FairJourney Bio has helped engineer a reversible antibody switch designed to activate the potent cancer cytokine IL-12 only in the tumour environment.

IL-12 has long attracted interest as an anti-tumour therapy because of its ability to stimulate immune responses against cancer. But systemic toxicity has made it difficult to develop IL-12 into a broadly usable treatment.

A study published in mAbs describes an antibody-engineering approach designed to tackle that problem by keeping IL-12 inactive until the molecule encounters fibronectin-EDB (FN-EDB), a matrix protein associated with tumours.

The work involved scientists from FairJourney Bio, IONTAS, Third Rock Ventures and Certara. FairJourney Bio carried out the antibody discovery and engineering campaign across its teams in Porto and Cambridge.

A molecular switch for IL-12

The approach uses a dual-specificity antigen-binding fragment, or Fab, as a molecular switch.

One part of the switch binds IL-12 while another recognises FN-EDB. The binding properties were deliberately balanced so that IL-12 can be masked away from the tumour, but become available when the molecule encounters FN-EDB in the tumour microenvironment.

A separate, higher-affinity FN-EDB targeting arm is intended to concentrate the molecule at the tumour site.

That gives the format two jobs: targeting the tumour-associated matrix and controlling when IL-12 becomes available.

The researchers used quantitative systems pharmacology (QSP) modelling to establish the binding characteristics needed for the switch before engineering a candidate molecule.

FairJourney Bio then introduced IL-12 binding into existing FN-EDB binders using targeted mutagenesis and optimised the two binding specificities through a combinatorial engineering campaign.

The resulting molecule had to sit within a relatively narrow affinity window. Too much binding in the wrong place could interfere with the switching mechanism, while insufficient binding could prevent effective tumour localisation.

Testing the conditional activation

The resulting format was tested using biochemical and cell-based experiments.

The study reported FN-EDB-dependent availability and activity of IL-12, supporting the proposed mechanism in which the cytokine becomes accessible after interaction with the tumour-associated matrix.

The researchers also used QSP modelling to predict how the switch could affect IL-12 exposure and activity compared with approaches that do not use the same conditional activation mechanism.

The modelling predicted an improved therapeutic window, although this remains a preclinical finding and the experimental work reported in the study is in vitro.

Teresa Barata, chief scientific officer and co-author at FairJourney Bio, said: “Harnessing the potent anti-tumor activity of IL-12 while limiting systemic toxicity has challenged researchers for almost 30 years.”

She added that the campaign required engineering to a predefined specification while balancing two unrelated binding targets within the same molecule.

Why the IL-12 angle matters

IL-12 has been investigated as a cancer immunotherapy for decades, but its potency can become a liability when the cytokine is active throughout the body.

Previous attempts to improve its therapeutic window have included changing how IL-12 is delivered, extending its half-life and designing versions that are activated by tumour-associated conditions.

The FairJourney Bio approach takes a different route by using antibody binding as a reversible control mechanism.

That makes the engineering challenge particularly interesting. Rather than simply creating an antibody that binds a tumour target, the researchers had to tune competing interactions so the molecule could behave differently depending on whether it was exposed to free IL-12 or FN-EDB.

The authors describe the work as the first reported demonstration of a reversible trans-activation logic gate for tumour-conditional cytokine delivery.

There is an important caveat: the study does not establish whether the approach works as a cancer treatment in animals or humans. No mouse or other animal experiments are reported. The evidence comes from biochemical and cell-based experiments alongside QSP modelling.

For now, the significance is therefore the engineering concept rather than a new oncology therapy ready for clinical development.

But it is a good example of where antibody engineering is moving beyond simply finding molecules that bind a target. Here, the binding characteristics themselves are being used to create a conditional biological response.

That makes this one worth watching as the field looks for ways to harness powerful cytokines without exposing the whole body to their effects.