Alterations in TCR-MHC contacts subsequent to cross-recognition of class I MHC and singly substituted peptide variants

Vesicular stomatitis virus (VSV) elicits H-2K^b-restricted CTLs specific for the immunodominant VSV octapeptide RGYVYQGL. To study the structural features important for interaction between the TCR β-chain and the peptide/MHC complex, we immunized TCR α-chain transgenic mice with the VSV peptide and raised a panel of anti-VSV CTL clones with identical TCR α- chains. Consistent with our previous analysis of uncloned populations of primary CTLs, the anti-VSV CTL clones were all Vβ13⁺ and expressed TCR β- chains with highly homologous complementarity-determining region 3 (CDR3) loops. Although the clones expressed similar TCRs, they differed in their ability to cross-react with VSV peptide variants singly substituted at TCR contact positions 4 and 6. These findings allowed us to identify short stretches of amino acids in the C-terminal region of the CDR3β loop that, when altered, modify the cross-reaction capability of the TCR to position 4 and position 6 variant peptides. To further probe the structural correlates of biologic cross-reactivity, we used cross-reactive CTL clones and cell lines expressing point mutations in H-2K(b) to investigate the effect of single amino acid changes in the peptide on the pattern of recognition of the TCR for the peptide/MHC complex. Single conservative substitutions in the peptide were sufficient to alter the recognition contacts between a cross- reactive TCR and the MHC molecule, supporting the idea that the TCR can make overall structural adjustments in MHC contacts to accommodate single amino acid changes in the peptide.