Alemtuzumab

Alemtuzumab is a humanized monoclonal antibody that binds to CD52, a glycoprotein expressed on the surface of most mature lymphocytes. By engaging immune effector mechanisms such as antibody-dependent cellular cytotoxicity and complement-dependent cytolysis, it causes rapid depletion of circulating B and T cells. The level of lymphocytes then gradually recovers over time, a process that can alter immune regulation.

Clinical use and regulatory status vary by disease and country. Alemtuzumab has been approved for certain hematologic malignancies, most notably B-cell chronic lymphocytic leukemia (CLL), and has been used in other lymphoid disorders. It is also approved for relapsing forms of multiple sclerosis (MS) under the brand Lemtrada, where it is employed as an immune reconstitution therapy.

For multiple sclerosis, the recommended regimen consists of two annual treatment courses. The first course is given as 12 mg daily on five consecutive days (total of 60 mg). The second course, given at least one year after the first if needed, is 12 mg daily on three consecutive days (total of 36 mg). Administration is by intravenous infusion in a monitored setting, with premedication to reduce infusion reactions.

Adverse effects are significant and include infusion-related reactions, infections (such as herpes zoster and cytomegalovirus), and prolonged lymphopenia. Autoimmune phenomena, including thyroid disorders and immune thrombocytopenia, can occur. There is also an elevated risk of malignancies in some patients. Because of these risks, treatment requires careful patient selection, detailed monitoring (blood counts, infection surveillance, thyroid function), and counseling on potential pregnancy risks.

Overall, alemtuzumab is a potent immunotherapy used in select indications, with a profile that necessitates vigilant monitoring and management of infectious and autoimmune complications.