Biophysical mechanism of T-cell receptor triggering in a reconstituted system

A T-cell-mediated immune response is initiated by the T-cell receptor (TCR) interacting with peptide-bound major histocompatibility complex (pMHC) on an infected cell. The mechanism by which this interaction triggers intracellular phosphorylation of the TCR, which lacks a kinase domain, remains poorly understood. Here, we have introduced the TCR and associated signalling molecules into a non-immune cell and reconstituted ligand-specific signalling when these cells are conjugated with antigen-presenting cells. We show that signalling requires the differential segregation of a phosphatase and kinase in the plasma membrane. An artificial, chemically controlled receptor system generates the same effect as TCR–pMHC, demonstrating that the binding energy of an extracellular protein–protein interaction can drive the spatial segregation of membrane proteins without a transmembrane conformational change. This general mechanism may extend to other receptors that rely on extrinsic kinases, including, as we demonstrate, chimaeric antigen receptors being developed for cancer immunotherapy. After introducing the T-cell receptor and other essential signalling genes, a non-immune cell is capable of displaying the early events of T-cell activation when placed in contact with antigen-presenting cells, and the initial signalling in this reconstituted system is shown to require the spatial reorganization of molecules at the cell interface. The basics of T-cell-receptor action This study probes a long-standing and unresolved question: how does the T-cell receptor (TCR) transduce a signal across the T-cell membrane after it binds peptide-bound major histocompatibility complex on an antigen-presenting cell? John James and Ronald Vale transplanted 13 genes into a non-immune cell to create an 'artificial T cell'. In this minimal system, chemical equilibrium established by the expression of the T-cell receptor, three kinases, an adaptor and a transmembrane phosphatase can control TCR homeostasis and triggering. T-cell-receptor signalling requires the differential segregation of a phosphatase and kinase in the plasma membrane.