Bispecific Antibodies for DLBCL: Mechanisms and Applications

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. While many patients respond well to initial treatments, relapsed or refractory cases remain a challenge. Advances in immunotherapy have led to the development of bispecific antibodies, which engage multiple targets simultaneously to enhance anti-tumor activity.

Mechanisms Of Bispecific Antibodies

Bispecific antibodies (BsAbs) bind to two distinct antigens, setting them apart from conventional monoclonal antibodies. This dual specificity enhances therapeutic effects by facilitating interactions that single-target agents cannot achieve. In DLBCL, BsAbs engage tumor-associated antigens while recruiting immune effector cells or modulating survival pathways. Their structural diversity allows for precise engineering to optimize function, stability, and pharmacokinetics.

A key mechanism of BsAbs in DLBCL is T-cell redirection. These antibodies recognize CD3, a component of the T-cell receptor complex, while binding to a tumor-associated antigen such as CD20 or CD19. This interaction brings cytotoxic T cells into proximity with malignant B cells, triggering targeted cell lysis through perforin and granzyme-mediated apoptosis. Unlike traditional monoclonal antibodies that rely on endogenous immune activation, BsAbs directly link immune cells and tumor cells, bypassing antigen presentation or co-stimulatory signals. Clinical trials of CD20xCD3 BsAbs have shown promising response rates in relapsed or refractory DLBCL.

BsAbs can also block multiple signaling pathways involved in lymphoma progression. Some target both CD19 and CD22, disrupting redundant survival mechanisms that contribute to resistance. Preclinical models suggest this dual blockade enhances tumor cell apoptosis and reduces disease burden more effectively than monotherapies.

Additionally, BsAbs enhance antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). By engaging Fc receptors on natural killer (NK) cells or macrophages, they amplify immune-mediated tumor clearance. Some BsAbs are designed with Fc-silent formats to minimize off-target immune activation and reduce toxicity risks such as cytokine release syndrome.

Formats And Targeting Approaches

The structural diversity of BsAbs influences their functionality, stability, and clinical efficacy in DLBCL. Various formats have been developed to optimize their therapeutic potential, ranging from small fragment-based constructs to full-length immunoglobulin G (IgG)-like molecules. Each format presents unique advantages in half-life, manufacturability, and immune engagement.

One widely studied format is the fragment-based bispecific T-cell engager (BiTE), which consists of two single-chain variable fragments (scFvs) linked by a peptide. BiTEs are highly specific and facilitate rapid tumor cell engagement with immune effectors, making them effective in hematologic malignancies. Their small size enhances tumor infiltration but results in a short half-life, requiring continuous intravenous infusion. To improve pharmacokinetics, longer-acting formats such as dual-affinity re-targeting (DART) antibodies and tandem diabodies have been developed.

Full-length IgG-like bispecifics, including those using “knobs-into-holes” technology, offer extended half-life and enhanced stability. This format enables less frequent dosing while maintaining potent bispecific activity. Some IgG-like BsAbs feature modified Fc regions to minimize off-target effects and excessive immune activation, balancing efficacy and safety.

Target selection is critical, as antigens must be highly expressed on malignant B cells while showing minimal presence on normal tissues to reduce toxicity. The most commonly targeted antigens in DLBCL include CD19, CD20, and CD22. CD20 has been well-established due to its high expression on mature B cells and its success in monoclonal antibody therapies. BsAbs targeting CD20 and CD3 have demonstrated significant clinical activity in relapsed or refractory DLBCL, with response rates exceeding 50% in some trials.

CD19 is another key target due to its broad expression across B-cell malignancies and role in B-cell receptor signaling. BsAbs co-targeting CD19 and CD3 have shown promise, particularly in patients who have relapsed after CD19-directed CAR T-cell therapy. Some investigational BsAbs explore dual B-cell antigen targeting, such as CD19/CD22 or CD20/CD22, to prevent antigen escape mechanisms that contribute to resistance.

Applications In DLBCL

BsAbs are transforming DLBCL treatment, particularly for relapsed or refractory cases. Standard therapies, including chemoimmunotherapy and autologous stem cell transplantation, often fail in aggressive or resistant disease. BsAbs offer a targeted approach that circumvents traditional resistance mechanisms.

Clinical trials have shown BsAbs’ efficacy in heavily pretreated DLBCL patients, including those relapsed after CAR T-cell therapy. Early-phase studies of CD20xCD3 BsAbs have reported overall response rates exceeding 50%, with some patients achieving complete remission. This success has led to exploration of their use earlier in treatment, as a bridge to transplantation or consolidation after initial therapy.

Personalized approaches are emerging, with biomarker-driven strategies identifying patients most likely to benefit, particularly those with high-risk genetic features like double-hit or triple-hit lymphoma. Studies are investigating whether specific molecular subtypes of DLBCL respond differently to BsAbs, which could guide treatment selection. Efforts are also underway to refine dosing regimens to maximize efficacy while managing toxicity, including cytokine release syndrome.

How They Differ From Single-Target Antibodies

BsAbs offer a level of therapeutic complexity that sets them apart from conventional monoclonal antibodies. Their ability to simultaneously engage two targets enables more sophisticated mechanisms of action, enhancing efficacy in DLBCL. Single-target antibodies, by contrast, bind to one antigen, limiting their ability to address tumor heterogeneity and adaptive resistance.

A key advantage of BsAbs is their ability to counteract tumor escape mechanisms. In DLBCL, antigen loss is a common cause of treatment failure, particularly with CD19- or CD20-targeting therapies. BsAbs mitigate this risk by engaging multiple tumor-associated markers, reducing the likelihood of immune evasion. Clinical observations show that patients who relapse after CD19-directed therapies can still respond to BsAbs targeting CD20, highlighting their potential to prolong treatment effectiveness in resistant disease.