Nevertheless, these approaches have succeeded in identifying peptide-specific TCRm Abs. Hit rates are low, given than Abs can bind to any epitope on the pMHC because, unlike TCRs, Abs are not naturally biased to engage the composite peptide and MHC surface, which constitutes only a minor fraction of the total pMHC surface available for binding. In each case, a de novo screening campaign must be undertaken for each pMHC target 5, 6, 13, 14, 15, 16, 17. TCRm Abs are generally isolated through conventional approaches such as mouse hybridoma and phage-display library technologies 12. Isolation of MHC-restricted Abs that bind with high affinity to pMHC surfaces and with complete peptide selectivity is a difficult technical challenge that is time-consuming and has a low yield 11.Ĭurrent technologies available for isolation of TCRm Abs do not account for the structural energetic differences between Ab- and TCR-mediated recognition of antigens (Fig. Ab binding sites were not evolved for antigen-specific recognition of the composite peptide–major histocompatibility complex (pMHC) surface. This delicate energetic balance between MHC helical recognition and peptide specificity enables the TCR to finely discriminate between different self and foreign peptides in a process called scanning 10. TCRs principally, although not exclusively, use germline-derived CDR1s and CDR2s to engage MHC helices with very low affinity, while the focused genetic diversity of CDR3 loops is largely, although not exclusively, for engaging ‘up-facing’ amino acid residues of the peptide antigen bound in the MHC groove 8, 9. In contrast, αβ-TCRs use a more nuanced, MHC-restricted recognition scheme due to the composite nature of the peptide–MHC surface 7 (Fig. Antibodies use both complementarity-determining region 3 (CDR3) diversity and somatic hypermutation to achieve high affinity for surfaces of protein targets using all six CDR loops. However, antibodies and αβ-TCRs have evolved fundamental structural differences in how they recognize their targets, which limits current TCRm technology (Fig. Such TCRm Abs can be used in a variety of formats to achieve different modalities of target killing, including IgG for antibody–drug conjugates (ADC) and/or antibody-dependent cellular cytotoxicity (ADCC), bispecific T cell engager (BiTEs) 5 and in the context of chimeric antigen receptor-T (CAR-T) 6. mAbs specific for peptide tumor antigens presented by major histocompatability complex (MHC) proteins, termed TCR-mimic (TCRm) Abs, are an emerging immunotherapy modality capable of recognizing a broad array of tumor antigens expressed at low levels on the tumor cell surface 3, 4. Monoclonal antibodies (mAbs) are effective therapeutic agents because of their high affinity and target specificity, as well as their drug-like properties 1, 2. This approach can yield tumor antigen-specific antibodies in several weeks, potentially enabling rapid clinical translation. Crystallographic analysis of one selected pMHC-restricted Ab revealed highly peptide-specific recognition, validating the engineering strategy. We created structure-based libraries focused on the peptide-interacting residues of TCRm Ab complementarity-determining region (CDR) loops, and rapidly generated MHC-restricted Abs to both mouse and human tumor antigens that specifically killed target cells when formatted as IgG, bispecific T cell engager (BiTE) and chimeric antigen receptor-T (CAR-T). Here, we present a strategy for rapid isolation of highly peptide-specific and ‘MHC-restricted’ Abs by re-engineering preselected Abs that engage peptide–MHC in a manner structurally similar to that of conventional αβ-TCRs. However, isolation of ‘TCR-mimic’ (TCRm) Abs is laborious because Abs have not evolved the structurally nuanced peptide–MHC restriction of αβ-TCRs. Monoclonal antibodies (Abs) that recognize major histocompatability complex (MHC)-presented tumor antigens in a manner similar to T cell receptors (TCRs) have great potential as cancer immunotherapeutics.
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