Development of DARPin T cell engagers for specific targeting of tumor-associated HLA/peptide complexes

The balance between affinity and specificity in T cell receptor (TCR)-dependent targeting of HLA-restricted tumor-associated antigens presents a significant challenge for immunotherapy development. T cell engagers that circumvent these limitations are therefore of particular interest. We established a process to generate bispecific designed ankyrin repeat proteins (DARPins) that simultaneously target HLA-I/peptide complexes and CD3e. These high-affinity T cell engagers elicited CD8⁺ T cell activation against tumor targets with strong peptide specificity, as confirmed by X-scanning mutagenesis and functional killing assays. A cryo-EM structure of the ternary DARPin/HLA-A∗0201/NY-ESO1_157-165 complex revealed a rigid, concave DARPin surface spanning the full length of the peptide-binding cleft, contacting both α-helices and the peptide. The present findings reveal promising immuno-oncotherapeutic approaches and demonstrate the feasibility of rapidly developing DARPins with high affinity and specificity for HLA/peptide targets, which can be readily combined with a new generation of anti-CD3e-specific DARPins.