Dendritic cells with potent Ag-presenting function can be propagated from peripheral blood using recombinant cytokines, and these cells have potential usefulness as immunotherapeutic agents in the treatment of cancer and other disease states. However, it is not known if these in vitro differentiated dendritic cells have the capacity to migrate in vivo, especially to T cell areas of lymphoid tissue. We have used a fluorescent marker system to track the migration of dendritic cells, propagated in vitro from chimpanzee peripheral blood, following s.c. injection. We report that injected dendritic cells migrate spontaneously and rapidly to draining lymph nodes, where they remain for at least 5 days. The injected cells interdigitate with T cells in the parafollicular and paracortical zones and retain high level expression of CD86, CD40, and MHC class II molecules, reflecting a phenotype of potent APC. We conclude that dendritic cells differentiated in vitro from peripheral blood and administered s.c. behave in a manner very similar to endogenous Langerhans cells. These data provide strong experimental support, in a highly relevant large animal model, for the use of in vitro differentiated dendritic cells as vehicles for immunotherapy. More importantly, they show that the s.c. route of injection delivers these APC to sites of T cell activation, a prerequisite for the generation of an effective immune response.