VLA-4 (very late antigen 4,3 α4β1-integrin, CD49d/CD29) plays a major role in the regulation of immune cell recruitment to inflamed endothelia and sites of inflammation. It is expressed on the cellular surface of mononuclear leucocytes: eosinophils, basophils, lymphocytes and monocytes, and mediates cell-cell adhesion to vascular cell adhesion molecule-1 (VCAM1) on the endothelium[1]. VLA-4 thus participates in antigen presenting cell-lymphocyte interactions, retention and mobilization of immature progenitors in the bone marrow, cancer cell trafficking, metastasis, and other events[2]. In recent years, VLA-4 antagonists have shown great promise in treating inflammatory disorders in a number of animal models[3].