A TCRα framework–centered codon shapes a biased T cell repertoire through direct MHC and CDR3β interactions
Kristin Støen Gunnarsen, … , Inger Sandlie, Geir Åge Løset
Kristin Støen Gunnarsen, … , Inger Sandlie, Geir Åge Løset
Published September 7, 2017
Citation Information: JCI Insight. 2017;2(17):e95193. https://doi.org/10.1172/jci.insight.95193.
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Research Article Immunology

A TCRα framework–centered codon shapes a biased T cell repertoire through direct MHC and CDR3β interactions

Abstract

Selection of biased T cell receptor (TCR) repertoires across individuals is seen in both infectious diseases and autoimmunity, but the underlying molecular basis leading to these shared repertoires remains unclear. Celiac disease (CD) occurs primarily in HLA-DQ2.5+ individuals and is characterized by a CD4+ T cell response against gluten epitopes dominated by DQ2.5-glia-α1a and DQ2.5-glia-α2. The DQ2.5-glia-α2 response recruits a highly biased TCR repertoire composed of TRAV26-1 paired with TRBV7-2 harboring a semipublic CDR3β loop. We aimed to unravel the molecular basis for this signature. By variable gene segment exchange, directed mutagenesis, and cellular T cell activation studies, we found that TRBV7-3 can substitute for TRBV7-2, as both can contain the canonical CDR3β loop. Furthermore, we identified a pivotal germline-encoded MHC recognition motif centered on framework residue Y40 in TRAV26-1 engaging both DQB1*02 and the canonical CDR3β. This allowed prediction of expanded DQ2.5-glia-α2–reactive TCR repertoires, which were confirmed by single-cell sorting and TCR sequencing from CD patient samples. Our data refine our understanding of how HLA-dependent biased TCR repertoires are selected in the periphery due to germline-encoded residues.

Authors

Kristin Støen Gunnarsen, Lene Støkken Høydahl, Louise Fremgaard Risnes, Shiva Dahal-Koirala, Ralf Stefan Neumann, Elin Bergseng, Terje Frigstad, Rahel Frick, M. Fleur du Pré, Bjørn Dalhus, Knut E.A. Lundin, Shuo-Wang Qiao, Ludvig M. Sollid, Inger Sandlie, Geir Åge Løset

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Figure 5

A structural basis for the reduced responsiveness of the TRAV26-1/TRAV26-2 T cell receptor (TCR) variants.

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A structural basis for the reduced responsiveness of the TRAV26-1/TRAV26...
TCR α-chain, light gray; MHC β-chain, pale green; DQ2.5-glia-α2 peptide, yellow; canonical CDR3β, wheat. Residues of TCR3 in red; TCR2 in light pink; TCR4 in magenta. All residues mutated in the TCRs are specified in Table 1. H-bonds, green dashes; salt bridges, pink dashes. Based on PDB: 4OZH (14). (A) Of the variant FR2 residues, only Y40TRAV interacts directly with pMHC (R70MHCβ). Y40H of TCR3 partly disrupts the polar interactions network between TRAV, HLA-DQ2.5β, and CDR3β. Residue 39TRAV is close to 40TRAV and is illustrated. (B) The direct interaction of N36 with p2Q of DQ2.5-glia-α2 is abrogated by the N36T mutation of TCR2. (C) The K58T alteration in TCR7 disrupts the salt bridge formed between K58 of TRAV26-1 and D76 of MHCα. (D) The effect of the single Y40H mutation on T cell responsiveness was assessed using HLA-DQ2.5+ EBV-B cells loaded with 33merE peptide. Dotted line indicates half-maximum response. (E) Titrated amounts of A20 B cells expressing HLA-DQ2.5 or HLA-DQ2.2 with covalently linked peptide were used as antigen-presenting cells (APCs) to stimulate BW T cells transduced with either 364WT, the TRAV26-2 exchange variant, or the 364 Y40H variant as indicated. (D and E) Error bars indicate ± SD of triplicates and the experiments were conducted 2 independent times. Figures were prepared using GraphPad Prism 7. Nonlinear regression analysis (3 parameters) was used to derive IL-2 concentrations from the standard curves.