Structures of human γδ T cell receptor-CD3 complex.

Gamma delta (γδ) T cells, a unique T cell subgroup, are crucial in various immune responses and immunopathology 1-3 . The γδ T cell receptor (TCR), generated by γδ T cells, recognizes a diverse range of antigens independently of the major histocompatibility complex 2 . The γδ TCR associates with CD3 subunits, initiating T cell activation and holding great potential in immunotherapy 4 . Here, we report the structures of two prototypical human Vγ9Vδ2 and Vγ5Vδ1 TCR-CD3 complexes 5,6 , unveiling two distinct assembly mechanisms that depend on Vγ usage. The Vγ9Vδ2 TCR-CD3 complex is monomeric, with considerable conformational flexibility in the TCRγ/TCRδ extracellular domain (ECD) and connecting peptides (CPs). The length of CPs regulates the ligand association and T cell activation. Additionally, a cholesterol-like molecule wedges into the transmembrane region, exerting an inhibitory role in TCR signaling. The Vγ5Vδ1 TCR-CD3 complex displays a dimeric architecture, where two protomers nestle back-to-back via their Vγ5 domains of TCR ECDs. Our biochemical and biophysical assays further corroborate the dimeric structure. Importantly, the dimeric form of the Vγ5Vδ1 TCR is essential for T cell activation. These findings reveal organizing principles of the γδ TCR-CD3 complex, providing insights into the γδ TCR unique properties and facilitating immunotherapeutic interventions.