CD28 and rheumatoid arthritis: Abatacept was the first CTLA-4-Ig fusion protein (Abatacept) designed to prevent CD28-mediated co-stimulation, and it was FDA-approved in 2005 for rheumatoid arthritis (RA) and later for psoriatic arthritis and juvenile idiopathic arthritis; however, while effective for autoimmune diseases, abatacept was not potent enough to prevent rejection after organ transplantation.