CD27 is a member of the TNF-receptor superfamily. This receptor is required for generation and long-term maintenance of T cell immunity. It binds to ligand CD70, and plays a key role in regulating B-cell activation and immunoglobulin synthesis. When CD27 binds CD70, a signaling cascade leads to the differentiation and clonal expansion of T cells. The cascade also results in improved survival and memory of cytotoxic T cells and increased production of certain cytokines. It is currently of interest to immunologists as a co-stimulatory immune checkpoint molecule, and is the target of an anti-cancer drug in clinical trials.