Selective co-stimulation blockade. CTLA4-Ig (Abatacept)

Abatacept is a soluble fusion protein comprising the extracellular domain of human CTLA4 linked to the modified Fc portion of human IgG(1). It is approved for the treatment of rheumatoid arthritis (RA) in combination with methotrexate and juvenile chronic arthritis by blocking the co-stimulatory signal required for full T-cell activation. Abatacept has added to the growing armamentarium of targeted therapies for RA, including the challenging group of RA patients who are refractory to TNF-alpha blockade. To date, abatacept has its main application in cases failing to respond to TNF-alpha blockade. In several studies, the efficacy and safety of abatacept was not only shown for TNF-IR patients, but also for DMARD-IR patients. Recently, the EU has approved abatacept in combination with methotrexate in DMARD-IR patients. The significant and similar response rates in TNF-alpha blockade failure to those observed in only DMARD failure implies that the pathways targeted with the two treatments remain distinct. In terms of safety profile, incidence rates of malignancy in the abatacept trials were consistent with those in a comparable RA population. The rate of opportunistic infections does not seem to be increased in patients treated with abatacept.