Alemtuzumab is a humanized monoclonal antibody against CD52, a small 
glycosylphosphatidylinositol-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. Over the past several years, a 
number of clinical trials have demonstrated the clinical activity of alemtuzumab 
in treating patients with chronic lymphocytic leukemia, T-cell malignancies such 
as T-prolymphocytic leukemia and cutaneous T-cell lymphoma, as well as in the 
prevention and therapy of graft-versus-host disease in the setting of allogeneic 
stem cell transplantation. Its application in a number of autoimmune disorders 
is currently under investigation. The most significant side effect of 
alemtuzumab is predisposition to infections related to the associated profound 
lymphopenia. Despite this, and with appropriate and more effective antibiotic 
prophylaxis, it is likely that we will witness an expansion of the role of 
alemtuzumab in the future.