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 4

Fine-mapping the effect of germline-encoded TRAV26-1 and TRBV7-2 residues on T cell responsiveness.

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Fine-mapping the effect of germline-encoded TRAV26-1 and TRBV7-2 residue...
BW T cells engineered to express versions of TRAV26-1 and TRBV7-2 where either framework (FR) or germline CDR loops were mutated to the corresponding residues of TRAV26-2 and TRBV7-3 (exchanged residues are specified in Table 1) were evaluated for effect on T cell responsiveness. (A and B) Overview of the panel of T cell receptor (TCR) mutants (TCR 1–13) and the residues mutated in (A) TRAV26-1 and (B) TRBV7-2. TCR7 and TCR13 are combination mutants as indicated. TCR α-chain, light gray; TCR β-chain, pale blue. The crystal structure of TCR S16 containing TRAV26-1/TRBV7-2 was used (PDB: 4OZH) (12). (C and D) The left panels show the responsiveness of (C) TRAV and (D) TRBV variants to HLA-DQ2.5+ EBV-B cells loaded with titrated amounts of 33merE peptide given as relative IL-2 secretion. Dotted line indicates half-maximum response. The right panels show the EC50 values derived from the responses to the 33merE peptide of the (C) TRAV and (D) TRBV variants. The EC50 value of TCR7 (marked with a circle) could not be reliably determined, as saturation was not reached. The dotted line indicates the EC50 value of WT364. Four independent experiments were conducted and a representative experiment is shown. Untransduced BW T cells and T cells or antigen-presenting cells (APCs) with peptide alone were included as controls. Error bars indicate ± SD of triplicates. Figures were prepared using GraphPad Prism 7. Nonlinear regression analysis (3 parameters) was used to derive IL-2 concentrations from the standard curves. Graphs were normalized and EC50 values calculated using nonlinear regression analysis (log[agonist] vs. normalized response).