Abatacept is used: alone or in combination with other medications to reduce the pain, swelling, difficulty with daily activities, and joint damage caused by rheumatoid arthritis (a condition in which the body attacks its own joints causing pain, swelling, and loss of function) in adults who have not been helped by other medications. alone or in combination with methotrexate (Otrexup, Rasuvo, Reditrex, Trexall, Xatmep) to treat polyarticular juvenile idiopathic arthritis (PJIA; a type of childhood arthritis that affects five or more joints during the first six months of the condition, causing pain, swelling, and loss of function) in children 2 years of age or older. alone or in combination with other medications to treat psoriatic arthritis (condition that causes joint pain and swelling and scales on the skin) in adults. in combination with a calcineurin inhibitor (e.g., cyclosporine [Gengraf, Neoral, Sandimmune], tacrolimus [Astagraf, Prograf]) and methotrexate to prevent graft-versus-host disease (GVHD; a complication of hematopoietic stem-cell transplant [HSCT; a procedure that replaces diseased bone marrow with healthy bone marrow]) in adults and children 2 years of age and older. Abatacept is in a class of medications called selective costimulation modulators (immunomodulators). It works by blocking the activity of T-cells, a type of immune cell in the body that causes swelling and joint damage in people who have arthritis.