CTLA4 and rheumatoid arthritis: Aligning with the importance of the T cell response in RA progression, CTLA-4 fusion protein (CTLA-4-Ig; Abatacept), a soluble protein that binds CD80/CD86 expressed by activated APCs and outcompetes CD28 expressed by T cells at the beginning of the immune response, was approved for use in RA in 2005.