CD52 is present on the surface of mature lymphocytes, but not on the stem cells from which these lymphocytes were derived. It also is found on monocytes and dendritic cells. Further, it is found within the male genital tract and is present on the surface of mature sperm cells. It is not found on resting T cells but is expressed on activated T cells.
CD52 is a peptide of 12 amino acids, anchored to glycosylphosphatidylinositol (GPI). Since it is highly negatively charged and present on sperm cells and lymphocytes, it has been conjectured that its function is anti-adhesion, allowing cells to freely move around.
It is the protein targeted by alemtuzumab, a monoclonal antibody used for the treatment of chronic lymphocytic leukemia. A phase III trial into treatment of relapsing-remitting Multiple Sclerosis showed a reduction in relapse rate, but no statistically significant reduction in accumulated disability, when used as a first-line therapy. However, a sister study looking at patients in whom relapses had occurred despite treatment with interferon beta or glatiramer demonstrated reduction in both relapse rate and accumulated disability. 20% patients randomised to interferon beta 1a had "sustained accumulation of disability" compared with 13% in the alemtuzumab group. .