Belimumab is a biologic therapy approved for the treatment of systemic lupus erythematosus (SLE) and lupus nephritis. It is a monoclonal antibody that targets BAFF (B-cell activating factor), reducing abnormal B-cell activity that drives lupus inflammation.

Belimumab is a second-line treatment used when standard therapies (like corticosteroids, hydroxychloroquine, or immunosuppressants) are not sufficient to control disease. It is given IV or subcutaneously and is often added to background medications to help reduce flares and steroid use. It is generally well tolerated, but may increase the risk of infection and depression. Belimumab is particularly useful in patients with autoantibody-positive lupus and has also been approved for lupus nephritis in combination with other immunosuppressants.