CCL25, which signals through CCR9 receptor, is mainly expressed in the thymus and small intestine. In the thymus, CCL25 contributes to correct thymocyte maturation by promoting CD4+CD8+ thymocyte trafficking through the cortex via alpha4beta1-dependent adhesion to VCAM-1, and also stimulates CD4+CD8- cell attachment to fibronectin in the medulla. In the small intestine, CCL25 is expressed by intestinal epithelium and controls segmental specialization of the intestinal immune system by recruiting gut-specific memory/effector T cells. CCL25 also promotes melanoma, ovarian cancer, breast cancer, leukemia, and prostatic carcinoma cell migration. A recent report shows that multiple myeloma cells can produce CCL25 and induce mesenchymal stromal cell migration. Bone marrow pre-pro-B cells also migrate in response to CCL25. CCL25 expression can be induced in the liver of patients with primary sclerosing cholangitis. Intestinal epithelial cell expression of CCL25 is also reduced in HIV-positive individuals.