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

Abstract

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 TCRαβ heterodimer selection and resultant diversity is unclear. The D b PA 224 -specific TCR repertoire in influenza A virusinfected C57BL/6J (B6) mice exhibits a preferred TCRV-region bias toward the TRBV29 gene segment and an optimal complementarity determining region (CDR3) β-length of 6 aa. Despite these restrictions, D b PA 224 -specific BV29 + T cells use a wide array of unique CDR3β sequences. Structural characterization of a single, TRBV29 + D b P A224 -specific TCRαβ-pMHCI complex demonstrated that CDR3α amino acid side chains made specific peptide interactions, but the CDR3β main chain exclusively contacted peptides. Thus, length but not amino acid sequence was key for recognition and flexibility in Vβ-region use. In support of this hypothesis, retrovirus expression of the D b PA 224 -specific TCRVα-chain was used to constrain pairing within a naive/immune epitope-specific repertoire. The retrogenic TCRVα paired with a diversity of CDR3βs in the context of a preferred TCRVβ 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.T cell repertoire | T-cell receptor bias | crystal structure T he adaptive T-cell response to viruses is mediated via T-cell receptor (TCR)-αβ glycoprotein heterodimer recognition of pathogen-derived peptides (p) complexed to cell-surface MHC glycoproteins. During T-cell development, somatic recombination of variable (V) and joining (J) or V, diversity (D), and J gene segments (1) leads to the emergence of a diverse spectrum of TCRα-and TCRβ-chains. Segments of hypervariability within the Vα and Vβ domains, termed complementarity determining regions (CDRs), form the TCRαβ binding site and mediate contact with a given pMHC complex. Although the CDR1 and -2 regions are determined by germ-line sequences of V-genes, the CDR3 region is encoded at the junction of spliced VJ (TCRα) and VDJ (TCRβ) gene segments. The murine TCRβ (TRB) locus consists of 35 V, 2 D, and 12 J gene segments and the TCRα (TRA) locus has 71 V and 60 J gene segments (2). Beyond the random splicing of different TCRα and TCRβ genes, the overall spectrum of TCR diversity largely reflects the inefficient splicing of DNA encoding the CDR3α and CDR3β loops (3) plus the addition of nontemplated encoded nucleotides at the V(D)J junctions (4). Finally, different pairings of rearranged TCRα-and TCRβ-chains are selected during thymic differentiation to give the naive TCRαβ repertoire.

Fixed Expression of Single Influenza Virus–Specific TCR Chains Demonstrates the Capacity for TCR α– and β–Chain Diversity in the Face of Peptide–MHC Class I Specificity

“…The strong pattern of amino acid conservation within the CDR3a region suggests that the SGGSNYKL sequence might play an important role in determining TCR specificity for D b PA 224 . This prediction is consistent with our previous work, which showed that the PA 6218 TCR used specific residues within the SGGSNYKL CDR3a sequence to make direct contacts with the PA 224 peptide and provide exquisite peptide specificity (41). To demonstrate that the biased usage of this CDR3a motif was Ag-driven and not a consequence of its prevalence in the global naive TRAV21 + repertoire, we performed CDR3a sequence analysis of TRAV21 + chains expressed by GFP + CD8 + T cells from naive PAb Rg mice and demonstrated extensive sequence diversity in this repertoire (Supplemental Table I Table I).…”

Organization of lampreyvariable lymphocyte receptor Clocus and repertoire development

“…From a genomic standpoint, the incomplete germ-line VLRC gene serves as an equivalent of the constant gene segment, whereas the clusters of different types of donor genomic cassettes represent the functional correlates of the clusters of V, D, and J gene segments of Ig or TCR loci in jawed vertebrates (20)(21)(22). Interestingly, the donor LRRencoding cassettes are not used equally for VLR assembly, in analogy with the preferential use of certain V, D, and J segments in Ig/TCR recombinations in jawed vertebrates (23)(24)(25)(26).…”

MHC-derived allopeptide activates TCR-biased CD8+ Tregs and suppresses organ rejection

“…This appears to be the case in our model, suggesting that this process may be modified by either TCR expansion or TCRα chain pairing. More recent reports have revealed the important contribution of the α chain in specific pMHC recognition and how TCRαβ diversity should be taken into consideration, as some specific TCR Vα pairings dictate and alter MHC restriction (48,49). In the literature, a consensus on TCR diversity of naive CD4 + Tregs was obtained, stating that more is better.…”