Anti-CD52 therapy of rheumatic diseases: Revisited in the era of immune reset

Alemtuzumab is a humanized monoclonal antibody targeting CD52, a glycosylphosphatidylinositol-anchored surface antigen broadly expressed on lymphocytes and other immune cells. Although currently approved for multiple sclerosis and used in selected transplantation settings, alemtuzumab was among the earliest lymphocyte-depleting biologics explored across a wide spectrum of autoimmune rheumatic diseases. With renewed interest in deep immune-depleting strategies, including CAR-T cells and bispecific T-cell engagers, revisiting the immunobiology and clinical experience of alemtuzumab is timely. This review summarizes current knowledge of CD52 structure, expression, and immunological function, highlighting its dual role as both a co-stimulatory and immunoregulatory molecule. We examine the mechanisms underlying alemtuzumab-induced lymphocyte depletion, subsequent immune reconstitution, and the paradoxical development of secondary autoimmunity. Clinical evidence for alemtuzumab use in rheumatic diseases, including rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, vasculitis, idiopathic inflammatory myopathies, ocular inflammatory disease, and Behçet's syndrome, is reviewed, with emphasis on efficacy, durability of response, and safety outcomes. Across multiple refractory disease settings, alemtuzumab has demonstrated the capacity to induce rapid clinical improvement and, in some cases, prolonged drug-free remission. However, treatment is limited by risks of infection, delayed immune reconstitution, and immune dysregulation. We conclude that alemtuzumab remains a potent immunomodulatory option in selected refractory rheumatic diseases, provided that careful patient selection, cautious monitoring, and long-term follow-up are implemented.