Bispecific Antibodies for DLBCL: Mechanisms and Applications

Bispecific antibodies represent a class of engineered immune therapies that have transformed the treatment landscape for diffuse large B-cell lymphoma, particularly for patients whose disease has returned after or resisted standard chemotherapy. These drugs work by physically bridging a patient’s own T cells to lymphoma cells, forcing an immune attack that the cancer had previously evaded. Several CD20/CD3-targeting bispecific antibodies, including epcoritamab, glofitamab, mosunetuzumab, and odronextamab, have moved rapidly through clinical development, and the data emerging from trials and real-world use paint a picture of genuine promise tempered by meaningful challenges around resistance, toxicity, and durability.

How the Bridge Works

The core idea behind these therapies is deceptively simple. One arm of the antibody grabs CD20, a protein found on the surface of most B-cell lymphomas. The other arm grabs CD3, a protein on T cells. By binding both simultaneously, the antibody forces T cells into close physical contact with lymphoma cells, triggering T-cell activation and killing of the tumor cell. This happens regardless of whether the T cell would have naturally recognized the lymphoma as a threat, essentially overriding the tumor’s immune evasion.

Engineering a molecule with two different binding arms is harder than it sounds. Natural antibodies are symmetric, with two identical heavy chains pairing together. Forcing two different heavy chains to pair correctly rather than mismatching was a central design problem. One widely used solution involves reshaping the interface where the two halves of the antibody meet. Researchers introduced bulky amino acid substitutions on one chain and complementary smaller ones on the other, creating a “knob-into-hole” fit that strongly favors correct pairing, with some designs achieving greater than 95% correct assembly.¹ The specific structural formats differ across the approved drugs. Epcoritamab and glofitamab, for example, have distinct molecular architectures: glofitamab uses a “2:1” format with two CD20-binding domains and one CD3-binding domain, designed to boost tumor-cell engagement, while epcoritamab uses a more conventional IgG-like format. These structural differences influence how the drugs behave in the body, including how they are dosed and administered.

Clinical Results in Relapsed or Refractory Disease

The patients who most urgently need these treatments are those with relapsed or refractory DLBCL, meaning their lymphoma came back after initial therapy or never responded to it. In the EPCORE NHL-1 trial, epcoritamab produced an overall response rate of about 63% and a complete response rate of roughly 39% in this heavily pretreated population, with a median duration of response of 12 months. Among patients who achieved a complete response, the median duration had not yet been reached at the time of analysis.² Those numbers matter because the patients in these trials had typically failed two or more prior lines of therapy, a situation where conventional options offer little.

The broader class has shown similar ballpark efficacy. The four most studied agents, epcoritamab, glofitamab, mosunetuzumab, and odronextamab, all target the same CD20/CD3 axis but differ in dosing schedules, routes of administration, and structural design.³ Glofitamab is given intravenously for a fixed duration, while epcoritamab is injected under the skin on an ongoing schedule. These practical differences shape patient experience and healthcare burden in ways that go beyond response rates.

Managing Cytokine Release Syndrome

When bispecific antibodies force T cells into action, the resulting immune activation can spill over into a systemic inflammatory response called cytokine release syndrome, or CRS. Symptoms range from mild fever and chills to dangerously low blood pressure and organ dysfunction in severe cases. CRS is the most common serious side effect of this drug class, and managing it has been a central focus of clinical development.

The solution adopted across most bispecific antibody programs is step-up dosing. Rather than starting at the full therapeutic dose, patients receive one or two smaller priming doses first. For epcoritamab, the approved regimen uses 0.16-mg and 0.8-mg step-up doses before reaching the 48-mg full dose. These initial low doses activate T cells gradually, reducing the spike in inflammatory cytokines that triggers severe CRS.⁴ When CRS does occur, treatment with tocilizumab (a drug that blocks the inflammatory molecule IL-6) and corticosteroids is well established.⁵

A related but distinct concern is immune effector cell-associated neurotoxicity syndrome, or ICANS, which involves confusion, difficulty speaking, tremor, or other neurological symptoms linked to inflammation crossing the blood-brain barrier. ICANS appears to be less common with bispecific antibodies than with CAR-T cell therapy. In a multi-institution real-world study of 86 patients treated with bispecific antibodies for lymphoma, ICANS occurred in about 7% of patients, with the large majority being mild to moderate and managed with steroids. No cases of the most severe grade were observed.⁶

Infections and Immune Suppression

Because bispecific antibodies deplete normal B cells along with malignant ones, and because the patients receiving them are already immunocompromised from prior treatments, infection is a persistent and sometimes underappreciated risk. A real-world study of patients receiving CD3/CD20 bispecific antibodies found severe neutropenia in about 40% of patients, lymphopenia in over 80%, and low immunoglobulin levels in roughly two-thirds. Prior CAR-T exposure, aggressive lymphoma subtype, and the number of previous treatment lines all correlated with higher infection risk.⁷

In practice, patients on bispecific antibodies typically receive prophylaxis against common infections, including antiviral medications to prevent herpes reactivation and sometimes immunoglobulin replacement therapy when antibody levels drop too low. Monitoring blood counts and immunoglobulin levels becomes a routine part of treatment, and clinicians need to stay vigilant for opportunistic infections that can emerge months into therapy.

Why Bispecific Antibodies Stop Working

Not every patient responds to these drugs, and among those who do, relapse is common. Understanding why they fail has become an active area of research, and two main resistance mechanisms have emerged.

The first is target antigen loss. If the lymphoma cells stop displaying CD20 on their surface, the antibody’s tumor-targeting arm has nothing to grab. In one study that tracked tumor samples over time, truncating mutations in the gene encoding CD20 were found in 80% of patients whose disease progressed after CD20-targeting bispecific therapy.⁸ This is a stark reminder that cancer evolves under therapeutic pressure: eliminate the cells with the target and you select for the cells that have lost it.

The second mechanism involves the T cells themselves. Even when CD20 remains on tumor cells, the T cells recruited by the bispecific antibody can become exhausted, a state where they lose their killing ability despite being activated. Research using detailed single-cell analysis of patients with glofitamab resistance found that while the proportion of active T cells in the tumor did increase with treatment, so did the proportion of exhausted and regulatory T cells. The net effect was an immunosuppressive environment despite active T-cell recruitment. Shared genetic signatures between effective and exhausted T cells suggested that the same T cells were being driven into exhaustion during treatment.⁹ The finding that both antigen loss and T-cell exhaustion operate simultaneously in many patients helps explain why overcoming resistance will likely require attacking the problem from multiple directions.

How Bispecific Antibodies Compare to CAR-T Therapy

CAR-T cell therapy is the other major T-cell-redirecting approach in DLBCL, and the two are increasingly compared head to head. CAR-T involves collecting a patient’s own T cells, genetically engineering them to target CD19, expanding them in a lab, and infusing them back. It is a powerful therapy but comes with significant logistical and safety constraints: the manufacturing process takes weeks, costs are very high, and toxicities including severe CRS and neurotoxicity are more common than with bispecific antibodies.

A meta-analysis of 16 studies including over 1,300 patients found that CAR-T therapy produced a pooled complete response rate of about 51%, compared with 36% for bispecific antibodies. One-year progression-free survival similarly favored CAR-T, at roughly 44% versus 32%. However, CAR-T came with substantially higher rates of severe adverse events: grade 3 or higher CRS occurred in about 8% of CAR-T patients versus 2% for bispecific antibodies, and severe neurotoxicity was 11% versus 1%.¹⁰ The efficacy gap is real, but so is the safety and accessibility gap. Bispecific antibodies are available off the shelf, require no manufacturing wait, and can often be given in an outpatient setting, making them accessible to patients who would not qualify for or survive the rigors of CAR-T preparation.¹¹

One unresolved question is how to sequence these therapies. A patient who relapses after CAR-T can receive a bispecific antibody, and vice versa, but the optimal order is unclear. Prior CAR-T exposure does not seem to preclude response to bispecific antibodies, though it may influence infection risk and T-cell fitness. Clinical groups are actively studying whether bispecific antibodies should be used before CAR-T as a bridge, after CAR-T as salvage, or even instead of CAR-T in patients who are unlikely to tolerate the manufacturing delay and toxicities.¹²

Combination Strategies

Because single-agent bispecific antibodies cure only a fraction of patients, combining them with other treatments is a logical next step. The rationale is twofold: adding cytotoxic agents can kill tumor cells that escape immune attack, while immunomodulatory drugs can counteract the T-cell exhaustion and immunosuppressive microenvironment that drive resistance.¹³

One particularly promising avenue is combining bispecific antibodies with chemotherapy regimens in newly diagnosed patients. The SKYGLO trial is a global phase III study testing whether adding glofitamab to Pola-R-CHP (a modern chemotherapy-plus-antibody-drug-conjugate backbone) improves outcomes in previously untreated large B-cell lymphoma. This trial was motivated by phase Ib data showing a complete metabolic response rate of about 92% when glofitamab was combined with Pola-R-CHP in untreated DLBCL patients, with a manageable safety profile.¹⁴ If confirmed in the randomized phase, this could mark the first time a bispecific antibody becomes part of standard first-line treatment rather than being reserved for patients who have already failed multiple therapies.

Practical Realities of Treatment

One of the underappreciated dimensions of any cancer therapy is how much time and energy it demands from patients beyond its clinical effects. Bispecific antibodies vary considerably on this front. A study comparing patient-reported healthcare burden found that DLBCL patients on glofitamab averaged about 2.2 healthcare visits and 43 hours of cancer-related time per month, while those on epcoritamab averaged 3.0 visits and roughly 88 hours per month.¹⁵ The difference reflects their distinct dosing schedules: glofitamab is given as a fixed-duration course (typically 12 cycles over about 8 months), while epcoritamab is administered continuously until disease progression. In a survey of patients with relapsed or refractory DLBCL, roughly 69% preferred a treatment with fixed-duration, less-frequent dosing over continuous, more-frequent administration.¹⁶

Outpatient administration is another practical advantage that separates bispecific antibodies from CAR-T therapy, which typically requires hospital admission and intensive monitoring. Data from the EPCORE NHL-6 study showed that 92% of patients receiving their first full dose of epcoritamab were monitored in the outpatient setting, supporting the feasibility of keeping patients out of the hospital during treatment initiation.¹⁷

Cost Considerations

The economics of these treatments are complex and depend heavily on the time horizon considered. An institutional cost model found that epcoritamab required the least personnel and infusion-chair time across most time horizons and was cost-saving compared to the CAR-T product axicabtagene ciloleucel, while costing similarly to glofitamab on a per-month basis.¹⁸ However, a separate cost-effectiveness analysis comparing axicabtagene ciloleucel with the bispecific antibody odronextamab reached a different conclusion: CAR-T patients had total discounted lifetime costs of about $603,000 compared with roughly $1,135,000 for odronextamab, making CAR-T the more cost-effective option when factoring in long-term outcomes.¹⁹

The contradiction is instructive. Short-term per-month costs favor bispecific antibodies, but if CAR-T produces more durable remissions, its high upfront cost may be offset by years of no further treatment. For a bispecific antibody given continuously until progression, treatment costs accumulate over time. The answer depends on durability data that are still maturing, and it will likely differ by agent and by patient.

Emerging Targets and Next-Generation Designs

The CD20/CD3 axis is dominant but not the only game in town. Researchers are exploring bispecific antibodies that target different tumor antigens or engage the immune system through additional pathways. One early-phase trial is testing an antibody that binds CD19 on B cells and 4-1BB on T cells, providing a co-stimulatory signal rather than directly triggering killing.²⁰ The idea is that co-stimulation could sustain T-cell activity and prevent the exhaustion that limits current therapies. Trispecific antibodies, molecules with three different binding specificities, are also in development, aiming to recruit multiple immune cell types or target multiple tumor antigens simultaneously to reduce the escape routes available to the cancer.

Alternative antigen targets could also address the problem of CD20 loss after treatment. If a lymphoma loses CD20 expression under pressure from a CD20-targeting drug, having a second bispecific antibody that targets CD19 or another B-cell marker could provide a fallback strategy. The sequential antigen loss documented in clinical samples underscores why a single-target approach has inherent limits.⁸ The field is moving toward a more flexible toolkit where clinicians can match the right bispecific antibody, or combination, to the biology of each patient’s lymphoma at each stage of treatment, rather than relying on a one-size-fits-all approach.