Butyrophilin-like 3 Directly Binds a Human Vγ4+ T Cell Receptor Using a Modality Distinct from Clonally-Restricted Antigen

Carrie R Willcox,Pierre Vantourout,Mahboob Salim,Iva Zlatareva,Daisy Melandri,Leonor Zanardo,Roger George,Svend Kjaer,Mark Jeeves,Fiyaz Mohammed,Adrian C Hayday,Benjamin E Willcox

doi:10.1016/j.immuni.2019.09.006

Carrie R Willcox, Pierre Vantourout + Show 10 more

Open Access

https://doi.org/10.1016/j.immuni.2019.09.006

Copy DOI

Abstract

SummaryButyrophilin (BTN) and butyrophilin-like (BTNL/Btnl) heteromers are major regulators of human and mouse γδ T cell subsets, but considerable contention surrounds whether they represent direct γδ T cell receptor (TCR) ligands. We demonstrate that the BTNL3 IgV domain binds directly and specifically to a human Vγ4+ TCR, “LES” with an affinity (∼15–25 μM) comparable to many αβ TCR-peptide major histocompatibility complex interactions. Mutations in germline-encoded Vγ4 CDR2 and HV4 loops, but not in somatically recombined CDR3 loops, drastically diminished binding and T cell responsiveness to BTNL3-BTNL8-expressing cells. Conversely, CDR3γ and CDR3δ loops mediated LES TCR binding to endothelial protein C receptor, a clonally restricted autoantigen, with minimal CDR1, CDR2, or HV4 contributions. Thus, the γδ TCR can employ two discrete binding modalities: a non-clonotypic, superantigen-like interaction mediating subset-specific regulation by BTNL/BTN molecules and CDR3-dependent, antibody-like interactions mediating adaptive γδ T cell biology. How these findings might broadly apply to γδ T cell regulation is also examined.

Highlights

Few direct ligands of the gd T cell receptor (TCR) underpinning innate-like or adaptive responses are known
We show that a human Vg4 TCR binds the BTNL3 IgV domain via germline-encoded regions, somewhat analogous to superantigen binding to an ab TCR
The BTNL3 IgV Domain Directly and Binds Vg4 TCRs Previously, we demonstrated that exposure of Jurkat cells transduced with Vg4+ gd TCRs to 293T cells expressing BTNL3.8 heterodimers (293T.L3L8) led to CD69 upregulation and TCR downregulation, consistent with TCR triggering (Melandri et al, 2018)

Summary

Introduction

Few direct ligands of the gd TCRs underpinning innate-like or adaptive responses are known. Adaptive processes highlight powerful clonotypic focusing even within specific V region subsets (e.g., Vd1 T cells, Vd1negVd2neg T cells, and Vg9negVd2 T cells), strongly suggesting that somatically recombined CDR3 regions are involved (Davey et al, 2018a). A diverse range of ligands has been proposed for such populations, including those few supported by evidence of direct TCR-ligand interaction, many of which favor roles for CDR3 residues (Willcox and Willcox, 2019)

Methods

Results

Discussion

Conclusion