Insights from an in vitro derived T cell receptor

Abstract

Abstract Heterodimeric alpha-beta T cell receptors (TCRs) play a key role in cell-mediated immune responses of adaptive immunity. T cells continuously probe peptides presented by major histocompatibility complex (MHC) found on the cell surface. T cell activation initiates through the binding of antigenic peptides on MHCs. Yeast display technology has proven an effective way to gain insight into the underpinnings of peptide-MHC specificity enabling the switching of TCR affinity and specificity to unrelated antigens through directed evolution. Interestingly, in vitro directed evolution also generates mutants that lose peptide specificity. Here, we provide further detail of one of these cross-reactive TCRs, S3–4, which binds tightly but with a highly unusual geometry. Despite binding with an affinity that is characteristic of a strong agonist, S3–4’s odd binding geometry does not support T cell signaling. Further investigation with functional experiments and 2D kinetics shows that lack of signaling by S3–4 is ultimately attributable to the TCR’s inability to reach ligand. Although S3–4 is an example from a constrained system generated outside the bounds of usual immune function, our results show how unusual binding can influence T cell function and further demonstrate how divergences between 3D and 2D binding parameters can emerge.