CD28 and rheumatoid arthritis: For example, CTLA4‐Ig (a fusion CTLA4 protein with human immunoglobulin) blocks the CD28/B7 co‐stimulation signal, and has shown high efficacy in rheumatoid arthritis and type 1 diabetes;124, 125 (ii) inducing in vivo expansion of Tregs and/or enhancing their functions with IL‐2, rapamycin or anti‐CD3.