CD52 is a small glycoprotein consisting of 12 amino acids, anchored to the cell membrane via a glycosylphosphatidylinositol (GPI) anchor. It is widely expressed on the surface of various immune cells, including normal and malignant T and B lymphocytes, monocytes, and some epithelial cells. Although its exact biological function remains unclear, CD52 is believed to play roles in T-cell migration, activation, and immune regulation. Importantly, CD52 is the target of alemtuzumab, a humanized monoclonal antibody used to treat diseases like chronic lymphocytic leukemia (CLL) and multiple sclerosis. Alemtuzumab induces cell destruction through mechanisms such as antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Recent studies also suggest that CD52 may have immunosuppressive effects by binding to the SIGLEC-10 receptor and inhibiting T-cell function.