CD4 and rheumatoid arthritis: TGN1412 was developed primarily for the immunotherapy of T cell primary immunodeficiency disorders, as well as B cell chronic lymphocytic leukemia and rheumatoid arthritis (RA), the latter because of the preferential expansion of Th2 cells and CD4+, CD25+ regulatory T cells (Tregs) induced by a murine counterpart antibody, which had demonstrated no indication of immunological hyperreactivity during pre-clinical assessment (5).