To precisely control the nanoscale spatial arrangement of T cell-activating cues and permit remodeling after cellular contact, Hellmeier et al. anchored anti-TCR scFv or peptide-MHC (pMHC) complexes to supported lipid bilayers on a DNA origami platform. T cell activation, assessed through calcium flux and ZAP-70 recruitment, depended on anti-TCR scFv spacing; a minimum of two scFvs, especially when located adjacent to one another (10-20nm), triggered T cell activation. In contrast, a single isolated pMHC effectively induced T cell activation, suggesting serial activation of TCR clusters by a single pMHC.
Contributed by Alex Najibi
ABSTRACT: T cells detect with their T cell antigen receptors (TCRs) the presence of rare agonist peptide/MHC complexes (pMHCs) on the surface of antigen-presenting cells (APCs). How extracellular ligand binding triggers intracellular signaling is poorly understood, yet spatial antigen arrangement on the APC surface has been suggested to be a critical factor. To examine this, we engineered a biomimetic interface based on laterally mobile functionalized DNA origami platforms, which allow for nanoscale control over ligand distances without interfering with the cell-intrinsic dynamics of receptor clustering. When targeting TCRs via stably binding monovalent antibody fragments, we found the minimum signaling unit promoting efficient T cell activation to consist of two antibody-ligated TCRs within a distance of 20 nm. In contrast, transiently engaging antigenic pMHCs stimulated T cells robustly as well-isolated entities. These results identify pairs of antibody-bound TCRs as minimal receptor entities for effective TCR triggering yet validate the exceptional stimulatory potency of single isolated pMHC molecules.