Abatacept, sold under the brand name Orencia, is a medication used to treat autoimmune diseases like rheumatoid arthritis, by interfering with the immune activity of T cells.

[1][3] Abatacept is a fusion protein composed of the Fc region of the immunoglobulin IgG1 fused to the extracellular domain of CTLA-4.

Abatacept was developed by Bristol-Myers Squibb and is licensed in the United States for the treatment of rheumatoid arthritis in the case of inadequate response to anti-TNFα therapy.

[7] Because abatacept, anakinra, and TNF antagonists suppress the immune system, using them in combination may significantly increase the risk for severe infections.

Common adverse effects (occurring in between 1% and 10% of people) include lower respiratory tract infections, urinary tract infections, herpes infections, pneumonia, flu, cough, high blood pressure, stomach pain, diarrhea, nausea, vomiting, upset stomach, mouth sores, elevated transaminases, rashes, fatigue, weakness, local injection site reactions, and systemic injection reactions.

[7] Abatacept is a soluble CTLA-4 analog that prevents antigen-presenting cells (APCs) from delivering the co-stimulatory signal.