises due to clonal evolutions, epigenetic modifications, and selective pressures from the tumor microenvironment. Other mechanisms include tumor antigen loss, lineage switch, gene expression shift, and posttranslational modifications.⁵⁴ Major mechanisms of T cell engagers’ resistance are showcased in Fig. 1.

Fig. 1.

Major mechanisms of treatment resistance to T cell engagers. (A) Tumor antigen heterogeneity. (B) Tumor antigen loss. (C) Lineage switch. Created in BioRender. Nahle T. (2025) https://BioRender.com/kc28yl3.

To address off-tumor toxicity concerns associated with systemic T cell activation, newer-generation BiTE constructs incorporate conditional activation strategies, such as protease-activated or tumor-selective designs, enabling functionality primarily within the tumor microenvironment. These engineered BiTEs remain inactive (masked) while circulating systemically and undergo selective activation (unmasking) upon exposure to proteases highly expressed by tumor cells or the tumor stroma such as matrix metalloproteinases or cathepsins.⁵¹ One example would be CytomX’s CX-904, a probody therapy, in a phase 1 study (NCT05387265) in patients with advanced metastatic solid tumors, which frequently express epidermal growth factor receptor.⁵⁵ Upon proteolytic cleavage, these BiTE molecules undergo structural rearrangements that expose previously hidden antigen-binding domains, allowing selective T cell engagement specifically at tumor sites while minimizing engagement of healthy tissues. Preclinical data demonstrate that such conditionally activated formats significantly reduce systemic CRS and off-target toxicities compared with conventional BiTEs.⁵⁶

All these challenges and innovation to get around them is setting the stage for advancements toward safer, more convenient, and more effective treatments that could change the course of many diseases in oncology and offer new or alternative treatments for patients with cancer.

In summary, BiTEs represent a rapidly evolving class of immunotherapy with proven efficacy in B-ALL and growing potential in solid tumors. Innovations in constructing designs and combination regimens are expected to expand their role in future cancer treatment paradigms, with new molecules such as TriTEs being under development.

4. Trispecific T cell engagers in cancer

4.1. Mechanism of action and design

TriTEs were conceived to lift the 3 major constraints that limit first-generation bispecifics: continuous-infusion dosing, antigen-loss resistance, and modest activity in solid tumors.^38,57 By adding a third functional arm and reengineering molecular scaffolds, TriTEs aim to deliver longer exposure, prevent escape, and amplify T cell potency where BiTEs struggle.

TriTEs fall into 2 architectures: IgG-like formats retain an Fc (or albumin-binding) domain, extending serum half-life to several days and enabling weekly/biweekly dosing^58,59; and non-IgG formats are compact, Fc-less tandem–single-chain variable fragment chains that trade half-life for rapid tissue penetration and easier manufacturing. Each class balances stability, size, and manufacturability for specific clinical settings,⁶⁰ and both are engineered so the 3 epitopes can be engaged simultaneously without steric clash, preserving an optimal immune synapse geometry.⁵⁸

Every TriTE pairs 3 coordinated binding arms: first, a tumor-binding arm that binds to tumor-associated antigens such as CD38 in hematologic malignancies,^61,62 an effector T cell arm such as CD3,⁶³ and an add-value arm that binds to either a second tumor-associated antigens or a costimulatory receptor.

Building on recent structural innovations, advances such as Fc fusion and albumin-binding domains now extend TriTEs’ serum half-life to approximately 2–7 days, supporting convenient once-weekly or even less frequent outpatient dosings. For instance, the albumin-binding HPN328 (DLL3 × albumin × CD3) exemplifies this shift, showing linear pharmacokinetics, a mean half-life approaching 3 days, and early antitumor activity in the ongoing phase I/II study for DLL3-positive small-cell lung cancer and neuroendocrine tumors.⁶⁴ Costimulatory designs further intensify pharmacodynamics: the Fc-bearing IgG SAR442257 (CD38 × CD28 × CD3) induces superior granzyme-B release and tumor lysis in preclinical myeloma models, and its first-in-human trial (NCT05912081) has already reported objective responses with predominantly grade 1–2 CRS at submicrogram-per-kilogram doses.^65,66 Additional hematologic programs include Harpoon’s HPN217 (BCMA × albumin × CD3)⁶⁷ and Johnson & Johnson’s dual-antigen BCMA × GPRC5D × CD3 IgG (JNJ-5322),⁶⁸ both of which are delivering very good partial responses or better in R/R MM cohorts, in addition to Sanofi/Innate’s NK cell–redirecting IPH6101/SAR443579 (CD123 × NKp46 × CD16), which has achieved 5 complete remissions of 15 initial patients (33.3%) in acute myeloid leukemia at its target 1 mg/kg dose.^69,70

Solid tumor development similarly shows some advancements in the TriTE domain, with prostate cancer efforts feature the first-in-class TriTAC HPN424 (PSMA × albumin × CD3).⁷¹ Preclinical platforms are already layering in 4-1BB costimulation, as illustrated by IMT030122 (EpCAM × 4-1BB × CD3), which eradicated colorectal cancer xenografts, while attenuating cytokine release.⁷² Collectively, more than 20 trispecific antibodies are now in active or announced clinical trials spanning MM, acut myeloid leukemia/ myelodysplastic syndrome, small-cell lung cancer, prostate cancer, colorectal cancer, and glioblastoma, underscoring rapid maturation from proof-of-concept to broad translational exploration.⁷³ If ongoing studies confirm their superior exposure, escape resistance, and built-in costimulatory control, TriTEs are poised to extend off-the-shelf T cell redirection beyond hematology and to serve as rational backbones for combination regimens in solid tumor oncology.

One potential advantage that TriTEs hold against BiTEs is the escape-proof dual-antigen designs, where 2 different tumoral antigens are targeted, preventing treatment escape. An example of that woud be JNJ-79635322 (BCMA × GPRC5D × CD3), which binds simultaneously to 2 myeloma antigens and curbs antigen-loss relapse, with objective responses being already yielded in patients with heavily pretreated MM.⁶⁸

The question remains whether these molecules have the capacity to surpass the efficacy of BiTEs in the treatment of cancer. A recent study by Passariello et al in 2025⁶³ compared the efficacy of a series of TriTEs, called 53X triodies, which bind 5T4 on the tumor; CD4 on the T cell; and PD-1 in 53D, PD-L1 in 53L10, or LAG-3 in 53G, to their equivalent in BiTE plus an ICI in mice with human tumor xenografts (human A-549 lung carcinoma cells plus activated human peripheral blood mononuclear cells). TriTE therapy showed superior results than their respective ICI, alone or in combination with BiTEs.

4.2. Innovations and future directions

Even with many TriTEs being under development and no single agent being approved to this day, multiple attempts are being made to add to the innovation of these promising drugs, with recent engineering breakthroughs pushing the envelope further. Nanobodies (Nbs) are a unique class of antibody fragments, with a small size of approximately 15 kDa, and are derived from camelid heavy-chain only antibodies.⁷⁴ Ding et al⁷⁵ successfully developed a novel Nb-TriTE (fibroblast activation protein × CD3 × PD-1), which remains inactive until it encounters cancer-associated fibroblasts and coinhibitory PD-1 signals within the tumor niche, with fibroblast activation protein being targeted by the Nb domain. In vitro and in vivo studies show that it not only facilitates tumor-specific T cell cytotoxicity but also alleviates PD-1/PD-L1–mediated suppression, leading to enhanced T cell activation, proliferation, and deeper tumor infiltration.

Tetraspecific T cell engagers mark the next evolutionary step, packing 4 functional domains into a single antibody to deliver tumor-targeting T cell (or NK cell) activation, costimulation, and checkpoint blockade in 1 dose-sparing molecule. The first clinical example is emfizatamab (GNC-038), an octavalent CD19 × CD3 × CD137 × PD-L1 IgG, that simultaneously directs cytotoxic T cells to B-cell malignancies, provides CD137 costimulation, and locally blocks PD-L1; it is now in 2 phase-1/2 trials for relapsed or refractory non–Hodgkin lymphoma (NCT04606433 and NCT05623982).⁷⁶ Many trials are currently being conducted for BiTE and TriTE development; we present the main trials in Table 3.77, 78, 79 A summary of T cell engagers’ mechanism of action, pharmacokinetics, challenges, and timeline are presented in Fig. 2.

Table 3.

Summary of the current status of clinical trials of T cell engagers

Agent	Targets	Indication(s)	Phase/Regulatory Status (as of August 14, 2025)	Key Trial(s)
Ubamatamab (REGN4018)77	MUC16 × CD3	Recurrent ovarian/endometrial cancers	Phase 1/2 (ongoing)	NCT03564340
Odronextamab (Ordspono)78	CD20 × CD3	R/R FL; R/R DLBCL	EU approved (August 2024); US: complete response letter (August 2025)	ELM-1/ELM-2; NCT03888105; NCT02290951
HPN217 (MK-4002)73	BCMA × albumin × CD3	R/R MM	Phase 1/2	NCT04184050
HPN32879	DLL3 × albumin × CD3	SCLC, neuroendocrine tumors, neuroendocrine prostate cancer	Phase 1/2 (ongoing)	NCT04471727
HPN42471	PSMA × albumin × CD3	mCRPC	Phase 1/2a (completed or near completion)	NCT03577028
SAR44225765	CD38 × CD28 × CD3	R/R MM; R/R-NHL	Phase 1 (active, not recruiting)	NCT04401020
JNJ-79635322 (JNJ-5322)68	BCMA × GPRC5D × CD3	R/R MM	Phase 1 (ongoing)	NCT05652335

DLBCL, diffuse large B-cell lymphoma; mCRPC, metastatic castration-resistant prostate cancer; SCLC, small-cell lung cancer.

Fig. 2.

T cell engager mechanism, design, and development. Created in BioRender. Shah V. (2025) https://BioRender.com/x586wby. HLE, half-life –extended; MHC, major histocompatibility complex; SC, subcutaneous.

5. Conclusion

Despite the different challenges faced in oncology, efforts are still ongoing to offer patients more and more options with greater potential and less toxicity. Approved T cell engagers are already being used to treat malignancies and set the stage for the next generation of antibodies that can overcome the key limitations of their predecessors, such as antigen escape, modest activity in solid tumors, and inconvenient dosing schedules. This new frontier is defined by multispecific platforms, primarily TriTEs and tetraspecific T cell engagers, which are engineered for superior performance. With numerous multispecific antibodies already showing promising responses in early clinical trials, this rapid evolution in molecular engineering is poised to deliver safer, more convenient, and more powerful immunotherapies, potentially redefining the standard of care for a growing number of cancers.

Conflict of interest

The authors declare no conflicts of interest.