Structural basis for enabling T-cell receptor diversity within biased virus-specific CD8⁺ T-cell responses

Pathogen-specific responses are characterized by preferred profiles of peptide+class I MHC (pMHCI) glycoprotein-specific T-cell receptor (TCR) Variable (V)-region use. How TCRV-region bias impacts TCRalphabeta heterodimer selection and resultant diversity is unclear. The D(b)PA(224)-specific TCR repertoire in influenza A virus-infected C57BL/6J (B6) mice exhibits a preferred TCRV-region bias toward the TRBV29 gene segment and an optimal complementarity determining region (CDR3) beta-length of 6 aa. Despite these restrictions, D(b)PA(224)-specific BV29(+) T cells use a wide array of unique CDR3beta sequences. Structural characterization of a single, TRBV29(+)D(b)P(A224)-specific TCRalphabeta-pMHCI complex demonstrated that CDR3alpha amino acid side chains made specific peptide interactions, but the CDR3beta main chain exclusively contacted peptides. Thus, length but not amino acid sequence was key for recognition and flexibility in Vbeta-region use. In support of this hypothesis, retrovirus expression of the D(b)PA(224)-specific TCRValpha-chain was used to constrain pairing within a naive/immune epitope-specific repertoire. The retrogenic TCRValpha paired with a diversity of CDR3betas in the context of a preferred TCRVbeta spectrum. Overall, these data provide an explanation for the combination of TCRV region bias and diversity within selected repertoires, even as they maintain exquisite pMHCI specificity.