An efficient immune response requires coordination between innate and adaptive immunity, which act through cells different in origin and function. Here we report the identification of thymus-derived αβ-T-cell receptor(+) cells that express CD11c and major histocompatibility complex class II, and require FLT3 ligand for development (T(DC)). T(DC) express genes heretofore found uniquely in T cells or dendritic cells, as well as a distinctive signature of cytotoxicity-related genes. Unlike other innate T-cell subsets, T(DC) have a polyclonal T-cell receptor repertoire and respond to cognate antigens. However, they differ from conventional T cells in that they do not require help from antigen-presenting cells, respond to Toll-like receptor-mediated stimulation by producing interleukin-12 and process and present antigen. The physiological relevance of T(DC), found in mice and humans, is still under investigation, but the fact that they combine key features of T and dendritic cells suggests that they provide a bridge between the innate and adaptive immune systems