Trispecific eFab-eIg T-cell engagers targeting HER2 and HER3.

Trispecific antibodies have emerged as molecules for enhanced cancer immunotherapy by addressing the complexity of cancer cell biology and anti-cancer immune responses. Here, we present a novel approach to generate trispecific antibodies based on the previously developed eIg technology. These trispecific antibodies comprise one Fab and two eFab moieties, fused to obtain an asymmetric eFab-eIg molecule. The design principle employs two different eFab building blocks, characterized by divergent arrangements of heterodimerizing hetEHD2 domains. Specifically, the first (inner) eFab arm comprises the hetEHD2-1 domain in the heavy chain and the corresponding hetEHD2-2 domain in one of the light chains, while in the second eFab (outer) this arrangement is reversed. The feasibility of this approach was demonstrated for a trispecific eFab-eIg T-cell engager (TCE) targeting HER2, HER3, and CD3. Importantly, the trispecific TCE retained binding activity for all three antigens and was capable of recruiting T-cells to HER2 and/or HER3-expressing cancer cells and mediating effective cancer cell killing, as shown in 2D and 3D model systems. Due to the modular architecture, this approach should be suitable to generate trispecific antibodies of any specificity and for a multitude of applications.