T-cell Receptor (TCR) Targeting with Multivalent T-cell Engagers

Area of Science:

• Immunology
• Oncology
• Biotechnology

Background:

• Traditional T-cell engagers (TCEs) targeting CD3 exhibit systemic toxicity and non-specific T-cell activation.
• High-affinity single chain fragment variable (scFv) domains in TCEs can lead to severe inflammation and cytokine release.
• Limitations of current TCEs necessitate novel strategies for improved safety and specificity in cancer immunotherapy.

Purpose of the Study:

• To design and evaluate novel multivalent TCEs utilizing nanobodies targeting the T-cell receptor (TCR) for enhanced specificity and safety.
• To compare the efficacy and safety of moderate-affinity nanobody-based TCR binders against high-affinity scFv-based CD3 binders.
• To investigate the potential of targeting the TCR/CD3 complex's α/β constant region for antigen-specific T-cell activation.

Main Methods:

• Development of multivalent TCEs using Chemically Self-Assembled Nanorings (CSANs) with moderate-affinity αTCR nanobodies (αTCR VHH).
• Comparison of αTCR VHH CSANs against high-affinity αCD3 scFv CSANs in solid tumor models expressing EGFR and PSMA.
• Assessment of T-cell activation, cytotoxicity, and safety profiles in vitro and in 3D tumor spheroids.

Main Results:

• Moderate-affinity αTCR VHH CSANs demonstrated antigen-dependent cytotoxicity, significantly reducing non-specific T-cell activation compared to αCD3 scFv CSANs.
• αTCR VHH CSANs exhibited a more favorable safety profile by requiring strict antigen engagement for T-cell activation.
• Comparable endpoint cytotoxicity was achieved with αTCR VHH CSANs across various antigen densities and in 3D tumor spheroids, despite slower initial activation kinetics.

Conclusions:

• Nanobodies are effective T-cell targeting domains for TCE development, offering superior properties over scFvs.
• Moderate-affinity TCR binders enhance specificity and safety of TCEs by enabling antigen-specific T-cell activation.
• Diversifying T-cell targeting epitopes, such as the TCR/CD3 complex's α/β constant region, can improve TCE efficacy and safety without compromising therapeutic outcomes.