Writing in Cell, Sušac et al. use a melanoma-specific peptide-loaded MHC to trap and isolate a corresponding TCR, and determine the structure of the complete complex using cryo-electron microscopy. The structure shows that the complex is stabilized by a network of interlocking multivalent interactions, with the loaded peptide stabilizing the interactions at the interface between the TCR and the MHC. Moreover, sterol lipids observed between the transmembrane helices of the TCR indicate their involvement in the assembly of the complex.