Immunobiological analysis of TCR single-chain transgenic mice reveals new possibilities for interaction between CDR3 alpha and an antigenic peptide bound to MHC class I

The interaction between TCRs and peptides presented by MHC molecules determ ines the specificity of the T cell-mediated immune response. To elucidate t he biologically important structural features of this interaction, we gener ated TCR beta -chain transgenic mice using a TCR derived from a T cell clon e specific for the immunodominant peptide of vesicular stomatitis virus (RG YVYQGL, VSV8) presented by H-2K(b). We immunized these mice with VSV8 or an alogs substituted at TCR contact residues (positions 1, 4, and 6) and analy zed the CDR3 alpha sequences of the elicited T cells. In VSV8-specific CTLs , we observed a highly conserved residue at position 93 of CDR3 alpha and p referred Ja usage, indicating that multiple residues of CDR3 alpha are crit ical for recognition of the peptide. Certain substitutions at peptide posit ion 4 induced changes at position 93 and in J alpha usage, suggesting a pot ential interaction between CDR3 alpha and position 4. Cross-reactivity data revealed the foremost importance of the J alpha region in determining Ag s pecificity. Surprisingly, substitution at position 6 of VSV8 to a negativel y charged residue induced a change at position 93 of CDR3 alpha to a positi vely charged residue, suggesting that CDR3 alpha may interact with position 6 in certain circumstances. Analogous interactions between the TCR alpha - chain and residues in the C-terminal half of the peptide have not yet been revealed by the limited number of TCR/peptide-MHC crystal structures report ed to date. The transgenic mouse approach allows hundreds of TCR/peptide-MH C interactions to be examined comparatively easily, thus permitting a wide- ranging analysis of the possibilities for Ag recognition in vivo.