CD70 and autoimmune disease: ,9 CD70, a member of the tumor necrosis factor family, is a costimulatory molecule that is absent on resting lymphocytes but expressed after activation.10, 11, 12 Engagement of CD70 with its sole receptor CD27 plays a crucial role in T-cell activation13, 14, 15 and has been implicated in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus.16