Purple Biotech's 'Capped' Antibody Shows Major Safety Leap in Cancer

REHOVOT, Israel – January 07, 2026 – Purple Biotech has announced a significant preclinical milestone for its next-generation cancer immunotherapy, IM1240, demonstrating a vastly improved safety profile that could overcome a critical hurdle limiting current treatments. In a toxicology study using non-human primates, the novel tri-specific antibody was administered at doses up to 300 times higher than a comparable uncapped version, with minimal immune-related toxicity.

This achievement validates the company's proprietary CAPTN-3 platform, which is designed to unleash a powerful immune attack specifically within the tumor microenvironment while shielding the rest of the body from collateral damage. The results position IM1240 for advancement toward human clinical trials, with a regulatory submission planned for the latter half of 2026.

The Science of Safety: Deconstructing the CAPTN-3 Platform

The central challenge for many potent immunotherapies, particularly T-cell engagers, is managing toxicity. These drugs work by linking a patient's own T-cells directly to cancer cells, triggering a powerful killing response. However, this activation can occur systemically, leading to a dangerous condition known as cytokine release syndrome (CRS), where widespread inflammation can cause severe, life-threatening side effects and ultimately limit the effective dose a patient can receive.

Purple Biotech's CAPTN-3 platform addresses this problem with an innovative “capping” technology. The IM1240 antibody is engineered with a molecular mask, or cap, that physically blocks the part of the antibody that binds to T-cells (the CD3 arm). This cap keeps the antibody inert as it circulates through the bloodstream, preventing off-target immune activation.

Only upon reaching the tumor microenvironment—a unique biochemical landscape rich with specific enzymes called proteases—is the cap cleaved off. This localized unmasking unleashes the antibody's full power precisely where it is needed. The successful toxicology study showed this design works as intended, with only modest cytokine release observed even at extremely high doses.

“In the Study, IM1240 demonstrated a favorable safety and tolerability profile, with hematologic findings that align with its expected pharmacodynamic effects on immune activation,” stated Gil Efron, CEO of Purple Biotech. “The CD3 capping design of IM1240 showed clear differentiation compared with the non-capped comparator, IM1222, enabling a significant reduction in immune-related effects... we believe that collectively, these data provide translational guidance that may inform optimal dose selection, dosing strategy, and safety monitoring plans for the next phase of advanced toxicological assessments.”

Furthermore, IM1240 is a tri-specific antibody, meaning it has three distinct targets. It simultaneously binds to the 5T4 antigen on the tumor cell, the CD3 receptor on T-cells, and the NKG2A checkpoint on both T-cells and Natural Killer (NK) cells. This triple-action mechanism not only engages the adaptive immune system (T-cells) but also the innate immune system (NK cells), creating a coordinated, two-pronged assault on the tumor that could prove more effective at overcoming cancer's defense mechanisms.

Targeting a Stubborn Foe: The Promise of 5T4

The target selected for IM1240, 5T4, is an oncofetal antigen. This protein is highly expressed during embryonic development but is largely absent in healthy adult tissues. Its re-emergence on the surface of a wide range of solid tumors—including ovarian, pancreatic, lung, breast, and colorectal cancers—makes it an attractive bullseye for targeted therapy. High levels of 5T4 are often associated with more aggressive disease, metastasis, and poor patient outcomes, highlighting a significant unmet medical need.

Despite its promise, no 5T4-targeted therapy has yet received global approval. Previous attempts by other companies have faced challenges, including dose-limiting toxicities. For instance, an antibody-drug conjugate (ADC) developed by Pfizer targeting 5T4 was discontinued due to ocular toxicity. This history underscores the importance of developing therapies that can effectively target 5T4-expressing cells without causing unacceptable off-target harm. The expanded therapeutic window demonstrated by IM1240 suggests it may have a crucial advantage in this pursuit.

The recent study also revealed a favorable pharmacokinetic profile for IM1240. Its design, which includes a human serum albumin moiety, resulted in increased systemic exposure and a prolonged circulating half-life, potentially allowing for less frequent dosing in a clinical setting.

Navigating a Crowded Field and the Path to the Clinic

The field of multi-specific antibodies is intensely competitive, with numerous companies developing T-cell engagers, NK-cell engagers, and ADCs. Purple Biotech aims to differentiate its platform not only through its unique tri-specific, dual-immune action but critically, through its superior safety profile. The ability to dose higher without triggering severe CRS could translate directly into better efficacy, allowing the therapy to destroy more cancer cells before the tumor can develop resistance.

With this key toxicology milestone achieved, Purple Biotech is preparing for the next steps on the path to clinical trials. The company is working to complete advanced, formal toxicology studies required for a regulatory filing. The goal is to submit an Investigational New Drug (IND) application to regulators in the second half of 2026, which would clear the way for a Phase 1 first-in-human study.

Given the high unmet need in 5T4-expressing cancers and the novel mechanism with a strong safety rationale, IM1240 could be a candidate for accelerated development programs if early clinical data proves promising.

This milestone serves as a powerful validation for the entire CAPTN-3 platform, which the company describes as a "plug and play" system. The same capping technology is being applied to other candidates, including IM1305, which targets TROP2, another well-validated tumor antigen. This modular approach provides a strategic foundation for expanding the company's pipeline and addressing a wider array of hard-to-treat cancers in the future.