Tuning the potency and selectivity of ImmTAC molecules by affinity modulation

Area of Science:

• Immunology
• Oncology
• Biochemistry

Background:

• T-cell-engaging bispecifics show promise for treating cancer and infectious diseases.
• Understanding the relationship between binding affinity/kinetics and bispecific molecule potency/specificity is crucial but incomplete.

Purpose of the Study:

• To investigate how altering target and CD3 binding affinities impacts the potency and specificity of redirected T-cell responses.
• To model these relationships using immune mobilizing monoclonal TCRs against cancer (ImmTAC) molecules.

Main Methods:

• Utilized ImmTAC molecules, which feature an affinity-enhanced T-cell receptor for target binding and an anti-CD3 effector moiety.
• Systematically varied the binding affinities of both the targeting and CD3 domains.
• Measured T-cell activation, cytokine release, and selectivity.

Main Results:

• Optimal T-cell activation was achieved with a high-affinity T-cell receptor and an intermediate-affinity anti-CD3 domain.
• High affinity in both targeting and effector domains reduced maximum cytokine release.
• Optimizing affinities for both domains improved the molecule's selectivity.
• Experimental observations were explained by a kinetic proofreading model with limited signaling.

Conclusions:

• The affinity of both targeting and CD3 domains significantly influences bispecific molecule efficacy and specificity.
• Excessively strong binding can lead to T-cell receptor inactivation via a signaling 'dark state'.
• Findings provide critical insights for designing potent and selective anti-CD3-based bispecific therapies.