CD52, a small glycoprotein (12-amino acid peptide) that is highly expressed on the surface of normal and malignant T and B lymphocytes, monocytes, and macrophages, but not on their hematopoietic stem cell precursors. Its physiological function remains incompletely understood. In the context of therapy, the high density of CD52 on target immune cells makes it an ideal antigen for efficient antibody-mediated cell killing. Alemtuzumab's humanized IgG1 isotype optimally engages both complement (CDC) and Fc receptors on effector cells (ADCC), leading to rapid and extensive cytolysis. This results in a prolonged depletion of the adaptive immune cell pool, which, upon reconstitution, is hypothesized to shift towards a more tolerant, less autoreactive state in autoimmune diseases like MS.