Abstract PR04: Anti peptide-HLA (TCR-like) antibodies specific for the KRAS G12V neoantigen

Abstract

Abstract The remarkably high prevalence of Ras driver mutations in tumors of diverse origins and stages indicates that Ras neoantigens are poor substrates for HLA-mediated detection by the native immune system. Nevertheless, immunotherapies based upon tumor-infiltrating lymphocytes targeting Ras neoantigens have been reported, indicating that such mutations are subject to HLA display and immune surveillance. Antibodies capable of recognizing specific peptide-HLA complexes at the cell surface have the potential to target intracellular tumor neoantigens for therapeutic intervention. However, such reagents have proved to be challenging to develop. Using a novel antibody discovery platform in combination with a proprietary human germline scFv library, we have developed a rapid method for the isolation of antibodies against peptide-HLA complexes. Applying this technology to KRAS G12V, we have isolated two scFvs that recognize the peptide VVVGAVGVGK in complex with HLA-A*11:01. This peptide-HLA combination forms functional complexes both in vitro and at the cell surface and has been reported to elicit CTL responses in vivo. In contrast, the native peptide is a poor substrate for binding to HLA-A*11:01. Binding affinities of the two scFv binders for the target HLA complex are in the sub-100nM range. Both show highly specific, peptide-dependent recognition of the KRAS-HLA-A*11:01 complex, as demonstrated by the failure to bind complexes containing wild-type KRAS peptides or other control peptides. Alanine scanning mutagenesis reveals multiple residues within the neoepitope peptide that are critical for antibody binding, including the mutated valine residue. The extended binding footprint encompassing the neoepitope and the poor presentation of the unmutated peptide are likely to contribute to the on-target specificity of these antibodies. Incorporation of the scFvs into a bispecific T-cell engager (BiTE) format has demonstrated the simultaneous engagement of both the KRAS HLA-A*11:01 complex and the CD3 surface marker of T cells. Ongoing work is aimed to demonstrate BiTE-dependent CTL-mediated lysis of target cells displaying the KRAS HLA-A*11:01 complex. We are currently developing CAR-T cells carrying peptide-HLA specific scFvs and are screening further mutant Ras peptides in the context of other HLA-A subtypes. This abstract is also being presented as Poster B48. Citation Format: Avisa Maserati, Dahna Makris, Ben Kiefel, Matt Beasley, Brad McColl, Ben Clifton. Anti peptide-HLA (TCR-like) antibodies specific for the KRAS G12V neoantigen [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr PR04.