A recombinant DNA-derived humanized monoclonal antibody directed against the cell surface glycoprotein CD52. Alemtuzumab is an IgG1 kappa with human variable framework and constant regions, and complementarity-determining regions derived from a rat monoclonal antibody. This agent selectively binds to CD52, thereby triggering a host immune response that results in lysis of CD52 + cells. CD52 is a glycoprotein expressed on the surface of essentially all normal and malignant B and T cells, a majority of monocytes, macrophages and natural killer (NK) cells, a subpopulation of granulocytes, and tissues of the male reproductive system. or A drug used to treat B-cell chronic lymphocytic leukemia. It is also being studied in the treatment of other types of cancer. Alemtuzumab binds to a protein called CD52, which is found on some types of immune cells and cancer cells. This may help the immune system kill cancer cells. Alemtuzumab is a type of monoclonal antibody. Also called Campath.