Alemtuzumab is a monoclonal antibody against the CD52 antigen present at high 
levels on the surface of lymphocytes. While treatment of multiple sclerosis 
patients with alemtuzumab results in marked depletion of lymphocytes from the 
circulation, it has not been associated with a high incidence of serious 
infections. In a human CD52 transgenic mouse, alemtuzumab treatment showed 
minimal impact on the number and function of innate immune cells. A transient 
decrease in primary adaptive immune responses was observed post-alemtuzumab but 
there was little effect on memory responses. These results potentially help 
explain the level of immunocompetence observed in alemtuzumab-treated MS 
patients.