Abatacept is the first in a class of agents for the treatment of rheumatoid arthritis (RA) that selectively modulates the CD80/CD86 : CD28 co-stimulatory signal required for T-cell activation.1 Abatacept has demonstrated efficacy in the treatment of RA.2, 3, 4, 5 Although abatacept has also demonstrated a favourable safety and tolerability profile in RA clinical trials, its potential risk for rare adverse events such as malignancies has not been addressed in the published literature. Here, CD28 is linked to rheumatoid arthritis.