Moritz et al. demonstrated that introduction of a disulfide (DS) bond in a peptide-binding region allows for production of a stable empty HLA-A*02:01 molecule, which could be loaded with peptide via quick incubation at room temperature. TCRs bound to the cognate peptide-loaded DS-A*02:01 and wild-type A*02:01 molecules with similar affinities. The DS-stabilized empty MHC molecules were suitable for high-throughput screening of bispecific (bs)TCR binding affinities and for identification of cross-reactive peptide motifs that could cause off-target toxicities. pMHC-bsTCR binding affinities generally correlated with in vitro T cell activation.

Major histocompatibility complex (MHC) class I molecules present short peptide ligands on the cell surface for interrogation by cytotoxic CD8(+) T cells. MHC class I complexes presenting tumor-associated peptides such as neoantigens represent key targets of cancer immunotherapy approaches currently in development, making them important for efficacy and safety screenings. Without peptide ligand, MHC class I complexes are unstable and decay quickly, making the production of soluble monomers for analytical purposes labor intensive. We have developed a disulfide-stabilized HLA-A*02:01 molecule that is stable without peptide but can form peptide-MHC complexes (pMHCs) with ligands of choice in a one-step loading procedure. We illustrate the similarity between the engineered mutant and the wild-type molecule with respect to affinity of wild-type or affinity-matured T cell receptors (TCRs) and present a crystal structure corroborating the binding kinetics measurements. In addition, we demonstrate a high-throughput binding kinetics measurement platform to analyze the binding characteristics of bispecific TCR (bsTCR) molecules against diverse pMHC libraries produced with the disulfide-stabilized HLA-A*02:01 molecule. We show that bsTCR affinities for pMHCs are indicative of in vitro function and generate a bsTCR binding motif to identify potential off-target interactions in the human proteome. These findings showcase the potential of the platform and the engineered HLA-A*02:01 molecule in the emerging field of pMHC-targeting biologics.

Author Info: (1) Department of Immunology, Institute for Cell Biology, University of Tubingen, Tubingen, Germany. andreas.moritz@student.uni-tuebingen.de maurer@immatics.com. Immatics Biotechno

Author Info: (1) Department of Immunology, Institute for Cell Biology, University of Tubingen, Tubingen, Germany. andreas.moritz@student.uni-tuebingen.de maurer@immatics.com. Immatics Biotechnologies GmbH, Tubingen, Germany. (2) Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany. (3) Immatics Biotechnologies GmbH, Tubingen, Germany. (4) Immatics Biotechnologies GmbH, Tubingen, Germany. (5) Immatics Biotechnologies GmbH, Tubingen, Germany. (6) Immatics Biotechnologies GmbH, Tubingen, Germany. (7) Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany. (8) European Molecular Biology Laboratory (EMBL), Hamburg Outstation, Notkestrasse 85, D-22607 Hamburg, Germany. (9) European Molecular Biology Laboratory (EMBL), Hamburg Outstation, Notkestrasse 85, D-22607 Hamburg, Germany. (10) Department of Immunology, Institute for Cell Biology, University of Tubingen, Tubingen, Germany. (11) Department of Life Sciences and Chemistry, Jacobs University, Bremen, Germany. (12) Immatics Biotechnologies GmbH, Tubingen, Germany. andreas.moritz@student.uni-tuebingen.de maurer@immatics.com.