The recent success of monoclonal antibodies in the treatment of various 
hematological and nonhematological cancers is the result of several decades of 
research in immune therapy of cancer. The identification of cancer-specific 
surface markers has led to the development of numerous monoclonal antibodies 
directed at these antigens, which have been associated with variable success in 
treating patients with different malignancies. Alemtuzumab, one such monoclonal 
antibody, is a humanized antibody directed against CD52. The target antigen is a 
small glycosylphosphatidylinositol (GPI)-anchored glycoprotein that is highly 
expressed on normal T- and B-lymphocytes and on a large proportion of malignant 
lymphoid cells, but not on hematopoietic progenitor cells. A number of clinical 
trials have demonstrated the clinical activity of alemtuzumab in chronic 
lymphocytic leukemia (CLL), T-cell malignancies such as T-prolymphocytic 
leukemia (T-PLL) and cutaneous T-cell lymphoma (CTCL), and have examined its 
role as an immunosuppressive agent in transplantation and for the treatment of 
autoimmune disorders. Effective antibiotic prophylaxis can limit the incidence 
of infections, which are the major side effect associated with the profound 
lymphopenia occurring as a result of treatment with this agent.