One such novel therapy, alemtuzumab (Campath[R]) is a humanized IgG1 monoclonal antibody directed against the CD52 protein, which is highly expressed on all lymphoid cells and monocytes. Alemtuzumab (Campath[R]), produces profound and persistent lymphopenia, affecting predominantly the CD4+ T cell subset. This property has made it attractive in the treatment of a wide range of diseases including rheumatoid arthritis, multiple sclerosis, ocular inflammatory disease, lymphoid malignancies, organ allograft rejection, and in conditioning regimens in stem cell transplantation to prevent graft failure and graft-versus-host disease.