Taming 4-1BB: TJ Biopharma Enters the CLDN6 Race with Novel Bispecific

HANGZHOU, China – October 26, 2026 — In the relentless pursuit of more effective cancer treatments, the biopharmaceutical industry frequently encounters a frustrating paradox: the most potent immune-stimulating mechanisms are often the most toxic to the human body. For years, researchers have sought ways to untangle this efficacy-toxicity knot, particularly when it comes to powerful co-stimulatory receptors that can turbocharge the body's natural defenses against tumors. Today, a new chapter in this ongoing effort is unfolding.

TJ Biopharma, a fully integrated biotech company known for its focus on innovative biologics, announced a critical milestone in its next-generation immuno-oncology pipeline. The company has officially dosed the first patient in a Phase 1 clinical trial evaluating TJ-C64B, a proprietary Claudin 6 (CLDN6) by 4-1BB bispecific antibody. Designed for patients with CLDN6-positive advanced solid tumors, this novel therapeutic approach represents a sophisticated attempt to harness a notoriously difficult immune pathway while shielding healthy organs from collateral damage.

As the industry watches this trial progress, the implications extend far beyond a single molecule. It offers a window into the evolving strategies of modern drug design, the intensifying global race to target the CLDN6 protein, and the strategic maturation of biopharmaceutical companies transitioning from regional players to global innovators.

Cracking the 4-1BB Safety Bottleneck

To understand the significance of TJ-C64B, one must first look at the turbulent history of 4-1BB (also known as CD137). As a potent co-stimulatory receptor found on T cells, 4-1BB has long been recognized as a highly attractive target in immuno-oncology. When activated, it can dramatically enhance the proliferation, survival, and tumor-killing capacity of immune cells.

However, unlocking this potential has proven exceptionally difficult. First-generation 4-1BB agonists—antibodies designed to bind and activate the receptor systemically—were plagued by severe toxicities. Most notably, these early candidates induced dangerous levels of hepatotoxicity (liver damage), forcing clinical trials to halt and sending researchers back to the drawing board. The challenge was clear: how do you activate 4-1BB only where it is needed, without triggering a systemic immune storm?

TJ Biopharma's answer lies in conditional activation. TJ-C64B is engineered to remain largely inactive as it circulates through the bloodstream. Its 4-1BB agonistic activity is only triggered when the molecule simultaneously binds to CLDN6, a protein highly expressed on the surface of certain tumor cells. By relying on this CLDN6-dependent mechanism, the drug aims to localize immune activation strictly within the tumor microenvironment.

Preclinical data for TJ-C64B has been highly encouraging on this front. Studies demonstrated potent, durable anti-tumor activity across multiple models, alongside a favorable tolerability profile that notably lacked the liver enzyme spikes characteristic of older 4-1BB agonists.

Furthermore, the molecule is not a one-trick pony. It incorporates a functional IgG1 Fc domain designed to engage multiple anti-tumor mechanisms simultaneously. Beyond 4-1BB activation, it facilitates antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP), essentially tagging tumor cells for direct destruction by natural killer cells and macrophages. It also selectively depletes regulatory T cells, which tumors often use to suppress immune responses.

The Global Race for the Claudin 6 Frontier

The choice of CLDN6 as the targeting anchor for this bispecific antibody is far from accidental. CLDN6 is an oncofetal antigen, meaning it is typically expressed during embryonic development but silenced in healthy adult tissues. However, in several aggressive solid tumors—including ovarian, endometrial, testicular, and gastric cancers—the protein is abnormally re-expressed.

This stark contrast between high expression in tumors and minimal presence in normal tissue makes CLDN6 an ideal target for precision oncology, offering a wide therapeutic window. Unsurprisingly, the biopharma industry has taken notice, sparking a highly competitive global race to develop CLDN6-targeted therapies.

TJ Biopharma is entering a crowded and dynamic arena. BioNTech has made significant waves with BNT211, a CLDN6-targeted CAR-T cell therapy that has shown promising Phase 1/2 results, particularly when combined with an mRNA vaccine to boost CAR-T persistence. Meanwhile, Context Therapeutics recently initiated a Phase 1 study for CTIM-76, a CLDN6 x CD3 T-cell engager, and Torl BioTherapeutics is advancing Torl-1-24, a CLDN6-targeted antibody-drug conjugate (ADC).

Despite the stiff competition, there is ample room for differentiated approaches, particularly for patients facing advanced disease with few existing options.

"Patients with CLDN6-positive tumors currently have few targeted treatment options and often face poor outcomes," noted Professor Jin Li, Principal Investigator of the TJ-C64B Phase 1 study and President of Shanghai GoBroad Cancer Hospital. "TJ-C64B adopts a CLDN6-dependent conditional 4-1BB activation mechanism, providing a promising approach to achieve more precise immune activation within tumors. Early clinical studies are critical to translating innovative scientific concepts into potential clinical benefits for patients."

A Strategic Maturation for TJ Biopharma

Beyond the scientific intrigue, the advancement of TJ-C64B highlights a broader narrative about the evolution of TJ Biopharma's corporate strategy. Historically, many China-based biotech firms built their foundations by in-licensing regional rights to foreign drugs or out-licensing early-stage discoveries to multinational pharmaceutical giants.

While TJ Biopharma has successfully established a robust network of partnerships with industry leaders like Sanofi, Biogen, and CSPC to support its first wave of commercial assets, TJ-C64B represents a different path. The molecule was generated internally using the company's proprietary AntibodyPLUS platform, and crucially, TJ Biopharma retains full global rights to the asset.

This shift underscores a strategic maturation. By building a "differentiated two-wave pipeline," the company is leveraging the momentum and revenue potential of its late-stage and commercial-ready products to fund the development of wholly owned, first-in-class innovations.

"Dosing the first patient with TJ-C64B marks an important milestone for the Company as our next-generation innovation pipeline advances into clinical development," stated Dr. Xi Chen, Chief Scientific Officer of TJ Bio. "TJ-C64B is an internally discovered asset for which TJ Bio retains global rights, and we are committed to advancing it efficiently through clinical development."

This transition from regional partner to global innovator is a difficult bridge to cross, requiring not just sophisticated discovery platforms but also the clinical execution capabilities to run high-quality trials that meet international regulatory standards. The successful execution of this Phase 1 trial will be a critical litmus test for TJ Biopharma's broader global ambitions.

The Clinical Path Forward

The newly initiated Phase 1 study is designed with a careful, stepwise approach to ensure patient safety while hunting for early signs of efficacy. The trial will begin by evaluating TJ-C64B as a monotherapy in dose escalation cohorts. This phase is critical for determining the maximum tolerated dose and understanding the drug's pharmacokinetics—how it moves through and is processed by the human body.

Once a safe and optimal dose is established, the trial will transition into dose expansion studies. These expansion cohorts will specifically target patients with ovarian cancer, endometrial cancer, and gastric cancer—tumor types known for high CLDN6 expression and significant unmet medical need.

As the trial progresses, the oncology community will be watching closely for two distinct signals. First, safety data will reveal whether the conditional activation mechanism successfully prevents the liver toxicity that derailed previous 4-1BB agonists. Second, efficacy data will indicate whether the dual-action mechanism of 4-1BB stimulation and Fc-mediated tumor destruction translates from preclinical models into meaningful clinical responses for patients facing aggressive, hard-to-treat cancers.