A DNA-Based T Cell Receptor Reveals a Role for Receptor Clustering in Ligand Discrimination

Highlights

• A synthetic T cell signaling system was created using receptor ligands made of DNA

• T cell signaling can discriminate between DNA ligands differing by a single base pair

• Higher-affinity ligands promote the clustering and phosphorylation of receptors

• Receptor clustering provides a kinetic proofreading mechanism for ligand discrimination

Summary

A T cell mounts an immune response by measuring the binding strength of its T cell receptor (TCR) for peptide-loaded MHCs (pMHC) on an antigen-presenting cell. How T cells convert the lifetime of the extracellular TCR-pMHC interaction into an intracellular signal remains unknown. Here, we developed a synthetic signaling system in which the extracellular domains of the TCR and pMHC were replaced with short hybridizing strands of DNA. Remarkably, T cells can discriminate between DNA ligands differing by a single base pair. Single-molecule imaging reveals that signaling is initiated when single ligand-bound receptors are converted into clusters, a time-dependent process requiring ligands with longer bound times. A computation model reveals that receptor clustering serves a kinetic proofreading function, enabling ligands with longer bound times to have disproportionally greater signaling outputs. These results suggest that spatial reorganization of receptors plays an important role in ligand discrimination in T cell signaling.