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

T-cell engagers (TCEs) for cancer immunotherapy have traditionally relied on high affinity single chain fragment variable (scFv) domains to target CD3, specifically the ε chain, for the activation of T-cells. Despite their clinical success, there have been reports of TCEs driving systemic toxicity, non-specific T-cell activation, on-target off-tumor effects, and severe inflammation due to cytokine release. To address these limitations, we designed multivalent TCEs using Chemically Self-Assembled Nanorings (CSANs) that target the α/β constant region of the T-cell receptor (TCR) in the TCR/CD3 complex using a moderate affinity αTCR nanobody (αTCR VHH ). Nanobodies offer superior physical and chemical properties over scFvs-including higher solubility, stability and lower production cost-making them increasingly popular as structural units of TCEs. We compared the efficacy and safety profile of this moderate affinity, nanobody-based TCR binder against high affinity αCD3 scFv based CSANs across EGFR and PSMA expressing solid tumor models. While the αCD3 scFv CSANs offered potent cytotoxicity, they also induced antigen independent T-cell activation bypassing the requirement of tumor crosslinking for cytotoxicity. In contrast the αTCR VHH CSANs required strict antigen engagement to trigger cytotoxicity, significantly reducing non-specific T-cell activation and thus enhancing the safety profile. Although the initiation of cytotoxicity was kinetically slower than the αCD3 scFv counterpart, αTCR VHH CSANs achieved comparable end point cytotoxicity across multiple antigen densities, as well as in 3D tumor spheroids. Through this study we demonstrate the applicability of nanobodies as T-cell targeting domains, enhanced specificity and safety of moderate affinity T-cells binders and the diversification of T-cell targeting epitopes without compromising the efficacy of TCEs.