Cystatin-7 (CST7) is also known as Cystatin-F, Cystatin-like metastasis-associated protein (CMAP), Leukocystatin, which is a disulfide-linked homodimer belongs to the cystatin family. CST7 is primarily expressed in peripheral blood cells and spleen. CST7 inhibits papain and cathepsin L but with affinities lower than other cystatins. CST7 may play a role in immune regulation through inhibition of a unique target in the hematopoietic system.