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. (NCI04)