Cluster of Differentiation 70 (CD70), also known as CD27 ligand (CD27L/CD27LG) or TNFSF7, is a type II transmembrane glycoprotein belonging to the Tumor Necrosis Factor (TNF) superfamily. CD70 is a surface antigen expressed on activated T- and B-lymphocytes and mature dendritic cells. The interaction of CD70 with its receptor CD27 leads to the priming, effector functions, differentiation, and memory formation of T-cells. Consequently, CD70 is involved in biological processes including T-cell activation, proliferation of costimulated T-cells, and the generation of cytolytic T-cells. On T-cells, CD70 provides costimulatory signals necessary for T cell proliferation, clonal expansion, and the promotion of effector T cell formation. In mice, CD70 on B-cells has been shown to inhibit the terminal differentiation of activated B cells into plasma cells and to enhance commitment to memory B cell responses. Additionally, CD70 induces proliferation and IFNγ production in NK cells.