T cells compete by cleaving cell surface CD27 and blocking access to CD70-bearing APCs

T cells compete against each other for access to molecules on antigen presenting cells (APC) in addition to peptide:MHC complexes. However, the identity of cell surface molecules that influence T cell competition, other than peptide:MHC, have yet to be defined. Here we identify CD70, a TNF ligand expressed on activated APCs, as an important mediator of T cell competition for APCs. Upon engagement of CD27 by CD70, CD27 is proteolytically cleaved from the surface of the interacting CD8+ T cell and captured by CD70 expressing dendritic cells. The capture of CD27 effectively masks CD70 on APCs, disallowing the interaction with CD27 on other competing T cells. Collectively, our data indicate that T cells compete against each other for access to the TNF-ligand CD70, an interaction that affects the duration and potency of T cell:DC interactions, thus influencing the repertoire of responding CD8+ T cells to self or foreign antigens.