Abatacept is primarily used in the treatment of autoimmune conditions, particularly rheumatoid arthritis. It works by inhibiting the activation of T-cells, which play a key role in the immune response that leads to inflammation and joint damage in rheumatoid arthritis. By modulating this immune response, abatacept helps to reduce symptoms such as pain, swelling, and stiffness, and can slow the progression of joint damage. It is often prescribed for patients who have not responded adequately to other disease-modifying antirheumatic drugs (DMARDs). Additionally, abatacept is used in some cases to prevent graft-versus-host disease in patients undergoing stem cell transplants, as it helps to regulate the immune system’s activity and reduce the risk of rejection.