Canonical T cell receptor docking on peptide–MHC is essential for T cell signaling

Most T cells use a T cell receptor (TCR) that recognizes major histocompatibility complex molecules bound to peptides (pMHCs) derived from both self- and foreign antigens. Although there is great variability in the interface because of the diversity of both partners, this interaction displays a canonical docking topology for reasons that remain contested. Zareie et al. tested an assortment of both canonical and reversed-polarity TCRs that were all specific for the same cognate pMHC-I bearing a peptide derived from influenza A virus (IAV) (see the Perspective by Horkova and Stepanek). The authors determined that docking topology was the primary driver of in vivo T cell activation and recruitment when mice were infected with IAV. The canonical topology was required for the formation of a functional signaling complex, suggesting that T cell signaling constraints dictate how TCR and pMHC meet. Science , abe9124, this issue p. eabe9124 ; see also abj2937, p. 1038 The highly conserved nature of T cell antigen receptor recognition is required for the colocalization of key signaling molecules. T cell receptor (TCR) recognition of peptide–major histocompatibility complexes (pMHCs) is characterized by a highly conserved docking polarity. Whether this polarity is driven by recognition or signaling constraints remains unclear. Using “reversed-docking” TCRβ-variable (TRBV) 17 + TCRs from the naïve mouse CD8 + T cell repertoire that recognizes the H-2D b –NP 366 epitope, we demonstrate that their inability to support T cell activation and in vivo recruitment is a direct consequence of reversed docking polarity and not TCR–pMHCI binding or clustering characteristics. Canonical TCR–pMHCI docking optimally localizes CD8/Lck to the CD3 complex, which is prevented by reversed TCR–pMHCI polarity. The requirement for canonical docking was circumvented by dissociating Lck from CD8. Thus, the consensus TCR–pMHC docking topology is mandated by T cell signaling constraints.