Height, but not binding epitope, affects the potency of synthetic TCR agonists

Abstract

Under physiological conditions, peptide-MHC (pMHC) molecules can trigger T-cell receptors (TCRs) as monovalent ligands, sparsely distributed on the plasma membrane of an antigen-presenting cell. TCR can also be activated by artificial clustering, such as with pMHC tetramers or antibodies; however, these strategies circumvent many of the natural ligand discrimination mechanisms of the T cell and can elicit non-physiological signaling activity. We have recently introduced a synthetic TCR agonist composed of an anti-TCRβ Fab′ antibody fragment covalently bound to a DNA oligonucleotide, which serves as a membrane anchor. This Fab′-DNA ligand efficiently activates TCR as a monomer when membrane-associated and exhibits a potency and activation profile resembling agonist pMHC. In this report, we explore the geometric requirements for effective TCR triggering and cellular activation by Fab′-DNA ligands. We find that T cells are insensitive to the ligand binding epitope on the TCR complex, but that length of the DNA tether is important. Increasing the intermembrane distance spanned by Fab′-DNA:TCR complexes decreases TCR triggering efficiency and T cell activation potency. These results establish design parameters for construction of synthetic TCR agonists that are able to activate polyclonal T cell populations, such as T cells from a human patient, in a similar manner as the native pMHC ligand.

Size-dependent activation of CAR-T cells

“…Spatial reorganization of proteins at the cell-cell interface serves as an important principle in understanding receptor activation (14,15). This is illustrated by the "kinetic segregation" model, in which T cell receptor (TCR)-peptide major histocompatibility complex (pMHC) interactions exclude a bulky phosphatase CD45 away from the TCR, leading to TCR phosphorylation by the kinase Lck (12,(16)(17)(18)(19)(20). A similar size-dependent spatial segregation is found in the phagocytic receptor (21,22), immunoglobulin E (IgE) receptor (23), and Notch receptor signaling (24).…”