Author: Alisha G C

Abstract

Teclistamab is a first-in-class bispecific antibody targeting B-cell maturation antigen (BCMA) and CD3 that has significantly advanced the treatment of relapsed or refractory multiple myeloma (RRMM). By simultaneously binding malignant plasma cells and cytotoxic T lymphocytes, Teclistamab redirects endogenous T cells to eliminate BCMA-expressing tumor cells through major histocompatibility complex (MHC)–independent immune activation. This mechanism bypasses limitations associated with conventional chemotherapy and antigen-restricted immunotherapies. Clinical trials have demonstrated substantial response rates in heavily pretreated multiple myeloma patients, including individuals refractory to proteasome inhibitors, immunomodulatory drugs, and anti-CD38 monoclonal antibodies. However, therapeutic resistance driven by antigen downregulation, T-cell exhaustion, and tumor microenvironment–mediated immune suppression remains a significant challenge. This review provides an in-depth analysis of Teclistamab’s molecular architecture, immunologic mechanism of action, pharmacokinetics, clinical efficacy, resistance pathways, and emerging strategies designed to enhance therapeutic durability.

Molecular Structure of Teclistamab

Teclistamab is a humanized bispecific IgG4 monoclonal antibody engineered to simultaneously bind:

• B-cell maturation antigen (BCMA) on malignant plasma cells

• CD3ε on T lymphocytes

This dual-binding configuration enables direct immune synapse formation between T cells and tumor cells, triggering targeted cytotoxic responses.

Unlike smaller bispecific T-cell engager (BiTE) molecules such as Blinatumomab, Teclistamab retains a modified Fc domain, which improves structural stability and pharmacokinetic properties while minimizing unwanted immune activation.

Key structural characteristics include:

• Full-length IgG-based bispecific antibody architecture

• Engineered Fc region with reduced Fcγ receptor binding

• Enhanced serum half-life compared with Fc-less bispecific antibodies

• Capability for subcutaneous administration

This design enables sustained therapeutic exposure while reducing the need for continuous infusion.

BCMA: The Plasma Cell Targeting Domain

B-cell maturation antigen (BCMA, also known as TNFRSF17) is a transmembrane receptor belonging to the tumor necrosis factor receptor (TNFR) superfamily. It is expressed primarily on:

• Long-lived plasma cells

• Malignant plasma cells in multiple myeloma

BCMA plays a central role in plasma cell survival by binding the ligands:

• BAFF (B-cell activating factor)

• APRIL (a proliferation-inducing ligand)

Upon ligand engagement, BCMA activates intracellular signaling pathways that promote plasma cell proliferation and resistance to apoptosis.

Major downstream pathways include:

• NF-κB signaling pathway

• PI3K–AKT signaling pathway

• MAPK signaling cascade

These pathways support the survival and expansion of myeloma cells within the bone marrow microenvironment.

From a therapeutic perspective, BCMA represents an ideal immunotherapy target because it exhibits:

• High expression in multiple myeloma cells

• Minimal expression in non-plasma cell tissues

• Essential role in plasma cell survival signaling

These properties allow selective targeting of malignant plasma cells while limiting off-target toxicity.

CD3ε: The T-Cell Engagement Domain

The second functional arm of Teclistamab binds CD3ε, a critical component of the T-cell receptor (TCR) complex.

The CD3 complex consists of several subunits:

• CD3γ

• CD3δ

• CD3ε

• CD3ζ homodimer

The CD3ζ chains contain immunoreceptor tyrosine-based activation motifs (ITAMs) that initiate intracellular signaling following T-cell receptor engagement.

When Teclistamab binds CD3ε:

• Polyclonal T cells are recruited to tumor cells

• T-cell receptor clustering occurs

• Intracellular signaling pathways are activated

Importantly, this process occurs independently of antigen presentation, allowing T cells to eliminate tumor cells even when major histocompatibility complex (MHC) expression is reduced or absent.

Fc Engineering and Pharmacologic Design

Teclistamab contains a modified IgG4 Fc region designed to optimize pharmacokinetic and safety profiles.

Key Fc modifications provide:

• Reduced binding to Fcγ receptors

• Decreased antibody-dependent cellular cytotoxicity (ADCC)

• Reduced complement activation

• Extended serum half-life (~3–4 days)

These features enable intermittent subcutaneous dosing rather than continuous intravenous infusion.

Mechanism of Action of Teclistamab

1. Immunologic Synapse Formation and T-Cell Redirection

Teclistamab functions by physically linking CD3-positive T cells to BCMA-expressing myeloma cells, thereby forming a functional cytotoxic immune synapse.

The process involves several sequential steps:

1. Teclistamab binds BCMA on malignant plasma cells.

2. The second binding arm engages CD3 on T cells.

3. Close cellular proximity induces T-cell receptor clustering.

4. Cytotoxic granules are polarized toward the tumor cell interface.

This artificial synapse mimics physiological immune cell interactions and triggers T-cell activation.

Intracellular Signal Transduction

Following CD3 engagement, a cascade of intracellular signaling events occurs:

1. Lck kinase phosphorylates ITAMs on CD3ζ chains

2. ZAP-70 is recruited and activated

3. Adaptor proteins including LAT and SLP-76 assemble signaling complexes

Downstream signaling pathways are subsequently activated:

Calcium–calcineurin signaling → NFAT activation

Protein kinase C signaling → NF-κB activation

MAP kinase cascade → AP-1 transcriptional activation

Together, these transcriptional programs drive T-cell activation, proliferation, and cytotoxic activity.

Effector Cytotoxic Functions

Activated T cells eliminate tumor cells through multiple mechanisms:

Perforin–Granzyme Cytotoxicity

Perforin forms pores in tumor cell membranes, allowing granzyme B to enter and trigger apoptosis.

Cytokine Release

Activated T cells release inflammatory cytokines such as:

• IFN-γ

• IL-2

• TNF-α

These cytokines enhance immune activation and recruit additional immune cells.

Serial Killing

A single activated T cell can disengage and sequentially destroy multiple tumor cells.

2. T-Cell Expansion and Immune Memory

In addition to immediate cytotoxic effects, Teclistamab promotes expansion of T-cell populations including:

• Effector memory T cells (T_EM)

• Central memory T cells (T_CM)

These memory populations may contribute to long-term immune surveillance and sustained disease control.

Pharmacokinetics and Immune Dynamics

Teclistamab demonstrates favorable pharmacokinetic properties due to its IgG-based structure.

Important characteristics include:

• Subcutaneous administration

• Half-life of approximately 3–4 days

• Gradual T-cell activation with step-up dosing

• Preferential expansion of CD8+ cytotoxic T cells

Step-up dosing protocols are implemented to reduce the risk of cytokine release syndrome.

Clinical Efficacy of Teclistamab in Multiple Myeloma

MajesTEC-1 Clinical Trial

The MajesTEC-1 phase I/II trial evaluated Teclistamab in patients with heavily pretreated relapsed or refractory multiple myeloma.

Participants had previously received multiple therapy classes including:

• Proteasome inhibitors

• Immunomodulatory drugs

• Anti-CD38 monoclonal antibodies

Key clinical outcomes included:

• Overall response rate (ORR): ~63%

• Complete response or better: ~39%

• Median duration of response: ~18 months

These results demonstrate strong activity in patients with otherwise limited treatment options.

Adverse Events and Toxicity

Despite its therapeutic efficacy, Teclistamab is associated with several immune-related adverse effects.

Cytokine Release Syndrome (CRS)

CRS is the most common toxicity and occurs due to rapid immune activation.

Symptoms may include:

• Fever

• Hypotension

• Hypoxia

• Elevated inflammatory cytokines

Most cases are grade 1–2 and manageable with supportive therapy or IL-6 blockade.

Infections

Teclistamab may reduce normal plasma cells, leading to:

• Hypogammaglobulinemia

• Increased susceptibility to bacterial and viral infections

Patients may require immunoglobulin replacement therapy.

Neurotoxicity

Immune effector cell–associated neurotoxicity syndrome (ICANS) may occur, though less frequently than with CAR-T therapy.

Symptoms can include:

• Confusion

• Aphasia

• Seizures (rare)

Mechanisms of Resistance to Teclistamab

1. BCMA Antigen Loss or Downregulation

Tumor cells may evade immune targeting by reducing BCMA expression through:

• Genetic mutations

• Transcriptional suppression

• Shedding of soluble BCMA

Loss of surface antigen reduces antibody binding and T-cell recruitment.

2. T-Cell Exhaustion

Chronic immune stimulation may lead to dysfunctional T cells characterized by:

• Upregulation of inhibitory receptors (PD-1, TIM-3, LAG-3)

• Reduced cytokine production

• Decreased cytotoxic capacity

3. Immunosuppressive Tumor Microenvironment

The bone marrow microenvironment of multiple myeloma contains several suppressive immune components:

• Regulatory T cells (Tregs)

• Myeloid-derived suppressor cells (MDSCs)

• Immunosuppressive cytokines such as IL-10 and TGF-β

These factors impair effective T-cell responses.

Strategies to Overcome Teclistamab Resistance

Several therapeutic strategies are under investigation.

Dual-Target Bispecific Antibodies

Targeting additional plasma cell antigens may reduce antigen escape.

Examples include:

• GPRC5D

• FcRH5

Immune Checkpoint Inhibition

Combining Teclistamab with checkpoint inhibitors may restore exhausted T cells.

Potential combinations include:

• Anti-PD-1 antibodies

• Anti-PD-L1 therapies

Enhancing T-Cell Fitness

Strategies to improve T-cell persistence include:

• Cytokine therapy (IL-7, IL-15)

• Combination with immunomodulatory drugs. More Teclistamab plus Daratumumab in Relapsed or Refractory Multiple Myeloma | New England Journal of Medicine

• Adoptive cellular therapies

Comparison With CAR-T Cell Therapy

Both Teclistamab and CAR-T therapies target BCMA but differ in their approach.

Teclistamab

• Off-the-shelf antibody therapy

• No genetic modification required

• Subcutaneous administration

CAR-T Therapy

• Requires genetic engineering of patient T cells

• Personalized manufacturing process

• Potentially longer-lasting responses

Each therapy offers unique advantages depending on clinical circumstances.

Conclusion

Teclistamab represents a major advancement in the immunotherapy of multiple myeloma by enabling potent BCMA-directed T-cell redirection. Its bispecific antibody design allows effective tumor killing independent of antigen presentation while maintaining favorable pharmacokinetic properties. Although challenges such as antigen escape, T-cell exhaustion, and immunosuppressive microenvironments remain, ongoing research into combination therapies and next-generation bispecific antibodies holds significant promise. Continued integration of molecular biology, immunology, and clinical innovation will be essential for optimizing Teclistamab-based treatments and achieving durable remissions in multiple myeloma.

Frequently Asked Questions (FAQ)

Q1. What is Teclistamab?
Teclistamab is a bispecific antibody that targets BCMA on multiple myeloma cells and CD3 on T cells, enabling immune-mediated tumor killing.

Q2. Why is BCMA an important target in multiple myeloma?
BCMA is highly expressed on malignant plasma cells and plays a crucial role in plasma cell survival signaling.

Q3. What are the main side effects of Teclistamab?
Common side effects include cytokine release syndrome, infections, and occasional neurotoxicity.

Q4. How does Teclistamab differ from CAR-T therapy?
Teclistamab redirects existing T cells using an antibody, whereas CAR-T therapy involves genetically modifying patient T cells.

Q5. What causes resistance to Teclistamab?
Resistance may arise from BCMA antigen loss, T-cell exhaustion, or immunosuppressive factors within the tumor microenvironment.